Primary treatment, the main removal of sewage in a suspended state of solid pollutants, most of the physical treatment method can only complete the requirements of primary treatment. After primary treatment of sewage, BOD can generally remove about 30%, not up to discharge standards. Primary treatment belongs to the pretreatment of secondary treatment.
Secondary treatment, the main removal of sewage in the colloidal and dissolved state of organic pollutants (BOD, COD substances), the removal rate of up to 90% or more, so that organic pollutants to meet the discharge standards.
Tertiary treatment, further processing of difficult to degrade organic matter, nitrogen and phosphorus can lead to eutrophication of the water body, such as soluble inorganic substances. The main methods are biological denitrification and phosphorus removal method, coagulation and precipitation method, sand filtration method, activated carbon adsorption method, ion exchange method and electro-osmosis analysis method.
The whole process is through the coarse grating of raw sewage through the sewage lifting pump, after lifting, through the grating or sand filter, and then into the sand sedimentation tank, after the sand-water separation of sewage into the initial sedimentation tank, the above for the first level of treatment (i.e., physical treatment), the primary sedimentation tank of the effluent into the biological treatment equipment, there are activated sludge and biofilm method, (which activated sludge method of the reactor aeration tank, oxidation ditch, etc.), biofilm method includes biofilter, and biofilm method includes biofilter, and so on. (The reactors of activated sludge method are aeration tank, oxidation ditch, etc., and biofilm method includes biofilter, bio-turntable, bio-contact oxidation and bio-fluidized bed), the effluent of the biological treatment equipment enters into the secondary sedimentation tank, and the effluent of the secondary sedimentation tank is disinfected and discharged or enters into the tertiary treatment, which is the end of the primary treatment to the secondary treatment, and the tertiary treatment includes the biological denitrification and removal of phosphorus, coagulation and sedimentation, sand filtration, activated carbon adsorption, ion-exchange and electrodialysis. Part of the sludge from the secondary sedimentation tank is returned to the primary sedimentation tank or biological treatment equipment, part of it enters the sludge thickening tank, and then it enters the sludge digestion tank, and after dewatering and drying equipment, the sludge is finally utilized.