---

Modern sewage treatment equipment technology can be divided into primary, secondary and tertiary treatment according to the treatment degree.
Primary treatment mainly removes the suspended solid pollutants in the sewage. Most of the physical treatment methods can only meet the requirements of primary treatment. After primary treatment, BOD can generally be removed by about 30%, which can not meet the discharge standard. Primary treatment belongs to the pretreatment of secondary treatment.
The secondary treatment mainly removes the colloidal and dissolved organic pollutants (BOD and COD) in the sewage, and the removal rate can reach more than 90%, so that the organic pollutants can meet the discharge standard.
Tertiary treatment, further treatment of refractory organic matter, nitrogen, phosphorus and other soluble inorganic matter that can lead to water eutrophication. The main methods include biological nitrogen and phosphorus removal, coagulation precipitation, sand ratio, activated carbon adsorption, ion exchange and electroosmosis analysis.
The whole process is that the raw sewage passing through coarse grid deletion is lifted by the sewage lift pump, then passes through grid deletion or screening device, and then enters the grit chamber. The sewage passing through sand water separation enters the primary sedimentation tank. The above is primary treatment (i.e. physical treatment). The effluent from the primary sedimentation tank enters the biological treatment equipment, including activated sludge method and biofilm method, (the reactors of activated sludge process include aeration tank, oxidation ditch, etc., and biofilm process includes biofilter, biological rotary table, biological contact oxidation process and biological fluidized bed) , the effluent from the biological treatment equipment enters the secondary sedimentation tank. The effluent from the secondary sedimentation tank is disinfected and discharged or enters the tertiary treatment. The primary treatment is the secondary treatment. The tertiary treatment includes biological nitrogen and phosphorus removal, coagulation sedimentation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis. Part of the sludge from the secondary sedimentation tank returns to the primary sedimentation tank or biological sedimentation tank Part of the treatment equipment enters the sludge concentration tank, and then enters the sludge digestion tank. After dehydration and drying equipment, the sludge is finally utilized.