According to the treatment degree and principle, wastewater treatment system can be mainly divided into three types: physical, chemical and biological. The physical treatment system removes suspended solids and floating objects in wastewater by physical methods such as screening, precipitation and air flotation. The chemical treatment system uses chemical reactions such as coagulation, neutralization and redox to remove colloidal substances, soluble pollutants or adjust water quality characteristics; The biological treatment system is the core link, which uses the metabolism of microorganisms to efficiently degrade organic pollutants and some nutrients such as nitrogen and phosphorus in wastewater under aerobic or anaerobic conditions. In practical application, these systems are usually combined into a process flow of "pretreatment → primary treatment → secondary treatment → advanced treatment" to achieve the multi-level treatment goal from primary purification to high-standard reuse or safe discharge.
