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Spot a celebrity!

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Everything You Need to Know Before Experiencing Lechon Festival in Batangas

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One word to describe this festival: FUN!

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Bagoong Balayan (Anchovy) production, a small-scale industry in Batangas, is one commodity Batangueños can be proud off. And the town of Balayan is where the best tasting anchovies are produced.

There are close to a dozen of backyard producers of anchovies, making it a profitable business in Balayan. Every manufacturer has its own special secret mixture in creating the anchovy sauce. Most of these surreptitious formulas are century old, which was passed through generations.

So, what is Bagoong Balayan? And how is it made?

It is a saline product achieved by partial fermentation. Brownish in color and cheese like in taste with a fishy scent.

Fish and salt are blended together and stored in containers called tapayan (large earthen jar). Intermittent mixing is essential to sustain an even absorption of salt in the mash. It is stored for several months for at least 4 to 6 months of fermentation.

There are two varieties of anchovy in Balayan. The special bagoong are made from dilis (a fish, Stolephorus commersonii) while the ordinary bagoong are made from galunggong (a fish Decapterus macrosoma).

According to a well-known manufacturer of the anchovy, fresh fish is the secret in making a good quality bagoong. The fish are drained to eliminate extra vapour and laid out on receptacles to dry to a semi moist condition before salting the fish and adding their secret ingredient. (I was told that wine is being added as a secret ingredient.)

Bagoong is the most used sauce or dip in different towns of Batangas. A favorite dip for the indian mango (a different variety of mango) or the unripe green mango. And a very common sauce for most fish based food. It is also used as a salt substitute in Balayan Ceasar Salad dressing and other vegetables.

A very popular recipe among Batangueños, is by sautéing garlic in cooking oil, then, adding bagoong, and cook for at least three minutes. This is the most common sauce used by majority of households in Batangas.

Bagoong is rich in protein and a cheap protein source in the diet for a wide sector of the residents of Batangas. The pleasant taste cannot be substituted by any different food preparation.

Since Batangas has ample fresh fish supply and surrounded with beaches, anchovy production has become a good source of income, among the town folks of Balayan. The industry has become a viable one, with a big capability to break through the international market.

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Bagoong Balayan (Anchovy) production, a small-scale industry in Batangas, is one commodity Batangueños can be proud off. And the town of Balayan is where the best tasting anchovies are produced. There are close to a dozen of backyard producers of anchovies, making it a profitable business in Balayan.

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Do you recognize them?

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A day after the Parada ng Lechon in Balayan, Batangas, we enjoyed a heritage tour of the town, which has an impressive church and a number of well-preserved ancestral houses, just like the neighboring town of Taal. One of the oldest towns in Batangas province, Balayan was once the capital of a Moro sultanate called Bon-bon, which occupied a large territory from Cavite to Mindoro. From the 11th to 14th centuries, the bayside settlement prospered with native Moro and lumad (indigenous tribes) trading with Chinese merchants.

Balayan was established as a Spanish settlement in 1571. Seven years later, Balayan was officially establish as a municipality in the name of the King of Spain, covering the present-day towns of Nasugbu, Lian, Tuy, Calaca and Calatagan. From 1581 until 1732, Balayan became a province that included the whole of Batangas, Marinduque, Mindoro, southern parts of Laguna and Quezon, and all the way up to Camarines in the Bicol Region.

Hiring a tricycle for a few hours, we started our exploration at the dominant colonial structure in town, the Immaculate Conception Parish Church. The first church was established in 1591 and replaced by built with stone from 1748 to 1752. The main church structure is built from coral stone, while the bell tower was made bricks. After a Moro pirate raid in 1754, the church complex was protected with stone walls referred to as the cota or fort, which was later taken down in the 1840s. Foundations of the wall, however, can still be seen to this day along the perimeter of the church grounds. The Balayan church was declared as a National Cultural Treasure in 2001.

Not far away from the church is the Balayan Presidencia, which houses the municipal government. Standing next to this structure is the Mariano Martinez House, a mansion built in the 1860s by an illustrious family who prospered in the cacao business. Others call this house the Buhay-Martinez House or Casa de Cacao Filipina. Unfortunately, as with other heritage houses in Balayan, this whitewashed mansion is not open to the public and can only be admired from the outside. From here, the parallel streets of Fe and Fraternidad stretch eastwards, home to a few more colonial mansions, one of which converted to a superb Italian restaurant called Chez Deo Ristorante Italiano (read more in the "Where to Eat" section below). The restaurant is an excellent example of adaptive reuse which should be emulated by other owners of heritage houses in Balayan.

From the rotunda, Antorcha Street is a main drag with larger heritage houses such as the Dr. Vicencio Ramos House and Pedro Martinez House with their capiz shell windows and wrought ironwork. At the end of this street are Leo Martinez Ancestral House and Don Sixto Lopez House. The former, dated in 1935, is the ancestral house of Filipino actor, comedian and director Leo Martinez, who we saw the day before enjoying the parade during the festival. Across the Leo Martinez House is an Art Deco-style house - perhaps also dating to the 1930s - that locals attributed to a certain Solis family who moved to Manila.

Also called the Casa Grande or "Big House", the Lopez House was built in the 1850s - the oldest surviving house in Balayan. It is the birth place of two wealthy patriots. One of the richest men in Balayan, Don Sixto Castelo Lopez (1863-1947) was also a revolutionary propagandist and friend of national hero Dr. Jose Rizal. He refused to pledge allegiance to the Spanish and American colonial governments, and was later exiled to the United States for 25 years. Also commemorated by a historical marker, Clemencia Castelo Lopez (1872-1963) was the younger sister of Sixto who lobbied in the United States against the American occupation in the Philippines. She later became one of the founders of Asociacion Feminista Filipina, the first women's club in the Philippines established in 1905, sparking the feminist movement in the country.

Where to Eat

Looking for a place to eat after all that exploring? Here are the best restaurants in town:

Located at 117 Fe St, Chez Deo Ristorante Italiano @Gliceria is an authentic-tasting Italian restaurant housed in a colonial mansion. We had generous servings of pasta like vongole, mare monte and cozze e gamberoni at PHP 200 to 220, and brick oven-baked pizza in quatro formaggi (four cheese) and tutte le carne (all meat) flavors for PHP 300 and 320, respectively. Tel. +63 43 2116868 or +63 9273064774. Email: chezdeo_ristorante@yahoo.com.ph

If you're looking for Filipino food, check out Agot's Bar & Restaurant at 168 Palikpikan St. This local favorite specializes in crispy pata (deep-fried pork knuckles) at PHP 320 and bulalo (beef shank soup) at PHP 380, among others. Their blueberry cheesecake at PHP 35 per slice is a sweet deal! Tel. +63 43 2114306, +63 9175058692 or +63 9178622096. Email: info@agotscatering.com

For Balayan's famous lechon (roasted pig), go for Mila's Lechon at Barangay 4, Plaza Mabini Ext (Tel. +63 43 3006480) or Rebekah's Seafood Paluto (Tel. +63 43 4073728 or +63 9163571439) at Palikpikan St (across Agot's Bar & Restaurant) - home to what locals consider the best roasted pig in town!

How to Get There
For information on how to get to Balayan from Manila and where to stay, read my previous post on the Parada ng Lechon. Tricycles are the best way to explore town with short hops for only PHP 10 per person. Our two-hour tricycle tour for four persons was PHP 150, inclusive of gratuity.
agot's bar and restaurant balayan balayan church chez deo ristorante italiano heritage tour immaculate conception parish church leo martinez house sixto lopez house

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Balayan, Batangas: Heritage Tour of the Immaculate Conception Church and Ancestral Houses -

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A day after the Parada ng Lechon in Balayan, Batangas, we enjoyed a heritage tour of the town, which has an impressive church and a number of well-preserved ancestral houses, just like the neighboring town of Taal. One of the oldest towns in Batangas province, Balayan was once the capital...

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Click to know more about Balayan.

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Another, Not As Famous Heritage Town in Balayan, Batangas

One of the oldest towns in Batangas province, and around the Philippines, is BALAYAN. Coined from the Visayan word "Balay", meaning house, it is one of the first settlements in the country with trade dating back to the mid-14th century. It was already known as Balayan since 1394 till it was "inherited" by a certain Datu Kumintang, after whom the town was called until 1578. The Augustinian missionaries arrived in this town in 1575 , then followed by Franciscan missionaries who built a small stone church in 1579.

We began our tour of Balayan with a visit to this national cultural treasure. Balayan Church was under the administration of "Indio Clergy" since the 19th century. This sets it apart from the other heritage churches found around the country. Considered as the first church in Batangas, and likely in the whole Tagalog Region, its claim to fame ironically involves a furor not so long ago over a proposed construction of a McDonald's outlet in the historic church grounds.

From inside the Church, we exited behind the altar out into a back courtyard. In one corner of this courtyard is a small chapel at the end of a passageway where we found some interesting art works.

I did not find any inscription and didn't have the chance to ask how old this piece of art is. The intricate woodcarving is lovely, just as the image of Our Lady holding an Infant Jesus.

From the Church, we visited the ancestral house of Leo Martinez. I knew the name sounds familiar. He is now a local politician here, but I remember him as an actor from a now defunct TV comedy show of long ago.

It is unfortunate that there was no tour guide to tell us more about the ancestral houses in this area. The house of Leo Martinez has a marker that says 1935, which renders it "new" compared to the ancestral house of Don Sixto Lopez just right across the street. You can view this older house from one of the wide windows of the Martinez house.

The oldest house in Balayan is that of Don Sixto Lopez, the Grand Old Man of Balayan. His house has wide windows framed by capiz shells, like many of the other ancestral houses to be found in the area. Lopes belongs to a rich illustrious family who owned vast tracts of sugarcane fields in Batangas. The house sits right across the ancestral house of Leo Martinez.

Not too many Filipinos are familiar with Sixto Lopez who belonged to the same generation as the great national hero, Jose Rizal. But some would be familiar with his high society granddaughter Diana Jean Lopez, and the equally famous if not more famous great grandchildren such as Claudia Bermudez (daughter of Diana Jean) and Nikki Prieto Teodoro(wife of Presidential candidate Gibo Teodoro, who is from another rich haciendero family, the Cojuangcos of Tarlac). Oh yes, you can say all these socialites certainly come with a lot of class, unquestionable pedigree and beauty genes!

We could have visited this house too across the street lining the Martinez and Lopez ancestral houses. But it was closed as someone allegedly committed suicide just a few days before our visit. Yay! 😦

Just like Vigan and Taal, Batangas , Balayan is yet another colonial town reminiscent of our Spanish heritage. Many heroes hail from this town too, and as the oldest town in Batangas if not of the Tagalog Region, it has a lot of history begging to be told and retold. My fingers and toes are crossed that the the local authorities do their job to promote this town as another tourist destination.

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Another, Not As Famous Heritage Town in Balayan, Batangas

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One of the oldest towns in Batangas province, and around the Philippines, is BALAYAN. Coined from the Visayan word "Balay", meaning house, it is one of the first settlements in the country with trade dating back to the mid-14th century. It was already known as Balayan since 1394 till it was "inherited" by a certain...

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Balayan, officially the Municipality of Balayan, , is a 1st class municipality in the province of Batangas, Philippines. According to the 2015 census, it has a population of 90,699 people.Balayan is bounded on the north by Tuy, west by Calatagan and Lian, east by Calaca, and south by the Balayan Bay. The town is rich among the natural resources of sugarcanes, coconuts and corn. Significant events includes the Parada ng Lechon and the Feast of Immaculate Conception celebrated annually every December 8. Widely known products originating from the area include the Bagoong Balayan.
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From Wikipedia, the free encyclopedia.

The Best Attractions In Balayan

Balayan Videos

Portulano Dive Resort 4k UHD - The best place to learn diving near Manila

Portulano is a boutique scuba diving resort located in Bauan, the more quiet, private side of Anilao, Balayan Bay, Batangas, the Philippines.

Portulano is at the heart of the world's coral triangle, where you can experience the richest marine biodiversity and the most colorful reefs in the world. A 2 hour drive from Manila International Airport brings you to the resort where you have easy access to popular diving and snorkeling sites.

This is what a feast looks like in the Philippines. This video will show a typical village fest that every barangay (Filipino for 'neighborhood') holds on a yearly basis.

We went to a typical Filipino feast in Lipa City, in the Philippine province of Batangas. There we witnessed how the Filipinos celebrate these yearly village fests.

To Puerto Galera, Mindoro, Philippines

Beautiful scenery of Puerto Galera from a Blue Penguin banca boat (banka boat), Mindoro Oriental, Philippines. Sony Handycam DCR-SR100.

Batangas. Eagle Point restaurant

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Destimap is a cool platform to present the best 10 attractions for every place (city,village) in the world. From Afghanistan to Florida Us. From small islands in south Thailand to Labrador in Canada.

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Goal 3: Good health and well-being | Joint SDG Fund

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Since the creation of the Millennium Development Goals there have been historic achievements in reducing child mortality, improving maternal health and tackling HIV/AIDS, tuberculosis, malaria and other diseases.

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The Scientific World - Let's have a moment of science

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Why living a healthy lifestyle is so important and How can we improve our health and well-being?

Good health is central to human happiness and well-being that contributes significantly to prosperity and wealth and even economic progress, as healthy populations are more productive, save more and live longer.
For a healthy life cycle, you need a healthy and balanced diet, good hygiene habits, staying in a proper shelter and getting enough sleep.
In addition, you will have to participate in physical activities, weight management, and stress management activities .

Health can be defined as a state of complete physical, mental, social and spiritual well being, which consists in maintaining the body as much as possible by following daily advice and preventive measures to reduce the possibility of diseases.

Health has an important role in feeling happy, as there are many people who suffer from diseases, but the health enables them to fight diseases, as a result, they achieve physical fitness and feel comfortable or enjoy life like any normal person.

Health is the body's functional and metabolic efficiency, and its ability to adapt to the physical, mental, and social changes that it is exposed to.
Health is the opposite of disease, and also means the safety of the body from physical, social, and mental disorders.
Health is the factor that helps a person perform his daily life tasks in a correct and right way.
A person's physical health means that the body does not have any diseases in all parts of his body, and the safety of all its membranes.
While mental and social health is represented by the ability of a person to accomplish social tasks entrusted to him without defect or error.

The importance of good health in a person's life is undoubtedly great. In this article, we will highlight some important points that fully define the importance of health in our lives.
Then, in the next part of the article, we'll discuss how we can achieve good health and well-being. Let's start!

➤ A healthy person is a person who is able to serve himself, his nation and his community.
An unhealthy person who suffers from illness sees him weak and meager, unable to properly carry out the duties and responsibilities incumbent on him.
When the disease develops, the person becomes dependent on other people and cannot meet his different needs in life, which affects his psyche as well due to his sense of helplessness and weakness.
Society is also affected by the presence of the disease among its members, as the productivity of these patients weakens and they become dependent on society.
As for the presence of healthy individuals in society, this means the presence of productive individuals who possess the power and the ability to give and serve.

➤ The importance of health for a person is that it saves him the costs of treatment and the hassle of going to hospitals.
A healthy person who is far from the disease sees him saving money that he would have spent on the disease if he neglected his health, so it is always said that "an ounce of prevention is worth a pound of cure".
You see many governments that are exposed to the spread of epidemics and diseases among their members spend a large part of the money to buy medications to treat these cases.
You also see governments and societies that are concerned with the safety of their people focusing on aspects of prevention and health guidance.

➤ Psychologically healthy people feel comfortable and happy in their lives and enjoy life well.
A person who suffers from mental illnesses always sees him as a gloomy and pessimist and does not feel happy in his life and in his relationships with people.
While you see a healthy person enjoying happiness in his life, establishing his relationships with people and showing love, kindness, and intimacy.

Finally, a person must consider many matters and behaviors in life in order to avoid diseases that interfere with his life and to know that illness may be part of the many trials that a person is exposed to.

The following ways can help you achieve good health and well-being:

What you eat is closely related to your health. Eating a healthy diet can help boost your immune systems, help you maintain a healthy weight and can improve your overall health.

Include fruits, vegetables, grain products, leafy greens, salmon, etc. in your diet. Adding fruits and vegetables is an ideal basis to start a healthy routine.

Drinking a lot of water keeps muscles and joints working, increases the amount of water in your blood, promotes healthy skin and cardiovascular health and helps cleanse toxins from your body.
You can save a lot of money and improve your health by drinking water all day.

Do a moderate workout for at least 30 minutes a day, as exercise can help prevent heart disease, stroke, colon cancer, and diabetes.

Lose weight if you are overweight. If you want to lose extra weight, you have to reduce the number of calories you consume, so you have to become a good record-keeper.
If you are obese, losing weight can mean "less heart disease, less cancer and less diabetes.

Hand washing before eating is a good habit and an effective way to prevent infection.
If you eat something without washing your hands, it is possible that the bacteria and germs that remain on your fingers and palms can be moved into your mouth.
This can affect your overall health and cause diseases and infections.

Your skin is the first layer of defense in the body, and you need to protect it. In summer, a lot of sunlight is very harmful to your skin cells because UV rays damage or even kill your skin cells.
In winter, fluctuations, redness, allergies and irritation are common skin diseases among many of us.
Cold temperatures and low humidity levels create dry air that pulls moisture away from the skin. Therefore, protect your skin in both seasons.

Sleep plays an important role in good health and well-being throughout your life because it enables the body to repair and be fit and ready for another day.
Getting enough sleep at the right times may help prevent physical health problems such as excess weight gain, heart disease, protect your mental health issues and improve your quality of life and safety.

Avoid smoking, tobacco, alcohol, caffeine and sugary drinks. Smoking, alcohol, and tobacco consumption are harmful to your health, so avoid such things as soon as possible.
When you quit, you will greatly reduce the risk of death from lung cancer and other life-threatening diseases such as heart disease, stroke, emphysema, chronic bronchitis, etc.

You can understand what you should do to enjoy a healthy, happy life.
Poor lifestyle choices contribute significantly to the development and progression of preventable chronic diseases.
Improve your lifestyle, adopt healthy lifestyle choices and create good and healthy habits so that you can make healthy changes in your life.
Carve out time to exercise and find a way to ratchet down stress and depression.

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Importance of Good Health in Our Life - How can We Achieve Good Health and Well Being?

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Good health is central to human happiness and well-being that makes an important contribution to prosperity and wealth and even economic progress, as healthy populations are more productive, save more and live longer. For a healthy life cycle, you need to have a healthy and balanced diet, have good hygiene habits, live in a proper shelter and take enough sleep.

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A study conducted by Lira et al. (2020) presented that there were microplastics and VOCs found in the fish pastes

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A study conducted by Lira et al. (2020) presented that there were microplastics and VOCs found in the fish pastes

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As seen in Fig. 4, there are 14 VOCs found in the fish paste that compromise health. These VOCs are proven to be harmful as they contain toxic chemicals that may jeopardize public safety. Moreover, Table 1 explains in detail what, where, and how much of these are found in the Bagoong.

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We should not eat food containing microplastics.

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Microplastics are very small plastic particles generally less than 5 mm in size. There are significant levels of microplastics polluting the ocean, freshwater and land, and research is showing that animals including humans are eating these microplastics. For some animals, they mistake the particles as food, while others are ingesting them when they consume animals that have eaten them.

So are these microplastics harmful for us and other animals?

Animals and microplastics

Microplastics can be ingested by various animals, ranging in size from tiny creatures like zooplankton to sharks and whales. The likelihood of microplastics being eaten is influenced by the amount in the environment and how closely they resemble food. Laboratory studies indicate that microplastics can potentially transfer through the food web when marine, terrestrial and freshwater species that have previously ingested microplastics are preyed on by other animals.

Microplastics eaten by larger marine animals will generally pass through their bodies. However, research does show that microplastics can be retained in the gut for extended periods where they may cause abrasion and damage to internal tissues. Nanoplastics can pass through the gut wall and travel to different parts of the body, such as the lungs and liver, where they can cause damage. Further research is required to understand the potential health implications from ingesting microplastics.

Smaller animals including marine and freshwater invertebrates can suffer a range of effects from ingesting microplastics including reduced reproduction and growth. These effects are generally caused by physical damage including lacerations and inflammatory responses as well as reduced feeding behaviour when microplastics are consumed instead of digestible food. Filter feeders such as mussels and oysters are particularly vulnerable to ingesting microplastics as they filter high volumes of water while feeding. Effects vary between species and by the types of plastic and the concentration of microplastics.

Research released in 2021 by University of Waikato Master of Science student, Anita Lewis found extremely high levels of microplastics across the Bay of Plenty moana. Every area she tested showed evidence of microplastics, and high levels were found in shellfish.

Toxic chemicals associated with plastics

Various chemicals incorporated into plastics as raw materials or additives during manufacture can leach from plastics into the environment. Humans and other animals are also exposed to these chemicals when they ingest plastics or when these chemicals leach into food or are released into the atmosphere when plastics are burned. Some chemicals directly associated with plastics have been detected in humans and wildlife including birds and various marine species.

Pollutants that stick to microplastics

Some pollutants and heavy metals can also adsorb or stick to plastic surfaces. As a result, plastics can act like sponges in the environment, passively collecting chemicals onto their surfaces.

While plastics can remove some persistent organic pollutants (POPs) from the surrounding water, there is concern about what happens when plastics containing these adsorbed pollutants are ingested by animals. The ability of some POPs to bind to plastics is particularly concerning due to their toxicity at low doses. These toxic and persistent chemicals are widely distributed in the marine environment and are readily concentrated onto plastic surfaces at up to 1 million times the concentration than in the surrounding water. Studies have shown that these chemicals can transfer from ingested plastics to animal tissue where they can become concentrated within the animal and transfer through the food chain.

Do plastics affect human health?

Plastics are beneficial to human health through their use in medical applications and for protecting our food and beverages. Plastics have revolutionised healthcare through improving sterility by the use of disposable syringes, gloves, IV tubes and catheters and providing increased comfort with hypoallergenic medical devices, heart valves, and flexible prosthetics (artificial body parts). Plastic bottles and containers provide a way of distributing water that is safe to drink in locations where there are major issues of water contamination. Plastic packaging limits food and beverage spoilage through microbial contamination.

It is likely that we are ingesting some level of plastics in our diet. A rapidly growing body of research is showing that ongoing accumulation of toxins associated with plastics poses a risk to our food safety and public health. However, the levels of plastics and associated chemicals we are exposed to in our diet compared with other everyday activities has not been assessed.

Microplastics have been found in many seafood species, including various kinds of fish and shellfish. Research into commercial fish species in the South Pacific identified microplastics in up to 25% of fish collected from Auckland, Sāmoa, Tahiti and Rapa Nui, Easter Island. These plastics are often in the gut, which is removed before eating. However, they may still pose a dietary risk through plastic-associated contaminants transferring to other tissues.

Microplastics have also been detected in common table salt, tap water and up to 90% of bottled water. Scientists found on average 325 microplastic particles per litre of bottled water. Most of these particles were very small in size (6.5-100 µm), and only about 10 particles per litre were larger than 100 µm.

Recently, microplastics have even been found to be present in the air and in household dust. Most of us are likely to breathe in microplastics on a day-to-day basis. However, it is not yet known what degree of harm this exposure could be causing us or what happens to such microplastics within the human body.

Nature of science

Knowledge gaps

A better understanding about the use, disposal and effects of plastics in the environment is required to help mitigate harmful effects of plastic debris and better manage disposal of plastics and plastic pollution.

There are some knowledge gaps on microplastics:

Where, how, how much and what types of plastic (particularly microplastic) enter the environment including into air, freshwater and terrestrial systems?

How much leaching takes place from plastics (particularly absorbed chemicals) into animals and humans compared with other routes of chemical exposure?

What level of microplastics do we encounter daily through our diet or airborne sources, and what are the potential health risks associated with these exposure rates?

To what extent does the ingestion of microplastics actually harm individuals and populations in the real environment?

ESR scientist Dr Olga Pantos and Grant Northcott (Northcott Research Consultants) are co-leading a 5-year research study in New Zealand. The research aims to assess the extent of microplastic contamination and to advance research on the mediation of that threat. The research is being carried out in two primary case study sites in the Auckland and Nelson regions.

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Microplastics are very small plastic particles generally less than 5 mm in size. There are significant levels of microplastics polluting the ocean, freshwater and land, and research is showing that animals including humans are eating these microplastics. For some animals, they mistake the particles as food, while others are ingesting them when they consume animals that have eaten them.

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The use of plastic is one of the conveniences of modern life, but in recent years microplastic contamination has become an emerging global concern. Microplastics --plastic particles measuring less than 5mm --are everywhere --from the deepest oceans to the air we breathe. Their small size and mass mean they are readily transported by wind and microplastics have been found in the remotest of places on Earth --including mountainous and polar regions.

Image Credit: Jose y yo Estudio/Shutterstock.com

Microplastics are even present in the food we eat and in the water we drink. They impact the living world and have been discovered to affect nearly all levels of biological organization. This article looks at what microplastics are and considers their potential effect on human health.

What are Microplastics?

Dunzhu Li, an environmental engineer, ceased microwaving his lunch at work each after he discovered that plastic food containers released tiny particles called nanoplastics. The same problem was found to apply to kettles and baby bottles. The finding was alarming, but scientists did not know how harmful it might be --after all we regularly ingest and inhale dust, for example.

Plastic can be of variable composition. And it contains a wide range of additives:

pigments

ultraviolet stabilizers

flame retardants

water repellents

stiffeners e.g., bisphenol A

softeners -phthalates

More plastic becomes waste after it is discarded and, due to its durability, the resultant pollution lasts for many years. In fact, the microplastic problem continues to worsen with every passing year. The annual projected mass of microplastics produced --around 400 million tonnes -- is expected to have more than doubled by 2050.

The ubiquity of airborne microplastics is a result of:

synthetic fibers

degradation and fragmentation of plastic products

waste incineration

industrial and traffic emissions

dust re-suspension

How Do They Affect Human Health?

Microplastics surround us and human exposure can occur through inhalation, ingestion, and dermal absorption due to their omnipresence in air, water, food, and consumer products.

Scientists think we may ingest anywhere from dozens, to more than 100, 000 microplastic particles each day --as a useful visual it could be around the mass of a credit card's worth in the space of a year. Even the synthetic clothing we wear can shed fibers --some studies have revealed textiles to be the major source of airborne microplastics.

No research has yet been done to directly study the effects of microplastics on people. The research available so far either exposes human cells or tissues to microplastics or has investigated animals, such as mice or rats, as part of the study.

Using the data that is available then, it is believed that microplastics may be hazardous to our health. It is thought they might act as irritants, in much the same way asbestos fibers are now known to inflame the lungs and cause cancer. Microplastics are also thought to act as vectors for microorganisms and toxic chemicals, thus posing further health risks.

Research has shown the potentiality for metabolic disturbance, neurotoxicity as well as carcinogenic effects. It has been shown that microplastics can act as endocrine disruptors, thus interfering with normal hormone function and potentially causing weight gain.

Certain microplastics, for example, flame retardants, are thought to interfere with fetal brain development, and likewise, they can affect normal brain development in children.

Marine Microplastics

Scientists have been looking at the potentially harmful effects of microplastics for over 20 years and most studies undertaken so far have concentrated on the risk to marine life (we currently know far less about airborne microplastics). Microplastics have been detected in a wide range of aquatic organisms from whales to minute zooplankton. It was a marine ecologist, Richard Thompson, at the University of Plymouth, UK who coined the term "microplastics" in 2004.

These microplastics pose a physical and physiological threat to marine organisms and because they are readily transferred and bioaccumulated in the food chain, they pose a threat to humans too.

But studying the impact of marine microplastics on human health is difficult:

humans cannot be used in experiments

plastics and additives act differently depending on the physical and chemical context

characteristics of microplastic may change as organisms in the food chain consume, metabolize, and excrete them

We do not know a great deal about how food processing and cooking might affect the toxicity of plastics in aquatic organisms, nor indeed what level of contamination could do harm.

A basic tenet of toxicology holds that the dose makes the poison, but many of these chemicals-BPA and its close relatives, for example-appear to impair lab animals at levels some governments consider safe for humans"

Royte, 2018

On a more positive note, it is thought that microplastics remain in the guts of fish rather than moving into the muscle tissue which is the part of the fish we consume.

The concern remains that microplastics are omnipresent --in 2015, oceanographers estimated between 15 - 51 trillion microplastic particles were floating about in surface waters across the globe (see Lim, 2021) --and that in time they'll inevitably degrade into nanoplastics, which are invisible to detect. But we need to bear in mind that plastic waste can be recycled or recovered.

These minuscule particles have the capacity to move into the cells, tissues, and organs of the body. Regulators have now taken steps towards measuring human exposure to microplastics and quantifying the risk they pose to our health.

But assessing their overall risk to our health is the challenging bit. In the case of ingested microplastics, the level of toxicity we are potentially exposed to depends very much on how quickly they pass through the system. This is something researchers are now beginning to address.

References:

Chen, G. et al. (2019) Mini-review of Microplastics in the Atmosphere and Their Risks to Humans. Science of the Total Environment. DOI: https://doi.org/10.1016/j.scitotenv.2019.135504

Lim, X. (2021) Microplastics Are Everywhere -- But Are They Harmful? Nature, 593, pp. 22-25 https://www.nature.com/articles/d41586-021-01143-3

Rahman, A. et al. (2021) Potential Human Health Risks Due to Environmental Exposure to Nano- and Microplastics and Knowledge Gaps: A Scoping Review. Science of the Total Environment. DOI: https://doi.org/10.1016/j.scitotenv.2020.143872

Royte, E. (2018) We Know Plastic is Harming Marine Life. What About Us? National Geographic. https://www.nationalgeographic.com/magazine/article/plastic-planet-health-pollution-waste-microplastics

Further Reading

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The use of plastic is one of the conveniences of modern life, but in recent years microplastic contamination has become an emerging global concern. Microplastics --plastic particles measuring less than 5mm --are everywhere --from the deepest oceans to the air we breathe.

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What are volatile organic compounds (VOCs)? | US EPA

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Volatile organic compounds are compounds that have a high vapor pressure and low water solubility. Many VOCs are human-made chemicals that are used and produced in the manufacture of paints, pharmaceuticals, and refrigerants. VOCs typically are industrial

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Long Term Effects of Volatile Organic Compounds (Benzene, Formaldehyde..)

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Carbon monoxide is famous because it can kill someone in a few minutes. But VOlatile Organic Compounds have adverse health effects over years.

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Technological Advancements to Solve Water Pollution

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Technological Advancements to Solve Water Pollution

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Across the country there is growing momentum to address traditional and emerging threats to the nation's water resources through innovative technology. EPA has highlighted the following examples of how innovation is currently being deployed in the water sector, organized by the 10 market opportunities defined by EPA.

Conserving and Recovering Energy

Gresham, OR Achieves Energy Net Zero

Through the use of biogas generation and recovery, as well as ground-mounted solar arrays, the City of Gresham's wastewater treatment plant is the first in the Pacific Northwest to generate more electricity than it consumes each year, which saves the city about $500,000 per year. More information on Gresham's Wastewater Treatment Plant.

DC Water Saves Energy

DC Water was the first plant in North America to adopt thermal hydrolysis process from the company Cambi. Using this process creates biogas and has enabled DC Water's Blue Plains Advanced Treatment Plant to generate 10 megawatts of electricity, which is about one-third of the plant's energy requirement. More information on a Greener Blue Plains.

Oakland, CA, Utility Goes Energy Positive

More than a decade ago, East Bay Municipal Utility District (EBMUD) in Oakland, CA, began accepting organic wastes from local food processors, food growers and livestock producers to better utilize the excess capacity in its existing anaerobic digesters. The result has been a doubling of biogas production, which allowed EBMUD's wastewater treatment plant to become the first facility in North America to produce more renewable energy on site than is needed to run the facility. More information on recycling water and energy.

Conserving and Recovering Nutrients

Madison, WI, and Boise, ID, Harvest Phosphorus

The Madison Metropolitan Sewerage District, in conjunction with Ostara Nutrient Recovery Technologies, recovers phosphorus at their Nine Springs Wastewater Treatment Plant, converting it into an environmentally friendly fertilizer, Crystal Green®. More information on Phosphorus Harvesting.

The City of Boise implemented the Multiform TM P-Recovery system at its West Boise Water Renewal Facility to manage nuisance struvite deposits and recover phosphorous. More information about Boise's phosphorous removal process.

Using Technology to Optimize Fertilizer Application

Researchers at University of Nebraska-Lincoln are working with farmers on Project SENSE (Sensors for Efficient Nitrogen Use and Stewardship of the Environment), which uses innovative technologies to optimize nitrogen fertilizer use. As part of the project, crop canopy sensors are used to measure the real-time nitrogen status of crops. This information is then used to produce nitrogen application rate recommendations that can ultimately lead to greater crop productivity, decreased fertilizer use, and improved water quality as a result of reduced fertilizer runoff. More information about Project Sense.

Improving and Greening of the Water Infrastructure

Rainwater Harvesting at EPA

EPA's Headquarters facility in Washington, DC recently upgraded an existing 6,000-gallon capacity rainwater harvesting system with OptiNimbus real-time controls to manage stormwater retention and use more effectively. The system allows EPA to monitor the volume of rainwater captured and used over time. More information on stormwater.

GreenPlan Bay Area

The GreenPlan Bay Area project developed a GIS-based tool and GreenPlans to help municipalities in California identify the optimal combination and location of green infrastructure/low impact development features to address water quality on a watershed scale. More information on GreenPlan Bay Area.

Greening of Our Cities

Green City, Clean Waters is the city of Philadelphia's 25-year plan to protect and enhance its watersheds by managing stormwater with intensely implemented green infrastructure. Recently, Philadelphia celebrated an impressive landmark in the program; 1,000 acres throughout the city have been greened, and counting! More information on what Philadelphia is doing.

Save the Rain is Onondaga County's and the city of Syracuse's visionary stormwater management and public outreach program, featuring over 200 projects, capturing over 120 million gallons of runoff each year to protect their watershed. Every project advanced through the program has a unique Web page where the public can review the project design elements, cost, and stormwater capture objectives. More information on Save the Rain.

Reinventing Urban Water Infrastructure

ReNUWIt is a multi-institution research center that works in close partnership with utilities, water service providers, equipment manufacturers and international research partners to convert great ideas for re-inventing the nation's urban water infrastructure into practical and sustainable solutions. More information on Reinventing the Nation's Urban Water Infrastructure.

Conserving and Eventually Reusing Water

Emory University Reclaims Wastewater

The WaterHub at Emory University is reducing its water footprint nearly 40% by reclaiming and reusing up to 146 million gallons of campus wastewater annually by using an adaptive ecological technology that naturally breaks down organic matter in wastewater for use as process (make-up) water in its steam and chiller plants. More information can be found at:

Potable Reuse

The communities of Big Spring and Wichita Falls, Texas, built the country's first two potable reuse facilities, using multiple barrier technologies and intense monitoring. Presently, Colorado River Municipal District's Big Spring facility provides water to five communities using direct potable reuse (DPR) processes. Wichita Falls implemented an emergency DPR system in response to severe drought in 2014. When drought conditions subsided, the DPR system was decommissioned and Wichita Falls subsequently implemented a permanent indirect potable reuse (IDR) system.

More information on these and other facilities with potable reuse capabilities can be found in EPA's 2017 Potable Reuse Compendium.

The World's Largest Potable Reuse System

The Groundwater Replenishment System operated by the Orange County Water District in California is the world's largest advanced water purification system for indirect potable reuse, taking treated wastewater that is purified to produce a high-quality water. More information on Groundwater Replenishment System.

Reducing Costs and Improving Techniques for Water Monitoring

Mobile App for Water Quality Data

A mobile and web application called KCWaterBug provides live water quality data so users can make real-time informed decisions about recreation in numerous streams in the Kansas City area.

Rocky River Hydrology

Cleveland Metroparks in Ohio studied the hydrology of the Rocky River headwater streams affected by runoff by using real-time flow and water quality sensors to attain precise, short-interval hydrograph and water quality data. More information on Cleveland Metroparks.

National Great Rivers Research and Education Center

The National Great Rivers Research and Education Center (NGRREC) created a network of monitoring buoys for real-time, continuous water quality data on the Mississippi, Missouri and Illinois Rivers. The data from these buoys, along with data collected from federal, state, local and private sources is publicly available through the Great Lake to Gulf Virtual Observatory. More information on NGRREC and Virtual Observatory.

Clemson University's Intelligent River

Clemson University's Intelligent River Research Enterprise is a data acquisition system supported by a network of sensors on the Savannah River. The sensors were implemented with the help of NSF and provide real-time water quality and flow rate data along the entire length of the Savannah River. More information on the Enterprise.

Monitoring Lake George

The Jefferson Project is a collaborative effort between Rensselaer Polytechnic Institute, IBM and the FUND for Lake George (New York) to develop a lake environmental monitoring and prediction system to provide a real-time understanding of lake health. More information on The Jefferson Project.

Monitoring the Hudson River

The Hudson River Environmental Conditions Observing System (HRECOS) is a network of real-time monitoring stations on the Hudson River Estuary. HRECOS is a collaborative effort between multiple agencies, including the New York State Department of Environmental Conservation, USGS and NOAA, among others. More information on HRECOS.

The River and Estuary Observatory Network is an effort between Clarkson University's Beacon Institute for Rivers and Estuaries and IBM to use real-time monitoring technologies to better understand the Hudson River ecosystem from the headwaters in the Adirondack Mountains to the ocean. More information on River and Estuary Observatory Network.

Third Party Technology Evaluation

The Water Environment Federation and The Water Research Foundation have established LIFT (Leaders Innovation Forum for Technology), a program designed to enable technology evaluations for municipal and industry end-users to share the cost of conducting demonstrations to accelerate adoption of new and innovative technologies. More information on LIFT.

Improving Performance of Small Systems

Padre Dam Municipal Water District

Padre Dam Municipal Water District's Board of Directors recently approved the next phase of work on the East County Advanced Water Purification Program. The program will reclaim treated wastewater and use it to reduce the region's dependence on imported water; by 2032, it is expected to provide thirty percent of Padre Dam's current drinking water demands. More information on advanced water purification.

Algae-Based Wastewater Treatment

The Indiana Department of Natural Resources worked with Commonwealth Engineers, Inc. and One Water Group to install algae-based wastewater treatment systems at two of its state parks. Both locations use an algaewheel® system, which works similarly to a rotating biological contactor. Wastewater is conveyed to a basin containing partially submerged paddles (wheels), which are rotated via a blower. Biofilm, made of a consortium of algae and bacteria, attached to the wheels supply oxygen to the wastewater while removing nutrients. These small, decentralized systems are ideal for low flow facilities. Little land space is required and the system is capable of handling variable flows with changes in seasonal demands. More information on the Indiana facilities.

Small Systems Innovation Research

Using funding from EPA's STAR grant program, two national research centers conduct research on innovative technologies that can be implemented in small systems. More information on the centers' grants.

The Design of Risk-reducing, Innovative-implementable Small-system Knowledge ( DeRISK) Center is led by the University of Colorado Boulder with five affiliated research organizations. DeRISK researchers are exploring topics, including: applications of photochemical processes for small systems, distribution system innovations, and extended biofiltration.

The Water Innovation Network for Sustainable Small Systems ( WINSSS) is led by the University of Massachusetts Amherst with six affiliated research organizations. Some of the current research efforts at WINSS include studying the use of ferrate for disinfection, research on electrodialysis with nanofiltration, and developing a mobile application to assist small systems with asset management.

Reducing Water Impacts from Energy Production

Cleaning Hydraulic Fracturing Wastewater

Researchers at the University of Colorado Boulder have developed a method using microbes to clean both organic contaminants and salts from hydraulic fracturing wastewater, while producing renewable energy. More information on the University of Colorado Boulder project.

Use of Reclaimed Water as Makeup for Cooling Towers

The Public Service Enterprise Group's Linden, NJ, Generating Station does not currently employ a cooling water intake structure. Instead, the Linden Generating Station uses reclaimed wastewater from the nearby Linden Roselle Sewerage Authority (LRSA) for all its cooling water needs. After being used for cooling, any remaining water (e.g., cooling tower blowdown) is pumped back to LRSA for treatment again. More information on Public Service Enterprise Group.

Improving Resiliency of Water Infrastructure to the Impacts of Climate Change

Adapting to Climate Change and Water Reuse

Due to damage from Hurricane Ivan in 2004, Florida's Emerald Coast Utilities Authority had to relocate it's Main Street Wastewater Treatment Plant away from the coastal plain and rebuilt. The new Central Water Reclamation Facility has treatment technology that enables the reuse of 100 percent of the nearly 22.5 million gallons per day (average flow) treated at the facility. Additionally, the new plant was built to withstand Category Five hurricanes and now stands 50 feet above sea level, thereby increasing resilience to sea level rise and flood risk. More information on Emerald Coast Utilities.

Improving Access to Safe Drinking Water and Sanitation

Improving Onsite Systems

The Massachusetts Alternative Septic System Test Center (MASSTC) aids in the development, testing, and piloting of new and innovative onsite technologies. More information on MASSTC. Currently, MASSTC is working with EPA, USGS and other partners to screen technologies as part of the Advanced Septic System Nitrogen Sensor Challenge, which was launched in January 2017 to challenge innovators to design a nitrogen sensor for use in advanced onsite wastewater treatment systems. EPA News Release on Technology Challenge.

Reinventing the Toilet

The Bill and Melinda Gates Foundation challenged universities to design toilets that capture and process human waste without piped water, sewer or electrical connections, while capturing useful resources. Since 2011, the Foundation has awarded 16 grants to research organizations through the challenge and continues to strive to spur change to improve worldwide drinking water while reducing sanitation-related problems. More information on water, sanitation and hygiene.

Improving Water Quality of Our Oceans, Estuaries, and Watersheds

Protecting Lake Tahoe

The Lake Clarity Crediting Program uses a suite of stormwater tools and protocols to target ongoing effective actions to reduce urban stormwater fine sediment and nutrient pollutants to Lake Tahoe. More information on Lake Tahoe.

Using Roleplaying to Manage Watersheds

The University of Virginia (UVA) Bay Game is a computerized simulation based on the Chesapeake Bay watershed. The simulation allows players to take the roles of stakeholders, such as farmers, developers, watermen and local policy-makers, and make decisions about their watershed.

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Examples of Innovation in the Water Sector | US EPA

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Across the country there is growing momentum to address traditional and emerging threats to the nation's water resources through innovative technology. EPA has highlighted the following examples of how innovation is currently being deployed in the water sector, organized by the 10 market opportunities defined by EPA.

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A pollution prevention (P2) technology is one that creates less pollution in its life cycle than the one it replaces. P2 can be achieved in many ways, from better housekeeping and maintenance to redesign of products and processes. The range of P2 technologies is therefore very broad. It includes relatively cleaner technologies, technologies that help other technologies to be cleaner, and certain mass-market technologies. All of them reduce environmental impacts compared to their alternatives. It is important to understand that P2 technology does not include pollution-control or -treatment technologies that do not make the technology producing the pollution any cleaner itself. They just manage the resulting waste.

Relatively Cleaner Technologies

Technology is always advancing and improving. Many new technologies are naturally more energy efficient and less polluting than the ones they replace. Sometimes, this is because they were designed with environmental improvement in mind. Usually, however, it is simply the result of using newer and better materials and components. Therefore, pollution-preventing technologies can be found in every area of a product's life cycle.

Life cycle analysis (LCA) is needed to determine if a particular technology really pollutes less than its alternatives. LCA is the examination of the environmental impacts of a product, from its origins as raw material through processing and production to use and final disposal. This can be a complex process. For example, fluorescent light bulbs may seem to be less polluting than incandescent light bulbs because they use much less energy. However, they actually use polluting chemicals such as mercury that are not found in incandescent light bulbs. So they use less energy, but more toxic chemicals. The choice of indicators for P2 performance and LCA, such as toxicity or energy efficiency, is important for evaluation.

Facilitative Technologies

Some technologies are important for helping other technologies reduce pollution. For example, process controls such as meters and sensors can make many production processes more efficient and less polluting by providing improved control, which reduces waste and defects. Centrifuges can reduce the amount of solids in wastewaters, thereby reducing water pollution. Catalytic converters on engine exhaust systems can reduce air pollution. There are many such examples of technologies that help other technologies be cleaner. This is important in situations where there is a large investment in an existing technology already installed that cannot be easily or economically replaced with new and cleaner technology.

Technologies Designed to Prevent Pollution

Some technologies are designed specifically for protecting the environment while also improving business performance. For example, recycling technologies can help recover valuable materials from wastes, cutting manufacturing costs, while also preventing pollution. Examples include gene-engineered plants that do not need protection using chemical insecticides and fuel cells for generating electricity. However, it is surprisingly challenging to identify such technologies. Most technologies that stop pollution were usually created to simply reduce costs and save on materials. Technologies designed to prevent pollution usually rely on cost efficiency, rather than pollution prevention, as their main selling point.

One important and fundamental exception is P2 in chemical design. Thousands of chemicals are used in industry, commerce, and daily life. Many of them have environmental impacts, from mild to serious. By developing alternative chemicals with better environmental performance, significant reductions in pollution can be obtained throughout product life cycles. A common application of green chemistry is in the design of environmentally benign solvents. Traditional solvents such as acetone, xylene, and methylene chloride are being replaced by new chemicals designed specifically to be less hazardous or less polluting.

Mass-Market P2 Technologies

Mass-market P2 technologies are those that can be used in many different industries or even in consumer households. These technologies create new markets because their production creates jobs and spin-offs, and they generate ready demand from producers who want to reduce input costs. Each has the following criteria:

1. The technology is widely applicable across a variety of industry types and sizes.

2. The technology does not require very large capital expenditures.

3. The technology's usefulness has been proven through years of implementation experience.

4. The technology has demonstrated free-market feasibility, that is, a positive payback in the productivity of materials, not including reductions in disposal costs.

5. The technology can be supported in the field by local technicians with basic competence.

6. Parts for repair are locally available at reasonable cost.

Example mass-market technologies for P2 include household water-conservation fixtures, variable-speed motors, programmable heating and air conditioning controls, citrus-based solvent cleaners, plastic films for reducing heat transmission through windows, and many others.

International P2 Technologies

The major differences in P2 technologies among countries lie in the age of the technology and the level of process control. In less developed countries, much of the technology is old and would be considered out of date and uncompetitive in developed countries. Consequently, it usually produces much more pollution per unit of output. Less developed countries also tend to use fewer process controls and instrumentation. Much of the operation is controlled by hand or based on experience, rather than real-time data. Human error thus potentially creates more waste and pollution in such situations. But there are no hard and fast rules for differences in P2 technologies between countries. In Thailand, for example, there has been significant investment in new factories in the electronics and auto parts industries. These plants use the latest technology and management practices and are much less polluting than older plants in the same industries operating nearby.

Bibliography

European Environment Agency. (1997). Comparing Environmental Impact Data on Cleaner Technologies, Copenhagen: European Environment Agency.

U.S. Environmental Protection Agency. (2001). Cleaner Technologies Substitutes Assessment, Washington: U.S. Environmental Protection Agency.

EU COMMISSION ON THE ENVIRONMENT

Each citizen of the European Union produces an average of 3.5 tonnes (3.85 U.S. tons) of total waste annually. In view of this, on May 27, 2003, the European Union Commission announced a formal communication or policy statement aimed at reducing waste generation and the use of natural resources, and developing a coherent policy on recycling. Current recycling regulations in the EU are inconsistent. For instance, cardboard and paper packaging are recycled but office paper and newsprint are not. Recycling also often costs more than landfilling or incineration. More industry involvement, tradable environmental permits, national landfill bans and taxes, pay-as-you-throw schemes, and producer responsibility initiatives are among the communication's proposals.

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A pollution prevention (P2) technology is one that creates less pollution in its life cycle than the one it replaces. P2 can be achieved in many ways, from better housekeeping and maintenance to redesign of products and processes. The range of P2 technologies is therefore very broad.

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Application of micro bubble generator as low cost and high efficient aerator for sustainable fresh water fish farming

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Application of micro bubble generator as low cost and high efficient aerator for sustainable fresh water fish farming

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Enter words / phrases / DOI / ISBN / authors / keywords / etc. SEARCH CITATION SEARCH

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Aeration is a process that involves connecting air with water to increase dissolved oxygen or degas dissolved gases in water, such as hydrogen sulfide and volatile organic compounds.

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EFFECTIVE AGAINST: Aeration water treatment is effective for management of dissolved gases such as radon, carbon dioxide, some taste and odor problems such as methane, and hydrogen sulfide, as well as volatile organic compounds, like MTBE or industrial solvents. It is also effective in precipitating dissolved iron and manganese. Aeration raises the pH of water.

NOT EFFECTIVE AGAINST: Aeration is not effective for removal of heavy metals, or pathogenic (disease-causing) organisms like bacteria and viruses.

Aeration is an in-line point-of-entry process that reduces the concentration of volatile organic compounds. Aeration also removes dissolved gases such as hydrogen sulfide, methane, and radon.

Aeration oxidizes dissolved iron, although the resulting iron particles can foul the packing material in some aeration devices.

Aeration treatment consists of passing large amounts of air through water and then venting the air outside. The air causes the dissolved gases or volatile compounds to release from the water. The air and the contaminants released from the water are vented. In the case of iron and manganese, the air causes these minerals to move from their dissolved state to a solid state and precipitate out of solution. The water can then move through a filter to trap the iron and manganese particles.

Aeration devices range from a simple, open holding tank that allows dissolved gases to diffuse into the atmosphere to a more complex aeration system that has a column or tower filled with packing material. As water passes through the packing material, the gases are released.

Adjusting the water pressure is usually necessary following treatment. This involves installing a pump after the treatment device to distribute the water throughout the home.

Types of aeration devices

The three types of aeration devices in home usage are packed tower aerators, multi-stage diffused bubble aerators, and spray aerators.

This system has a tower that may be as tall as 10 feet, filled with packing material. This packing material can range from ¼ inch to 3 inches in size and may be pieces of ceramic or plastic. There is no strong evidence indicating that one type of packing material is better than another. In general, however, the smaller the individual pieces of a particular type, the greater the removal efficiency but the higher the energy costs for air pumping.

In this system, water falls from the top of the tower by gravity while air is blown from the bottom of the unit in a direction opposite to the water flow. Volatile contaminants are transferred to the air by rising to the top of the tower and venting to the outside.

Diffused-bubble aerator

A diffused-bubble aerator has several chambers and a diffuser through which air blows. The diffuser produces fine bubbles that rise through the water as it flows from chamber to chamber. These bubbles carry the volatile chemicals through a vent system to the outside air. The more chambers the system has, the greater the air-to-water contact. Some diffused bubble aerators have a high-float switch that triggers an alarm when the chambers are in danger of flooding.

Spray aeration removes low levels of volatile contaminants, especially radon. In a spray aeration system, water enters through the top of the unit and emerges through spray heads in a fine mist. Treated water collects in a vented tank below the spray heads. Radon and other volatile contaminants are released and vented to the outside.

Air intakes for the aerator can be positioned either outside or inside the home. Avoid areas that have moisture, mold, odors or airborne particles. For locations inside the home, the intake should be at least a foot above the floor and preferably near the ceiling. If the home is "air-tight" construction, an interior intake location may result in a vacuum being created within the home. This will prevent proper venting of the heating system combustion gases unless a fresh air source is provided. If the intake is outside the home, the intake should be high enough to avoid contaminant discharges from such devices as power lawn mowers, leaf blowers, automobiles, boiler exhausts, as well as splash from roof runoff and garden hoses. The intake also needs to be positioned away from the waste air discharge location on the aeration treatment system. An air filter can be installed at the air intake to ensure clean air. Steps should be taken to prevent entry of animals and insects into the intake air.

Waste air from the aerator needs to be disposed of outside the home. Waste air is moist and has a higher concentration of the contaminant that was removed from the water. The waste air discharge point should be above the eave of the roof. Place the vent away from windows and on the downwind side of the prevailing wind direction. The waste air line should include a manufactured vent cap that prevents the entry of dust, bird droppings, small animals, and other bacterial hazards. Mist will carry over from the aerator into the waste air vent line and condensation may also occur. Both the intake and waste air line need to be sloped to allow drainage for moisture. The waste air line connections need to be air tight within the home to prevent leakage of hazardous gas.

Maintenance of aeration systems

Regardless of the quality of the equipment purchased, it will not perform satisfactorily unless maintained in accordance with the manufacturer's recommendations for maintenance, cleaning, and part replacement. Packed tower and diffused bubble aerators must have the blowers maintained by periodically lubricating the motor and changing the air filters. Keep a log book to record water test results, equipment maintenance, and repairs. Proper, adequate ventilation is a must when operating an aeration system. The tanks and trays need occasional cleaning as precipitated sulfur, iron sulfide, rust, and algae collect. A valve controlled drain line to the ground surface makes flushing the storage tank once or twice each year easier.

Other considerations for aeration systems

Ensure the system is installed and operated according to the manufacturer's instructions. After installation, retest both the raw water (prior to treatment) and the treated water at a state certified laboratory to ensure the system is working properly and removing the contaminants. Continue to test the quality of both the raw and treated water annually or more frequently (quarterly or semi-annually) if high levels of contaminants are present in the raw water. Frequent testing will help determine how well the treatment system is working and whether maintenance or replacement of components may be necessary.

If there are elevated levels of dissolved iron or manganese in the water, the aeration process can cause rust and other solids to form, staining plumbing fixtures and clothing unless a post treatment filter is installed to trap the solid forms of iron and manganese. On the other hand, if the raw water coming into the house contains elevated levels of iron and manganese in its solid, precipitate form, a filter may need to be installed before the water enters the aeration system.

Bacterial slime may grow in aerators, requiring continuous or periodic chlorination. Chlorination may oxidize iron and cause it to precipitate out, requiring the need for a filter to remove the iron particles. The advantage of aeration is that there is no disposal or regeneration of treatment media necessary. This is especially important when the contaminant being treated would constitute a hazardous waste disposal problem, such as radon.

Re-pressurizing the treated water is usually necessary. This involves installing a pump after the treatment device to distribute the water throughout the home.

Aeration systems are generally more expensive than other water treatment systems. They are most often used in situations where the levels of volatile compounds are extremely high. If the volatile compound concentration is below 1 milligram per liter or if radon levels are below 5,000 picocuries per liter, activated carbon may be a more economical treatment method.

Another consideration is the length of time the treatment is required. If the water source is only temporarily contaminated, aeration may be a more complex system than is necessary and activated carbon may be more appropriate.

Questions to ask before you buy

Before purchasing a water treatment device, have your water tested at a state certified laboratory to determine the contaminants present. This will help determine if aeration is an effective treatment method for the situation. See Questions to Ask Before You Buy A Water Treatment System for more information.

Adapted from: Wagenet,L., K. Mancl, and M. Sailus. (1995). Home Water Treatment. Northeast Regional Agricultural Engineering Service, Cooperative Extension. NRAES-48. Ithaca, NY.

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EFFECTIVE AGAINST: Aeration water treatment is effective for management of dissolved gases such as radon, carbon dioxide, some taste and odor problems such as methane, and hydrogen sulfide, as well as volatile organic compounds, like MTBE or industrial solvents. It is also effective in precipitating dissolved iron and manganese.

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In the rotary biological contactor approach, a number of circular discs are connected to a rotating axis. Microorganisms can easily stick to the discs, which are normally constructed of reinforced plastic fiber with complex-shaped folding lines, and live on them.

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The disc is made out of light-weighted material such and usually ridged, corrugated, or lattice-like to make as much as surface available for the biofilm to attach. Source: NSFC (2004)

A series of circular lightweight rotating discs are mounted on a shaft through which wastewater flows. The partially submerged discs rotate through the wastewater slowly. The disks are most commonly made of high-density plastic sheets (e.g. Polyethylene, polystyrene or polyvinylchloride) and are usually ridged, corrugated, or lattice-like to increase the specific surface area (NSFC 2004). The surface of the disks provides an attachment site for bacteria and as the discs rotate, a film of biomass grows on their surfaces (NSFC 2004; WSP 2008). This biofilm is alternately exposed to either the air or the wastewater as it rotates. The oxygen necessary for the growth of these microorganisms is obtained by adsorption from the air as the biofilm on the disk is rotated out of the liquid (CRITES & TCHOBANOGLOUS 1998; SANIMAS 2005). As the biofilm passes through the liquid phase, nutrients and organic pollutants are taken up.

All oxygen, nutrients and organic pollutants are necessary for the growth of the microorganism and the conversion of the organic matter to CO2. Nitrogen is removed by nitrification and subsequent denitrification transforming it to gaseous N2, which is released to the air. The process is optimised by adjusting the speed of rotation and the depth of submergence (METCALF & EDDY Inc. 2003). In some designs, air is added to the bottom of the tank to provide additional oxygen in case of high-strength influents (CRITES & TCHOBANOGLOUS 1998).

The submerging level varies from 40 to 80 % (CRITES & TCHOBANOGLOUS 1998) and a usual rotating speed is 1 to 2 rpm (U.S.EPA 1980). The common disc diameter is between 0.6 and 3 m (SANIMAS 2005).

The degradation process is similar to the one in a trickling filter with a high rate of recirculation (CRITES & TCHOBANOGLOUS 1998). The higher contact time in RBCs due to rotation allows up to 8 to 10 times higher levels of treatment than in trickling filters (WSP 2008). Also because the rotation allows both optimum wetting and oxygen supply, RBCs are generally more reliable than other fixed-film processes. Additionally, the disc design is made in such a way that large amounts of biofilm can attach, which means that there is a large amount of biological mass present to degrade the pollutants (WSP 2007). The large amount of biomass and the stability of contact also results in an improved stability and a reduced susceptibility to changes in hydraulic or organic loading compared to conventional activated sludge processes (WSP 2007).

As for all fixed-film processes, primary settling and/or screening is required for the removal of grit, debris, and excessive oil (U.S. EPA 1980, WSP 2008). Such primary treatments are typically septic tanks, Imhoff tanks or anaerobic reactors. To remove sloughing sludge, a post-settling unit (i.e. a clarifier) is also required.

RBCs are a secondary treatment and as for all fixed-film processes, primary settling as well as sedimentation of sloughed sludge in a tertiary clarifier is required (example: greywater treatment in Germany). Source: GTZ (2006)

The performance of RBC systems depends on the design, the temperature, the concentration of the pollutants, the rotating velocity and the hydraulic retention time. RBCs can achieve biological oxygen demand (BOD) reductions of 80 to 90 % (SANIMAS 2005; WSP 2007; WSP 2008). The removal of nitrogen (which is mostly present as ammonia) by nitrification and subsequent denitrification is also high, because both aerobic nitrifying bacteria and anaerobic denitrifying bacteria can simultaneously live in the attached biofilm (HOCHHEIMER 1998), depending on weather they are situated on the bottom of the film, close to the disc support (and thus in anaerobic or anoxic conditions) or at the top of the film exposed to the air.

Both aerobic and anaerobic microorganisms can live in the biofilm and contribute to the removal of pollutant form the water. Source: WIKIPEDIA (2007)

Some other microorganisms which can transform ammonia (NH3) in one single step to gaseous N2 under anaerobic conditions have also been discovered in biofilms growing on RBC. These bacteria were called annamox and resulted in the development of innovative aerobic ammonia removal and wastewater treatment processes.
Little is known about the removal of phosphorus in RBCs, but it can be presumed that large parts of the phosphorus present is either accumulated in the biofilm or in the settled and collected sludge.

RBCs can be arranged in a variety of ways depending on specific effluent characteristics and the secondary clarifier design (e.g. specifically for BOD removal or nitrification, NSFC 2004).

Excess biomass sloughs off the discs by the shearing forces exerted as the discs rotate, combined with the force of gravity (WSP 2008). The rotation movement helps to keep sloughed solids in suspension so they can be carried to a clarifier (gravity settler) for secondary settling. The collected sludge in the clarifier requires further treatment (WSP 2008) for stabilisation, such as anaerobic digestion, composting, constructed wetlands, ponds or drying. Very often in small installations, accumulated sludge is also directed back to the septic tank for storage and partial digestion (U.S.EPA 1980).

Effluents from RBC do not contain high levels of nutrients and are therefore not particularly interesting for agriculture, although they constitute a source of water. However, due to reduced removal of microorganisms (1 to 2 log units, U.S. EPA 2002), RBC effluents require a further treatment, such as sand filtration, constructed wetlands or another form of disinfection (e.g. chemical disinfection or UV disinfection).

RBCs are usually designed on the basis of hydraulic and organic loadings derived from pilot plants and other full-scale installation (WSP 2007). Hydraulic retention times (HRTs) generally lye within some hours up to two days.
Even though RBCs are resistant to shock loading, long-term high organic loading may cause anaerobic conditions, resulting in odour and poor treatment performance (U.S.EPA 1980).

Example of an underground RBC for the decentralised treatment of domestic blackwater. Source: BIOSEPTIC (n.y.)

Recirculation is not normally practised in package fixed-film systems since it adds to the degree of complexity and is energy and maintenance intensive. However, recirculation may be desirable in certain applications where minimum wetting rates are required for optimal performance (U.S.EPA 1980).

Units may be installed at or below ground depending upon site topography and other adjacent treatment processes. Access to all moving parts and controls is required, and proper venting of the units is paramount, especially if natural ventilation is being used to supply oxygen (U.S.EPA 1980).

RBCs are often covered with a fibreglass housing to protect the disks from sunlight, wind, rain and low temperatures as performance of RCS drops considerably at air temperatures below 12°C (U.S.EPA 2002; NSFC 2004).

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Rotating biological contactors (RBC) are a conventional aerobic biological wastewater treatment unit. Conventional biological treatment means activated sludge systems and fixed film systems such as trickling filters, or RBC (NOLDE 1996). The advantage of all these systems is that they are compact (i.e. in densely populated urban settings) and that they efficiently reduce organic matter (JENSSEN 2004).

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Goal 13: Climate action - The Global Goals

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Take urgent action to combat climate change and its impacts.

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"Let's be clear: Human activities are at the root of our descent towards chaos. But that means human action can help solve it."

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From unprecedented wildfires across the US to the extraordinary heat of Siberia, the impacts of climate change were felt in every corner of the world in 2020. We have come to a "moment of truth", United Nations Secretary General Antonio Guterres said in his State of the Planet speech in December. "Covid and climate have brought us to a threshold."

BBC Future brings you our round-up of where we are on climate change at the start of 2021, according to five crucial measures of climate health.
1. CO2 levels
The amount of CO2 in the atmosphere reached record levels in 2020, hitting 417 parts per million in May. The last time CO2 levels exceeded 400 parts per million was around four million years ago, during the Pliocene era, when global temperatures were 2-4C warmer and sea levels were 10-25 metres (33-82 feet) higher than they are now.

"We are seeing record levels every year," says Ralph Keeling, head of the CO2 programme at the Scripps Institution of Oceanography, which has been tracking CO2 concentrations from the Mauna Loa observatory in Hawaii since 1958. "We saw record levels again this year despite Covid."
Read more on the solutions:
The effect of lockdowns on concentrations of CO2 in the atmosphere was so small that it registers as a "blip", hardly distinguishable from the year-to-year fluctuations of the carbon cycle, according to the World Meteorological Organization, and has had a negligible impact on the overall curve of rising CO2 levels.

"We have put 100ppm of CO2 in the atmosphere in the last 60 years," says Martin Siegert, co-director of the Grantham Institute for climate change and the environment at Imperial College London. That is 100 times faster than previous natural increases, such as those that occurred towards the end of the last ice age more than 10,000 years ago.

"If we keep tracking the worst-case scenario, by the end of this century levels of CO2 will be 800ppm. We haven't had that for 55 million years. There was no ice on the planet then and it was 12C warmer," says Siegert.

3. Arctic ice
Nowhere is that increase in heat more keenly felt than in the Arctic. In June 2020, the temperature reached 38 C in eastern Siberia, the hottest ever recorded within the Arctic Circle. The heatwave accelerated the melting of sea ice in the East Siberian and Laptev seas and delayed the usual Arctic freeze by almost two months.

"You definitely saw the impact of those warm temperatures," says Julienne Stroeve, a polar scientist from University College London. On the Eurasian side of the Arctic Circle, the ice did not freeze until the end of October, which is unusually late. The summer of 2020 saw sea ice area at its second lowest on record, and sea ice extent (a larger measure, which includes ocean areas where at least 15% ice appears) also at its second lowest.

As well as being a symptom of climate change, the loss of ice is also a driver of it. Bright white sea ice plays an important role in reflecting heat from the Sun back out into space, a bit like a reflective jacket. But the Arctic is heating twice as quickly as the rest of the world - and as less ice makes it through the warm summer months, we lose its reflective protection. In its place, large areas of open dark water absorb more heat, fueling global warming further.

Multi-year ice is also thicker and more reflective than the thin, dark seasonal ice that is increasingly taking its place. Between 1979-2018, the proportion of Arctic sea ice that is at least five years old declined from 30% to 2%, according to the IPCC.

"White ice reflects a lot of energy from the Sun and helps slow the rate of global warming," says Michael Meredith, a polar researcher at the British Antarctic Survey. "We are accelerating global warming by reducing the amount of Arctic sea ice."

The loss of ice is believed to be disrupting weather patterns around the world already. According to the Grantham Institute, it is possible - though not conclusively shown - that 2018 Arctic conditions provoked the "Beast from the East" winter storm in Europe in 2018 by altering the jet stream, a current of air high in the atmosphere.

"Temperature difference between the equator and poles drives a lot of our large-scale weather systems, including the jet stream," says Stroeve. And because the Arctic is warming faster than lower latitudes, there is a weakening of the jet stream.

"Everything is interconnected. If one part of the climate system changes, the rest of the system will respond," says Stroeve.

4. Permafrost
Across the northern hemisphere, permafrost - the ground that remains frozen year-round for two or more years - is warming rapidly. When air temperatures reached 38C (100F) in Siberia in the summer of 2020, land temperatures in several parts of the Arctic Circle hit a record 45C (113F), accelerating the thawing of permafrost in the region. Both continuous permafrost (long, uninterrupted stretches of permafrost) and discontinuous (a more fragmented kind) are in decline.

Permafrost contains a huge amount of greenhouse gases, including CO2 and methane, which are released into the atmosphere as it thaws. Soils in the permafrost region, which spans around 23 million square kilometres (8.9 million square miles) across Siberia, Greenland, Canada and the Arctic, hold twice as much carbon as the atmosphere does - almost 1,600 billion tonnes. Much of that carbon is stored in the form of methane, a potent greenhouse gas with a global warming impact 84 times higher than CO2.

"Permafrost is doing us a big favour by keeping that carbon locked away from the atmosphere," says Meredith.

Thawing permafrost also damages existing infrastructure and destroys the livelihoods of the indigenous communities who rely on the frozen ground to move around and hunt. It is thought to have contributed to the collapse of a huge fuel tank in the Russian Arctic in May, which leaked 20,000 tonnes of diesel into a river.

5. Forests
Since 1990 the world has lost 178 million hectares of forest (690,000 square miles) - an area the size of Libya. Over the past three decades, the rate of deforestation has slowed but experts say it isn't fast enough, given the vital role forests play in curbing global warming. In 2015-20 the annual deforestation rate was 10 million hectares (39,000 square miles, or about the size of Iceland), compared to 12 million hectares (46,000 square miles) in the previous five years.

"Globally forest areas continue to decline," says Bonnie Waring, senior lecturer at the Grantham Institute, noting that there are big regional differences. "We are losing a lot of tropical forests in South America and Africa [and] regaining temperate forests through tree planting or natural regeneration in Europe and Asia."

Brazil, the Democratic Republic of the Congo and Indonesia are the countries losing forest cover most rapidly. In 2020, deforestation of the Amazon rainforest surged to a 12-year high.

An estimated 45% of all carbon on land is stored in trees and forest soil. "Soils globally contain more carbon than all plants and atmosphere put together," says Waring. When forests are cut down or burned, the soil is disturbed and carbon dioxide is released.
Read more on the solutions:
The World Economic Forum launched a campaign this year to plant one trillion trees to absorb carbon. While planting trees might help cancel out the last 10 years of CO2 emissions, it cannot solve the climate crisis on its own, according to Waring.

"Protecting existing forests is even more important than planting new ones. Every time an ecosystem is disturbed, you see carbon lost," she says.

Allowing forests to regrow naturally and rewilding huge areas of land, a process known as natural regeneration, is the most cost-effective and productive way to capture CO2 and boost overall biodiversity, according to Waring.

As well as showing how much the climate has changed already, these five climate indicators also point the way to the solutions that can curb global warming to safer levels by the end of the century.

As Guterres noted in his December State of the Planet speech, "Let's be clear: Human activities are at the root of our descent towards chaos. But that means human action can help solve it."

--
With data research by Miriam Quick.
--
If you liked this story, sign up for the weekly bbc.com features newsletter, called "The Essential List". A handpicked selection of stories from BBC Future, Culture, Worklife, and Travel, delivered to your inbox every Friday.

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After the turbulent year of 2020, BBC Future takes stock on the state of the climate at the beginning of 2021.

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The law mandates that bioethanol be mixed into every gallon of gasoline sold in the United States, which is currently at 10%. The bioethanol requirement was not met due to a lack of locally available bioethanol. As a result, the government was forced to rely on imports to maintain RA 9367.

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The Importance of Bioethanol and Biodiesel from Biomass

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(2008). The Importance of Bioethanol and Biodiesel from Biomass. Energy Sources, Part B: Economics, Planning, and Policy: Vol. 3, No. 2, pp. 177-185.

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The Philippines used 15.42 million gallons of biofuel every day in 2019. From 0 thousand barrels per day in 2000 to 15.42 thousand barrels per day in 2019, biofuel use in the Philippines climbed by 208.09 percent per year. This is due to the increasing number of people buying tricycles, motorcycles, cars, and other utility vehicles (Lim, 2020). Furthermore, you can see from study conducted by Gatdula et al. (2020) that the Philippines has been largely using imported biofuel than locally produced from years 2007 to 2015.

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Open access peer-reviewed chapter

DOI: 10.5772/intechopen.94357

Abstract

To pursue the continuous implementation of the bioethanol blending mandate by the Philippine Biofuels Law, part of the roadmap of the National Biofuels Board (NBB) through the Department of Energy (DOE) is to find a sustainable feedstock. This is due to the deficit in locally produced bioethanol as there is an insufficient supply of currently used feedstock, sugarcane. There are several biomasses available in the country with components viable for ethanol fermentation. Aside from sugarcane, these include sweet sorghum and cassava (first-generation), rice straw and corn stover (second-generation), and macroalgae (third-generation). Among which, sweet sorghum can be considered as the best complementary feedstock to sugarcane as its syrup can be directly fermented to produce bioethanol. Considering its maximum bioethanol potential yield of 100 L/ton for two croppings annually, a comparably low production cost of PhP 36.00/L bioethanol was estimated, competitive enough with the PhP33.43/L bioethanol from sugarcane. Aside from finding a promising feedstock, the bioethanol production volume in the country must be increased to meet the demand through either working on the optimum processing conditions to increase the capacity utilization from the current 77.9% or through installation of additional distilleries.

chapter and author info

Authors

Kristel M. Gatdula*

Department of Chemical Engineering, College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, Los Baños, Laguna, Philippines

Rex B. Demafelis

Department of Chemical Engineering, College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, Los Baños, Laguna, Philippines

Butch G. Bataller

Department of Chemical Engineering, College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, Los Baños, Laguna, Philippines

*Address all correspondence to: kmgatdula@up.edu.ph

DOI: 10.5772/intechopen.94357

From the Edited Volume

Bioethanol Technologies

Edited by Freddie Inambao

1. Introduction

The use of biofuels in the Philippines was initiated due to the oil crisis of the 1970s. However, the implementation did not immediately push through as the domestic cost of production of biofuels was higher than the cost of importing oil. Hence, to reduce the biofuels production cost and correspondingly its selling price, the Philippine Department of Agriculture (DA), as a member of the NBB, is tasked to develop a sustainable and viable feedstock for the production of biofuels. For each feedstock assessed based on its availability and accessibility, a suitable and economically competitive conversion technology is applied, usually developed through the research programs of the Philippine Council for Industry, Energy and Emerging Technology Research and Development (PCIEERD) of the Department of Science and Technology (DOST). On the other hand, for the implementing policies supporting the Philippine Biofuels program, the enactment of the Republic Act No. 9367 (RA 9367), also known as the Biofuels Act of 2006, designates specific mandates on government agencies particularly to ensure feedstock supply like sugarcane for bioethanol under the Sugar Regulatory Administration (SRA) and coconut for biodiesel under the Philippine Coconut Authority (PCA) [ 1].

RA 9367 aims to increase the contribution of biofuels in the country's energy mix, specifically in the transport sector, by reducing its dependence on fossil-based fuels, mitigating climate change while creating more job opportunities for the national socio-economic development. The law took effect last February 6, 2007, and after two years, 2% by volume blending of biodiesel with diesel and 5% by volume blending of bioethanol with gasoline were implemented. The monitoring of this blending mandate and the evaluation of policy execution are by the NBB, headed by the Philippine DOE. The law also encourages investments in the biofuels sector by providing incentives in the production, distribution and use of locally produced biofuels. Incentives include zero specific tax per liter of volume for biofuels component, exemption from value added tax (VAT) on the sale of raw material used in the production of biofuels, exemption from wastewater charges of all water effluents from the biofuels production in accordance with the Republic Act No. 9275 (Philippine Clean Water Act of 2004), and high priority from government financial institutions if engaged in production, storage handling and transport of biofuels feedstock, biofuels and blending with petroleum as certified by the Philippine DOE [ 2]. Additional incentives such as income tax holiday (ITH), duty-free importation, and low-income tax rate of 10% after the ITH may also be availed as implied by the Republic Act No. 9513 or the Renewable Energy Act of 2008. In tandem with these and with the aim to further boost the country's rural economy, the Joint Administrative Order No. 2008-1 was released providing guidelines governing biofuels feedstock production and emphasizing that feedstocks for biofuels production must only be sourced locally [ 3].

Currently, DOE has maintained the ethanol and biodiesel blends at 10% and 2% by volume, respectively and still unclear whether the blending targets based on the RA 9367 will be increased for the succeeding years. Until now, the insufficient feedstock supply is one of the major dilemmas in the ethanol industry. From the utilization of sugarcane, the ethanol industry players have been in transition to using molasses as source of bioethanol fuel. Molasses, as a byproduct of sugar manufacturing process from sugarcane, also has a limited supply resulting to unwarranted escalation in the price of gasoline when blended with bioethanol. Same case with the biodiesel industry, there is a fluctuation in the price of copra. Coprarefers to the dried coconut kernel or meat from which the oil that is processed to biodiesel is obtained. Unlike sugarcane or molasses, there is oversupply of . Hence, the gradual upward adjustments in the biodiesel blend would not be a problem.

To provide sufficient feedstock to existing ethanol plants, the joint Oversight Committee on Energy of the Philippine Congress and Senate arrived with the interim solutions last year 2019. These include exploring the high yielding varieties of sugarcane and revisiting the available feedstocks in the country for bioethanol production. There is also a continuous conduct of research and development on feedstock sources as imposed by DOE through its Philippine Energy Plan on biofuels for the year 2020 to 2040 [ 4]. Some of the biomass under research and deployment for bioethanol production include sugarcane, cassava and sweet sorghum for first-generation, agricultural and forest residues such as rice straw and corn stover for second-generation, and macroalgae, commonly known as seaweeds for third-generation biofuel. Hence, this book chapter is a consolidation of information on the potential of different biomass available in the Philippines that can be utilized as feedstock for bioethanol production. A brief overview of the bioethanol market in the Philippines is also discussed which supports the need for complementary feedstocks to sugarcane for the different generations of bioethanol. The criteria for selection of a good feedstock for bioethanol, challenges that maybe encountered upon using the biomass as starting raw material, and appropriate conversion technologies are also provided.

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2. Bioethanol situation in the Philippines

2.1 Bioethanol market size and trends

A joint sales report by the Chamber of Automotive Manufacturers of the Philippines, Inc. (CAMPI) and Truck Manufacturers Association (TMA) showed a boost in vehicle sales of 3.5% relative to last year 2018 [ 5]. The increase in purchase of cars, motorcycles, tricycles, and utility vehicles had been attributed to the increasing income of the middle class and improvements in the infrastructure. In addition, the lowering of the amortization costs of most vehicles and lower interest rate make the acquisition of these vehicles more affordable to many. This trend is projected to continue in the future. This surge in the vehicle industry sales brings in the transport sector as the most energy intensive sector contributing the 37.2% in the country's final energy demand. This corresponds to 39.9% gasoline's share out of the 96.4% bulk share of petroleum products used as the sector's primary fuel. The continuous growth in gasoline consumption brought by rapid urbanization and motorization would require larger volume of ethanol [ 6].

For the year 2020, a higher blend of 20% should have been imposed according to the Philippine Energy Plan 2016-2030 ( Figure 1), with the goal also to increase the bioethanol blending up to 85% in 2030 [ 2, 6]. The planned increase is still under review due to several factors such as high feedstock and production cost, insufficient and competing feedstock supply, inadequate bioethanol production plant capacity, as well as importation and price regulations. To meet the country's ethanol demand, the Biofuels Act allowed the importation of bioethanol within four (4) years from the effectivity of the law and only to the extent of the shortage as may be determined by the NBB [ 7]. Imports were sourced from the United States of America, Australia, and South Korea [ 8]. This defeats the purpose of the National Biofuels Program which seeks to reduce dependence on imported oil. Even beyond the imposed period and in the current year, the bioethanol from local sources is still insufficient to meet the demand resulting to huge importation ( Figure 2) despite the disallowance of the law.

There are twelve (12) accredited bioethanol producers with a total production capacity of 380.50 million liters since 2018 ( Figure 3) [ 9, 10] and as of the end of March 2020 ( Table 1) [ 11]. These refineries operate at 77.9% capacity ( Figure 3) [ 9, 10]. Additional three (3) plants with a total capacity of 113 million liters will be on-stream supposedly in 2020, two are still under construction and one completed the pilot plant test [ 11]. This leads to a total of 493.5 million liters production capacity, still lacking to meet the projected bioethanol demand of 847.61 million liters (supposedly at 20% blending rate) for the current year.

From 2007 to 2014, majority of bioethanol produced in the Philippines was sourced from sugarcane ( Figure 4). Due to the SRA's mandate on prioritizing sugarcane for sugar production and the increasing demand in domestic bioethanol, the share of molasses (a by-product in sugar production) in the bioethanol feedstock mix increased in the recent years. In 2018, about 99.2% of domestic bioethanol was produced from molasses [ 9, 10].

The bioethanol price index in the Philippines is determined by the SRA bi-monthly and is based on the equivalent prices of sugarcane and molasses, the two major bioethanol feedstock sources in the country. Figure 5 shows the monthly average prices of sugarcane, molasses, and bioethanol from 2011 to 2020 [ 12]. The bioethanol price shows a general slight increase during this period, which can be attributed to the increase in molasses price. The price of molasses has become more expensive than sugarcane during the period in which its share on the bioethanol feedstock mix has increased. Before, molasses was an under-utilized by-product of sugar mills in the country, but it has found value as a bioethanol feedstock after the implementation of the RA 9367. In the point of view of the sugar mills, the increase in molasses price is advantageous due to the added income that it brings to the mills. But for the bioethanol industry, an increase in molasses price and in general, an increase in feedstock price, would mean an increase in the bioethanol selling price. Currently, bioethanol is more expensive than gasoline. Perhaps, this is one of the bottlenecks in increasing the bioethanol blend as it will drive the price of blended gasoline to increase. One of the possible ways to dampen the increase in feedstock price is to diversify feedstock sources and to increase the domestic bioethanol production capacity.

2.2 Bioethanol industry outlook

In the next 20 years, the country is still expected to heavily rely on petroleum products for fuel ( Figure 6). With the projected increase in bioethanol blend, its demand is also expected to increase to 2616.38 million liters in 2040 [ 8]. More distilleries will be needed to meet this demand as well as land area to be planted for additional bioethanol feedstock.

In the projections by the Philippine DOE, the total gasoline consumption would grow annually by 1.9%, while bioethanol at 9.7%. To meet the 2020 bioethanol demand at 20% blend without importation, the Philippines necessitates 15 additional distilleries. However, starting from 2021 and every other year, there is a need to put up five (5) more bioethanol plants to meet the blending requirements in 2030 ( Table 2) [ 9].

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3. Suitability assessment and challenges of producing bioethanol from biomass sources

3.1 Abundance and availability of feedstock supply

There are three generations of feedstocks that can be used as source of bioethanol and these feedstocks can be further classified based on the substrates present on their structure, suitable for ethanol conversion. One of these includes saccharine-based feedstocks or those containing sugars readily fermentable into bioethanol. Examples of these saccharine feedstocks are sugarcane and sweet sorghum. There are also land-based feedstocks that must undergo pre-processing conditions to make the substrates cellulose and hemicellulose available for ethanol fermentation. These include agricultural and forest residues. On the other hand, the third-generation biofuel feedstock such as macroalgae, commonly known as seaweed, can thrive and expand without taking the land used for agriculture. With the aim also to find a sustainable source of fuel that will not compete with food production, macroalgae's potential as feedstock was explored.

As shown in Table 3, sweet sorghum has the highest ethanol productivity among the potential feedstocks, based on the availability of lands for cultivation and with the assumption of maximum full biomass conversion to bioethanol. Sweet sorghum is drought tolerant and can survive in a range of environmental conditions making it a suitable complementary feedstock to sugarcane. Like sugarcane, sweet sorghum can be regenerated through ratooning. It has a shorter life cycle of four (4) months and its ratoon can be harvested for as early as three (3) months, relatively shorter compared with the 10-month crop duration of sugarcane [ 13]. This crop could be the solution on the issues of land availability for planting sugarcanes in the Philippines.

Rice straw is the 2nd biomass with the highest potential as source of bioethanol based on Table 3. If the establishment of bioethanol plants using rice straw will be realized, this biomass can contribute to about 11% of the total bioethanol demand of the country by 2030 at 85% blending rate. However, currently, there are a lot of emerging applications of rice straw which may lead to competing use of the biomass for ethanol fermentation. Rice straw can be also utilized for practices like soil improvement through carbonization and composting, fuel for power generation, mushroom production, animal feeds and as starting material to produce silica and bio-fiber [ 17].

In terms of maximum bioethanol potential, the seaweed has the highest recorded yield with 467 L bioethanol per ton biomass. is a brown macroalgae which belongs to the phylum Phaeophyta.It has a high content of degradable carbohydrates to bioethanol such as alginate, laminaran, mannitol, fucoidan and cellulose [ 18]. Most of these seaweeds are found in cold waters and grow in the intertidal belt and in the upper littoral region [ 19]. However, seaweed farming is encouraged for feedstock acquisition to avoid compromising and threatening the balance in the marine ecosystem because of uncontrolled harvesting which happened in 2014. It was only in 2018 when the Bureau of Fisheries and Aquatic Resources (BFAR) lifted the ban and allow fisherfolk to collect, sell, trade and transport through Administrative Order 250-2, subject to seasonal restrictions and permit requirements [ 20].

3.2 Low product inhibition and reduced byproduct formation

In the Philippines, fermentation is the commonly used process in producing ethanol from various types of biomass. It is a biochemical conversion of biomass into sugars using acids or enzymes and the transformation of these sugars into ethanol and other chemicals with the aid of yeast, typically Saccharomyces.Parameters that have relative effects on fermentation include pH, temperature, sugar concentration, types of yeast, variation in medium constituents and in the incubation time for inoculum preparation [ 21]. Employing optimum fermentation conditions increases the yeast growth rate and metabolism of substrates, achieving high ethanol yield and reducing byproduct formation.

Saccharomycesis highly specific in converting glucose units to ethanol. However, no biomass contains purely glucose. Thus, low substrate concentration corresponds to low product formation. Since the total sugar in the biomass is regarded as the sum of glucose, fructose and sucrose [ 22] and also comprise of other types such as xylose, ribose, arabinose, sorbose, galactose, mannose, etc., high amounts of substrates remain unconverted. For some feedstocks such as starchy crops, dextrification using an enzyme α-amylase is necessary to hydrolyze first the starch into maltose ( Eq. 1). This step is followed by the use of exoenzyme glucoamylase to achieve conversion of maltose into glucose ( Eq. 2) for then to be converted to ethanol using Saccharomyces. In addition to sugars, there are also salt and sulfated polysaccharides in the biomass structure which inhibit ethanol formation. These are usually removed through chemical treatment prior to fermentation. Nutrient supplementation during fermentation is also done to enhance the activity of the yeast or to improve its substrate consumption rate.

3.3 Low ethanol production cost

Eq. (3) is the established formula for bioethanol reference price provided for producers who use molasses and sugarcane as feedstocks. The equation is a function of average feedstock price and the processing cost per liter of ethanol produced [ 3]. Considering these two variables in comparing the different biomass for ethanol production, sugarcane and sweet sorghum are the cheapest with PhP 33.43/L and PhP 36.00/L respectively, because both can be subjected to direct fermentation. On the other hand, the estimated production cost for seaweed-based bioethanol is around PhP 45.45/L as more pretreatment processes are required to degrade the polymers alginate, cellulose, mannitol, and laminarin into reducing sugars prior to fermentation. Highest production costs for cassava, rice straw and corn stover of PhP 64.45/L, PhP 59.39/L and 46.08 PhP/L, respectively ( Figure 7) are due to use of enzymes or additional chemicals to saccharify the starch to glucose units before fermentation.

The low production costs of bioethanol from sweet sorghum and macroalgae lead to a competitive and comparable farmer's potential annual income from cultivating and harvesting these feedstocks, with PhP 50,000/ha per cropping for sweet sorghum and PhP 97,000/ha for [ 14, 16].

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4. Review on conversion technologies for first to third-generation bioethanol

Bioethanol may be produced from sugary or saccharine feedstocks such as sugarcane and sweet sorghum, starchy feedstocks such as rice and corn, and lignocellulosic feedstocks such as agricultural and forest residues. Bioethanol may also be produced from macroalgae such as .

The general process flow in producing bioethanol from these feedstocks is shown in Figure 8. The juice from sugarcane and sweet sorghum stalks can be directly converted to ethanol via fermentation. Starchy and lignocellulosic feedstocks need to be pretreated and saccharified prior to fermentation adding to the cost of producing ethanol. The pretreatment step is discussed further in Sections 4.1 to 4.3.

The fuel ethanol plant composed of the fermentation, distillery, and anhydrous plant, is the most critical and most complicated part of the processing plant. Figure 9 shows a schematic diagram of the fermentation plant. It is typically composed of a series of seed culture vessels of increasing volume, pre-fermenter, and fermenters. Nutrients needed by the yeast are added to the reactors and typically composed of urea (150 ppm), di-ammonium phosphate (75 ppm). Magnesium sulfate (35 ppm) and biocide (10 ppm). Sulfuric acid is also added at 0.2 ml per 200 ml mash to maintain the pH at 4.1-4.5. The process starts with the sterilization of the substrate at 70°C for 30 minutes and then cooled. The yeast and the nutrients are then added, and fermentation is allowed for 24 hours at 32-34°C. The overall efficiency of the fermentation process is about 80-90% and the alcohol content of the clarified fermented mash is around 7-8% by volume.

The distillation plant, shown in Figure 10, is composed of a primary column, de-aldehyde column, and rectifier column. The primary column concentrates the alcohol content of the clarified fermented mash to about 20-30% alcohol by volume. The de-aldehyde then removes the aldehyde side-product from fermentation. The bottoms from this column is composed of 30-40% alcohol, which is fed to the rectifier column to concentrate it to 95-96% alcohol.

The dehydration plant is composed of a recovery column and two-column pressure swing adsorption (PSA) system containing molecular sieves ( Figure 11). The recovery column removes some water from the rectified spirit, which is then superheated to 140-144°C before feeding to the PSA system. The anhydrous plant produces 99.5-00.95% ethanol with an efficiency of 99.8%.

4.1 First-generation bioethanol production process

4.1.1 Sugarcane and sweet sorghum (saccharine feedstock)

Sugarcane is a grass grown in tropical and subtropical regions propagated for its sugar. In the Philippines, the sugarcane stalk yield of 60 metric ton per hectare can yield about 65 liters ethanol per metric ton per year. A 7692-hectare sugarcane plantation is needed to supply the feedstock requirement of a distillery with a 30-million-liter ethanol capacity.

On the other hand, sweet sorghum [Sorghum bicolor(L.) Moench] is a drought-resistant crop with high agronomic yield and sugar content of stalks. It is considered an alternative to sugarcane as a bioethanol feedstock. It can be harvested after 115 to 120 days, which makes it amenable for multiple cropping through ratooning. Stalk yield can reach 50 metric ton per hectare with an ethanol potential of 100 liters per metric ton per year. A 6000-hectare land planted to sweet sorghum will be needed to support an ethanol distillery producing 30 million liters of ethanol per year [ 23].

Juice extraction and syrup production from sweet sorghum requires the same operations and equipment in sugarcane processing, which includes cane handling and preparation, milling, juice heating, clarification, and evaporation.

4.1.2 Cassava (starchy feedstock)

Cassava is considered the cheapest among the major starch-based feedstock for ethanol production due to its high starch content (about 74% by weight) and starch-to-sugar conversion ratio. It can be harvested year-round in areas with evenly distributed rainfall. The crop is relatively typhoon and drought-resistant and requires minimum crop maintenance. Cassava tubers can also be chipped, dried, and stored for utilization during periods of lean supply [ 24].

During the period of April to June 2020, production of cassava from 110,780.04 hectares planted area was recorded at 722.82 thousand metric tons [ 25]. This is equivalent to a national average yield of 6.52 MT/ha. In ideal production areas for cassava, the yield can reach up to more than 20 metric tons per hectare. Ideal plantation sites are characterized by plain to rolling areas with even rainfall distribution throughout the year and soil types ranging from loam, sandy loam, fine sandy loam and silty clay loam [ 24].

Based on a distillery plant's capacity of 30 million liters per year, at a conservative estimate of 180 L ethanol per metric ton cassava, an estimated 8333 hectares of cassava plantation would be required to supply the feedstock for the plant's optimal operation [ 24].

Before processing to ethanol, the freshly harvested cassava tubers should be transformed first into cassava flour through washing, cleaning, peeling, chipping, drying, storage, and milling. The flour is then mixed with water to make a slurry, which is then gelatinized with steam, liquefied with alpha-amylase, and saccharified with glucoamylase.

Liquefaction consists of gelatinization and dextrinization. Gelatinization is the dissolution of starch into a mash by steam cooking. Gelatinization can be done in a steam jet cooker at 120°C at a residence time of only a few seconds. This step requires steam at 138°C and 2 bar pressure. The gelatinized starch then passes through a holding coil at 120°C for 1 minute and a flash tank before undergoing dextrinization. Dextrinization is the breakdown of the gelatinized starch into smaller fragments by means of alpha- or beta-amylase or dilute acid. This step results to the reduction of the solution's viscosity and the production of maltodextrins. Dextrinization must be done immediately without allowing the solution to cool to prevent recrystallization of starch. The last pretreatment step prior to fermentation is saccharification, which can be accomplished by addition of glucoamylase and thin slops to the liquefied mash. This process is undertaken at 60°C and pH 4.5 for 30-60 minutes. The saccharification reaction is particularly fast up to 70% dextrose; as the 95% dextrose is reached, it starts slowing down [ 24].

4.2 Second-generation bioethanol production process

Second-generation feedstocks for bioethanol production include non-food sources such as agricultural and forest residues and grasses. They are also called lignocellulosic feedstocks since these materials are composed of lignin, cellulose, and hemicellulose. Lignin cross-links with other cell wall component making the hydrolysis of cellulose and hemicellulose to their component monomeric sugars difficult. Delignification and pretreatment are therefore required to make the cellulose and hemicellulose fraction amenable to hydrolysis and fermentation.

Pretreatment can be done physically, chemically, and biologically. Physical pretreatment involves the disruption of the lignocellulose structure by physical and mechanical means to increase the surface area of the biomass and provide access to cellulases upon hydrolysis. Physical pretreatment methods include uncatalyzed steam explosion, liquid hot water, mechanical comminution, and high energy radiation. Chemical pretreatment involves the use of chemicals to delignify the biomass and sometimes to dissolve the hemicellulose fraction to enhance enzymatic digestibility of the cellulose. This pretreatment method includes hydrolysis via concentrated acid and dilute acid, alkaline pretreatment, ammonia fiber/freeze explosion (AFEX), organosolv, pH-controlled liquid hot water, and ion liquids (ILs) pretreatment. Biological pretreatment used wood-degrading microorganisms to modify the chemical composition and/or structure of lignocellulosic biomass and make it more suitable to enzyme digestion [ 14].

Rice straw and corn stover are examples of lignocellulosic materials. They are agricultural wastes; thus, their cost is low if they are to be used as feedstock for bioethanol. However, the high cost of pretreatment makes them unattractive for bioethanol production. For every ton of rice produced, a ton of rice straw is also produced. At 20% moisture content, rice straw's ethanol potential is about 158 L per metric ton. At a yield of 2.6 metric ton of rice per hectare during the dry season, about 50,215 hectares of land planted to rice is needed to support an ethanol plant with a capacity of 30 million liters per year. For corn stover, 20,877 hectares of land planted to corn is needed to provide enough feedstock to an ethanol plant producing 30 million liters per year considering that 3.92 metric ton corn stover can be obtained per hectare and 176 liters ethanol can be produced per metric ton of corn stover [ 26].

4.3 Third-generation bioethanol production process

Over 80 species of are found in the Philippines, widely distributed in the islands of Luzon, Visayas and Mindanao. It has several local names like Aragan, Boto-boto, Lusay-lusayand In the old days, is used as a wrapper to maintain the freshness of fish and other sea commodities. It also functions as animal feed, a healthy beverage, fertilizer and other agricultural uses. Nowadays, the use of these species has been lessened because of modern technologies and concerns on preservation of marine biodiversity [ 27].

The most notable characteristic of brown macroalgae, in particular, is the absence of lignin in its cell walls [ 18]. Lignin, a component of biomass which holds typically the celluloses, is a protective material that provides rigidity to the biomass and the resistance from microbial attack [ 28]. In Figure 12, even though there is no need for delignification process, series of pretreatment methods are necessary to convert the target polymeric constituent to bioethanol.

The seaweed shall undergo physical treatment such as drying and milling for the biomass to be more susceptible to enzyme or chemical. Mannitol can be precipitated through hot (i.e. boiling) water extraction at 96.1% efficiency. Alginic acid, on the other hand, is produced by mixing the seaweed with 4% w/w sodium bicarbonate solution. The supernatant that will be collected after treatment should be stored at 4°C prior to precipitation of alginic acid by adding sulfuric acid. Laminarin can be extracted through sequential hydrochloric acid and ethanol treatment at a working temperature of 70°C. Hydrolysis of cellulose and laminarin can be carried out using the enzyme at 50°C, while the alginic acid using the enzyme lyase at 37°C. Mannitol as a sugar alcohol can be directly fermented into bioethanol [ 29].

Upon fermentation and purification, a maximum ethanol yield of 467 L per ton dried seaweed could be attained from with the following composition (w/w): 21% laminarin, 5% mannitol, 32.65% alginic acid and 6.20% cellulose [ 16]. To produce 30 million liters of bioethanol, which is the typical capacity of distilleries established in the Philippines, a cultivation area of 1918 ha of is needed [ 29]. The seaweed composition dictates the resulting ethanol yield. The variation in composition depends on the maturity of the seaweeds. The maturity can be assessed based on the length of the plant from the holdfast to the tip of the longest shoot. The average of increase in lengths was referred as the periodic mean thallus length. The maturity is also influenced by the habitat as the rocky coralline environment of the sea was reported to be favorable for growth [ 30].

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5. Recommendations on enhancing biomass use for bioethanol production

There are two major gaps in the Philippine bioethanol industry: insufficient feedstock availability and the high domestic ethanol price due to the inefficiency of the process. In selection of complementary feedstock to sugarcane, the potential of crops and their residues should be screened out based on three sustainability criteria: social, economic, and environmental aspects to ensure that the implementation is attainable in the long run. In coordination with an agriculturist, best farm practices and agronomic conditions when the crops should be harvested considering its substrate content (i.e. through sugar analysis) should be recommended. On the processing side, it must be ensured to reduce the byproduct generation by optimizing the fermentation efficiency or the microbial activity and/or improving the pretreatment for lignocellulosic and starchy feedstocks. For agricultural crops as starting raw materials, yield intensification or breeding of good crop varieties are recommended for sufficient feedstock supply. Identification of potential cultivation areas for expansion should also be initiated to continuously sustain the bioethanol blending mandate. Policy support is also one of the most significant on these renewable energy efforts, through concerned agencies headed by the National Biofuels Board.

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6. Conclusions

The enactment of Philippines RA 9367, also known as the Biofuels Act of 2006 makes the country the pioneer in biofuels blending in the Southeast Asia. The law mandates the blending of bioethanol to all gasoline sold in the country which is currently at 10%. However, the bioethanol demand was not met due to insufficient supply of locally sourced bioethanol. Hence, the country resorted to importation to sustain the implementation of RA 9367. DOE which serves as the lead agency of NBB developed roadmap and issued policies to address the feedstock concerns on bioethanol production. These include the proposal for an improved breeding program for sugarcane which is currently used as feedstock for bioethanol. Another goal is to find complementary or alternative feedstocks through extensive research and developments.

In this chapter, the criteria for selecting an ideal feedstock for bioethanol production was based on the abundance and availability of feedstock supply, low product inhibition and reduced byproduct formation, and low ethanol production cost. Upon considering the maximum bioethanol potential and available area for harvesting, the following biomass is recommended for producing bioethanol: sweet sorghum (first-generation), rice straw (second-generation), and macroalgae (third-generation). Among these three, sweet sorghum has the lowest ethanol production cost comparable to sugarcane. Hence, it can be regarded as good complementary feedstock to sugarcane for ethanol production.

The potential of other biomass as source of bioethanol can still be enhanced by applying the appropriate conversion technologies and by working on the optimum conditions of the five (5) major processes: Pretreatment, Saccharification, Fermentation, Distillation and Dehydration. The pre-processing methods of the biomass vary depending on its compositional structure (i.e. saccharine, starchy or lignocellulosic). Aside from the aim of increasing the process efficiency, technical support must also be provided to farmers and fisherfolks on sustainable management of feedstocks.

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Acknowledgments

Results presented in this book chapter are from researches supported by the Philippine DA-BAR, DOE, National Economic Development Authority (NEDA), Philippine Agricultural Development and Commercial Corporation (PADCC), and Philippine National Oil Company - Alternative Fuels Corporation (PNOC - PAFC). Authors would also like to thank all involved stakeholders that made the research projects successful, including the farmers, key industry players and researchers.

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Conflict of interest

The authors declare that they have no known competing financial interests or affiliations that could have appeared to influence the work reported in this book chapter.

Kristel M. Gatdula, Rex B. Demafelis and Butch G. Bataller (February 4th 2021). Comparative Analysis of Bioethanol Production from Different Potential Biomass Sources in the Philippines, Bioethanol Technologies, Freddie Inambao, IntechOpen, DOI: 10.5772/intechopen.94357. Available from:

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Comparative Analysis of Bioethanol Production from Different Potential Biomass Sources in the Philippines

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To pursue the continuous implementation of the bioethanol blending mandate by the Philippine Biofuels Law, part of the roadmap of the National Biofuels Board (NBB) through the Department of Energy (DOE) is to find a sustainable feedstock. This is due to the deficit in locally produced bioethanol as there is an insufficient supply of currently used feedstock, sugarcane.

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Agricultural biomass as a source of energy has a number of environmental and economic benefits, and it has the potential to significantly contribute to today's fuel demands. At this time, thermochemical techniques for converting agricultural biomass to energy appear promising and practicable.

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Biofuels Production from Biomass by Thermochemical Conversion Technologies

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Agricultural biomass as an energy resource has several environmental and economical advantages and has potential to substantially contribute to present days’ fuel demands. Currently, thermochemical processes for agricultural biomass to energy transformation seem promising and feasible. The relative…

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According to the Department of Energy's forecasts, total gasoline consumption will increase by 1.9 percent annually, while bioethanol will increase by 9.7 percent. The Philippines will need 15 more distilleries to meet its 2020 bioethanol needs at a 20% blend without importing. However, starting in 2021 and every other year thereafter, five more bioethanol units will be required to achieve the 2030 blending standards (Gatdula et al., 2021).

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The progress of biofuel production in the Philippines

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The progress of biofuel production in the Philippines

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Philippines Biodiesel production, 1949-2020 - knoema.com

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In 2019, biodiesel production for Philippines was 3.79 thousand barrels per day. Biodiesel production of Philippines increased from 0 thousand barrels per day in 2000 to 3.79 thousand barrels per day in 2019 growing at an average annual rate of 304.37%. Biodiesel is a fuel typically made from soybea…

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Microalgae are microorganisms that can be used to make biofuels, bioactive pharmaceutical compounds, and food ingredients. They are renewable, sustainable, and cost-effective. By addressing the inherent hurdles and limits, algal fuel and bioproducts technologies can be upgraded from pilot to commercial scale.

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Microbial Cell Factories 17, Article number: 36 (2018) Cite this article

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Abstract

Microalgae have recently attracted considerable interest worldwide, due to their extensive application potential in the renewable energy, biopharmaceutical, and nutraceutical industries. Microalgae are renewable, sustainable, and economical sources of biofuels, bioactive medicinal products, and food ingredients. Several microalgae species have been investigated for their potential as value-added products with remarkable pharmacological and biological qualities. As biofuels, they are a perfect substitute to liquid fossil fuels with respect to cost, renewability, and environmental concerns. Microalgae have a significant ability to convert atmospheric CO ₂ to useful products such as carbohydrates, lipids, and other bioactive metabolites. Although microalgae are feasible sources for bioenergy and biopharmaceuticals in general, some limitations and challenges remain, which must be overcome to upgrade the technology from pilot-phase to industrial level. The most challenging and crucial issues are enhancing microalgae growth rate and product synthesis, dewatering algae culture for biomass production, pretreating biomass, and optimizing the fermentation process in case of algal bioethanol production. The present review describes the advantages of microalgae for the production of biofuels and various bioactive compounds and discusses culturing parameters.

Introduction

Algae are photosynthetic organisms that grow in a range of aquatic habitats, including lakes, pounds, rivers, oceans, and even wastewater. They can tolerate a wide range of temperatures, salinities, and pH values; different light intensities; and conditions in reservoirs or deserts and can grow alone or in symbiosis with other organisms [ 1]. Algae are broadly classified as Rhodophyta (red algae), Phaeophyta (brown algae), and Chlorophyta (green algae) and classified by size as macroalgae or microalgae. Macroalgae (seaweed) are multicellular, large-size algae, visible with the naked eye, while microalgae are microscopic single cells and may be prokaryotic, similar to cyanobacteria (Chloroxybacteria), or eukaryotic, similar to green algae (Chlorophyta).

Microalgae can be a rich source of carbon compounds, which can be utilized in biofuels, health supplements, pharmaceuticals, and cosmetics [ 2]. They also have applications in wastewater treatment and atmospheric CO ₂ mitigation. Microalgae produce a wide range of bioproducts, including polysaccharides, lipids, pigments, proteins, vitamins, bioactive compounds, and antioxidants (Fig. 1) [ 3]. The interest in microalgae as a renewable and sustainable feedstock for biofuels production has inspired a new focus in biorefinery. Growth enhancement techniques and genetic engineering may be used to improve their potential as a future source of renewable bioproducts.

Microalgae convert atmospheric CO ₂ to carbohydrates, lipids, and other valuable bioproducts by using light. Microalgae biomass is a rich source for biofuels and bioactive compounds

The industrial cultivation of microalgae to produce biofuels and bioproducts has increased dramatically over the last few decades [ 4]. Algae are produced in quantity and sold directly as food and nutrient supplements, while their processed products or extracts are used in biopharmaceuticals and cosmetics [ 5, 6, 7].

Bioenergy and microalgae

The rapid growing population of the world continuously increases the global demand for fuel energy. The intensive use of fossil fuels worldwide leads to its depletion and will bring them close to the point of exhaustion due to unsustainable and nonrenewable nature. Thus, biofuels are now a growing opportunity throughout the world as alternative to fossil fuels. Some developed countries are already producing biofuels at the commercial level. Biofuels such as biodiesel and bioethanol are proving to be excellent alternative fuels and can be produced from several resources of biomass, such as food crops, crop wastes or fruits, woody parts of plants, garbage, and algae [ 8, 9]. The advantageous features of biofuels produced from biomass are renewability and a significantly smaller contribution to environmental pollution and global warming. The emission of greenhouse gases mainly CO ₂ from burning of fossil fuels are the main cause of global warming. Fossil fuels are responsible for 29 gigatons/year release of CO ₂ with a total of 35.3 billion tons CO ₂ till now [ 10]. Biofuels including algal fuels have oxygen levels of 10-45% and very low levels of sulphur emission while petroleum-based fuels have no oxygen levels with high sulphur emission. Biofuels are non-polluting, locally available, accessible, sustainable and reliable fuel obtained from renewable sources. Microalgae algae-based fuels are ecofriendly, nontoxic and with strong potential of fixing global CO ₂. It has been reported that 1 kg of algal biomass is can fix 1.83 kg of CO ₂ furthermore some species use SOx and NOx as nutrient flow along with CO ₂ [ 11]. CO ₂ constitutes 50% of dry weight of algal biomass. The selection and development of biomass is a crucial, cost-limiting phase in biofuels generation for adjusting and optimizing energy structure and cost. Selection of biomass for biofuels production is also directly related to greenhouse gas emissions, environmental and economic sustainability [ 12]. The current focus is on microalgae as a feedstock for bioenergy production as the most promising raw material to compensate and balance the ever-increasing demands for biofuels, food, feed and valuable chemicals production [ 9, 10]. Many countries in Asia, Europe, and America have started industrialization of bioenergy from microalgae biomass.

Microalgae are rapidly growing photosynthetic organisms having potential of transforming 9-10% of solar energy (average sunlight irradiance) into biomass with a theoretical yield of about 77 g/biomass/m ²/day which is about 280 ton/ha/year [ 13, 14]. At lager scale cultivation this yield is lower both in outdoor and indoor culture system. In Photobioreactors the actual yield is lower due to loss of absorbed active radiation [ 15, 16, 17], Proper shaking and mixing of the culture in the bioreactor is necessary for uniform distribution of light energy to avail the same strength to all the cells to convert maximum light energy to biomass.

In several aspects, microalgae feedstock is competent and preferable to produce biofuels for examples microalgae don not require cultivable land and fresh water for cultivation, they are not edible therefore no effect on human and animal's food chain, can be grown to serval folds irrespective to seasonal conditions, mitigation of atmospheric CO ₂ and treatment of waste water [ 18, 19]. Absence of lignocellulosic materials in microalgae cell wall facilitate the pretreatment process and reduce overall cost of production. Microalgae can feed on industrial wastes and the processing energy is less than the energy produced by the algae [ 20, 21, 22]. Second generation biofuels involve terrestrial plants, especially food crops as feedstocks, a highly controversial issue, since biofuels production from food crops can only occur at the expense of their use as food and feed. Additionally, crop foods require arable land and large amounts of water, which makes their use for fuel production unsustainable and thus, incomputable as alternative liquid fuels [ 23, 24]. The algal fuels technology is still incipient, and much improvement is required to make it commercially attractive to both, investors and consumers.

Most of the microalgae species are favorable for biodiesel production due to high lipids contents 50-70% and may reach to 80% such as in case of the microlaga B. braunii which accumulate up to 80% of oil in it biomass [ 25, 26, 27]. Microalgae are capable of producing algal oil 58,700 L/hac which can produce 121,104 L/hac biodiesels [ 11, 28, 29]. The infeasibility of algal biodiesel is due to the associated high operational, maintenance, harvesting and conversion cost [ 30].

Bioethanol is one of the major and clean biofuel used as transportation fuel. Bioethanol has many advantages over fossil fuels, such as (i) high octane number in bioethanol prevents knocking of cylinders in engines (ii) due to the presence of higher oxygen contents, bioethanol burning produces much less greenhouse-effect gasses (iii) Bioethanol is the only biofuel that can be used directly in the current automotive industry without any modifications (iv) Bioethanol can be mixed with oil [ 31, 32, 33]. Global production of biofuels has increased from 4.8 to 16.0 billion of gallons from 2000 to 2007 [ 34]. Currently, the USA and Brazil are the world leaders in the production of bioethanol. Their contribution is approximately 75-80% of the world total bioethanol production [ 32, 34]. The USA have 187 commercial bioethanol plants, which mainly produce bioethanol from corn grain [ 31]. In 2013, Brazil produced 37 billion l of bioethanol using sugar cane as the main feedstock. The European Union (EU), uses wheat and sugar beet as the preferred feedstock for bioethanol production and produces 2.0 billion gallons annually [ 31, 32].

Biofuels from renewable and sustainable feedstock are the future permissive energy sources in place of fossil liquid fuels. Today, bioethanol is the most common biofuel, mainly produced from sugars of corn and sugarcane, but the technology is now shifting towards algal carbohydrates as potential raw materials for bioethanol production [ 35, 36, 37]. Global bioethanol production has vigorously increased from 1 billion to 39 billion l within a few years and will reach 100 billion l soon [ 38].

Microalgae possess high contents of different carbohydrates, such as glycogen, starch, agar and cellulose, etc. which can be easily converted to fermentable sugars for bioethanol production [ 39]. Figure 2 presents carbohydrate-rich microalgae species suitable for algal bioethanol production.

Different species of carbohydrate-rich microalgae that compose feasible feedstock for bioethanol production

Extraction of the stored carbohydrates from algae cells needs lysis of the cells. This may be accomplished in different ways, such as enzymatic, acidic or solvent extraction. However, ethanol yields depend on the method followed for the extraction. The extracted sugars need pretreatment to break the polymer molecules to monomeric forms that can be subjected to microbial fermentation to yield bioethanol [ 8].

Bioethanol production from microlage is an excellent effort in the development of sustainable biofuels, still there are some challenges regarding large-scale production and commercialization of this clean biofuel. The main areas in the development of algal bioethanol technology, which should be optimized for the commercialization of bioethanol are, selection of the algal biomass, pretreatment and an efficient fermentation process. Fermentative ethanol yield greatly depends on the potential of the fermenting microorganisms used. The fermentation process should be carried out in an aseptic environment to avoid contamination, which greatly reduces final yields [ 40]. The potential of microalgae to become a competitive feedstock for bioethanol production will require a continued effort to overcome current limitations regarding (i) culturing algae and producing carbohydrate- rich biomass (ii) dewatering and harvesting (iii) pretreatment of biomass (iv) ensuring maximum yielding fermentation. Development of a cost-effective algal system can be achieved by improvement and optimization of each of the above mentioned. Both biomass and carbohydrate productivity of algal cells need to be increased for economical and feasible production of bioethanol [ 7]. Some carbohydrates rich microalgae like Chlamydomonas reinhardtii and Chlorella vulgaris are considered to be potential for techno-economic analysis (TEA) of bioethanol production [ 41]. TEA of commercial bioethanol production from microalgae estimate suitability of the plant with respect to total investment, total cost ant total net profit [ 42].

Increasing the feasibility of microalgae for higher bioethanol yields through fermentative production, requires careful consideration of several parameters. The key factor for economic feasibility of microalgae biofuels are maximizing the algal biomass with reduction of operational and maintenance cost [ 43]. It has been stated that the economic viability of algal fuels need at least more 10 years research and development to achieve a stable position [ 44]. US Renewable Fuels Standard (RFS) estimated to obtain 36 billion gallons of microalgae-based fuels by the year 2022 [ 45].

Algae culturing

Large-scale microalgae cultivation will decisively contribute to the development of a sustainable industry for biomass production as well as generating cost-effective high-value products. Many species of microalgae show potential for large-scale cultivation, but there is insufficient information to run commercial trials. A huge amount of microalgae biomass is required to compete with other feedstocks for sustainable production of bioethanol. Successful microalgae culturing technologies will need to create larger amounts of biomass, which will make the use of food stuffs for bioethanol production comparatively less attractive.

Microalgae can be cultured by different methods and under different conditions. They need light as an energy source to convert the absorbed water and CO ₂ into biomass through photosynthesis [ 49]. Photosynthetic products accumulate in various forms, such as cell components or storage materials, and vary from 20 to 50% of total biomass [ 25]. Algae also need nitrogen and phosphorus as major nutrients, which account for 10-20% of algae biomass [ 50]. Other requirements for growth are the macronutrients Na, Mg, Ca, and K; micronutrients, such as Mo, Mn, B, Co, Fe, and Zn; and other trace elements. Wastewater is a good source of the required nutrients for microalgae cultivation. Thus, application of organic effluents from the food and agriculture industries can nourish microalgae.

During growth, the algae cells pass through different phases (e.g., lag, exponential, stationary, death). Different species of microalgae may vary in their need for growth media. However, the major requirements are the same for almost all species and include essential nutrients, an organic or inorganic carbon source, nitrogen, phosphorus, and iron [ 51].

One of the most important parameters in algae culturing is the type of bioreactor used. This should be designed according to the species and the purpose of culture. On a large scale, algae can be cultured in open ponds (high-rate ponds). Open culture systems are comparatively inexpensive, but they become easily contaminated. Other bioreactors have continuous or batch culture facilities [ 52, 53]. Some species of algae grow very well in heterotrophic culture [ 54]. For commercial cultivation it is feasible to grow microalgae in waste water treatment plant to get dual advantages of water treatment and biomass production. See water is also a good alternative for commercial cultivation of microalgae. Using see water instead of fresh water for microalgae culturing will reduce the cost of production. Marin water is a good media for microalgae culture avoiding nutrients cost and enhancing productivity of lipids and other useful products in microalgae biomass [ 55]. Most recently ocean cultivation system has attracted attention for commercial scale production of algae due the advantages like mixing of the culture by ocean waves, utilizing dissolve nutrients large area availability, etc. which result in the reduction of culturing and maintenance cost [ 55, 56, 57].

To make the algae biotechnology sustainable, feasible and economically viable it is necessary to develop successful culturing technologies for targeted production of biomass. For a feasible algal culture, the biomass output should be > 30 g/m ²-day [ 58]. Approximately 40,000 different species of microalgae have been reported [ 59]. Microalgae culture depends on the species and is affected by factors such as nutrient availability (N, P, K, etc.), temperature, pH, salinity, inorganic carbon, oxygen, light intensity, and CO ₂ [ 60]. Other important factors that determine the success of culture include stirring and mixing, width and depth of the bioreactor, harvest frequency, and dilution rate. Following are the important parameters of culture which has great influence and impact on the overall yield of biomass and bioproducts in microalgae.

Light

Light intensity is one of the major limiting factors in microalgae cultivation. Light duration and intensity directly affect photosynthesis of microalgae and has influence on the biochemical composition of microalgae and biomass yield [ 61]. In modeling of the outdoor or indoor algal culture system, growth rate and biomass productivity are predicted as a function of light [ 62]. Light intensities vary inside the culture and reduce in culture depth this should be taking in consideration for modeling of the bioreactor or open pond system. Algae species vary in terms of their light requirements for maximum growth and biomass accumulation.

At very low and very high light intensities, microalgae cannot grow efficiently [ 60, 63, 64, 65]. At the compensation point, where photosynthetic CO ₂ uptake exactly matches respiratory CO ₂ release, net growth is zero. Higher light intensities will increase photosynthetic rate to some maximum point, after which it levels off until the photosynthetic rate is balanced by photorespiration and photoinhibition. Thus, optimal light intensity needs to be determined experimentally in each case to maximize CO ₂ assimilation with a minimum rate of photorespiration and as little photoinhibition as possible [ 65]. A specific duration of light/dark periods is required for algal photosynthesis. Light is required for synthesis of ATP and NADPH, which drive the dark reactions of photosynthesis that produce carbon skeletons [ 66]. There is a direct relationship between microalgae growth and light intensity and duration, up to the saturation point. Khoeyi et al. [ 67] experimentally proved the differences in the growth rate and biomass yield by growing the same algae strain under different light intensities and for various durations. The growth rate and biomass productivity decreased with decreasing light duration [ 68]. Most studies have shown that 16 h light/8 h dark is most suitable for algae growth. Appropriate light intensity and duration is necessary in bioreactors for microalgae to avoid photo-oxidation and growth inhibition [ 69]. Appropriate penetration and uniform distribution of light is also needed to avoid photoinhibition, also called the self-shading effect, in which algae at lower layers are shaded from the light by upper layers. LED lights are a good choice for this purpose, although fluorescent tubes can also be used [ 70]. Mata et al. [ 60] reported that an aerated culture of microalgae under 12,000 lx intensities for 12 h of daylight produced a higher biomass yield, whereas biomass decreased when the light intensity was reduced. Khan et al. [ 71] reported that microcystis aeruginosa give maximum biomass and carbohydrates productivity at red LED light of about 5000 lx. Daliry et al. most recently reported the maximum growth rate and lipid production by Chlorella vulgaris at light intensities of 5000-7000 lx [ 72]. The optimum level of light intensities for most of the microalgae species are about 200-400 μM photons/m ²/s [ 73]. Photoinhibition can be prevented by increasing the light intensity or by thoroughly mixing the culture continuously. Hence, light directly affects the final yield of biomass and synthesis and accumulation of carbohydrates in the algal cells. Kitaya et al. [ 74] experimentally proved that a light intensity of 100 µmol/m ²/s is optimum for some microalgal species.

Temperature

Temperature is another important factor in the growth of microalgae and directly influences the biochemical processes, including photosynthesis, in the algal cell factory. Each species has its own optimal growth temperature. Increasing temperature to the optimum range exponentially increases algal growth, but an increase or decrease in the temperature beyond the optimal point retards or even stops algae growth and activity [ 75]. The optimum temperature range for most algal species is 20-30 °C [ 76] although thermophile algae such as Anacystis nidulans and Chaetoceros can endure temperatures up to 40 °C and algae growing in hot spring near temperature 80 °C [ 77]. Growing microalgae cultures at non-optimal temperatures will result in high biomass losses, particularly in outdoor culture systems [ 63, 78, 79]. Temperature is important factor for large scale cultivation specially in open pond culture and need careful monitoring as the algae experience significant temperature change over time [ 80].

Low temperatures affect photosynthesis by reducing carbon assimilation activity, whereas too-high temperatures reduce photosynthesis by inactivating the photosynthetic proteins and disturbing the balance of energy in the cell. Higher temperature also reduces cell size and respiration. The decline in photosynthesis results in a decreased growth rate [ 81]. The key effect of temperature on photosynthesis is due to a decline in the activity of ribulose-1,5-bisphosphate (Rubisco), an enzyme with dual functions. It can act as an oxygenase or as a carboxylase, depending on the relative amounts of O ₂ and CO ₂ present in the chloroplasts. CO ₂ fixation activity of Rubisco enzyme increases with rising temperature up to a certain level and then declines [ 82]. Hence, temperature is a limiting factor for algal growth rate and biomass production through its influence on the affinity of ribulose for CO ₂.

Temperature can also be used as a stress treatment to induce the production of valuable metabolites [ 83]. Converti et al. [ 84] found that a culture of Chlorella vulgaris produced more carbohydrates and lipids if grown at 25 °C than at 30 °C. Kitaya et al. [ 74] found that temperatures between 27 and 31 °C were optimum for several microalgae species.

Nutrients

Different microalgae species may vary in their nutritional needs; however, the basic requirements are same for all species. Nitrogen, phosphorus, and carbon form the backbone of microalgae (CH 1.7 O 0.4 N 0.15 P 0.0094) [ 85] and are classified as macronutrients required for algal growth. Some marine microalgae species also require silicon as a macronutrient. Microalgae absorb O ₂ and H ₂ from water. The quantities of macronutrients such as nitrogen and phosphorus may vary for different species of microalgae. It has been reported the growth of chlorella declined when the concentrations of nitrogen and phosphors reduced from 31.5 and 10.5 mg/l respectively [ 86]. Quantities of the available nitrogen in the culture directly alter cell growth. Nitrogen limitation in the microalgae culture, can reduce growth and biomass productivity although they increase production of carbohydrates and lipids. 0.5 g/l nitrogen has been proved to be optimum concentration for Chlorella vulgaris at which it produces 3.43 g/l biomass [ 72].

the micronutrients Mo, K, Co, Fe, Mg, Mn, B, and Zn are only required in trace amounts but have a strong impact on microalgae growth, as they influence many enzymatic activities in algal cells [ 78, 87] Usually, inorganic nitrogen and phosphorus are absorbed as nitrates and phosphates. Urea is also a suitable source and a cost-effective alternative to other inorganic nitrogen sources. Carbon can be added to the algae culture in organic forms, such as glycerol or acetates, or as CO ₂. However, for large-scale cultivation of microalgae, environmental CO ₂ must be used as a carbon source, which is not only low cost but adds the benefit of CO ₂ mitigation. P, N, and C are the primary inorganic nutrients that are essential for microalgal growth [ 88]. Nutrient deficiency greatly affects the microalgae growth rate and results in low biomass [ 89, 90, 91, 92]. The nutrient supply strongly affects the synthesis and accumulation of carbohydrates and lipids in microalgae [ 91].

For commercial production of microalgae biomass, the culture must be grown rapidly; thus, providing the proper nutrients is very important to speed algal growth. Some strongly limiting substances can be used as growth enhancers for microalgae. In addition, certain bacteria can enhance the growth rates of microalgae by supplying important nutrients. These bacteria degrade nutrients into forms that can be readily assimilated by microalgae, such as ammonia or nitrate [ 93].

Mixing

Mixing and aerating provide uniform distribution of nutrients, air, and CO ₂ in microalgae culture. They also enable the penetration and uniform distribution of light inside the culture and prevent the biomass from settling and causing aggregation [ 94]. If all the other requirements are met but there is no mixing, biomass productivity will be lowered significantly. Thus, microalgae cultures must be continuously mixed to keep all cells in suspension with free access to light. A proper mixing system in a photo-bioreactor not only enables nutrient dissolution and light penetration into the culture but also provides for efficient gaseous exchange [ 95].

pH and salinity

The pH of the culture media is another important factor affecting microalgae growth. Microalgae species have different pH requirements. Most grow well in the pH range from 6 to 8.76 Different sources of growth media have different pH values. Most algae species are pH sensitive and few can endure a range of pH as broad as that tolerated by C. vulgaris [ 96]. C. vulgaris can grow in broad range of pH however the maximum growth rate and biomass productivities are reported at pH 9-10 [ 72]. Increasing the pH will increase the salinity of the culture media, which is very harmful for algae cells [ 85].

Mixotrophic cultivation

In autotrophic cultivation, microorganisms rely on light energy to generate energy, whereas in heterotrophic cultivation, organic carbon sources are used for metabolism. Mixotrophic conditions combine autotrophic and heterotrophic models so that the cultured microorganisms have both a supply of inorganic carbon to be fixed via photosynthesis and some organic carbon source, such as glucose, glycerol, and acetate [ 97]. The microorganisms in mixotrophic cultures grow faster and can synthesize compounds through both autotrophic and heterotrophic pathways. Moreover, they have a reduced cost of light energy (compared with autotrophic culture) and organic compounds (compared with heterotrophic culture) [ 98].

Modifications and improvement of the algal strains

Hence, efforts are increasing to develop carbohydrate-rich microalgae strains with the help of engineering approaches. Rapid development in genetics has made a number of transformation methods available, and successful trials encourage the use of genetic tools for a variety of purposes. Although the technology has not made satisfactory progress in the field of algal bioethanol yet, expectations for the near future are high.

Pretreatment of algal biomass

Pretreatment of algal biomass involves the degradation or disruption of biomass to convert, accumulate, and process the carbohydrates and lipids it contains (Fig. 3). On a large scale, biomass pretreatment is a bottleneck and potentially costly step in biofuels production. Many different methods have been described for the pretreatment of algal biomass, but there is still no optimal, highly productive method. Researchers need to develop feasible and economical methods of biomass pretreatment for bioethanol production, optimized for different feedstocks.

Pretreatment of microalgae biomass for biofuels production. Different types of biofuels can be produced depending on the raw materials used (carbohydrates and lipids) and the pretreatment prior to fermentation

Pretreatment of the algal biomass for fermentation involves lysis of algal cells to release the stored carbohydrates from inside the cells. The next step is the saccharification of the accumulated sugars to monomeric units, as fermenting microorganisms can only convert the fermentable forms of sugars (disaccharides and monosaccharides, usually hexoses and pentoses) into ethanol [ 104]. Algal biomass for bioethanol production is usually pretreated with acids and alkalis. Depending on the purpose of pretreatment, chemical, biological, thermochemical, or thermophysical methods are used, sometimes in combination [ 105, 106]. After lysis of the cells the macromolecules of sugars need saccharification which mean to break the α-(1 → 4), α-(1 → 6), β-(1 → 3) and β-(1 → 6) glycosidic linkages between the monomers to release the monomers units [ 107]. Lignocellulose present in the biomass impedes the pretreatment process, as this material is recalcitrant to conversion. The amount of lignocellulose also increases the cost of the whole pretreatment process. Hence, it is ideal if algal biomass has few or no lignocellulosic components present. This would make it economically more competitive than other feedstocks, such as terrestrial plants [ 108, 109]. Furthermore, the presence of cellulose in algal cell walls requires efficient degradation and conversation, approaches that also need to be optimized.

Algal biofuels technology needs to face the challenges of biomass harvesting and efficient pretreatment at low cost, with reduced emission of gases and high yields with scalable co-products. As different products are obtained from different source materials, pretreatments of biomass are often related to the products of interest. Thus, mechanical methods of pretreatment yield biodiesel, while enzymatic and chemical methods (including acidic hydrolysis) are used in bioethanol production, because fermentative bioethanol production requires degradation of cellulose, hemicellulose, and starch. In some cases, hydrothermal methods are also applied in combination with these. The cost of pretreating microalgae is far less than that of pretreating terrestrial plant biomass. Microalgae store photosynthetic products as cellulose, starch, and hemicellulose; some species also accumulate galactan. Algal cells are almost like lakes of lignin, which makes them a suitable and preferable feedstock for bioethanol production. Some of them contain other forms of carbohydrates that can be fermented to produce bioethanol and chemical feedstocks.

Some researchers have used mechanical methods, such as ultra-sonication, microwaves, and beating, to degrade algal biomass [ 114, 115]. Mechanical methods can be combined with chemical methods to reduce chemical waste and enhance the pretreatment process. They do not contaminate the environment, but they do impose higher costs, due to the consumption of energy [ 116, 117]. Enzymatic pretreatment of algal biomass is more productive and advantageous for fermentation processes [ 118, 119]. Enzymes such as amylases, cellulases, and invertases are common catalyzers that can hydrolyze a specific sugar substrate by selectively breaking the linkages between the units of the polysaccharide and releasing the monomer sugars. However, the high cost of enzymes makes this method exceedingly expensive for large-scale biomass pretreatment. An appropriate solution is to identify a microorganism that can overexpress the genes encoding these enzymes [ 120].

Fermentation of the algal sugars to generate bioethanol

Fermentation is the biological process whereby sugars are converted to bioethanol by the action of fermenting microorganisms. Fermentable sugars, such as glucose, fructose, maltose, and rhamnose, are used as substrates by microorganisms in the fermentation process, which converts them to ethanol and CO ₂ [ 121, 122]. Several types of microorganisms, such as bacteria, yeasts, and fungi, have been identified for their potential for fermenting sugars to bioethanol [ 123, 124, 125]. The yield and quality of the bioethanol produced is strongly dependent on the fermentation process, which is affected by several factors, such as temperature, pH, oxygen, substrate concentration, and the fermenter organism used [ 126, 127, 128, 129, 130].

The algal sugars are excellent materials for bioethanol production. As mentioned above some species of microalgae are most adventitious for bioethanol production due to their higher sugars profile. However, the carbohydrates in algal biomass are mostly in polymeric form and need conversion to monomers unit to be readily fermented by microorganisms to produce bioethanol [ 131]. Veracious scientist reported various yields of fermentable sugars and ethanol from different species and strains of microalgae.

Scenedesmus dimorphus accumulated 53.7 w/w carbohydrate contents which on hydrolysis with sulfuric acids produced 80% fermentable sugars, indicating its feasibility for bioethanol production [ 132]. 11.7 g/l final ethanol yield was reported from Chlorella vulgaris [ 111]. Sivaramakrishnan et al. [ 133] recently reported 93% of ethanol yield from fermentation of Scenedesmus sp. derived sugars.

To scale up the fermentation process and define a commercialization strategy for bioethanol, the problems associated with alcoholic fermentation must be overcome. For bioethanol production to be viable, all the different types of sugars (pentoses and hexoses) must be converted to bioethanol. Fermenting microorganisms are substrate-dependent, so the substrate should be chosen carefully to maximize yields. Algae biomass contains different types of fermentable sugars, therefore combination of the fermenter microorganisms is preferable and effective, because different microorganisms have different rates of conversion for different substrates [ 134].

Use of microalgae for food feed and bioproducts

The indigenous use of algae as food sources is an ancient practice. Many species of green algae have been utilized as food from ancient times [ 135]. Cultivation of microalgae started only a few decades ago, when it became clear that the fast-growing world population was likely to suffer a lack of protein-rich food stuffs [ 136]. Microalgae are an excellent source of food and other important bioproducts, such as natural antibiotics [ 137, 138, 139]. The world energy crisis in the 1970s led to the identification of algae as renewable and sustainable sources for biofuels production, prompting the exploration of microalgae as a new field of research for fuels and other valuable products [ 10, 140]. The first large-scale culture of the microalga Chlorella for commercial purposes was reported in Japan, in the 1960s [ 141]. Over the last few decades, algae culturing expanded to new fields, such as food and feed, biofuels, and biopharmaceuticals. Natural products in algal extracts are used in cosmetics and medicinal products [ 5]. According to one estimate, about 5000 metric tons of dry algal biomass processed for bioproducts generates US$ 1.25 × 109 each year [ 140].

Microalgae produce a wide range of other commercially important and valuable products. They produce vitamins, which elevates their importance as a nutritional food for people and animals [ 136, 142]. They also produce different types of medicinally important polysaccharides. Various species produce bioactive and commercially important pigments, such as chlorophyll, β-carotene and other carotenoids, phycobiliproteins, and astaxanthin. These pigments are crucial in therapies for tumorigenesis, neuronal disorders, and optical diseases. Microalgae are also rich sources of protein. Their production of essential amino acids increases their potential for use as protein-rich foods [ 143, 144]. Microalgae synthesize starch, cellulose, hemicelluloses, and other polysaccharides from simple monomeric sugars: basically, glucose. The higher amounts of carbohydrates in algal cells make them an important food source [ 144]. Microalgae also produce and accumulate large amounts of lipids, which vary among species and are affected by various factors [ 145]. Lipids in algal cells are present mainly in the form of glycerol, esterified sugars to different types of fatty acids (12-22 carbon atoms). Algal fatty acids have nutritional and medicinal applications. Most of the substances produced by microalgae have therapeutic effects. Therefore, a new area of research is extracting and identifying substances from microalgae and determining their biological and medicinal activities. Microalgae are becoming economical sources of natural substances for use as food and in cosmetics [ 146].

Pharmaceuticals on the market mainly consist of tablets or liquid forms of health-promoting substances, but several microalgae species are available as a supplement of various active substances in extract form, a new trend in the market. The microalgae market is growing due to the increasing demand for beneficial algal food and health products [ 147]. Polyunsaturated fatty acids produced by microalgae are important commercial products of high therapeutic value for cardiac diseases, asthma, and arthritis [ 148]. Many important microalgae products, such as eicosapentaenoic acid and docosahexaenoic acid (DHA), have been marketed by various biotechnological companies. Some species of microalgae produce protective substances against free radicals to prevent oxidative stress. These compounds are utilized as antioxidants in nutraceuticals and foods.

Researchers are taking a keen interest in algal substances with antioxidant properties that may be used in beverages and functional foods. These natural substances are highly important in pharmaceutical formulations for the treatment of free radicals and oxidative stress-associated diseases and complications. Blue-green microalgae (cyanobacteria) are rich in various pigment compounds that enhance the efficiency of light energy utilization (phycobiliproteins) and protect photosynthetic pigments from photo-oxidation (carotenoids). Currently, microalgae products with high nutritional value are available both in pure form as extracts, tablets, or capsules and as additives to several food products, such as candy bars, gums, pastas, and beverages [ 149]. These products are either used as nutrients or food coloring agents. Many microalgae strains, such as Aphanizomenon flos- aquae, Chlorella, and Arthrospira, are being cultured at a commercial scale for their high protein content and other health-promoting substances [ 143]. These products reportedly have important biological effects, such as anti-hyperglycemia and anti-hyperlipidemia, which are helpful in diabetes and obesity control because they affect the elevated serum glucose level.6

Stress conditions

Although microalgae have many potential applications for biofuel and other useful products, 48 their production has not been fully commercialized because of several obstacles and challenges. Under normal conditions, microalgae may not produce important metabolites or produce them only in very small amounts. However, microalgae can be induced to synthesize these compounds by subjecting them to stressful conditions. This property of microalgae is considered very important for enhanced production of carbohydrates, lipids, astaxanthin, and other products [ 150, 151]. Stress conditions are unfavorable environmental factors, such as strong light, high salinity, high temperature, deprivation of nitrogen or other nutrients, short-term exposure to UV radiation, or a combination of these factors [ 152].

Astaxanthins are multifunctional carotenoids usually obtained from Haematoccocus pluvialis. This microalga synthesizes astaxanthin in response to environmental stress [ 153]. Microcystis sp. also synthesizes many important metabolites in response to unfavorable conditions, as a defense mechanism. Microcystis aeruginosa produces blooms in response to unfavorable environmental conditions, with excessive synthesis and release of toxic metabolites known as microcystins. Many researchers have reported that cyanobacteria produce compounds in response to environmental stress [ 154] Synthesis of microcystins and other metabolites by M. aeruginosa is greatly induced and influenced by light intensity, temperature, pH, and nutrients, such as carbon, nitrogen, and phosphorus [ 155].

Significant compounds produced by microalgae

Some of the highly valuable bioactive products isolated from microalgae are discussed below. Figure 4 shows their chemical structure.

Some value-added compounds produced by microalgae. a Astaxanthin, a strong antioxidant produced by the microalga Haematococcus pluvialis. b β-Sitosterol, produced by various genera of micro algae. Different species of Glaucocystophyte produce β-sitosterol. c Microcolin-A, an immunosuppressive agent produced by the microalga Lyngbya majuscule. d Docosahexaenoic acid DHA produced by the engineered strain of diatom Phaeodactylum tricornutum. e Structure of vitamin E (tocopherols), the microalga Haslea ostrearia naturaly produce vitamin E. f Chemical structure of okadaic acid, an anti-fungal agent produced by some species of dinoflagellates. g Chemical structure of microcystin-LR, produced by the blooming Microcystis aeruginosa

Carotenoids

Carotenoids are important bio compounds having strong role in food, feed cosmetics and biopharma [ 156]. have Algae synthesize different types of pigments that possess important biological activities and thus are of great commercial interest. Among the most important are the phycobiliproteins, phycocyanin, phycoerythrin, β-carotene, lutein and astaxanthin [ 157]. Phycobiliprotein pigments are used in microscopy as fluorescent agents [ 158]. Phycocyanin and other pigments from red algae have antioxidant and anti-inflammatory effects; thus, they are used in food and cosmetic products [ 159, 160]. The microalga Dunaliella salina produces the carotenoid pigment β-carotene in quantities that represent about 10-14% of its dry mass [ 161]. β-carotene has a crucial role in vision and the immune system, due to its relation to vitamin A. Another important carotenoid pigment is astaxanthin, which is sold for 2500 US$/kg in the market. The microalga Haematococcus. pluvialis produce 4-5% astaxanthin per dry biomass [ 162]. Dried biomass of Haematococcus pluvialis has been commercialized as astaxanthin rich source. Because of their strong antioxidant activity, carotenoids are therapeutic in oxidative stress-related diseases and their complications, such as diabetes, aging, cancer, obesity, and stroke [ 163, 164, 165]. β-carotene and astaxanthin also have strong effects on the enzymatic antioxidant defense system by preventing oxidative stress through scavenging of free radicals [ 166]. β-Carotene protects membrane lipids from peroxidation, which is linked with many severe and lethal diseases, such as cancer, cardiovascular disease, Parkinson's disease, and atherosclerosis [ 167, 168, 169]. The cis and trans forms of β-carotene are different isomers that confer the anticancer effect [ 170].

Many other compounds besides carotenoids have strong antioxidant activities, such as phenolic compounds and vitamins.

Sterols

Sterols produced by plants are called phytosterols. Microalga have a good contribution in the production of phytosterols and are considered potent and promising sources for the large-scale production. Some microalgae species have high levels of sterols. Microalgal sterols have some beneficial health effects like hypo-cholesterolemia, anticancer, anti-inflammatory and neurological diseases like Parkinson disease [ 171, 172]. Phytosterols used in pharmaceutical formulation for health benefits and nutraceuticals as food ingredients [ 173, 174]. Some microalgae species, such as those in the Pavlova and Thalassiosira genera, are rich in sterols [ 175, 176]. The microalga Chaetoceros has been reported to produce 27.7 μg sterols per gram of dry weight [ 177]. 40 different sterols have been identified in 100 different species of diatoms. These sterols are differed in chemical structures and some genera, e.g. Amphora produce distinctive types of sterols [ 178]. Recently the microalgae annochloropsis sp, Pavlova lutheri, Tetrasellimis sp have been screened to produce sterols with a net yield of 0.4-2.6%/dry weight) [ 179]. Euglena gracilis produce a mixture of sterols, 0.68-3.24 mg/g of dry biomass [ 180]. The major types of sterols reported in Glaucocystophyte are sitosterol, campesterol and stigmasterol, [ 181]. 24-Ethylcholesterol are mostly produced by cyanobacteria [ 182]. Dinoflagellates mostly produce 4α-methyl sterols and 24-propylidenecholesterol is mostly produced by Pelagophyceae [ 183, 184]. Synthesis of sterols is also influenced by a number of factors in microalgae affecting the final yield.

Proteins and enzymes

Some proteins, peptides, and amino acids have strong therapeutic effects on health or are necessary for cells and tissues to perform their normal activities. If the human body is unable to synthesize them, they must be obtained from an external source, usually food. Many species of microalgae produce higher quantities of various essential amino acids and proteins, which can be utilized in food and to protect against several diseases. Some species of microalgae can produce as much proteins as other rich sources of proteins, e.g. egg, meat and milk etc. [ 185]. Microalgae proteins have comparatively high nutritionals value. Microalgae produce 2.5-7.5 tons/Ha/year of proteins [ 186] the green microalga Chlorella is a rich source of different types of proteins, which have been marketed. Another protein-rich microalga is Arthrospira. Proteins from microalgae or plants cam reduce cholesterol levels by activating cholecystokinin. They also have important enzymatic effects [ 187]. Lyngbya majuscula produces microcolin-A, an immunosuppressive agent [ 188]. Nostoc produce the protein Cyanovirin which have been reported for its antiviral activities against HIV an influenza virus [ 189]. Anabaena and Porphyridium produce the enzyme SOD (superoxide dismutase), which protects against oxidative damages, while Isochrysis galbana produces the vital enzyme carbonic anhydrase, which plays a crucial role in converting CO ₂ into carbonic acid and bicarbonate. M. aeruginosa produces a variety of amino acids, including proline, serine, glycine, and valine.

Polyunsaturated fatty acids

Polyunsaturated fatty acids are important in tissue integrity and have beneficial health effects. Omega-3 and omega-6 fatty acids in particular are crucially important for humans, but the human body cannot produce these fatty acids. Thus, intake from external sources such as foods or cosmetics is essential. DHA, linoleic acid, eicosapentaenoic acid, arachidonic acid, and gamma-linolenic acid have been shown to suppress cholesterol levels, delay aging, guard membrane integrity, and prevent cardiovascular diseases [ 190, 191]. Many microalgae species (e.g. Porphyridium cruentum, Arthrospira platensis, Odontella, I. galbana) have been explored for their ability to synthesize these valuable fatty acids. Pavlova lutheri produces polyunsaturated fatty acids in large quantities, [ 192] while A. platensis produces and accumulates stigmasterol, sitosterol and γ-linolenic acid [ 177].

Eicosapentaenoic acid (EPA) and docosahexaenoic acid DHA are the medicinally important Omega-3 Polyunsaturated crucial in inflammatory diseases, heart problems, arthritis, asthma, and headache etc. [401]. EPA, DHA are produced by serval microalgae species sustainable and promising source and the only alternative to fish oils which are limited and unable to fulfill the required demands of EPA and DHA [ 193, 194]. Some efforts have been made recently to enhance the production of EPA and BHA by altering the metabolic pathways via genetic manipulation [ 195]. Most recently Phaeodactylum tricornutum attracted attentions as a potential source of EPA and DHA production [ 196, 197, 198]. The diatom P. tricornutum has been genetically sequenced and modified for enhance production of Omega-3 polyunsaturated fatty acids like EPA and DHA etc. It has been reported that the genetically engineered strain of P. tricornutum produce a maximum yield of 36.5 and 23.6% of DHA and EPA per total fatty acids of biomass indicating its feasibility for production of EPA and DHA at commercial scale [ 199].

However, commercial scale production of these significant and useful products such as EPA and DHA from microalgae need to overcome several hurdles and challenges which are responsible for its low product yields [ 200]. Up scaling required optimization in several areas, e.g. screening and selections of strains, culture development, products induction and extraction technologies. The algae growth and productions of Omega-3 Polyunsaturated fatty acids is greatly influence by carbon sources and light strength [ 201, 202, 203].

Vitamins

Microalgae are also rich sources of different vitamins. Haslea ostrearia is a rich source of vitamin E (tocopherols). P. cruentum produces high quantities of vitamins E and C, as well as β-carotene (vitamin A) [ 204]. The microalga D. salina readily produces vitamins A and E, pyridoxine, nicotinic acid thiamine, riboflavin, and biotin [ 205].

Toxic metabolites

Most microalgae species, especially cyanobacteria, produce a variety of toxic substances, generally called cyanotoxins. The most common examples are the microcystins produced by the blooming Microcystis species. M. aeruginosa is the dominant microalga of the bloom-secreting microcystins, which have been reported to be lethal for animals and humans. The bloom is also responsible for shellfish poisoning, due to the presence of toxins. Different types of microcystins have been identified. The microcystins are hepatocyclic peptides with a C20 amino acid chain, which determines the degree of toxicity [ 206]. Among all the microcystins produced by M. aeruginosa, microcystin LR is the most toxic and causes the death of animals and humans upon oral contact. Studies have shown that cyanobacterial toxins can treat tumors [ 207, 208].

Cyanotoxins are of great interest as environmental hazards and due to the chemistry of their toxicology [ 209]. They are broadly classified on the basis of (1) effects on vertebrates, divided into neurotoxins, hepatotoxins, and dermatotoxins; and (2) chemical structure as cyclic peptides, alkaloids, or lipopolysaccharides [ 210]. These toxic substances also have important antibacterial and antifungal activities [ 211, 212]. Other microalgae species have been explored for the production of toxic products. The diatom Nitzschia pungens produces domoic acid, which causes poisoning of shellfish [ 213]. Gambierdiscus toxicus produces gambieric acids, which have antifungal activities [ 214]. Karatungiols are active antimycotic agents produced by Amphidinium, which also have antiprotozoal activities [ 215].

Biological activities of natural products from microalgae

Antioxidant activity

Antioxidants are very important substances used by the human body to protect itself from the hazardous effects of free radicals. ROS (reactive oxygen species) and NOS (nitrogen reactive species) attack biomolecules like DNA, proteins, and membrane lipids, leading to many severe diseases including cancer, coronary arteries disease, obesity, diabetes, ischemic stroke, and Alzheimer disease [ 216].

Free radicals cause lipid peroxidation both in food lipids and biological membranes. Peroxidation results in various diseases and complications. In food materials, lipid peroxidation reduces shelf life and nutritional value. Antioxidants can prevent oxidative damage to cells and tissues by scavenging free radicals. The human body has its own enzymatic antioxidant system that prevents oxidative stress and protects the body from the hazardous effects of free radicals. However, when free radicals overcome the body's natural antioxidants, oxidative stress occurs, which is one of the major causes of various dangerous and life-threatening diseases. In such cases, the uptake of external antioxidants is crucially important. Many natural antioxidant compounds have been reported. Compounds such as flavonoids, carotenoids, and vitamins like ascorbic acid and tocopherols have strong antioxidant activity.

In the pharmaceutical and food industries, several synthetic or natural antioxidants have been used to prevent oxidation and peroxidation processes [ 217]. As synthetic antioxidants have been shown to have side effects, natural antioxidants are sought after [ 218]. Recently, the exploration of natural antioxidants for nutraceuticals and pharmaceuticals industries has increased. Researchers are looking for antioxidants from natural sources, such as medicinal plants. Because of their huge potential for producing biologically active natural products, microalgae are one of the richest and most economical sources of natural compounds with strong antioxidants effects [ 219]. The antioxidant potential of these substances has been determined by various methods, including ABTS, DPPH radicals scavenging assay, ferric reducing potential, and metals chelating essays. Structural features such as a phytyl chain, a porphyrin ring, and conjugated double bonds are responsible for the antioxidant qualities [ 220]. Chlorophyll a and its metabolites produced by microalgae species are reported to have antioxidant activities [ 221]. as do most of the pigment metabolites of microalgae. The pigment fucoxanthin and its derivatives, such as auroxanthin, isolated from the microalga Undaria pinnatifida, have strong radical scavenging action [ 222]. Fucoxanthin is reported to have higher antioxidant effects than β-Carotene in tests of rat liver and plasma [ 223, 224]. The chemical structure of fucoxanthin shows two hydroxyl groups in a ring structure, which are considered the active moiety for free radical scavenging [ 225]. Phycobiliproteins (e.g., C-phycocyanin, R-phycoerythrin) are commercially used in the food and cosmetic industries as natural dyes [ 226]. Phycoerythrobilin, produced by some species of microalgae, has been shown to possess antioxidant activity [ 227]. Hence, the widespread existence of natural products with strong antioxidant activity increases the economical and nutritional potential of microalgae for the food, pharmaceutical, and nutraceutical industries.

Anti-angiogenic, cytotoxic, and anticancer activities

Many reports indicate the potential of natural products, including those produced by microalgae, to treat cancer and tumors by inhibiting angiogenesis. Fucoxanthin, found in many species of microalgae, significantly inhibits human blood cell proliferation and tube formation of HUVECs (human umbilical vein endothelial cells). Fucoxanthin and fucoxanthinol have been shown to inhibit the angiogenesis process in the aortic ring of rats by suppressing the growth of microvessels [ 233]. Some species of algae produce siphonaxanthin, which also possess antiangiogenic activity [ 234]. Fucoxanthin also has therapeutic effects for diabetes and induced the synthesis of arachidonic acid and DHA content in mouse livers [ 235]. It inhibits skin melanogenesis by negative regulation of the transcriptional factors involved [ 236]. Moreover, fucoxanthin has been shown to protect DNA from photooxidation [ 237]. Aerucyclamide is used in pharmaceutical products as an anti-plasmodial agent isolated from the blooming of M. aeruginosa [ 238]. Microalgae, particularly blue-green algae, are now being considered potential sources of active ingredients that can be utilized in the treatment of cancer. Many studies have shown the anti-cancer activity of these active products in the lab [ 239]. The mode of action and the mechanism of the activities may differ. Some of the microalgae-derived anti-cancer agents have been shown to induce apoptosis in tumorous cells by destroying the chromatin network, leading to cell death [ 240]. Cyanobacteria produce various metabolites by the ribosomal or non-ribosomal pathway. Most of these compounds are either peptides or alkaloids [ 241]. Peptides, including but not limited to those from cyanobacteria, tend to be toxic substances possessing strong cytotoxic activity. Cytotoxicity of these compounds is crucial in inducing apoptosis, which leads to cell death [ 242].

Many species of cyanobacteria (blue-green algae) produce apoptosis-inducing compounds. Apoptotic cells can be identified by their specific morphology, as they typically have a large cytoplasm and compressed organelles, with alterations of the chromatin materials. Extracts of Synechocystis sp. and Synechococcus sp. have been shown to drive HL-60 cells into apoptotic conditions. After treatment with extracts, cells express apoptotic markers, such as fragmentation of nucleus, shrinkage of cells, and release of apoptotic substances [ 240]. Similarly, Lyngbya sp. produce the glycoside biselyngbyaside, which can drive the mature osteoclasts into apoptotic conditions [ 243]. Extracts of Anabaena sp. have induced apoptosis in a leukemia myeloid cell line [ 244]. Some species of Nostoc produce cryptophycin, which is several hundred to a thousand times more active on cancer cells, such as human colorectal cancer, more effective than vinblastine or taxol [ 245]. The Oscillatoria boryana extract was active against human breast cancer [ 246]. Microcystis sp. in particular have great potential in the fields of toxicology and pharmacology, due to their production of bioactive metabolites and toxic substances with anti-cancer activity. The isolation of these compounds and determination of their biotechnological and toxicological applications continues to be studied by various researchers [ 247].

Anti-obesity activity of algal products

Obesity is the overaccumulation of adipose tissues (fats) in the body [ 248]. Obesity is considered a multifactorial metabolic disorder linked to many complications and diseases, such as cancer, cardiovascular disease, diabetes mellitus, and aging [ 249]. The overgrowth of adipose tissue occurs because of adipogenesis, so obesity can be controlled by guarding the cells against adipogenesis [ 250]. Research has revealed various anti-hyperlidimic and fat-lowering agents from natural sources, such as medicinal plants. Microalgae are now being studied as potential sources of these products. ROS and NOS have also been reported to be involved in the progression of obesity. Thus, antioxidants can be used to control free radical-induced accumulation of fats. Fucoxanthin and fucoxanthinol can inhibit the differentiation of 3T3-L1 cells to adipocytes. Fucoxanthin and fucoxanthinol inhibit adipocyte differentiation by down-regulating peroxisome proliferator-activated receptor-c [ 251].

Okada et al. [ 252] reported that neoxanthin and fucoxanthin inhibited the accumulation of fats and stated that allenic and hydroxyl groups must be present to differentiate adipocytes. These compounds are reportedly crucial for lowering fat in high-fat mouse feeds [ 253] In obese mice, fucoxanthin suppresses adiposity by activating the mitochondrial protein UCP1 (Uncoupling protein1) in abdominal WAT [ 254] Fucoxanthin significantly reduced body fat in obese individuals in a clinical trial by Abidov et al. [ 255] Cylindrotheca closterium and Phaeodactylum tricornutum are the two microalgae species that produce fucoxanthin, [ 256] which shows potential as an anti-cancer, anti-oxidant, anti-obesity, anti-diabetic, and anti-inflammatory agent [ 257].

Antimicrobial activities of microalgae metabolites

Bacteria and fungi are the major causes of severe diseases in plants and animals, including humans. They reduce crop yields and are the major causes of food spoilage. The widespread use of various antibiotics over the past few decades has given rise to increased resistance of microbes to antibiotics, making it necessary to search for new antimicrobial agents. Synthetic antibiotics have not achieved a satisfactory level of disease control due to side effects, high cost, and risk of generating severe resistant pathogenic strains. Therefore, researchers are searching for new natural antibiotics with a broad action spectrum from natural sources like plants and microorganisms. Natural products have comparatively fewer or no side effects.

Microalgae show a wide range of bioactive natural products that are effective, either in crude or purified form, as antioxidant, anti-cancer, and anti-microbial agents. The first reported antibacterial products in microalgae were in the green microalga Chlorella, which significantly inhibits the growth of both Gram-positive and Gram-negative bacteria [ 215]. Some microalgae also produce compounds that have antifungal activities [ 212]. Okadaic acid and ciguatoxin are effective antifungal agents produced by Prorocentrum lima and G. toxicus, respectively. Antimycotic activities have been reported for karatungiols, a group of compounds synthesized by the dinoflagellate Amphidinium [ 215]. Chaetoceros lauderi produces lipid metabolites that have been found to inhibit the growth of serval bacteria strains. M. aeruginosa is a rich source of several toxic metabolites that possess strong cytotoxic and antimicrobial effects. The crude extract of M. aeruginosa displays high antifungal and antibacterial activity [ 258]. Dunaliella salina also produces compounds that are active against several bacterial and fungus strains (e.g., Staphylococcus aureus, Escherichia coli, Candida albicans, Psuedomonas aeruginosa, Aspergillus niger) [ 259]. The extract of D. salina significantly inhibits the growth of Klebsiella pneumoniae. Substances synthesized by Dunaliella primolecta also showed antibacterial activity against S. aureus and against other bacterial strains [ 260].

Conclusions

Microalgae are tiny factories and renewable, sustainable and economical sources of biofuels, bioactive medicinal products and food ingredients. Microalgae useful in mitigation of elevated CO ₂ level and treatment of waste water. Upgradation of algal fuel and bioproducts technology from pilot scale to commercial level is possible by overcoming the associated challenges and limitations. In this review we describe the extensive applications of the microalgae in bioenergy, nutraceutical and pharmaceutical industry, the associated challenges and limitations and how it can be overcome to make them feasible and viable for commercialization.

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MIK wrote the manuscript and analyze the data. MIK and JDK collected the information and reviewed literature. MIK, JDK and JHS revised the manuscript. All authors read and approved the final manuscript

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1. Department of Biotechnology, Chonnam National University, San 96-1, Dun-Duk Dong, Yeosu, Chonnam, 550-749, South Korea

Muhammad Imran Khan, Jin Hyuk Shin & Jong Deog Kim

2. Research Center on Anti-Obesity and Health Care, Chonnam National University, San 96-1, Dun-Duk Dong, Yeosu, Chonnam, 550-749, South Korea

Jong Deog Kim

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Correspondence to Jong Deog Kim.

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Khan, M.I., Shin, J.H. & Kim, J.D. The promising future of microalgae: current status, challenges, and optimization of a sustainable and renewable industry for biofuels, feed, and other products. Microb Cell Fact 17, 36 (2018). https://doi.org/10.1186/s12934-018-0879-x
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Keywords

Microalgae

Biofuels

Carbon dioxide mitigation

Viable biomass

Culture parameters

Pretreatment

Bioactive compounds

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The promising future of microalgae: current status, challenges, and optimization of a sustainable and renewable industry for biofuels, feed, and other products - Microbial Cell Factories

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Microalgae have recently attracted considerable interest worldwide, due to their extensive application potential in the renewable energy, biopharmaceutical, and nutraceutical industries. Microalgae are renewable, sustainable, and economical sources of biofuels, bioactive medicinal products, and food ingredients. Several microalgae species have been investigated for their potential as value-added products with remarkable pharmacological and biological qualities.

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The availability of low-cost feedstocks determines the profitability of biofuels.

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Highlights:

With near record oil prices, the future of biofuel-made from plant material-is of keen interest worldwide. Global biofuel production has tripled from 4.8 billion gallons in 2000 to about 16.0 billion in 2007, but still accounts for less than 3 percent of the global transportation fuel supply. About 90 percent of production is concentrated in the United States, Brazil, and the European Union (EU). Production could become more dispersed if development programs in other countries, such as Malaysia and China, are successful. The leading raw materials, or feedstocks, for producing biofuels are corn, sugar, and vegetable oils.

While rapid expansion in biofuel production has raised expectations about potential substitutes for oil-based fuels, there have been growing concerns about the impact of rising commodity prices on the global food system. According to the International Monetary Fund, world food prices rose 10 percent in 2006 because of increases in corn, wheat, and soybean prices, primarily from demand-side factors, including rising biofuel demand. The Chinese Government put a moratorium on expanded use of corn for ethanol because of rising feed prices and is promoting other feedstocks that do not compete directly with food crops, such as cassava, sweet sorghum, and jatropha (an oil-bearing plant originally from South America).

Mexico capped tortilla prices in early 2007 to contain food price inflation from higher priced corn imports. Real sugar prices hit a 10-year high in 2006, stressing budgets of low-income people in Brazil and elsewhere. Prices have since declined. The Indonesian Government increased the export duty on crude palm oil, also used in biodiesel production, in mid-2007 to slow the rising cost of domestic cooking oil.

U.S. livestock producers are facing increased costs for corn and other feed, which may translate into higher retail meat prices. And in Japan, historical concerns have been revived about the country's almost complete dependence on imports of feed grain and oilseeds to support its large livestock sector.

The outlook for global biofuels will depend on a number of interrelated factors, including the future price of oil, availability of low-cost feedstocks, sustained commitment to supportive policies by governments, technological breakthroughs that could reduce the cost of second-generation biofuels, and competition from unconventional fossil fuel alternatives.

A New Era of High Oil Prices Attracts Investment in Biofuels

The rise in oil prices is the most important factor boosting the competitiveness of alternative fuels, including biofuels. The unprecedented 6-year rise in oil prices has prolonged opportunities for efficiency gains, stimulated energy conservation, and generated increased supply from traditional and alternative energy sources. While these adjustments may eventually lower oil prices, most forecasts do not show real prices falling below $50 per barrel.

Previous periods of high oil prices were short. Prices tended to rise very sharply, usually induced by military conflict, peaked in a matter of weeks or months, and then declined sharply. Following these price spikes, the rapid decline in petroleum prices made it difficult to sustain alternative fuel programs and reduced incentives for consumers to curb their use of petroleum products.

Unlike previous high-price periods, the current oil market is driven by strong demand-side factors. These factors include robust economic growth and rising oil demand from rapidly growing middle-income economies, where consumers are demanding a higher standard of living and exhibiting big appetites for energy. Almost two-thirds of recent global growth in oil demand has come from China and other middle-income economies.

Profitability of Biofuels Depends on the Availability of Low-Cost Feedstocks

Feedstock costs are the most significant cost of biofuel production, ranging from 37 percent for sugarcane-based ethanol in Brazil in 2003-04 to 40-50 percent for corn-based ethanol in the United States. Sugar beets represented 34 percent of the cost of sugar-based ethanol production in the EU. With rising commodity prices, these cost shares are even higher now. Another major cost component is energy, which may account for as much as 20 percent of biofuel operating costs in some countries.

The ratio of crude oil prices to feedstock prices offers a simple indicator of the competitiveness of biofuel made from various feedstocks. The ratio of crude oil to corn prices, for example, rose sharply after 2004 as oil and ethanol prices increased and corn prices were stable. But the ratio dropped sharply after September 2006, making biofuels less cost competitive. Biodiesel producers in Europe and Southeast Asia also faced declining competitiveness as soy and palm oil prices rose in 2006-07. World sugar prices, on the other hand, declined by 50 percent from 10-year highs in 2006, boosting relative prospects in Brazil's ethanol sector.

The sale or productive use of byproducts also contributes to a biofuel plant's profitability. Dried distillers' grain (DDG), a byproduct of corn ethanol production, can be used as a protein-rich livestock feed additive. Sales of DDG can add as much as 10-15 percent to ethanol producers' incomes. Carbon dioxide, usually released into the atmosphere, is captured by some ethanol plants and sold for use in the food and beverage sector. Bagasse, the fibrous material left over from pressing sugarcane, can be burned to provide heat for distillation and electricity to power machinery or sold to local utilities. Glycerin, a byproduct of biodiesel production, has a wide number of pharmaceutical, food-processing, and feed applications.

Government Support Is Used To Reduce Volatility

Strong long-term government intervention is a feature in the two top biofuel-producing countries-the United States and Brazil (see box, "Lessons From Brazil")-as well as the EU, China, and other countries. Governments justify support in the name of achieving broad societal goals: to diversify energy sources, to enhance energy security, and to meet environmental and rural development objectives. Governments tend to introduce support to help fledgling biofuel ventures overcome cost and scale disadvantages and weather the inherent volatility in profits.

Governments have introduced a variety of policy tools that reduce risk and uncertainty in response to investor and producer concerns about the double-edged uncertainty of volatile feedstock and energy input prices and biofuel output prices. The most common tool is a requirement to blend biofuel with its fossil fuel counterpart to provide a guaranteed market for biofuels. The nature of this requirement varies around the world in the extent to which it is mandatory, the phase-in period, the volume or blend percentage mandated, and whether a nationwide or regional strategy is used.

Countries also rely on subsidies, tax credits, and preferential taxes to overcome the higher cost of biofuel production relative to gasoline and diesel and to encourage consumers to buy biofuel-containing gasoline or diesel. Europe offers an 18.7-euro per acre energy premium for production of biofuel feedstocks. India's Government offers sugar mills interested in setting up ethanol production facilities subsidized loans for 40 percent of project costs. Brazil encourages consumption by imposing a lower sales tax for hydrous ethanol (containing water) and E25 (25 percent ethanol) than for gasoline.

The United States provides a $.51 per gallon tax refund for blenders of ethanol and $1.00 per gallon for biodiesel from vegetable oils and animal fat ($.50 for recycled cooking oil or animal fat). Some States also provide support, and other Federal incentives are provided for smaller biofuel plants.

Import restrictions are also used to promote the emerging biofuel industry. Effective tariffs range from 9 percent in Canada (for ethanol imports from Brazil, 0 tariff for renewable fuels from the U.S.) to about 45 percent for undenatured and 24 percent for denatured ethanol in the EU. Import duties and tariffs are waived by the EU for many developing countries (not including Brazil). The U.S. tariff on ethanol is currently about 25 percent when the 2.5-percent tariff is combined with the $.54 per gallon duty.

Brazil is the only country promoting biofuel use beyond minimal blending levels by allowing consumers to choose it as a fuel substitute. The Brazilian Government has promoted the availability of ethanol at almost every gasoline station and the manufacture of flexible fuel cars (capable of using pure gasoline, E25, or pure hydrous alcohol). Proposed U.S. legislation would also provide incentives for expanding E85 distribution and the manufacture of more E85-capable vehicles.

While biofuels share similar attributes with oil-based fuel, they are not perfect substitutes. Biofuels can be used in existing gasoline and diesel engines in blends of up to 10 percent in the case of ethanol and 20 percent for biodiesel with little or no engine modification. This compatibility contrasts with hydrogen fuel cell technology, which would require a radically different distribution system.

However, ethanol has only two-thirds the energy content of gasoline, and biodiesel has 90 percent that of diesel. Thus, a car will get fewer miles per gallon the greater the biofuel blend. Shipping ethanol is more expensive; it cannot be transported by low-cost pipelines because of potential contamination from ethanol's tendency to absorb water and to dissolve impurities on the inside surfaces of multiproduct pipelines. Dedicated pipelines for ethanol are being considered in Brazil and the United States and may become economical with expanded production.

Country

Ethanol feedstocks

Biodiesel feedstocks

2007 ethanol production forecast
(million gals.)

2007 biodiesel production forecast
(million gals.)

Blending targets

Looking to the Future: The Potential of Second-Generation Biofuels

Many uncertainties remain for the future of biofuels, including competition from unconventional fossil fuel alternatives and concerns about environmental tradeoffs. Perhaps the biggest uncertainty is the extent to which the land intensity of current biofuel production can be reduced. The amount of biofuel that can be produced from an acre of land varies from 100 gallons per acre for EU rapeseed to 400 gallons per acre for U.S. corn and 660 gallons per acre for Brazilian sugarcane.

Cellulosic ethanol could raise per acre ethanol yields to more than 1,000 gallons, significantly reducing land requirements. Cellulosic ethanol is made by breaking down the tough cellular material that gives plants rigidity and structure and converting the resulting sugar into ethanol. Cellulose is the world's most widely available biological material, present in such low-value materials as wood chips and wood waste, fast-growing grasses, crop residues like corn stover, and municipal waste.

U.S. cellulosic fuel production costs are now estimated at more than $2.50 per gallon, compared with $1.65 per gallon for corn ethanol. Venture capital and government subsidies are supporting companies interested in making cellulosic ethanol commercially viable, primarily in the United States, but also in several other countries, including Canada, Brazil, China, Japan, and Spain.

In the meantime, other costs of cellulosic ethanol production need to be fully assessed, such as the impacts of harvesting grasses, trees, and crop residues on the erodibility and fertility of land resources. There are also questions regarding the upstream logistical and environmental costs of harvesting, transporting, and storing large volumes of bulky feedstock used in processing.

Competitive Fossil Fuel Alternatives

High oil prices have drawn attention not only to biofuels, but to a range of other liquid fuel alternatives. Large investments are being made in developing more difficult-to-access conventional oil resources located in remote areas or deeper waters, unconventional sources, such as oil sands and heavy crude oil, and the conversion of coal to oil. While world oil production is expected to increase 30 percent by 2030, production from unconventional fossil fuels will increase even faster, according to the U.S. Department of Energy. Global biofuel production is projected to more than double. Many of the fossil fuel alternatives have lower costs of production than biofuels. Canada's oil sands, for example, can produce oil for $30 per barrel. Current production is more than 1 million barrels per day, with some forecasting production rising to more than 3.5 million barrels per day by 2030.

Another alternative is converting coal to oil, which is of particular interest to economies with abundant coal resources, such as China and the United States. Oil prices of $40 per barrel may be sufficient to make this process profitable despite high investment costs.

What Are the Environmental Tradeoffs?

A key interest in developing or expanding biofuel production and use is the environmental benefits, including the potential to reduce emissions, such as greenhouse gases (GHG). An estimated 25 percent of manmade global carbon dioxide (CO2) emissions, a leading GHG, comes from road transport. Global road transport has grown rapidly over the past 40 years and is projected to continue to increase, especially in middle-income countries experiencing rapid economic growth, middle-class expansion, and urbanization.

Both biofuels and gasoline give off CO2 when burned. Biofuels are theoretically carbon neutral, releasing CO2 recently absorbed from the atmosphere by the crops used to produce them. Gasoline and other fossil fuels add to the CO2 supply in the atmosphere by giving off CO2 absorbed and trapped in plant material millions of years ago.

The advantage of biofuels is less clear in a "life-cycle" analysis that examines not just combustion, but the production and processing of the feedstock into fuel. Most studies indicate that the net energy balance of biofuels is positive (energy output is greater than energy input), but estimates vary widely. Net balances are small for corn ethanol and more significant for biodiesel from soybeans and ethanol from sugarcane and from cellulose. The biofuel with the highest net energy balance reduces GHG the most when compared with that for gasoline.

Another important environmental consideration is the potential land requirements if biofuels become a more mainstream fuel. According to the University of Minnesota, devoting all U.S. corn and soybean acreage to ethanol and biodiesel production would offset only 12 percent and 6 percent of gasoline and diesel consumption for transportation fuel, respectively, and even less if adjustments were made for the fossil fuel requirements for producing the biofuel.

Use of so much land to meet a relatively small share of transportation fuel demand is improbable. The resource commitment to meet domestic fuel demand would be less in a lower income economy. Expanding feedstock production, however, that encroaches on fragile rainforest areas and wildlife habitats is still a concern in countries like Indonesia, Malaysia, and Brazil.

Future Role of Biofuels Depends on Profitability and New Technologies

Technological advances and efficiency gains-higher biomass yields per acre and more gallons of biofuel per ton of biomass-could steadily reduce the economic cost and environmental impacts of biofuel production. Biofuel production will likely be most profitable and environmentally benign in tropical areas where growing seasons are longer, per acre biofuel yields are higher, and fuel and other input costs are lower. For example, Brazil uses bagasse, which is a byproduct from sugar production, to power ethanol distilleries, whereas the United States uses natural gas or coal.

The future of global biofuels will depend on their profitability, which depends on a number of interrelated factors. Key to this will be high oil prices: 6 years of steadily rising oil prices have provided economic support for alternative fuels, unlike previous periods when oil prices spiked and then fell rapidly, undercutting the profitability of nascent alternative fuel programs. On the other hand, the sector's profitability has been negatively affected by rising feedstock prices (corn and vegetable oil, not sugar), which account for a very large share of biofuel cost of production. For this commodity-dependent industry, government support to reduce profit uncertainty has been a common theme in the U.S., Brazil, and the EU, where biofuel production has been most significant.

Biofuels will most likely be part of a portfolio of solutions to high oil prices, including conservation and the use of other alternative fuels. The role of biofuels in global fuel supplies is likely to remain modest because of its land intensity. In the U.S., replacing all current gasoline consumption with ethanol would require more land in corn production than is presently in all agricultural production. Technology will be central to boosting the role of biofuels. If the energy of widely available, cellulose materials could be economically harnessed around the world, biofuel yields per acre could more than double, reducing land requirements significantly.

<a name='box'></a>Lessons From Brazil

Brazil has the world's second largest ethanol program and is capitalizing on plentiful soybean supplies to expand into biodiesel. More than half of the nation's sugarcane crop is processed into ethanol, which now accounts for about 20 percent of the country's fuel supply.

Initiated in the 1970s after the OPEC oil embargo, Brazil's policy program was designed to promote the nation's energy independence and to create an alternative and value-added market for sugar producers. The government has spent billions to support sugarcane producers, develop distilleries, build up a distribution infrastructure, and promote production of pure-ethanol-burning and, later, flex-fuel vehicles (able to run on gasoline, ethanol-gasoline blends, or pure hydrous ethanol). Advocates contend that, while the costs were high, the program saved far more in foreign exchange from reduced petroleum imports.

In the mid- to late 1990s, Brazil eliminated direct subsidies and price setting for ethanol. It pursued a less intrusive approach with two main elements-a blending requirement (now about 25 percent) and tax incentives favoring ethanol use and the purchase of ethanol-using or flex-fuel vehicles. Today, more than 80 percent of Brazil's newly produced automobiles have flexible fuel capability, up from 30 percent in 2004. With ethanol widely available at almost all of Brazil's 32,000 gas stations, Brazilian consumers currently choose primarily between 100-percent hydrous ethanol and a 25-percent ethanol-gasoline blend on the basis of relative prices.

Approximately 20 percent of current fuel use (alcohol, gasoline, and diesel) in Brazil is ethanol, but it may be difficult to raise the share as Brazil's fuel demand grows. Brazil is a middle-income economy with per capita energy consumption only 15 percent that of the United States and Canada. Current ethanol production levels in Brazil are not much higher than they were in the late 1990s. Production of domestic off- and on-shore petroleum resources has grown more rapidly than ethanol and accounts for a larger share of expanding fuel use than does ethanol in the last decade.

This article is drawn from...

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The Future of Biofuels: A Global Perspective

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Global biofuel production tripled between 2000 and 2007, but still accounts for less than 3 percent of global transportation fuel supply. Increased demand for biofuels has contributed to higher world food and feed prices.

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Latest and future trends in biofuel production

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Latest and future trends in biofuel production

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If we can meet the acreage requirements to grow the resources available to make biofuels economically viable, we may be able to replace fossil fuels in the near future. The principal profit factor, based on commodities, will be able to offset the significant increase in oil prices. Biofuels will have a huge impact on the global economy and ecology if countries throughout the world are able to utilise them in the near future.

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In the past decade, we have seen technological advancements in motor vehicles that run on renewable energy sources. The increasing threat of fossil fuel depletion coupled with the need to maintain renewable sources continues to push for the demand for biofuel.
We live in a world where the global market for biofuels and renewable sources continues to grow in order to maintain the growing population. Our reliance on energy is a global necessity as our government attempts to mitigate the growing issue of climate change as a direct result of increased demand for automobile fuel.
The most obvious benefit of replacing fossil fuels is the environmental impact it will have on carbon emissions. Since biofuels burn faster and cleaner than fossil fuels, it will release greenhouse gases at a lower and slower rate. Secondly, the use of biofuels will allow the economy to reap its benefits.

What is biofuel and how is it made?

In an effort to reduce our use of carbon emissions and replacing fossil fuels to preserve our natural resources, it has led to the widespread use of biofuels.
A biofuel is any type of liquid fuel that can be derived from biological materials such as trees, agriculture, waste, or grass. Some of which, but are not limited to those such as: ethanol, biodiesel and other "green" fuels.
Biofuels are produced directly from organic materials or biomass. The most common producer being plant materials and animal waste. In terms of agriculture, biofuels can be taken from crops, forestry, and animal by-products.
Technology has allowed us to expand the variety of biofuels to include solids, liquids and gases from materials such as woods, crops, and waste. We commonly use biofuels as substitutes for fossil fuels such as petroleum, propane, coal, and natural gas. Biofuels consist of two types: primary and secondary. Primary biofuels refer to organic materials that are primarily used for heating purposes and electricity production. These include wood chips and pellets used to make fire and are usually kept in their natural state. Secondary biofuels refer to the processing of biomass and usually includes liquid biofuels such as ethanol and biodiesel which is commonly used in the production of vehicles.

History of biofuels and how it is used

Over time, with the invention of electricity and motor vehicles, the popularity of using biofuels decreased as the use of fossil fuels increased.
Many early vehicles in the United States ran on corn-based ethanol; these were phased out during the Great Depression when cheaper fossil-fuel based gasoline became available. During World War II, several countries, including Germany, could not procure gasoline, so they turned to biofuels as an alternative. Britain came up with the mixture of grain alcohol and petrol as a makeshift for fuel due to the shortage. In the post-war years, with advances in oil refining technologies, the Middle East became the largest supplier for cheap hydrocarbon based crude oil. Biofuel re-emerged in the 1990s due to the rising cost of oil prices and the emission of greenhouse gases. Despite these efforts to increase the use of biofuels, gasoline is still more widely used than plant-based alcohol.
The two most common types of biofuels that are used today are ethanol and biodiesel. Ethanol is a renewable fuel that consists of plant materials otherwise known as biomass. When ethanol - an alcohol - is mixed with gasoline, it allows flexible fuel vehicles to run with higher ethanol content than regular gasoline. In the United States about 97% of gasoline contains some mixture of ethanol. The process of fermentation, which is a chemical process by which molecules of glucose are broken down anaerobically, is a common method used for biomass to ethanol conversion.
The second type of biofuel is ethanol, which is a liquid fuel produced from vegetable oils and animal fats. It's commonly used as a replacement for petroleum-based diesel fuel. It can also be blended together with petroleum to fuel engines. The most commonly used blend is B20 which consists of 20% biodiesel and 80% petroleum diesel.

Latest trends in biofuel production

A common argument against biofuels, especially ethanol, is that it requires more energy to produce than it generates. Indeed, biofuels take substantially more energy to produce than fossil fuels; however, it is in fact less than the energy that it generates.
The notion that biofuels have a negative net energy balance is somewhat outdated, with advances in agriculture (eg, genetically modified crops and fertilisers) along with better conversion techniques have driven down the energy required to produce a gallon of ethanol. According to the US Department of Energy, ethanol produced by corn delivers at least 30% more energy than is used to produce it. This net energy balance is substantially higher for sugar and soy-based ethanol, such as that produced in Brazil. Similarly, biodiesels tend to have a higher net energy balance.
As such, the case against biofuels is primarily economic, with the future of biofuels being highly dependent on their profitability. It needs to fulfill factors such as environmental and economic stability as well as how technology allows these products to make advancements. As of right now, biofuel production is naturally most profitable in environmentally scarce tropical areas because biofuel yields are higher per acre while input costs are comparatively lower.
Brazil is a second leading middle-income country that produces and exports ethanol produced from sugarcane and soybeans.
They use ethanol and biodiesel in many of their car and truck models and at one time accounted for 70% of the world's production of biofuel. In contrast, the United States, which is currently the leading country in biofuels, was able to replace 75% of imported oil in 2006 with biofuels. American biofuel is primarily corn-based, despite being intensive to cultivate this crop in regard to both resources and land. The main issue with replacing global fuel supplies with biofuels is that it requires a significant amount of land and agricultural production to maintain those resources. In short, it would require agriculture rates to double, which is hard to predict if there is enough land available for biomass cultivation.
Despite their increased usage, fossil fuels are still cheaper to produce than biofuels, calling to question the use of biofuels from an economic standpoint. Feedstock prices have increased 37% for bagasse in Brazil and 40-50% for corn in the United States over the past decade. With this rise in pricing, the cost is even higher now than it was almost a decade ago. Since crude oil is naturally occurring and requires minimal refining to make gasoline and diesel, it carries a lower production cost; however, crude oil prices are driven by a number of socio-political factors and cost speculation. As such, the ratio of crude oil to biofuel feedstock has remained somewhat constant, such any reduction in biofuel costs typically coincides with a drop in crude oil prices.
However, has oil becomes more scarce and only available in unstable regions, biofuels become more appealing from an economic standpoint. Moreover, the oil market is somewhat volatile with socio-political disruptions in Iran or Venezuela resulting in large fluctuation in crude oil prices. These fluctuation in prices makes it difficult to depend on oil to continue to be a sustainable source of fuel.
This uncertainty has caused the motor industry to move towards electric cars that do not require oil, causing further disruption to oil demand.
As the effects of the COVID-19 pandemic have hit many industries in the United States, it has shown to cause negative effects on the biodiesel industry as well. The situation in which fuel demand is much lower due to supply chain and distribution disruptions as well as the decreased production in feedstocks has placed an immense amount of pressure on the biodiesel industry. European countries who receive their fuel product from corn have also seen a substantial drop in the demand for corn oil.
This is due to less people eating out as a result of the pandemic, which leads to lower demand for corn oil and less output.
In Canadian countries such as Quebec, where the biofuel industry was looming at large prior to the COVID-19 pandemic, their biodiesel plants also remained idle in April. Currently, they are operating at 50-70% capacity and the biodiesel industry has since slowly started to recover.
The Canadian exports of ethanol have also been met with a rise of pricing in May and June where they have produced approximately 17 million litres of pure alcohol. With a lower demand for gasoline in May of 2020, which was reflected by the lower domestic demand for ethanol, it dropped 60% in May. Although the pandemic has increased the market for ethanol-based products such as hand sanitiser, the product is less profitable than fuel-based ethanol. This is because hand sanitizer requires more work and materials to produce which ultimately leads to higher production costs as compared to biofuel.
As a result, the lower demand for ethanol has created many economic challenges for the advancement of biofuel in Canada.
Another region of the globe that is leading in biofuel production is Latin America. Biofuel accounts for the transition to clean energy in Latin American because it utilizes less than 8% of the world's transport energy but is responsible for 23% of the world's demand for biofuels. Argentina and Brazil are just two examples of the largest world markets. In addition, second to America, Brazil has the largest share of transport renewable energy in an effort to the oil crisis of 1973.
Since then, they have been trying to promote more clean energy sources such as biofuels as an alternative to fossil fuels.
As mentioned previously, Brazil receives most of their biofuel energy resources from the sugarcane industry as it is abundant in their country. It has been responsible for creating jobs and employment in the automobile and flex-fuel vehicle companies allowing more consumers access to this new variation of energy.
Similarly, it gives consumers the option to pump either ethanol or gasoline which is dependent on the pricing and consumer preference. As with most global economies, the COVID-19 pandemic has also taken a toll on Latin America's biofuel industry. With a similar problem in a decreased demand in fuel, it led to a drop in sugarcane prices. The impact of this pandemic can create a heavy debt as a result of the loss in competition with the gasoline industry. Although the growth in usage of biofuels appears to be stagnant, they expect the demand to grow over time as longer term investments are made in the effort to replace low oil prices.
The most difficult challenge in developing biofuels for the next few years is the cost for economic feedstocks. These feedstocks which are the raw material that are needed to supply or fuel a machine or industrial process contributes to 80 to 90% of the final fuel price for most fuel-making processes and is important to maintain the viability of future biofuels. When we refer to generations of biofuels, it usually indicates 30 years between each generation. First generation biofuels are usually created from feedstocks made from food such as corn and animal byproducts. Since the limitations for feedstocks include the quantity that can be produced, they have most likely reached their economic market share in order to keep prices low.
Second generation biofuels are usually made from feedstocks usually not consisting of food such as ethanol or agricultural residues. These costs remain high because of the long process that goes into handling and production. Lastly, we have third generation biofuels which are also made from feedstocks not consisting of food but are found mainly in petroleum products.
These are the biofuels that are the most promising for the future because they are usually referred to as advanced biofuels or green hydrocarbons. We are looking to use algae as a feedstock in the near future.
The use of these biofuels as a direct substitution for gasoline and diesel could mean that there will be renewable options that expand far beyond just the scope of fuel. The use of sea kelp is the innovation in biofuel that many researchers are looking forward to expanding in the near future.
Kelp is a raw material that requires minimal natural resources and is a fast growing organism meaning that producing it won't be a problem. Researchers at the University of Southern California are developing the growth of kelp on a larger scale and they plan to use solar-power buoys and underwater tetrahedron structure to bring kelp to the surface of the ocean.
This cycle will produce more biomass and will be maintained at a larger scale so that one day it might be able to meet the needs of the fuel industry in the U.S. and compete to replace the fossil fuel industry.

Conclusion

With the growing pressure to lower carbon emissions, the application of biofuels is a plausible solution to the replacement of oil in the near future. This change in energy source will bring a competitive advantage to the use of alternative fuels. In the near future, if we are able to meet the land requirements to increase the resources available to make biofuels economically profitable, then it might be able to replace the fossil fuel we use today. The key factor of profitability which is dependent on commodities will be able to undercut the high rising oil prices. In the near future, if biofuels become available for countries to utilize globally, then it will have a significant impact on the global economy and the environment.

This article was written by Dr. Raj Shah, who is currently a Director at Koehler Instrument Company, NY and an active ASTM member for the last 25 years, Dr. Vikram Mittal, Assistant Professor at the United States Military Academy in the Department of Systems Engineering and Ms. Serline Cai, a student at Stony Brook University

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In the past decade, we have seen technological advancements in motor vehicles that run on renewable energy sources. The increasing threat of fossil fuel depletion coupled with the need to maintain renewable sources continues to push for the demand for biofuel.

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Open access peer-reviewed chapter

DOI: 10.5772/53831

chapter and author info

Authors

Krzysztof Biernat

Automotive Industry Institute, Department for Fuels and Renewable Energy, Warsaw, Poland

Artur Malinowski

Automotive Industry Institute, Department for Fuels and Renewable Energy, Warsaw, Poland

Malwina Gnat

Institute for Ecology and Bioethics, University Cardinal Stefan Wyszynski, Warsaw, Poland

*Address all correspondence to:

DOI: 10.5772/53831

From the Edited Volume

Biofuels - Economy, Environment and Sustainability

Edited by Zhen Fang

1. Introduction

The Earth's energy requirements are estimated at 14 TW/ y. Considering the economic development, and therefore high consumption and constantly increasing number of people in the world, it is estimated that energy demand in 2050 will be amount 28 - 30 TW/ y. Fuels from crude oil supply about 96% of the worldwide energy demand for transport. On the other hand, known petroleum reserves are limited and will eventually run out. According to preliminary calculations, fossil fuels will be exhausted within 150-200 years. Fuel consumption causes the emission of carbon dioxide into the atmosphere, resulting in the collapse of the balance between carbon dioxide released to environment, and gas that can be absorbed by plants. It is estimated, that in case of continued use of traditional energy sources by 2030, carbon dioxide levels will rise to 40 billion Mg per year. The correlation of carbon dioxide emissions from the world's population is shown in Figure 1:

Global emissions of CO ₂ and other GHGs, despite commitments of the reduction made by developed countries, will continue to grow, because of increasing production in developing countries, for which clean technologies and investing in renewable energy sources are too expensive. Currently, such a trend can be observed, because the developed countries carbon dioxide emissions was reduced by 6.5% (according to IEA [ 2] data for 2009). On the other hand the developing countries increased the emissions up to 3.3% (mainly in Asia and the Middle East). In this way, the twenty-first century economy will be depend on fossil fuel resources. As a consequence of this state, GHG concentrations will increase, resulting in the continued progress of global warming. Club of Rome, in 1972, has presented a report: "The Limits to Growth" which predicted that before 2072, present industrial civilization will collapse, as a result of the lack of available energy resources, or because of polluted environment.

It is important to get alternative energy sources, that will be able increasingly replace the fossil fuels with reducing effect of carbon dioxide emissions at the same time. That may be renewable energy sources (RES), such as wind, water, geothermal or solar energy. The potential of the solar energy is estimated up to 100.000 TW/y. This huge amount of energy has high potential of application in thermochemical biomass conversion or artificial photosynthesis for processing carbon dioxide and water into the organic compounds.

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2. Solar radiation as an energy source

Solar energy is the most important source of the energy used on the Earth. According with hypothesis of H. Bethe and C. Weizsacker made in 1938 - the energy of the Sun, has its source in the fusion reactions that occur in the interior, according to the reaction ( 1): [ 3]

Solar radiation is in the form of a wide band of the electromagnetic spectrum, which is shown in Figure 2. It covers wavelengths from about 250 nm to 1000 nm over [ 4].

However, the full spectral range of solar radiation (including the ultraviolet (UV)) reaches only to the edge of Earth's atmosphere. The total energy that reaches the Earth's atmosphere is marked as Fs - a stream of sunlight that the average power is 1368 W/m ². Some of the radiation wavelength, passing through the layers of the Earth's atmosphere, are absorbed by the molecules. Even at the height of the Kármán line (about 100 km above sea level) there is the first interaction of solar radiation with occurring nitrogen and oxygen. Ultraviolet (UV), at a wavelength below 280nm, is high-energy radiation. The energy is enough to cause dissociation of molecules into atoms as is shown in following equations 2 and 3:

In the lower layer of the atmosphere - called the ionosphere - solar energy is absorbed by the reactions occurring in the ionization of chemical individuals (reactions 4 and 5).

Moving towards next layer - ozonesphere - sunlight meets molecules of ozone (O ₃). In this way the next part of the radiation is absorbed by the ozone, which leads to O ₃ dissociation, resulting in the formation of excited molecules and atoms of oxygen ( reaction 6):

In addition, a small amount of solar radiation is absorbed during its passage through the troposphere.

As a result, after the absorption and dispersion in the atmosphere, the spectral range of solar radiation flux reaching the Earth's surface is slightly changed, mostly free of long-range radiation from ultraviolet as seen in Figure 3.

By assuming the all solar energy which reaches the earth's atmosphere amount 100 units, as many as 19 of them will be absorbed by molecules and suspensions occurring in the Earth's upper atmosphere. Other relative flows of solar radiation towards the Earth shows Figure 4.

As shown in Figure 4, part of the solar radiation in general does not take part in the energy balance of the Earth - it is reflected to the space. 31 units is reflected including: 6 units directly reflected by the surface of the Earth, 8 units is reflected by aerosols, dust and other materials such as volcanic ash, and the remaining 17 units are reflected from the clouds. The value of solar radiation is expressed as a percentage by the number of . According to the calculations the Earth's Albedo amounts 31%. From the remaining part of the solar energy (50 units) - 4 units are still absorbed by clouds of drops suspended in the water, in consequence remains 46 units. In this way only 46% of solar radiation reaches the Earth's surface and can be absorbed by the land and water. Radiation - a relatively high-and shortwave (UV and VIS) - is partially stored and used in different processes on the Earth, and part of it is reemitted into space in the form of long-wave radiation (infrared, IR) with less energy. Therefore, the total amount of energy absorbing solar radiation reaching the earth shield can be expressed by equation 7:

- means the total amount of solar energy which is absorbed by the Earth (W)

- average flux of solar radiation (solar constant) (1368 W/m ²)

A- (albedo) of the radiation reflected back into space (0.31)

Therefore, the absorbed solar energy is approximately 1.2 10 ¹⁷W (about 124 600 TW) [ 7]. This amount of absorbed solar radiation is the driving force behind all the changes that are taking place on the globe. The solar energy transformation scheme, that reaches the Earth's surface is shown in Figure 5.

Most of the solar energy stream is directly converted into the heat, which is about 67% (nearly 83 700 TW) of the radiation reaching the Earth's surface. About 32% of this energy take part in the hydrological Earth cycle (about 40 400 TW). The energy of water (oceans, seas, inland waters), tidal wave energy can be used to produce electricity in hydroelectric power plants such as the, so-called, flow power plants, which is based on a natural flow. Part of the solar energy is converted into kinetic energy of the wind. Around 400 TW is used for air movement. Wind as an energy source was used in ancient times, and today the kinetic energy of winds is used to produce electricity by using wind turbines.

Other 100 TW of solar radiation are driving forces behind the production of biomass. That organic matter is produced from the processing of solar energy through photosynthesis.

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3. The processes of photosynthesis and their impact on the biomass growth

Green plants, some bacteria and protists have developed specific mechanism for synthesis of reduced carbon compounds, through which energy from the sun has been successfully transformed into a useful form of it. This process, which is one of the most important biochemical processes on the Earth, is called the photosynthesis. It's name comes from two ancient Greek words meaning "light" and "connect". Total formula for process of photosynthesis is a reaction combining water molecules and carbon dioxide, in the presence of energy from the sun, to give the product as a basic sugar molecule, and oxygen as a byproduct ( reaction 8).

If assumed the final product of photosynthesis is glucose, simple sugar molecule belongs to a group of a hexoses. Then the total reaction formula can be written as below ( Reaction 9):

Photosynthesis can be distinguished by two sets of reactions: the light-dependent reaction and light-independent reaction (also called dark reactions of photosynthesis). The photosynthesis is initiate by solar radiation, falling on the surface of green plant leaves, is absorbed by assimilation pigments, acting as a catalyst [ 4]. There are two types of these pigments: chlorophyll and chlorophyll Chlorophyll molecules have strong absorption properties, absorbs solar energy from the electromagnetic spectrum in the range of 400 nm to 700 nm. Radiation of this wavelength range is called Photosynthetically Active Radiation (PAR). The absorption spectrum of chlorophylls differing slightly from each other. Chlorophyll with total formula C ₅₅H ₇₂O ₅N ₄Mg have blue-green color and absorbs light violet wavelength of 417 nm, and the red one wavelength of 657 nm. Chlorophyll (C ₅₅H ₇₂O ₅N ₄Mg) absorbs blue light in the field of 460 nm and red one 650 nm wavelength [ 8]. These small shifts of the both colors absorption maximums is the result of a small difference in the construction. The methyl group present in the chlorophyll has been replaced by an aldehyde group in the molecule of chlorophyll ( Figure 6). The Range of the spectrum, useful for photosynthesis, is enhanced by auxiliary pigments - carotenoids, which have absorption properties of solar energy, not available for green chlorophyll. The color of the carotenoids is yellow-orange, which is the result of absorption by the blue-violet wavelength of 400 nm-495 nm ( Figure 7) [ 9].

Chlorophylls and carotenoids can be found in chloroplasts tylakoids. Dyes are arranged briefly to form units called photosystem I and photosystem II. Visible light beam falling on the chlorophyll molecule, starts the electron excitation state of the magnesium ion at the center of the porphyrin ring. Excited electron is transferred into a conjugated bonds, and then transported to the neighboring molecule dyes. Thus, to pass the initial electron acceptor in photosystem II (which is ferrodoksin molecule) to photosystem I (where particles of quinone are primary acceptor) that ends on the molecule of coenzyme NADP + and reduce it to NADPH. Chlorophyll molecule, after return the electron, has strong oxidizing properties. Thus chlorophyll molecule by a specific protein complex containing manganese ions is able to receive the missing electron from the molecule of water. As a result this process the hydrogen protons and oxygen, the product called "side" photosynthesis is obtained. The result of electron beam movement are two compounds: ATP and NADPH. Produced so-called power of assimilationis necessary to carry out the dark reactions of photosynthesis. A further step of photosynthesis does not require solar energy. At this stage there is a series of reactions called the Calvin cycle where carbon dioxide is assimilated from the air. Subsequently, carbon dioxide is converted and in support of enzyme Rubisco is build in natural organic molecules [ 9].

Formation one molecule of glucose (C ₆H ₁₂O ₆) required six Calvin rotation cycle and the energy in the form of 18 ATP molecules and 12 NADPH molecules.

A series of reactions, which constitute to the process of photosynthesis, are initiated by described light beam, falling into assimilation plants dye. Falling solar rays must have sufficient energy to cause an electron excited state in chlorophyll.

For full execution of photosynthesis, and specifically to reduce 1 mole of CO ₂ molecule is assumed that it takes 8 photons of red light having a wavelength (λ = 680nm), as shown in reaction 10.

One photon of this wavelength has energy = 174kJ/mol, therefore energy used in reaction is: 8 x 174kJ/mol. The free energy (∆ G°) of CO ₂ reduction reaction to CH ₂O, amounts 479.1 kJ/mol, than photosynthesis efficiency η f can be calculated:

Efficiency of photosynthesis (η f) = Energy used/Energy Supplied;

substituting: η f = 479,1 kJ mol⁻¹/8 174,0 kJ mol⁻¹ = 0,34 kJ mol⁻¹

Thus, the ratio between the used energy to the energy put into the photosynthesis process amounts approximately 34%. However, in real conditions only this part of the radiation that can be absorbed by the Earth's surface should be considered. However only about 0.1% of this energy takes part in photosynthesis. In more precise calculations and considering such losses such as "photobreathing" of plants or microbiological decomposition, in practice the efficiency of photosynthesis does not exceed 5% [ 11].

Each year around the globe are synthesized billions tones of organic compounds that serve as nutrients not only for producers, but also for living organisms, which are on higher levels of ecological pyramid. Biomass as an organic matter is simply result of change-over driven by solar energy.

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4. Biomass as an energy source

Solar energy, as a result of guided for over 3.5 bn years of photosynthesis, is accumulated in the form of organic matter called biomass. In this way, solar radiation is converted into a solid form, which can be used further, not only by organisms in the food chain, but also can provide a raw material for the production of effective energy.

The definition of biomass according with Directive 2009/28/WE is: „biodegradable fraction of products, waste and residues from biological origin from agriculture (including vegetal and animal substances), forestry and related industries including fisheries and aquaculture, as well as the biodegradable fraction of industrial and municipal waste"[ 12].

However, this definition does not fully covers the meaning of biomass, because its forms are not just a production side effect of other converting processes. There are also dedicated plantation for energetic purposes only. In other words are established the specific energy crops cultivation.

Biomass energy resources are divided into three main groups: [ 13, 14]:

agricultural biomass (energy crops),

forest biomass (firewood, waste from wood industry and paper industry),

and all organic waste from agriculture, forestry as well as gardening.

The basic division of biomass and their byproducts are distinguished as follows due to its physical state:

solid biomass (that is wood, straw, energy crops, briquette, pellets),

liquid (liquid and gaseous) energy carriers from biomass processing,

Depending on the degree of physical, chemical or biochemical processing of biomass, it can create:

primary energy sources - wood, straw, energy crops,

secondary energy sources - slurry, manure, sewage sludge and other organic waste,

processed energy sources - energy carriers, that is biofuels (bioliquids) [ 14, 15]

The potential of biomass in the world according to the German Electricity Industry Association (VDEW- German Verband der Elektrizitaetswirtschaft) is about 150 bn Mg per year, which equal to 120 bn Mg of coal. Resources of this biomass exceeds over ten times the current world demand for energy. However, from this potential biomass amount, only about 20-30% is suitable to be used, and in fact only 6 bn Mg of plant biomass is suitable for use [ 16]. Biomass resources in Poland are estimated at 30 mln Mg per year, which is the energy equivalent to 16-19 mln Mg of coal/ year and is about (110... 130) TW [ 16] (an average of about 11% of total consumption). For example, to supply biomass to power plant with a capacity of 1MW ( = 0.000001 TW) about 5000 Mg of dry weight of the raw material is needed. This amount is equivalent to the coverage of the field area less than 500 ha, and assuming 10% of the density the crops, which is to cover an area of approximately 50 km ² [ 17]. The sample calculations show, that required energy consumption for biofuels from biomass in the EU's cover area about 79 000 km ², which can be compared with the area of the Czech Republic [ 18].

According to the above figures, the existing biomass resources, and thus the energy efficiency of this raw material is not enough to cover the world's growing demand for energy. It is mean the agricultural land used for food crops should be replaced to a large extent by energy crops plantations, and this way increase the food prices.

Biomass as a solid biofuel is a raw material after suitable processing is used for heat and electricity generation. Conversion of solid biomass for energy purposes can occur by two main pathways ( Table 1 and 2) [ 14, 7]:

1. First one include processes of direct combustion of solid biomass such as in boilers and power plants or by biomass gasification and then combustion of the resulting gas (syngas).

2. The alternative path of energy accumulated in the biomass is to process biomass to liquid biofuels, which are liquid energy carriers for transport.

Conditions

∙ The excess oxygen in the combustion chamber
∙ Temperature: 800-1450˚C

Phase I: drying and degassing of the material the shortage of oxygen, temperature: 450-800 ˚ C Phase II: combustion gases in the presence of excess oxygen, at: 1000-1200 ˚ C Phase III: heat transfer in the heat exchanger

Energy

Heat energy/ electricity

Heat energy/ electricity

Combustion of solid biofuels is the most common and easiest, but inefficient method of getting energy. Because the biomass is a mixture of organic compounds such as carbohydrates, the combustion reaction can be presented in simpler form of equation (11):

Above equation is a simple reverse of the photosynthesis reaction. It can be assumed that this form of solar energy conversion, accumulated in the form of a green plant organic matter is completely depends on carbon dioxide emitted to the atmosphere. As it has been calculated, during the combustion of fossil carbon for every 1 GJ of energy is produced 112 kg of carbon dioxide emissions. In this calculation for biomass (assuming the simplified formula - CH ₂O) the amount of CO ₂ emitted per each 1 GJ of energy is around 100 kg, which is slightly advantage over the coal. However, it is suggested, the final energy balance of biomass combustion process is zero, because of CO ₂ emitted during combustion process is equal to the amount of gas which is absorbed by the organism during the plant growing season [ 4]. However, the rate of biomass growing in time is not enough, to compensate the CO ₂ emitted into the atmosphere. The plants during the growing season, green organisms need about 10 years [ 4] in ideal conditions for example with proper lighting, temperature and humidity. In order to support the performance of biomass energy crops increase are also used different mixes, fertilizers and pesticides, which are produced from natural gas. It is estimated, to get a 25% share of biomass fuels will lead to increase use of NPK fertilizers by 40% [ 4, 19]. Plant protection products and supporting substances causes additional emissions of greenhouse gases into the atmosphere such as N ₂O. Because of combustion of the solid biomass is not only CO ₂ or N ₂ O emission, but also carbon oxide (CO), sulfur compounds, or other combustion residues such as fly ash and dust.

The efficient combustion of such material needs advanced techniques for boilers, allowing the complete combustion of volatile products of biomass pyrolysis. The incomplete combustion of biomass significantly reduces the efficiency of the process. In addition, low-density of biomass causes difficulties in its storage and transport, which creates extra costs. A large range of moisture content, within the ranges 50... 60% gives the energy value (6... 9) MJ/ kg. On the other side biomass dried has calorific value up to 19MJ/kg [ 20]) which is also difficult and costly for preparation to use in the heat and electricity production. Consequently, because of the above reasons, considering the whole process, namely from the operation of farm machinery, through the transport, processing of biomass (drying, degassing of material, seal or change of boilers). Finally the combustion of biomass is not efficient to cover the still increasing demand for energy. A good solution of the shortage problem of biomass used for energy purposes could be manufacturing biomass by microorganisms such as algae, which will be discussed later in this chapter.

Mentioned alternative process for the recovery of solar energy collected in photosynthetic organisms is subjected to physical, chemical or biochemical conversion of biomass (pyrolysis, gasification, fermentation, distillation) [ 4]. In this way the converted form of biomass is called liquid biofuels, which sample preparation processes are shown in Table 2.

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5. Biofuels

In 1900 at the World Exhibition in Paris, Rudolf Diesel introduced the high-pressure engine driven with clean oil from arachidic peanuts. Twenty years later Henry Ford introduced the possibility to power the internal combustion engines with spark ignition by ethanol. Mixtures of alcohol and gasoline as a fuel (30:70 v/v) was reported for using in 1929 in Poland. One of the first scientific publications regarding the possibility of using these compounds to power the engines of tractors has been published in Polish journal "Chemical Industry" [ 22].

In the expected terms of production and use of biofuels (alternative fuels), it is assumed that those fuels should:

to be available in sufficiently large quantities;

demonstrate a technical and energetic properties of determining their suitability to supply the engines or heating devices;

to be cheap in production and has attractive price for costumers;

has a low risk for environment than the fossil fuels, by less emission of toxic compounds and greenhouse gases in the combustion process;

provide an acceptable economic indicators of engines or boilers and safety of their use, and enable the lower operating costs of the equipment;

increase the energy independence.

Until now, there are several complementary definition of biomass. Previously cited European definition mentioned in the European Directive 2009/28/EC and the biomass as the main source of raw materials for the biofuels production. The European definition distinguish two basic raw material pathways and corresponding them technologies, namely BtL processes ("biomass to liquid"), alternatively BtG ("biomass to gas") and WtL ("waste to liquid"), alternatively WtG ("waste to gas").

The Directive also introduced bioliquids as liquid biofuels for other than transport purposes, like production of electricity, heat and cooling. The introduction of "xtL processes" identifies general processes for conversion of biomass instead of distinguishing of second, third and fourth generation biofuels. Apart from this there was defined the term "synthetic biofuels" describing them as synthetic hydrocarbons or their mixtures gained from biomass, such as SynGas produced in the gasification process of forest biomass or SynDiesel.

This division resulted from the conditions described above, and first from the assess the suitability of fuels in modern engine technology and availability of raw materials and their impact on the environment. The formal division of biofuels on the appropriate generations has been published in the report "Biofuels in the European Vision, the Vision 2030 and Beyond". This report divided biofuels into the first generation biofuels, so-called "conventional biofuels" and the second generation biofuels, so-called "future biofuels".

The first generation biofuels („conventional biofuels") includes:

bioethanol (BioEtOH, BioEt), understood as a conventional ethanol gained from hydrolysis and fermentation processes from raw materials such as grain, sugar beets and so on.

pure vegetable oils (PVO-pure vegetable oils), got from cold pressing processes and the extraction of oilseeds;

biodiesel, which is rapeseed oil methyl ester (RME) or methyl and ethyl esters (FAME and FAEE) of higher fatty acids or from the other oleaginous plants, obtained by the process of cold pressing, extraction and transesterification;

biodiesel, which is the methyl and ethyl esters gained by transesterification of waste oils;

biogas got by purification processes of damp waste or agriculture raw biogas;

bio-ETBE, got from the chemical transformation of bioethanol.

To the biofuels of the second category ("future biofuels") have been classified as follows:

bioethanol, biobutanol and mixtures of higher alcohols and their derivatives got by the advanced hydrolysis and fermentation process of lignocellulose biomass (except of raw materials for food purposes);

synthetic biofuels, which are products of biomass change-over by gasification and follow by catalytic synthesis for hydrocarbon fuel components in BtL processes.

fuel for diesel engines gained from lignocellulosic biomass processing through the Fischer-Tropsch processes;

biomethanol obtained by the processes of lignocellulose transformation, including the Fischer-Tropsch synthesis and also with use of waste carbon dioxide;

biodimethylether (bioDME) obtained in thermochemical biomass conversion processes, including methanol, biogas and synthesis gases which are derivatives of biomass conversion processes;

biodiesel as a biofuel or as a biocomponent for diesel engines derived by hydrogen refining (hydrogenation) of vegetable oils and animal fats;

biodimethylfuran (bioDMF) derived from the processing of sugars, including cellulose, in biochemical and thermochemical processes;

biogas as a synthetically derived natural gas - biomethane (SNG), obtained through the lignocellulose gasification processes and the appropriate synthesis and by purification processes of biogas from agriculture, landfills and sewage sludge;

biohydrogen obtained by gasification of lignocellulose and synthesis of gasification products or through the biochemical processes.

The concept of the second generation biofuels is based on the assumption, the raw material for its production should be biomass as well as waste vegetable oils and animal fats, and any residual organic materials, unsuitable for the food industry or forestry.

Department of Transport and Energy of the European Commission proposed to separate the third generation biofuels, as those for which the technological development and their implementation into operation can be estimated for the years 2030 and beyond. To those fuels the biohydrogen and biomethanol were included as well.

The fourth generation biofuels has different definitions but one of the simplest says about crops that are genetically engineered to consume more CO ₂ from the atmosphere than they'll produce during combustion later as a fuel. Both of these biofuels groups are included in the future biofuels group ("advanced biofuels"). Thus, the third generation biofuels can be got through the similar method as the second generation biofuels, but from the modified (at the cultivation stage) raw material (biomass) by means of molecular biological techniques. The purpose of these modifications is to improve the process of converting biomass to biofuels (biohydrogen, biomethanol, biobutanol), for example by growing trees with low lignin content, development of crops with respectively built enzymes, etc.

The proposal of split the new, fourth generation of biofuels was established due to the need to close the balance of carbon dioxide or eliminate its impact on the environment. Road Map 2050 prepared by the European Commission talks about CCS (Carbon Capture and Storage) [ 23], but repeatedly claimed that it is a commercial unimplemented technology. Many companies and organizations have social and environmental objections to implement it. Something that is more reasonable and what should be lean is CCU (Carbon Capture and Utilization). It would be profitable to capture CO ₂ from the atmosphere or the exhaust of power stations and convert it to fuel by using a sustainable source of energy such as sunlight. Photocatalytic or termochemical conversion of CO ₂ to fuels by using semiconductors and metal oxides are two main routes. There is also combination of these routes by using water or hydrogen co-fed with CO ₂ for fuels generation.

There are developed new, forward-looking technologies in the U.S. and Europe characterized by high reduction of CO ₂ by means of LCA (Life Cycle Assessment) parameter of specific biofuel like:

biofuel production technologies, including Jet type, by culturing algae without sunlight from agricultural sludge, grass and waste substances, with the use of carbon dioxide (technology "SOLAZYME");

technology of plasma gasification of waste biomass and municipal and industrial waste (BtG and WtG processes), followed by processing upgraded synthetic gas towards liquid biofuels like GTL diesel and Jet type fuel ("SOLENA" technology, carried out in the UK and Italy);

technology of carbon dioxide use in the carrier energy production processes;

complex biorefinery technologies.

European strategy mentioned in the "European Strategic Research Agenda, Update 2010" defines the following biofuels as a prospective and showing the technological pathways of its getting:

synthetic fuels/hydrocarbons from biomass gasification (application: transport fuels from RES for jet and diesel engines);

biomethane and other gas fuels from biomass gasification (substitutes of natural gas and other gas fuels), (application: engine fuels and high efficient energy production);

ethanol and higher alcohols from sugars containing biomass (application: transport fuels from RES or as a petrol biocomponents, E85);

hydrocarbons from biomass, got from sugars, created in biological or chemical processes (application: renewable transport fuels for jet and diesel engines);

biofuels gained from the use of carbon dioxide for the microorganisms production or from the direct synthesis of carbon dioxide in thermal and biochemical processes (applications: transport fuels and for aviation).

International Energy Agency, have been identified also "solarfuels" ("solar fuel").

It is necessary to determine the best and universal technologies of their production. The technologies of biofuels production have to provide the possibility of safe operation of engines while reducing exhaust emissions of toxic ingredients under the needs of the relevant class "EURO" in Europe and the U.S./ California ULEV in the USA. At the same time it is important that biofuels with a similar composition and properties should be available in every country, because of the motor requirements.

That's why the developed by the International Energy Agency, road map for biofuels in transport ("Technology Road map. Biofuels for Transport") determines the perspective biofuel technologies in the world till 2050. Therefore it was proposed to divide the conventional ("conventional") and future ("advanced") biofuels. Distribution and severity of various biofuels in both groups, according to the MAE, is shown in Figure 8.

The target biofuels production in 2050 required a biomass material with a total energy potential estimated at 65 EJ, which is equivalent to 100 mln ha of cultivations in 2050. Assuming that 50% of the feedstock for the advanced biofuels production will come from waste substances (XtL processes). This means that it is necessary to increase the area devoted for cultivation of biomass for energy purposes. In an optimistic scenario, it is assumed the possibility to get 145 EJ per year of energy from biomass and all kinds of waste substances intended for liquid energy carriers for transport and for heat and electricity in the polygeneration. Estimated reducing of CO ₂ emissions is determined at 2.1 Pg per year, with the share of biofuels of 27% (v/v) of the total amount of transport fuels.

Considering the demand for biofuels that meet the future needs for transport, including air transport, and their ability for CO ₂ reduction, it was established by MAE the following biofuels and their technology paths:

obtained by anaerobic digestion of raw materials, such as organic waste, animal manure and sewage sludge, than purified to the biomethane form (SNG!!) by removing CO ₂ and hydrogen sulfide (H ₂ S). Can be applied in transport as methane fuels (bioCNG, bioLNG) or as a source of hydrogen, also for the fuel cell;

biobutanolhave a higher energy density than ethanol in petrol. It can be shared through the existing network for gasoline, Biobutanol can be produced by sugars fermentation using bacteria, Clostridium acetobutylicum. Demonstration plants are working in Germany and in the USA, the others are under construction.

In terms of the most promising biomass for the future biofuels production, considering so-called "land hunger" ("ground competition") and the needs in terms of CO ₂ emissions, can be distinguished following cultivation: algae, camelina, jatropha, and halophytes. Under development are new technologies without sunlight ("dark"), marine photosynthetic membrane systems for the algae production, as well the technologies for biomethanol production.

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6. Technologies of liquid energy carriers production based on waste substances

6.1. WtL (Waste to Liquid) and WtE (Waste to Energy) processes

Dynamically observed population increasing in the world stimulates fast economic growth. This is related with growing demand for all kinds of products and energy. In result of progressive consumption, waste generation is increasing. According to the data total amount of waste, which is generated in the European Union, maintains an upward trend. Municipal solid waste (MSW) amounted 150 million Mg in 1980. In 2005, increased up to 250 million Mg, and forecasts for 2015 growth is estimated up to 300 million Mg [ 25]. The constantly increasing amount of waste contributed in overfilled existed landfills, forces society for development of new landfills. The overfilled landfills are big the social and environmental problem. Therefore, novel energy technologies have preferences for waste treatment WTE (Waste to Energy), or for receiving new products from waste in the process of WTP (Waste to Product.). Waste treatment processes for liquid energy carriers are processes WTL (Waste to Liquid). The trends for conventional energetic waste utilization are based on direct combustion and more advanced thermochemical methods such as pyrolysis, gasification, and plasma technologies under development since 1970. Figure 9 shows the main alternative methods of converting waste to energy in WTL and WTE processes [ 25].

In the WTL and WTE processes, pre-treated waste is converted into secondary energy carriers using thermochemical methods: physico-chemical or biochemical. As a result of these changes is obtained biofuels solid, liquid or gas. These fuels are burned and converted into thermal energy. WTL processes path is shown in Fig.9..

A HTU is processing waste into liquid biocrude oil (Hydro-Thermal Upgrading), at high temperature and pressure near supercritical condition of water, which is usually the solvent in this process, the basic conditions are shown in Table 3.

HTU process developed by Shell in 80's occurs at a temperature up to 350°C and a pressure about 180 bars. HTU can be used to convert liquid fuel from a wide range of biomass feedstock, without the need of drying raw material. It has been designed to carry out the reaction in the excess of water, under supercritical condition of water. The final product is a "bio-oil" ("biocrude") with properties similar to crude oil, so it can be used after upgrading as fuel in boilers, turbines and so on. The calorific value (LHV) of biocrude obtained this way amount 30... 35 MJ/ kg [ 27].

Another an example of a technology for waste conversion is based on the catalytic thermal depolymerization patented by Alphakat GmbH, which principle of operation is shown in Figure 10.

KDV process takes place in a special industrial installation known as KDV Unit. As can be see from Figure 10, the whole system is a closed with strictly defined conditions: the process is carried out at ~350°C, under low vacuum 0.9 bar. The vacuum is maintained in the system by special vacuum pumps. As shown in the figure, the pump mix the raw material provided with a catalyst causing the circulation of the reaction mixture in a closed system. After heating the batch by thermal oil up to ~350 °C, volatile organic compounds (VOC) are formed, which at the main distillation column undergo separation for diesel and gasoline fraction [ 29, 30].

Using KDV technology a wide range of raw materials derived from biomass or waste materials, either organic or mineral, can be process. Table 3 summarizes the basic substances that can be used as a feedstock in KDV plant. We can see all kinds of biomass waste, agricultural, municipal and industrial sewage, as well as synthetic materials.

1

Biomass (C-3 and C-4 plants)

∙ grown energy sources like Jatropha,
∙ wood, biogenous residues like leaves, straw, etc.

2

Waste

∙ Industrial Waste (IW),
∙ Municipal Solid Waste (MSW),
∙ agricultural waste,
∙ waste oil (also contaminated oil),
∙ refinery residues, bitumen. etc,
∙ dried sludge from sewage treatment plants,
∙ rubber and tires.

3

Synthetic materials

∙ All kinds of plastics and synthetic materials (PVC, PP, PET, etc.)

The main products from KDV plant is synthetic diesel fuel or kerosene depends on process parameters [ 30]. However these fuels are available after catalytic hydrotreatment process (like hydrodesulphorization in refinery), because the product after distillation has still properties of biocrude oil. KDV were started as a demo units in Germany, Canada, Spain and Mexico and recently in Poland [ 31].

6.2. Overview of selected technologies for liquid biofuels from waste carbon dioxide

6.2.1. Conversion processes

Scientists all over the world are trying to learn the essence of the photosynthesis process. Already in 1912, the Italian chemist Luigi Giacomo Ciamician in the Science magazine, said the society should be transfered from a civilization based on oil and coal and start using clean energy from the sun. He thought that by using appropriate photochemical reactions and using the new compounds is possible to discover the mystery of the photosynthesis guarded plants.

In July 2010, in the United States was established Joint Center for Artificial Photosynthesis - JCAP, funded by the U.S. Department of Energy (DOE). The aim of this project is to develop a method able to copy the photosynthesis process, available to establish the path for the production of liquid fuels using waste carbon dioxide.

According to information provided by JCAP [ 32], major challenges facing scientists dealing with the artificial photosynthesis is a system that consists of key elements of the process: the visible light absorber, catalyst and membrane switches.Visible light absorber is a molecule that is designed to capture and convert the sunlight with the high efficiency, like the chlorophyll in plants. Absorbed energy puts absorber molecules into excited state, in which all the light energy is submitted to electron. Properly designed absorber pushes the electron from the shell, directing him to an adjacent molecule (in the same way as it does in natural photosynthesis, where electrons jump from photosystem I to photosystem II). In this way formed electron beam passes through a further conveyor releasing the energy required for further electrochemical reaction. At the point of detachment of the electron take place creation so-called. "Hole," or positive charge. At this point is necessary a catalyst that efficiently breaks the water molecule, this way is freed the missing electron in place of created "hole". In natural photosynthesis complex of the protein, which contains manganese ions act as the catalyst. This compound is still a great mystery because it is not yet possible to copy of its complex structure in the laboratory. Therefore, research is continuing to find a suitable replacement, which will perform a similar sequance cleavage involving water molecules processed by the solar energy absorber. Catalyst must not only be efficient and sustainable, but also cheap, and widely available on the Earth, preferably non-Nobel metal or his complex.

Copying plants, we can create something like artificial leaf. The function of the matrix is not only to act as a micro bioreactor, but also play role of separation reactants and products (fuel and oxygen). Oxygen is not a desirable product in artificial photosynthesis. Instead of molecular oxygen (O ₂), it can happen that forms oxygen radicals (O), very reactive with strong oxidizing properties.

With a listed part of the process of artificial photosynthesis, there is only lack of one element - the connector, through which various components interact with each other and create a functional whole.

In order to build a system composed of the described elements, there are carried out intensive research in the USA, Switzerland, UK, Japan and Poland.

The project regarding artificial photosynthesis in Poland started in 2006 at the University of Maria Curie Skłodowska (UMCS) University in Lublin and in collaboration with EKOBENZ company.

The concept of methanol synthesis based on the carbon dioxide formed as a result of different technological processes has been developed by Professor Nazimek from UMCS. The invention is based on the oxidation of water using titanium dioxide (TiO ₂) as a photocatalyst and at the same time the reduction of carbon dioxide (dissolved in NaOH aq). Reaction is carrying out in assistance of fixed ultraviolet radiation (UV) as is shown by reaction 12.

This technology will enable the production of methanol from the two cheap, universal components: carbon dioxide and water vapour. The proposed technology is one of the most promising methods of utilization of CO ₂, since this compound can be converted to a valuable product, under natural conditions by exposure to UV light.

Implemented technology is characterized by the synthesis reaction of carbon dioxide and water which takes place in aquatic environment at the presence of a photocatalyst at a temperature of 20 ° C and atmospheric pressure. Specifications referred this reaction on a laboratory are shown below:

Energy consumption 0.75 kWh/dm ³ of methanol

the solution flow rate 8 dm ³ / h;

carbon dioxide flow 370 dm ³/ h;

the concentration of methanol in the aqueous solution was 15%.

Based on these parameters has been developed preliminary schematic diagram of the planned production process, as shown in Figure 11.

Under the proposed scheme carbon dioxide is stored in the reservoir of raw material from which goes to the mixer where is absorbed in demineralized water. Then, in the reactor under the influence of UV radiation takes place photoreduction reaction. When reaction is completed, the distillation take place and methanol (CH ₃OH) and water (H ₂O) are separated. The methanol is sent to the product tank, and the water is reused in the production process - is transfered to the mixer. The active and stable catalyst is the key for obtaining methanol by CO ₂ photoreduction. For photocatalytic tests were applied TiO ₂ in the form of anatase supported by alumina as a carrier of the active phase.

The study at laboratory scale was carried out in flowing system, at atmospheric pressure and ambient temperature, equipped in quartz pipe reactor. In typical experiment 100cm ³ of distilled saturated by CO ₂, and air or nitrogen flowed through reactor. Bed catalyst was exposed on UV lamp radiation at fixed wavelength. The effluent was analyzed for content of organic compounds by using gas chromatograph. The conversion of CO ₂ to methanol was determined by the formula ( 13).

C ₁ - final concentration CO ₂ [mol/dm ³]

The conversion degree of carbon dioxide amounted only 6% [ 33]. It was found the titanium dioxide catalyst had a defect in the absorption spectrum, which was located only in the UV light range. Visible radiation even during long-term irradiation was not able to induce the active phase of the pure TiO ₂. The suspension of titanium dioxide could be the solving the problem, but it is related with separatation of the catalyst from the product liquid phase after reaction completion.

Therefore, the above measurements were carrying out involving a new nano-structured wall catalyst. This catalyst is protected by Polish national patent No. 208030. The catalyst is characterized as the active sites in the form of clusters TiO ₃ with aluminum III ions and sodium I ions (TiO ₃ content in the range 4.36 to 5.34% (m/m) of the total weight of the catalyst) supported by alumina. These clusters are deposited on the inner wall of the aluminum tube of the reactor.

The catalyst described above as the wall form allows to implement an artificial photosynthesis process in the new technology. Developed a new efficient photocatalyst created the conditions for process with performance sufficient for commercial applications, for example by design 0.5 m length of processing pipe reactor, photocatalysts (with φ = 5 cm) allowing to convert the 370 dm ³ of CO ₂/h into methanol with the degree of conversion at 97%.

Figure 12 shows the schematic diagram of the installation for methanol production applying artificial photosyntesis.

As shown in Figure 12 carbon dioxide with water are transfered into mixers arranged in series, which supply the reactors system. The catalyst is located on the reactor walls, as a result of reaction are products like oxygen molecule, water and methanol. Molecular oxygen is discharged to the gas collector, and the mixture of methanol and water is further transferred into the distillation tower, where separation these compounds take place. Water is returned to the mixer, where it is used in the subsequent cycles of the process, and desired the final product is separated as a pure methanol.

The methanol obtained through the described technology can be directly applied as a fuel in dedicated engines and adjusted fueling systems with seals, proper polymer pipes because methanol is known as a good solving agent for many materials used in cars now. On the other hand methanol can be catalytically converted towards gasoline fraction by using very well known from 70's Mobile process- MtG (Methanol to Gasoline). MtG method involves the synthesis of a higher hydrocarbons mixture (which are synthetic petrol) from methanol, the intermediate product according to the general reaction (14) are:

*The and values are variable depending on the temperature and pressure in the system, as well as catalyst used in the process.

Reaction (14) occurs at a temperature T = 723K and under the pressure of p = 200 bar. Water is a by-product of the reaction is, which is a limiting factor in MtG synthesis because it affect the catalyst performance. The catalysts used in the synthesis of synthetic gasoline from methanol are based on aluminosilicate matrix. These type of catalysts in some excess of water vapour, in the reaction mixture, lose their activity because of extraction for example Al ions from the matrix of catalyst. A new catalyst has been developed, which is water-resistant in the reaction mixture used in MtG method as well as related technology EtG (ethanol to gasoline, which will be discussed later in this chapter). Nano-structure catalyst developed for the synthesis of gasoline from the ethanol according to equation (14) is characterized by the active centers in the form of a copper ions coordinated in octahedral structure. Copper is supported by nano-structured aluminosilicate matrix with metal content in the range of 0.2-0.5% w/w. This catalyst has a high water resistance with content even more than 10% water by volume of the reaction mixture.

The final product of the described method MtG is appropriate mix of higher hydrocarbons, which are synthetic gasoline with an octane rating of up to 108, characterized by the same properties as gasoline derived from crude oil processing. Summary of the final products of described MtG method is shown in Table 5 [ 34].

According to preliminary estimates, this method is able for application within three years, and what is most important can cause the reduction of CO ₂ in the atmosphere by 25%.

Some inaccuracies in the calculation of the energy balance above process should be noted. The synthesis of methanol from CO ₂ and H ₂O is endothermic reaction, which means that for the occuring reaction is required determined amount of energy. It was found out, the total power consumption in order to obtain a 1 dm ³ methanol is 0.75 kWh. The balance of energy showed the following conclusions:

if: 1 kilomole of CH ₃ OH = 586 MJ

1 kilomole of CH ₃ OH = 32 kg

therefore: 32 kg CH ₃ OH = 586 MJ

specific weight CH ₃ OH is: 0.48 kg/l.

therefore: 1 kg = 5.08 kWh, which gives0.48 kg (=1liter) = 2.44 kWh

Conclusion: To make 1 liter of methanol from CO ₂ and H ₂ O is required 2.44 kWh, it is three times higher than reported by the inventor of the method - 0.75 kWh.

Therefore, the cost obtaining of 1 liter methanol will be about 0.31 USD, and not as referred value 0.03 USD [ 35]. Regardless, a drawback of this method is the fact the developing technology is based on the pure components. In the synthesis reaction of the methanol with carbon dioxide and water, is used 96.5% CO ₂ from the pressure cylinder, which occurs very rarely, only in some chemical processes (including fermentation). The effects of using carbon dioxide mixed with air in the reaction, such as is found in the nature, wasn't fully investigated yet.

In summary, the method of converting carbon dioxide into methanol at the moment is not applicable, because there is no beneficial economic and energy effects. For these reasons, the project in methanol synthesis in the process of photoreduction of carbon dioxide was suspended. The chance for this interesting project is replacing artificial sources of UV radiation by the natural sunlight. Then the project possibly would be cost and energy-effective. It depends on the active catalyst that would work efficiently in the visible light range.

The part of the project under investigation is still EtG process (Etanol to Gasoline). The coupling process of ethyl alcohol towards of higher hydrocarbons also take place with a suitable zeolite catalyst, at higher temperature and pressure. Replacing ethanol by its homologue methanol causes a significant reduction of pressure required for a reaction, from about 200 bar to 30 bar. Also, the temperature is much lower and amounts 653 K [ 36]. Reaction of ethanol conversion into higher hydrocarbons is exothermic, and therefore there is a problem with removal of the heat. if combined with endothermic process of methanol synthesis could improve the energy balance of carbon dioxide conversion into methanol. The tubular reactor is cooled at the moment by medium, which at the beginning of the research was air. Now it was changed to a more efficient oil. This method of catalyst cooling is not very effective, because it reduce the temperature only near the outer wall of the reactor. The gradient temperature within radius can reach the temperature up to 300 °C. Then, the catalyst located in the center of the reactor can be affected by sintering process, and then lose activity. The current research aim is to optimize the temperature of the entire length of the reactor, to avoid deactivation of the catalyst.

At the present stage of research, the experiments are carried out in one reactor, and the target is to operate six reactors cooperating with each other, forming so-called hexagonal reactor. The overall diagram of the EtG is shown on Figure 13.

Under the pictured diagram, ethyl alcohol is sampled into the heater, where in the electric heater spiral is heated to about 270 °C, and through the isolated pipes reaches the reactor. Outlet reaction mixture flows to the condenser, where the liquid products are out dropped. However the ethanol is converted not only towards the liquid fraction, but as a result of this reaction the gaseous products are also formed. Gases are recycled to the reactor, mixed with a new part of ethanol steam and are converted into gasoline fraction. The liquid fuel is further analyzed from point of view requirements of gasoline and diesel. The typical content of such products are benzene (as aromatization compound of ethanol on zeolite), olefins, paraffins and other aromatics. Research in this area is continued in Poland on the frame of "Operational Programe of Innovative Economy". The process is called ETG (ethanol to gasoline) is similar to the MTG (methanol to gasoline) process which was successfully used by Methanex in New Zealand.

6.3. Photoconversion technology using "artificial leaf"

On 241 Congress of National Meeting of the American Chemical Societyin Anaheim, Califfornia, it was announced the invention of the first functional artificial leaf. "A practical artificial leaf has been for decades the one of the Holy Grails of the science"- said the leader of the team, Dr. Daniel Nocera - "We believe that we did this" [ 37].

A breakthrough moment in the study of artificial leaf is development of a suitable catalyst, nickel (Ni) and cobalt (Co). These elements are widely available comparing with noble metals, what is important they act at ambient conditions and have a high stability during the reaction. Inventor reported very effective work of artificial leave for production hydrogen and oxygen.

The artificial leaf is a matrix composed of material used in most of the solar cells, semiconductor silicon. Surface is covered with a matrix of cobalt catalyst on the one side, and on the other side with the molybdenum-zinc alloy of nickel. Solar radiations falling on the surface are transformed into electricity which allow to decompose bond of water molecules in the presence of catalyst. On the first side of the matrix, the electrons are knocked out from the water molecules using cobalt catalyst. The water molecule is decomposed into hydrogen ions H⁺ and oxygen. Oxygen remains on first this side of the membrane, while the hydrogen ions are transported to the other side of the matrix, where the nickel is catalyzing the recombination reaction of hydrogen ions with the previously made free electrons. The result of the process is H ₂ molecules formation [ 37- 40]. Diagram of the act "artificial leaf" is shown in Figure 14.

In this way, as it is shown in Figure 14, one surface of an artificial leaf produces oxygen and the other - hydrogen.

According to data the authors team, with one gallon of water, exposed to solar radiation using artificial leaf; it is possible to produce enough electricity required for the daily demand for household energy in developing countries.

6.4. Solar reactor in technology of synthesis gas getting („solarfuels")

The research group of CalTech from United States published in December 2010 the paper regarding their latest achievement in artificial photosynthesis. Prototype solar device was constructed, where the heart of device is cerium dioxide (CeO ₂) catalyst. Diagram of the device is shown in Figure 15.

Reactor operation is based on the absorption of concentrated solar radiation, which falls on a quartz apparatus window, then passes into the insulated chamber of the receiver, which is filled with a porous cerium oxide. This compound has a specific property of the oxygen binding at low temperatures, and desorption it at high temperatures, without damage of its crystalline structure, according to the reactions (15), ( 16), and ( 17).

: M - pure cerium or cerium with mixtures; T H - at high temperatures; T L - at low temperatures [ 42]

In this way, it absorbs oxygen gained from supplied to the reactor carbon dioxide (CO ₂) and water vapor (H ₂O). Thus, inside the reactor are formed the carbon monoxide (CO) and hydrogen (H ₂), which is an ideal source of energy. Hydrogen is considered to be so-called "clean fuel" because in the result of its combustion the water is just produced. However, the reaction of hydrogen with carbon monoxide if presented by stechiometric reaction can be directed towards methane formation, popular heat, transport fuel and source of chemicals production ( reaction 18). The synthesis gas in proper molar ratio of CO/H ₂ and using FT catalyst (Co or bimetallic with Fe) can be converted towards higher hydrocarbons.

In the CalTech process the reactor was exposed to solar radiation at 1.9 kW of power. Such power is widely used in various types of solar antennas or solar towers; any of these devices has not reached the efficiency of the presented prototype. This can be explained by the fact, the reactor uses the entire spectrum of light, not only the selected wavelength. Disadvantages of the presented solar reactor is the energy losses as a result of energy radiation through the walls of the reactor (about 50% of the energy input) and the release of radiation through the quartz window (about 41% of supplied energy).

It can be assumed that further improvement of the process will be able to reduce the temperature of the reactor (today reactor operates at 1648 °C), and less energy losses through more efficient use of solar radiation. An initial analysis of the process effectiveness showed that improvements structure of cerium oxide will allow to increase activity of catalyst in the range of 16-19%.

This concept can be used for conversion carbon dioxide emitted from coal power plant to liquid energy carriers. The pure carbon dioxide is not required to carry out this reaction. This allows at least twice using of the same coal compund [ 42].

6.5. Biological processes using carbon dioxide as a raw material

As stated previously, the world's biomass resources are not enough for producing renewable energy with at the same time growing needs of modern civilization. For example in UK, replacement of diesel by biodiesel produced from rapeseed would required plantation more than half area of the country [ 43]. The areas for the production of liquid biofuels is competitive with the same areas for the cultivation of food crops. There is a conflict between energy and food use of agricultural land. In addition, oilseeds cultivation leads to monocultures over large areas, which is inconsistent with the Directive 2009/30/EC. As stated in mentioned Directive production of biomass for energy purposes should go hand in hand with biodiversity. Nowadays more and more we hear about a new raw material for the production of liquid fuels which can be tiny microorganisms such as algae. Algae growing is a good option for limited areas of cultivation of biomass for energy purposes. Algae can be grown in areas not suitable for the cultivation of the soil, such as deserts or oceans. In addition, they are a kind of "factory", able to convert waste carbon dioxide into valuable energy products.

The idea of using algae as a feedstock for bioenergy production has already appeared in the mid-twentieth century. In 1940, it was discovered that many species of microalgae growing in strictly definite conditions can produce large quantities of lipids. The concept of using the stock of lipids as an energy source has been caused by the oil crisis which arose from the imposition of the embargo in 1973 by the OPEC countries. The rapid increase in oil prices and the reduction of the energy carrier from Middle East to the United States contributed to the search for new sources of energy such as micro-algae. In 1978, Program of the Department of Energy for Aquatic organismshave been created (DOE's Aquatic Species Program), which focused on the acquisition of the fuel in the form of pure hydrogen supply by aquatic organisms. Already in the early 80's, this was changed and focused on trying to manufacture liquid fuels, mainly biodiesel. Over 300 000 existing algae strains were collected from different extreme environments. The next seven years were carried out research regarding tolerance of different salinity on temperature, pH, and the ability for the production of neutral lipids. After these tests, the study was limited up to 300 promising strains, in which the main role was played: diatoms algae (Bacillariophyceae), and green algae (Chlorophyceae) [ 44].

Algae are a valuable source of raw material for energy transformation because of fast growth of the biomass. Autotrophic algae contain chlorophyll molecule in their cells so they have the ability to carry out the process of photosynthesis. They are able to use about 10% [ 45] of the sunlight falling on it, in consequence able to double their weight during the day, and in the experimental conditions this time was reduced up to 3.5 hours [ 46]. The study shows that wit1hin one year cultivation of algae on the area of one hectare, it is possible to get 8,200 liters of biodiesel from extracted algae lipids, while for other oleic plants like only 2700 liters, 1560 liters from canola, and from soybean only 544 l [ 43]. These data are summarized in Table 5.

According to the literature, the production algae biomass is 40... 60 times higher than previously cultivated energy crops. The yield estimated with different cultures growing algae in closed photo bioreactors is about (400... 500) Mg/ ha/ y, which coresponds (400... 500) thousand m3 of bioethanol per year [ 47].

Another advantage is that algae cultivation is possible in wide variety of water sources: seawater, postproduction water, as well as in wastewater.

One of the key reasons to use algal biomass for energy purposes is these microorganisms absorb and convert a significant amount of residual carbon dioxide. To provide 100 g of biomass, algae consume about 183 g of carbon dioxide, which is associated with a 50% share of CO ₂ in dry weight of these microorganisms [ 48]. With the ability to bind CO ₂ algae opens the possibility of using waste carbon dioxide from the exhausted gase, for example coal-fired plants. In this way, they close the circulation of carbon in nature. They also show the ability to absorb other waste components, such as nitrogen or phosphorus for example from of chemical fertilizers. With this ability algae can lead the process of bioremediation of contaminated environments, thus contributing to reduce contamination of soil or surface waters (eutrophication) and groundwater.

Energy sources that can be produced from algae depend on the substrate used and the method used to process the obtained algae biomass. The main path of bioenergy production using algae is shown in Fig.16.

As shown in Figure 16, we can get bioenergy directly from algal biomass include electricity, syngas, biohydrogen and biomethane. However, two main liquid energy carriers gained from the cultivation of algae are biodiesel and bioethanol.

For the production of biodiesel from algae, the most important is choosing the right kind of algae for triacylglycerols (TAG) obtaining as well as made the ideal cultivation system of these microorganisms. It is necessary to use not only the knowledge of the bioenginering of the various strains of algae, but also integrate this knowledge with the best matching further process technologies [ 44].

It was observed that in the optimum conditions for the development of algae, which is a sufficient amount of nutrients (such as nitrogen and phosphorus) biomass increase, but the percentage of the dry weight of TAG is rather small. For example for the species Chlorella Vulgaris it is about 14-20% of TAG. However, in the lack of nutrients, algae forms a reserve of energy in the form of so-called TAG. The percentage of TAG per dry mass for Chlorella Vulgaris reaches up to 70%, when nutrition substances are limited. One proposed solution for this phenomenon is a two-step process of algae cultivation. It is based on the fact that in the first stage of breeding algae grown in optimal conditions, with a sufficient amount of nutrients, which results in a rapid increase of their dry biomass. In the second stage the algae are transferred to the place with significantly reduced amount of nutrients. So these micro-organisms, as they are stored in a nutrient deficient conditions lead to increased production of TAG cells.

Another solution is to use microtrophic algae. They are characterized that under conditions of sufficient amounts of nutrients, mainly easily assimilable carbon such as glucose, are transferred to the heterotrophic mode during which produces significantly greater amounts of lipids. Unfortunately, by introducing additional nutrients such as glucose, this solution entails the risk of contamination algae culture by heterotrophic fungi and bacteria [ 49]. Moreover, one of the main advantages of using algae for biodiesel production is the use of carbon dioxide from the combustion of fossil fuels.

Properly grown biomass is collected and processed in such a way to maximize the production of triacylglycerols cells for the production of biodiesel ( Fig. 17).

Algae farm is usually isolated as was shown in Figure 17. In order to reduce the water content, of the harvested biomass, is added the flocculant. Lipid fraction extraction take place with help of hot diesel fuel, than the mixture is separated by using centrifudge.The oil fraction is separated from the watery phase and the biomass waste. Oil fraction can then be used in transesterification reaction to produce FAME or synthetic hydrocarbons using HDO process. As a result, from showed processes already are produced fuels by Sapphire Energy, Petro-algae and Solix Biofuels.

For example, an American company Sapphire Energyin 2008 has successfully produced 91-octane gasoline from algae, which complies with U.S. standards. They made a flight test with the twin-engine Boeing using algae-based jet fuel in 2009. They started the construction of an integrated minibiorefinery based on biomass from algae in the southern part of the state of New Mexico in 2010 (called Intergrated Algal Bio-Refinery) [ 50, 51]

In the process of producing ethanol from starch contained in algae cells, the most plentiful in this hydrocarbon algal classes are: Chlorophyceae(green algae) of the types: Chlamydomonasand and Cyanophyceaeof species: Arthrospira, Oscylatoriaand Microcystis. Bioethanol from the sugar gained from algal biomass can be obtained by:

Breeding of certain species of algae in anaerobic and without the sun conditions (then the algae produce ethanol within the extracellular space);

Extraction starch from algal cells and then, through the enzymatic hydrolysis and fermentation ethanol is produced [ 45].

For example, patented by the company Algenol Biofuelsprocess is called Direct to Ethanol ®and is based on breeding of algae Cyanophytain specially designed flexible plastic photobioreactors. Using seawater and waste carbon dioxide (fed directly from industrial plants) and subjected to direct sunlight, the algae perform photosynthesis. Sugar molecule (starch) get by photosynthesis process is fermented to ethanol, which diffuses through the cell walls of algae to the solution of breeding. Because of raised temperature during the day, ethanol is evaporated from the solution. On the inner wall occurs condensation of ethanol vapors when the temperature decrease at night outside of photobioreactor,. The condensate drops down of the reactor, where on special internal basins is collected and transferred to distillation unit.

Except lipid molecules in the form of triacylglycerols, or hydrocarbons in the form of starch, which are precursors for the production of biofuels, from algae biomass may be obtained also other products such as proteins. Therefore, in the production of biofuels using algae is formed a wide range of products such as animal feed, fertilizers, pigments, bioplastics, detergents, cosmetics and even food [ 52].

6.5.1. Offshore membrane enclosures for growing algae - OMEGA system

OMEGA technology, originally developed by NASA, is derived from the space program aimed to closing the loop (called „close the loop") between the waste stream and the resources necessary for astronauts during long flights [ 53]. The modified system is to grow cultures of algae in specially designed, floating on the water surface, photobioreactors (PBR) composed of polymers. On the figure 18 is presented the idea of this system.

The system consists of a number of connected, floating photobioreactors, which are pumped by waste water from the mainland (the actual appearance of the plastic photobioreactors - "bags" floating on the water are shown in Figure 19).

Algae consume nutrients contained in the sludge, and they associate the carbon dioxide from the air, or waste CO ₂ emitted directly from industrial gas plants. By using solar energy, they embed CO ₂ into their cells and give off the oxygen into the atmosphere, at the same time producing biomass and oils in their cells. The temperature inside the photobioreactor is controlled by the heat capacity of the surrounding ocean waters, and the gradient between the wastewater and seawater was used for the drainage of photobioreactors. In case of leak the photobioreactor content into the ocean, freshwater algae are breaking up, because they are not able to survive in saltwater. These biochemical species of algae are decomposed into simpler chemical compounds. Thus sea water where are mounted plantations algae are not contaminated. The algae after the growing phase are transfered into the osmotic chamber to make them more dense. Then biomass material is transported into a collection chamber, from where are send to biorefineries. Waste water is returned to the cultivation unit, to maintain the adequate stock and optimum concentration of nutrients for carry out the photosynthesis process by algae. The OMEGA technology final products are biodiesel, jet fuel and by-products such as cosmetics, fertilizers, and animal feed.

The method of producing biofuels using microorganisms is an agree with the nature. There is not used genetic modifications organism and the risk of GMO species invasion into the natural sea environment. Strains of algae are biodegradable, which means it does not involve any risk of pollution of the seas, and oceans, and may even provide food for fish living there. The only added cost is the pumping wastewater into the photobioreactor. However, it was showed the idea of ​​driving the process using wind turbines or solar panels [ 54, 55].

6.6. Processes of sunless photosynthesis

Term of sunless photosynthesis may be used to define the process carried out by heterotrophic algae without the solar energy, but using the previously synthesized organic compounds as a source of carbon and energy.

Heterotrophic algae growth is dependent on many factors. A significant role in the stimulation or inhibition of heterotrophic microorganism's growth will play the access of sources organic compounds. Depending on the concentration as well as the amounts of organic compounds in a given nourishment, the algae biomass growth runs with different efficiencies. It was also found the positive effect on the growth of microorganisms in environment with poor carbon source mixture. Another factor that has an impact on the growth of algae biomass is the concentration of nutrients such as nitrogen. For example, the studies show the most effective source of nitrogen for the growing of microorganisms on the glucose nourishment is urea [ 56]. One of the companies dealing with the issue of sunless photosynthesis of algae on an industrial scale is a private company Solazyme Inc., which was found out in 2003. Method for waste biomass change-over to liquid fuels, developed in the company, uses various strains of heterotrophic genetically changed algae to produce different types of fuels. Figure 20 shows the main production pathway in Solazyme technology:

Alpha Algae, used by Solazyme, are heterotrophic organisms, which means they are developing without solar energy. Identified strains of algae, as it was shown in Figure 20, are transferred into the stainless steel containers. There, in darkness algae are fed by nourishment in the form of various types of raw material. This is mostly lignocellulosic biomass, so all kinds of grass, wood chips, agricultural sludge, as well as other waste substances. Depending on the type of nourishment, and the breeding strain, the algae produce different products. Some of them produces lipids, others provide a rich mixture of hydrocarbons, similar to those included in the light oil [ 58].

The biggest achievement of California's company happened on 13 March 2012. The ship LM 2500 fleet of U.S. Navy frigate, sailed successfully from the port in Everett (WA), to San Diego (CA), powered by fuel: Soladiesel HRD-76 ®. The ship was driven using 25,000 liters of 50/50 mixture of Soladiesel ® and pertoleum F-76. That was the first ever demonstration of alternative fuel mixture in the ship of naval fleet [ 59].

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7. Biohydrogen and Liquid Organic Hydrides (LOH) application

In the context discussed above solar fuels effective production of hydrogen could be the chance for application of LOH as chemical hydrogen storage medium.. The use of liquid organic hydrides in hydrogen storage provides high gravimetric and volumetric hydrogen density, low potential risk, and low capital investment because it is largely compatible with the current transport infrastructure, see Fig.21. Despite its technical, economical, and environmental advantages, the idea of hydrogen storage in liquid organic carriers has not been commercially proved yet. This is because of technical limitations related to the amount of energy required to extract the hydrogen from liquid organic hydride and dehydrogenation catalyst is not stable enough. Renewable hydrogen as well aromatic compounds can be obtained by direct catalytic conversion of methane or biomethane in dehydrocondensation (DHC) reaction. DHC processwas intensively was studied for the last decade by several groups of researchers, mostly from Japan [ 60- 63], China [ 64], USA [ 55- 67], and Hungary [ 68]. Following endothermic reaction represents methane direct conversion to benzene and hydrogen without participation of oxygen:

The most effective catalyst for this process is Mo/H-ZSM-5 and Re/H-ZSM5. Oxygen-free conditions used for this reaction result in high benzene selectivity (up to 80%). Nowdays, methane is mostly used for heating purposes, as a transport fuel (CNG) and for chemical synthesis. DHC is promising process from point of view petrochemical feed stocks synthesis, hydrogen production for fuel cells and possible conversion of the waste and difficult accessible resources of natural gas. It can be clathrate (methane hydrate), coal bed methane, post fermentation biogas, land fill and recently shale gas able to be converted into liquid fuels, chemicals easily transportable liquid products.

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8. Environmental conditions for xtL processes implementation

"XtL" processes include an indirect path of energy generation from different types of biomass by converting it to liquid energy carriers [ 70]. XtL processes means "x to liquid fuels", that is the conversion of various types of raw materials as feedstock for liquid biofuels. The previously presented innovative technologies of waste carbon dioxide conversion and other forms of organic matter into liquid energy carriers are part of a convention of XtL processes.

The environmental aspects of XtL technologies are related with:

1. Emission to the atmosphere the additional amounts of GHG.

2. Generating, recycling and removal of waste.

3. The use of natural resources, raw materials and energy.

4. Sludge production.

5. Space planning (development of the new areas on the Earth).

6. Impact on biodiversity.

7. The destruction of animal species and their habitats.

These methods are directed to the reuse, recycling of existing CO ₂ for its processing into useful forms of energy. Algae used for production of liquid fuels are characterized by an effective reduction of significant amount of wastewater, through their purification from toxic substances such as heavy metals. The result of this microorganisms activity are the extra amounts of clean drinking water. It also shows that they have no negative impacts for ecosystems biodiversity, there are also not the reason of the disappearance of certain group of animals or plants.

As it is clear from the review of literature, cultivation of algae for fuels production, seems to be a forward-looking technology for producing liquid energy carriers. The algae have many important advantages from the environmental point of view:

they are able to sequester waste carbon dioxide, which is used for production of oil and sugars, that are a substrate for the biofuels production,

they have the ability to bioremediation of contaminated environments,

they create a "biofertilizers" by absorbing elements such as nitrogen and phosphorus,

they do not compete with the food market,

they have a greater oil production capacity than terrestrial energy plants (more than 10 times greater than cultivated oilseed crops),

they are a group of organisms, with possibility of genetic changes for improvement of their production ability.

Concluding, it is clear from the above considerations, the discussed projects may be an excellent alternative to conventional resources of crude oil, gas and coal. Finally by reducing the concentration of carbon dioxide in the atmosphere, without any negative impact on the environment, above projects have large potential for limitation so-called Global Warming.

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10. Conclusions

Cultivation of oil plants for fuels production creates strong competition with crops for consumption. It's hard to talk about the promotion of biofuels, which production is based on energy crops and in many cases is a major cause of the food crops shortage. In many regions of the World are starving societies of so-called third world countries. Therefore as the most desirable features of technology is to use waste CO ₂ to produce liquid fuels related with:

In addition, all products and waste that may be generated during the manufacturing process for liquid energy carriers, should use the strategy - Recycling Reduce Reusein order to reduce energy costs and protect the environment. It is believed that the process of hydrolysis of water by solar energy, in the artificial leaf technology, occurs and is energy efficient.

Harry B. Gray, winner of many awards, including in chemistry, in an article on "" says:

„We need to stop burning hydrocarbon as soon as it is possible, because they are wonderful resources that we desperately need for the production of dyes, pharmaceuticals, T-shirts, chairs and cars - is irresponsible to burn them!"[ 71].

Waste Carbon dioxide is appropriate material. It is a resource that exists in plenty and causing a negative impact on the environment by including contributing to the greenhouse effect. Artificial photosynthesis is in the research phase and need more decades to make it economically profitable. Today we can see many successful trials to transform CO ₂ into various liquid fuel.

The presented analysis shows, that the most important goals for the energy sector should be utilization of carbon dioxide emissions by mentioned CCU idea. This target can be realized by using modern technology of CO ₂ reuse to produce liquid energy carriers.

Acknowledgments

The authors gratefully acknowledge financial support from the EKOBENZ Ltd

Krzysztof Biernat, Artur Malinowski and Malwina Gnat (January 23rd 2013). The Possibility of Future Biofuels Production Using Waste Carbon Dioxide and Solar Energy, Biofuels - Economy, Environment and Sustainability, Zhen Fang, IntechOpen, DOI: 10.5772/53831. Available from:

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The Possibility of Future Biofuels Production Using Waste Carbon Dioxide and Solar Energy

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Open access peer-reviewed chapter DOI: 10.5772/53831 Krzysztof Biernat Automotive Industry Institute, Department for Fuels and Renewable Energy, Warsaw, Poland Artur Malinowski Automotive Industry Institute, Department for Fuels and Renewable Energy, Warsaw, Poland Malwina Gnat Institute for Ecology and Bioethics, University Cardinal Stefan Wyszynski, Warsaw, Poland *Address all correspondence to: DOI: 10.5772/53831 Biofuels - Economy, Environment and Sustainability Edited by Zhen Fang The Earth's energy requirements are estimated at 14 TW/ y.

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Microalgae as a valuable feedstock for the manufacture of biofuels and other high-value products

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Microalgae as a valuable feedstock for the manufacture of biofuels and other high-value products

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Future prospects of microalgal biofuel production systems

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Climate change mitigation, economic growth and stability, and the ongoing depletion of oil reserves are all major drivers for the development of econo…