Sewage treatment equipment mainly removes suspended solid pollutants in sewage, and most physical treatment methods can only complete primary treatment requirements. For sewage that has undergone primary treatment, BOD can generally be removed by about 30%, which does not meet the discharge standards. Primary processing is a preprocessing of secondary processing. Further processing of refractory organic matter, nitrogen, phosphorus and other soluble inorganic matter that can lead to eutrophication of water bodies. The main methods include biological denitrification and phosphorus removal, coagulation sedimentation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis.