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