1. Bacteria

Bacteria are adaptable and grow fast. According to different nutrient requirements, bacteria can be divided into autotrophic bacteria and heterotrophic bacteria two categories.

Autotrophic bacteria use various inorganic substances (CO2, HCO3-, NO3-, PO43-, etc.) as nutrients to convert them into another inorganic substance, release energy, and synthesize cellular substances. The carbon, nitrogen and phosphorus sources are all inorganic substances.

Heterotrophic bacteria use organic carbon as carbon source and organic or inorganic nitrogen as nitrogen source, and convert it into inorganic substances such as CO2, H2O, NO3-, CH4 and NH3 to release energy and synthesize cellular substances. The microorganisms in sewage treatment facilities are mainly heterotrophic bacteria.

2. Fungi

Fungi include molds and yeasts. Fungi are aerobic bacteria, with organic matter as carbon source, growth pH is 2-9, the optimal pH is 5.6. Fungi require little oxygen, half as much as bacteria. Fungi often occur in environments with low pH and little molecular oxygen.

Eumycelium plays a skeleton role in the agglomeration of activated sludge, but the appearance of too many filamentous bacteria will affect the sedimentation performance of sludge and cause sludge swelling. The role of fungi in sewage treatment cannot be ignored.

3. Algae

Algae are unicellular and multicellular plant microorganisms. It contains chlorophyll, which uses photosynthesis to assimilate carbon dioxide and water to release oxygen, and absorbs nitrogen, phosphorus and other nutrients in the water to synthesize its own cells.

4. Protozoa

Protozoa are the lowest single-celled animals capable of division and proliferation. Protozoa in sewage are both water purifiers and indicators. Most protozoa belong to the aerobic heterotrophic type. Protozoa play a less important role than bacteria in sewage treatment, but because most protozoa can eat solid organic matter and free bacteria, they have a purifying effect on water quality. Protozoa are sensitive to environmental changes, and different protozoa appear in different water quality environments, so they are indicators of water quality. For example, when dissolved oxygen is abundant, clock worms appear in large numbers, and when dissolved oxygen is lower than 1/L, they appear less and are not active.

5. Metazoa

Metazoa are multicellular animals. Common metazoa in sewage treatment facilities and stabilization ponds are rotifers, nematodes and crustaceans.

Metazoa are aerobic microorganisms living in a better water quality environment. Metazoa feed on bacteria, protozoa, algae and organic solids. Their appearance indicates that the treatment effect is better and they are indicators of sewage treatment.