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After disinfection, the water is put back into a river, back into the natural water cycle. In our lab, we poured our disinfected waste water down the sink, equivalent to putting it back into the river.

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The wastewater from the Secondary Settling tank then enters the disinfection tank. Then chemicals such as chlorine, ozone gas or exposure to ultraviolet lights are used to kill the last remaining living organism in the water, such as germs and waste. In our lab, we poured 2 teaspoons of bleach into the water, then stirring the mixture, killing off the last of the organisms.

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The wastewater then enters the Secondary Settling tank, where it slows down. As it slows down, the tiny organisms from the bioreactor sink to the bottom and form a secondary sludge layer. This sludge is then removed from a pipe at the bottom of the tank, leaving clear water at the top, and is dried and can be used as fertilizer. In our lab, we poured the wastewater from the bioreactor into the Secondary Settling beaker. We then let the mixture stand for a minute to let everything settle and notice any changes before pouring into disinfection, leaving the secondary sludge behind.

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The water then enters the bioreactor, as tiny organisms feed on the dissolved nutrients such as Carbon, Nitrogen and Phosphorus, to prevent eutrophication later. The organisms then convert the nutrients into water, oxygen gas and more. In our lab, we added fine, dry sand to the bioreactor to act as the tiny organisms that feed on the nutrients. We stirred the dry sand in the mixture to break up the wastewater even more.

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When the wastewater enters the Primary Settling tank, light solids and germs sink to the bottom, creating primary sludge, while lighter substances like oil float to the surface. The primary sludge then is removed through a pipe at the bottom to be treated, while a scraper scrapes the surface of the water to remove the oils. In our lab we used a spoon and a cotton ball to simulate the scraper as we scraped the oils off the surface. Then as we poured the wastewater into the bioreactor, we made sure to keep the primary sludge on the bottom and used a finger to catch any that would transfer.

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In our lab we used a spoon to simulate the stirring that occurs during Grit Removal. The stirring makes the grit settle onto the bottom. We removed the grit by stirring the mixture, then pouring it into the Primary Settling container, making sure to leave the grit behind as we poured. In real life the slow stirring makes the grit sink and travel through another pipe to be removed.

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We used the plastic screen to catch solids as we poured the liquid into the Grit Chamber. In real life treatment the screens are much larger and are metal bars that catch the solids as the water travels to the grit chamber.

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