Three-stage treatment of integrated sewage treatment equipment

Primary treatment

Primary treatment primarily removes suspended solid pollutants from wastewater. Physical treatment methods can generally only meet the requirements of primary treatment. Primary treatment typically removes approximately 30% of the BOD in wastewater, failing to meet discharge standards. Primary treatment serves as a pre-treatment step for secondary treatment.

The entire process involves the raw sewage passing through the coarse screen being lifted by a sewage lift pump, then passing through a screen or sand filter before entering a grit tank. The wastewater, after separation of sand and water, enters a primary sedimentation tank. This constitutes primary treatment (i.e., physical treatment). Methods used in this step include filtration and interception—screens and screen filtration; gravity separation—grit tanks, sedimentation tanks, grease traps, and flotation tanks; and centrifugal separation—cyclones and centrifuges.

Secondary Treatment

Primarily removes colloidal and dissolved organic pollutants (BOD and COD) from wastewater, achieving a removal rate exceeding 90%, ensuring that organic pollutants meet discharge standards.

The effluent from the primary sedimentation tank enters biological treatment equipment, including activated sludge and biofilm processes. (Activated sludge reactors include aeration tanks and oxidation ditches, while biofilm processes include biofilters, biorotating discs, biological contact oxidation processes, and biological fluidized beds.) The effluent from the biological treatment equipment enters the secondary sedimentation tank. The effluent from the secondary sedimentation tank undergoes disinfection and is then discharged or enters tertiary treatment. This concludes primary treatment and enters secondary treatment.

The main target of the factory's integrated industrial domestic sewage treatment equipment is to treat chemical substances that seriously pollute the environment. The discharged waste liquid is carefully filtered to clean: screen residue, sediment, biological sludge, etc. Among them, biological sludge is very important. Excessive sediment is difficult to clean and also occupies a large area of ​​the sewage tank. When treating, this sludge should be treated first.

Tertiary Treatment

This treatment further treats recalcitrant organic matter, soluble inorganic substances such as nitrogen and phosphorus that can cause eutrophication, and other soluble inorganic substances. Tertiary treatment includes biological denitrification and phosphorus removal, coagulation and sedimentation, sand filtration, activated carbon adsorption, ion exchange, and electrodialysis. Sludge from the secondary sedimentation tank is partially returned to the primary sedimentation tank or biological treatment equipment, while another portion enters the sludge thickening tank and then the sludge digester. After dewatering and drying, the sludge is finally utilized.

The activated sludge process is a key method for chemical wastewater treatment. The primary process involves mixing and continuously cultivating various microorganisms to form activated sludge based on the organic pollutants in the wastewater under special conditions of continuous oxygen supply. The microbial communities in the wastewater remove toxic and harmful organic pollutants through adsorption, condensation, decomposition, precipitation, oxidation, and the formation of activated sludge, thereby further purifying the wastewater.