The treatment prior to biochemical treatment is conventionally referred to as pretreatment. Because the cost of biochemical treatment is relatively low, the operation is relatively stable, so the general industrial wastewater is treated by biochemical method, and the treatment of wastewater is also to biochemical method as the main treatment means. However, the wastewater contains some organic substances that inhibit and poison microorganisms, so necessary pretreatment must be carried out before the wastewater enters the biochemical tank. The purpose is to reduce or remove as much as possible the substances that inhibit and poison microorganisms in the wastewater, so as to ensure the normal operation of the microorganisms in the biochemical tank. The purpose of pretreatment is two: one is to reduce and remove as much as possible the substances in the wastewater that have inhibition, toxicity and inhibition effect on microorganisms, or convert them into substances that are harmless or favorable to microorganisms, so as to ensure the normal operation of microorganisms in the biochemical tank; The second is to reduce COD load in the pretreatment process to reduce. the operating burden of the biochemical tank.