Wastewater treatment uses physical, chemical and biological methods to treat wastewater, purify wastewater, reduce pollution, and even achieve wastewater recycling, reuse, and full use of water resources.

Wastewater mainly includes industrial wastewater, domestic sewage and farmland drainage, among which industrial wastewater is the most polluted. Industrial wastewater treatment can be divided into different types according to different methods. According to different functions, it can be divided into two categories: one is to separate harmful substances from wastewater by various external forces, which is called separation method; A class is a chemical or biological action that converts a harmful substance into a harmless or separable substance (which is removed by separation), and is called a conversion method.

According to the degree of processing, it can be divided into first, second and third levels. The primary treatment mainly pretreats the wastewater by physical methods such as sieve filtration and sedimentation, in order to remove suspended solids and floating matter in the wastewater; the secondary treatment mainly uses various biological treatment methods to remove colloid and dissolved state in the wastewater. The organic pollutants; the tertiary treatment is based on the primary and secondary treatments, and further treats the refractory organic matter, phosphorus, nitrogen and other nutritive substances.