Bacteria
Bacteria have strong adaptability and grow fast. According to different nutrient requirements, bacteria can be divided into two categories: autotrophic bacteria and heterotrophic bacteria.
Autotrophic bacteria use various inorganic substances (CO2, HCO3-, NO3-, PO43-, etc.) as nutrients to convert them into another inorganic substance, release energy, and synthesize cell substances. Their carbon source, nitrogen source, and phosphorus source are all inorganic.
Heterotrophic bacteria use organic carbon as a carbon source and organic or inorganic nitrogen as a nitrogen source, converting them into inorganic substances such as CO2, H2O, NO3-, CH4, NH3, releasing energy and synthesizing cell substances. The microorganisms in sewage treatment facilities are mainly heterotrophic bacteria.
Fungi
Fungi include molds and yeasts. Fungi are aerobic bacteria that use organic matter as a carbon source. The growth pH is 2-9 and the optimal pH is 5.6. Fungi require less oxygen, only half of that of bacteria. Fungi often appear in environments with low pH and less molecular oxygen.
Fungal mycelium plays a skeletal role in the coagulation 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.
Algae
Algae are unicellular and multicellular plant microorganisms. It contains chlorophyll, uses photosynthesis to assimilate carbon dioxide and water to release oxygen, and absorbs nutrients such as nitrogen and phosphorus in water to synthesize its own cells.
Protozoa
Protozoa are the lowest unicellular animals that can divide and proliferate. Protozoa in sewage are both water purifiers and water quality indicators.
Most protozoa are aerobic heterotrophic. In sewage treatment, the role of protozoa is not as important as bacteria, but because most protozoa can ingest solid organic matter and free bacteria, they have the effect of purifying water quality. Protozoa are sensitive to environmental changes, and different protozoa appear in different water quality environments, so they are water quality indicators. For example, when dissolved oxygen is sufficient, clock worms appear in large numbers, and when dissolved oxygen is less than 1㎎/L, they appear less and are not active.
Metazoa
Metazoa are multicellular animals. Common metazoans in sewage treatment facilities and stabilization ponds include rotifers, nematodes and crustaceans.
Metazoans are all aerobic microorganisms that live in a good water quality environment. Metazoans feed on bacteria, protozoa, algae and organic solids. Their appearance indicates that the treatment effect is good and they are indicator organisms for sewage treatment.
Common microorganisms
A. Paramecium
1. Classification: non-activated sludge protozoa
2. Body: length: 180-300 microns, width: 42-75 microns
3. Morphology: Paramecium is a larger protozoan. Its body is cylindrical, the widest in the middle of the back half, and there is a concave mouth groove on the ventral side of the front half. There is an elliptical cell mouth at the bottom of the middle groove. The body is evenly covered with cilia, and some cilia at the rear end are slightly longer; the exoplasm under the surface membrane is relatively transparent, the endoplasm is full of granular substances, there are more food bubbles, and there are two contractile bubbles, one located at one-quarter of the body length and the other located at three-quarters of the body length.
4. Ecology: It mainly feeds on bacteria, and the most suitable ecological environment is medium pollution and multi-pollution. It appears in large quantities in an environment where the dissolved oxygen concentration is almost undetectable. It appears more frequently in activated sludge when the purification level is poor.
B,Small-mouthed bellworm
1. Classification: activated sludge protozoa
2. Body: length: 32-70 microns, width: 22-48 microns, mouth diameter: 12-25 microns, handle length: 20-380 microns
3. Morphology: The body is approximately circular, but its length is usually still significantly longer than its width. The mouth is small and narrow in the front, and the widest in the middle part. It gradually tapers from the middle to the front and rear ends. The ciliated oral disc is slightly smaller than the mouth. The endoplasm is milky white or light brown, often containing a considerable number of food vacuoles. The handle is relatively slender, and there is a myofilament sheath inside the handle, which will stretch and retract when stimulated. It mainly lives alone and rarely has the habit of clustering. The swimming body is slender and cylindrical, and moves quickly.
4. Ecology: It feeds mainly on bacteria, and also preys on microscopic single-cell algae. The most suitable temperature for it is 25°C. If the temperature is above 35°C, it will form a capsule or deformity, and finally die. It appears in large numbers when the water quality is good, and the BOD is mostly below 20mg/L.
C. Plate shell insects
1. Classification: activated sludge protozoa
2. Body: Length: 55-65 microns, width: 28-32 microns
3. Morphology: The body is barrel-shaped and grenade-shaped, slightly swollen in the middle, and the ratio of body length to body width is about 2 to 1. The morphology is fixed and more or less brown; the plate shell formed by the ectoplasm has 15-20 rows, and the plate shell is divided into six sections by transverse grooves, each section forming a certain form and number of "window panes". Cilia are evenly distributed throughout the body, and the cell mouth is located at the front end, which is surrounded by cilia and is not easy to see.
4. Ecology: Plate shell insects can prey on algae, small flagellates, and small ciliates, and also suck dead rotifers. They often appear when the BOD load is low, the dissolved oxygen concentration is high, and the BOD of the treated water is low.
