Biochemical treatment microorganism in sewage treatment

Biochemical treatment of sewage is a method to realize purification by using the metabolism of microorganisms to convert the dissolved and colloidal organic pollutants in sewage into harmless substances. It can be divided into aerobic biological treatment method and anaerobic biological treatment method. The former mainly includes activated sludge method, biofilm method, oxidation pond method, sewage irrigation, etc.

The biochemical treatment of sewage belongs to secondary treatment, with the main purpose of removing non sediment suspended solids and soluble biodegradable organics. The biochemical treatment process of sewage has a variety of components, including activated sludge method, AB method, A/O method, A2/O method, SBR method, oxidation ditch method, stabilization pond method, land treatment method and other treatment methods.

At present, most urban sewage treatment plants adopt activated sludge process. The principle of biological treatment is to complete the decomposition of organic matter and the synthesis of organisms through biological action, especially the role of microorganisms, and transform organic pollutants into harmless gas products (CO2), liquid products (water) and solid products rich in organic matter (microbial community or biological sludge); Excess biological sludge is separated solid-liquid in the sedimentation tank and removed from the purified sewage.

The following two processes are commonly used for wastewater biochemical treatment:

1) Anaerobic biological treatment of sewage

Anaerobic biological treatment of sewage, also known as "anaerobic digestion", is a method that uses Anaerobic Microorganisms to degrade organic pollutants in sewage and purify sewage. Its mechanism is to decompose organic matters in sludge under the action of anaerobic bacteria, and finally produce methane, carbon dioxide and other gases.

The complete anaerobic digestion process can be divided into three stages: ① Solid organic compounds in sludge are dissolved by extracellular hydrolase secreted from anaerobic bacteria, and enter cells through cell wall. Under the catalysis of hydrolase, polysaccharides, proteins and fats are hydrolyzed into monosaccharides, amino acids, fatty acids, etc; ② Under the action of acid producing bacteria, the products of the first stage are further degraded into relatively simple volatile organic acids, such as acetic acid, propionic acid, butyric acid, etc; ③ Under the action of methane bacteria, the volatile acid produced in the second stage is converted into methane and carbon dioxide. The influencing factors include temperature, pH value, nutrients, organic toxins, anaerobic environment, etc. Advantages of anaerobic biological treatment: less energy is consumed in the treatment process, the removal rate of organic matters is high, the precipitated sludge is small and easy to dehydrate, which can kill pathogenic bacteria without adding nitrogen, phosphorus and other nutrients. However, anaerobic bacteria reproduce slowly, are sensitive to poisons, and are strict with environmental conditions. The final product still needs aerobic biological treatment. In recent years, it is often used for biochemical treatment of high concentration organic wastewater.

2) Aerobic biological treatment of sewage

The aerobic biological treatment method of sewage is a biochemical treatment method of sewage that uses aerobic microorganisms (mainly aerobic bacteria) to decompose organic pollutants in the sewage and make the sewage harmless. The mechanism is that when the sewage contacts with microorganisms, the soluble organic matter in the water is absorbed into the bacteria through the cell wall and cell membrane of the bacteria; Colloids and suspended organics are adsorbed on the surface of the bacteria, and then decomposed into soluble substances by external enzymes of the bacteria, and then enter the bacteria. These organics are oxidized and degraded through the process of catabolism in the bacteria, and the energy generated is for the needs of bacterial life activities; Some oxidation intermediates become new cellular substances through anabolism, enabling bacteria to grow and reproduce. The final products of treatment are stable inorganic substances such as carbon dioxide, water, ammonia, sulfate and phosphate. During treatment, microorganisms shall be supplied with sufficient oxygen and various necessary nutrient sources such as carbon, nitrogen, phosphorus, potassium, magnesium, calcium, sulfur, sodium, etc; Meanwhile, the living conditions of microorganisms should be controlled, such as pH 6.5~9 and water temperature 10~35 ℃. The main methods are active pollution method, biofilm method, oxidation pond method, etc.