At present, the energy consumption of sewage treatment, especially aerobic treatment, is very high. One ton of urban sewage treatment can reach about 0.3 yuan, while industrial sewage may consume more electricity. The more electricity is used, the more carbon dioxide is emitted, and power plants will also have an impact on the environment. According to statistics, the electricity consumption for sewage treatment accounts for about 7% of the total power supply. In addition, ordinary treatment technology will emit a lot of carbon dioxide, and there are problems such as sludge. Therefore, it is necessary to develop low-energy sewage treatment technology.

Modern sewage treatment technology can be divided into primary, secondary and tertiary treatment according to the degree of treatment. Generally, the degree of sewage treatment depends on the water quality and the direction of water treatment.

Primary treatment

It mainly removes suspended solid pollutants from sewage, and most 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.

Secondary treatment

It mainly removes colloid and dissolved organic pollutants (BOD, COD) in sewage, and the removal rate can reach above 90%, which makes the organic pollutants meet the discharge standard, and the removal rate of suspended solids can reach 95%, with good effluent effect.

Three-stage treatment

Further treatment of refractory organic matter, nitrogen and phosphorus and other soluble inorganic substances that can lead to eutrophication of water body. The main methods include biological nitrogen and phosphorus removal, coagulation and sedimentation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis.

The whole process is as follows: the raw sewage passing through the coarse grid is lifted by the sewage lifting pump, passes through the grid or screen, and then enters the grit chamber; Sewage separated from sand and water enters the primary sedimentation tank, which is primary treatment (i.e. physical treatment); The effluent from the primary sedimentation tank enters biological treatment equipment, including activated sludge process and biofilm process (the reactors of activated sludge process include aeration tank and oxidation ditch, etc.). ). Biofilm method includes biofilter, biological turntable, biological contact oxidation method and biological fluidized bed). The effluent from biological treatment equipment enters the secondary sedimentation tank, and the effluent from the secondary sedimentation tank is discharged after disinfection or enters the tertiary treatment. The primary treatment ends here as secondary treatment, and the tertiary treatment includes biological nitrogen and phosphorus removal, coagulation and precipitation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis. Part of the sludge in the secondary sedimentation tank flows back to the primary sedimentation tank or biological treatment equipment, and part of it enters the sludge concentration tank and then enters the sludge digestion tank. After dehydration and drying equipment, the sludge is finally utilized.