Generally can be divided into physical method, chemical method and biological method. Physical method is to treat, separate and recover pollutants in wastewater through physical action; Chemical method is to treat and recover soluble waste or colloidal substances through chemical reaction or physical and chemical action; Biological method is to treat organic pollutants in sewage through the biochemical action of microorganisms. According to the steps of urban sewage treatment, it can be divided into
Primary treatment (mechanical treatment);
Secondary treatment: (the main process is biochemical treatment);
Tertiary treatment: (control eutrophication and reuse.