Wastewater - Secondary Treatment: Activated Sludge


Michigan Environmental Education Curriculum
Wastewater Treatment

Microorganisms such as bacteria and protozoa can use the small particles and dissolved organic matter, not removed in primary treatment, as food. Secondary or biological treatment is performed in a tank containing a "soup" of starved microbes called activated sludge. Like us, these microbes require air to live (they are aerobic organisms) and thus air is pumped into the tank. Microorganisms in this aeration tank use the dissolved and particulate organic matter as food, producing more microorganisms. Thus the waste materials that left the primary clarifier are changed into microorganisms which can be collected and separated from the water in the next step.



Empty Aeration Tank

Empty aeration tank showing air diffusers

Operating Aeration Tank

Operating aeration tank

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