Physically, wastewater treatment methods that separate and recover insoluble pollutants (including oil film and oil bead) in wastewater by physical action can be divided into gravity separation method, centrifugal separation method and screen filtration interception method, etc. Treatment method based on heat exchange principle also belongs to physical treatment method. Chemistry is a wastewater treatment method that separates and removes dissolved and colloidal pollutants in wastewater or converts them into harmless substances through chemical reaction and mass transfer. In the chemical treatment method, the treatment units based on the chemical reaction produced by adding chemicals are coagulation, neutralization, redox and so on; The treatment units based on mass transfer include extraction, steam stripping, air stripping, adsorption, ion exchange, electrodialysis and reverse osmosis. The latter two treatment units are also called membrane separation technology. Among them, the treatment unit using mass transfer has both chemical action and physical action related to it, so it can also be separated from chemical treatment method and become another kind of treatment method called physical-chemical method. A wastewater treatment method in which organisms transform organic pollutants in the form of solution, colloid and fine suspension into stable and harmless substances through the metabolism of microorganisms. According to different microorganisms, biological treatment can be divided into aerobic biological treatment and anaerobic biological treatment. Aerobic biological treatment is widely used in wastewater biological treatment. Traditionally, aerobic biological treatment is divided into activated sludge method and biofilm method. Activated sludge process itself is a kind of treatment unit, which has many operation modes. Treatment equipment belonging to biofilm process includes biofilter, biological rotary table, biological contact oxidation tank and biological fluidized bed, etc. Biological oxidation pond method is also called natural biological treatment method. Anaerobic biological treatment, also known as biological reduction treatment, is mainly used to treat high-concentration organic wastewater and sludge. The treatment equipment used is mainly digestion tank. Treating wastewater by biological contact oxidation, that is, using biological contact oxidation process to fill the biological reaction tank with filler, the oxygenated wastewater immerses all the filler and flows through the filler at a certain flow rate. The filler is covered with biofilm, and the sewage is in extensive contact with the biofilm. Under the action of the metabolism of microorganisms on the biofilm, the organic pollutants in the sewage are removed and the sewage is purified. Finally, the treated wastewater is discharged into the biological contact oxidation treatment system, mixed with domestic sewage for treatment, and discharged after chlorine disinfection. Biological contact oxidation process is a biofilm process between activated sludge process and biofilter, which is characterized by setting filler in the tank, aerating at the bottom of the tank to oxygenate the sewage and make the sewage in the tank flow, so as to ensure the full contact between the sewage and the filler immersed in the sewage and avoid the defect of uneven contact between the sewage and the filler in the biological contact oxidation tank.