Slide 1
Microbes convert biodegradable material
Biological wastewater treatment uses microorganisms to consume biodegradable material. The process converts part of that material into new biomass and other products.
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This is not a way to make matter disappear. The plant must manage the resulting solids and gases as well as the treated water leaving the process.
Slide 2
Aeration supplies oxygen and mixing
In an aerobic treatment tank, equipment supplies oxygen and mixes the contents. The microbes need suitable conditions to maintain useful activity.
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Air delivery consumes energy, so operators balance adequate oxygen against unnecessary aeration. Temperature, incoming load and mixing can change the amount of air the process requires.
Slide 3
Returning microbial solids keeps a useful population
Activated-sludge systems separate microbial solids from treated water and return some solids to the aeration tank. Recycling maintains a useful population.
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The time solids remain in the process can differ from the time water remains. This allows operators to retain slow-growing organisms while water continues moving through the plant.
Slide 4
Those solids must then separate from the water
Microbial material must separate effectively after the biological stage. Poorly settling solids can carry contamination into the outgoing water.
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Changes in the microbial community can alter the structure of settling clumps. Biological performance and physical separation are therefore connected, even when oxygen supply appears adequate.
Slide 5
Nutrient removal can require additional conditions
Removing organic material is not identical to removing nitrogen or phosphorus. Nutrient-removal processes may require additional stages and carefully controlled environments.
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Some nitrogen transformations use oxygen, while others proceed without free dissolved oxygen. Routing and recycling flows between suitable zones lets a plant support these different microbial tasks.
Sources
- Primer for Municipal Wastewater Treatment Systems
U.S. Environmental Protection Agency
- Microbiology of Wastewater Treatment
U.S. Environmental Protection Agency