Aerated biological filter is also called submerged biological aerated filter. It is developed on the basis of common biological filter, high load biological filter, biological filter tower, biological contact oxidation and other biological membrane methods. It is called It is the third generation biological filter. The process principle is that a certain amount of granular filter material with a small particle diameter is filled in the filter, a highly active biofilm grows on the surface of the filter material, and the filter is aerated inside. When the sewage flows through, the oxidative degradation capacity of the high-concentration biofilm brought by the high specific surface area of the filter material is used to quickly purify the sewage, which is a biological oxidation degradation process; at the same time, the filter material is compacted when the sewage flows through. Utilizing the characteristics of the smaller particle size of the filter material and the biological flocculation of the biofilm, the suspended matter in the sewage is trapped, and the biofilm that has fallen off will not float out with the water. This is a retention effect; after a certain period of operation, the water head is lost. The increase of the filter requires backwashing to release trapped suspended matter and renew biofilm. This is the backwashing process.