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What are the main biological methods used for secondary wastewater treatment?
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Secondary wastewater treatment is designed to remove soluble organic matter and suspended solids that remain after primary treatment. This is primarily achieved through biological processes where microorganisms consume organic impurities as food, converting them into carbon dioxide, water, and energy for their own growth.1
The main biological methods used for secondary treatment include:
- Activated sludge process: A system where bacteria-rich sludge is mixed with incoming wastewater and agitated in the presence of an ample air supply. Microorganisms oxidize the organic matter, and the resulting solids are subsequently separated in a settling tank.2
- Trickling filter: A bed of coarse media, such as crushed rock, over which settled sewage is sprayed. As the liquid trickles downward, it comes into contact with a film of microorganisms attached to the media, which stabilize the organic matter through aerobic metabolism.3
- Oxidation pond: A natural or constructed basin that utilizes biological activity to stabilize organic waste.1
- Rotating biological contactor: A less common method that also utilizes biological films to treat wastewater.1