Now sewage treatment, especially aerobic treatment process, energy consumption is very high, urban sewage treatment, some of a ton of water treatment power consumption can reach about 0.3 yuan, while the industrial sewage may consume more power, the more power consumption, corresponding to the carbon dioxide emissions, and the power plant will also have an impact on the environment. According to some statistics, sewage treatment accounts for about 7% of the total electricity supply. In addition, the common treatment technology will emit a lot of carbon dioxide, there is a lot of sludge and other problems. So there is a great need to develop low energy wastewater treatment technologies.
Modern sewage treatment technology, according to the degree of treatment, can be divided into primary, secondary and tertiary treatment, generally according to the water quality conditions and the destination of treated water to determine the degree of sewage treatment.
Primary treatment
The main removal of solid pollutants in the sewage in suspension, physical treatment method can only be completed in most of the requirements of primary treatment. After primary treatment of sewage, BOD can generally remove about 30%, not up to the discharge standard. Primary treatment belongs to the pretreatment of secondary treatment.
Secondary treatment
The main removal of sewage in the colloidal and dissolved organic pollutants (BOD, COD substances), the removal rate of up to 90% or more, so that organic pollutants to meet the discharge standards, the removal rate of suspended solids up to 95% of the effluent effect is good.
Tertiary treatment
Further treatment 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 include biological nitrogen and phosphorus removal, coagulation and precipitation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis.
The whole process is through the coarse grating of raw sewage through the sewage lifting pump, after lifting, through the grating or sieve rate, and then into the sand sedimentation tank, after the sand and water separation of sewage into the initial sedimentation tank, the above for the primary 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 the biofilm method includes biofilter. (The reactors of activated sludge method include 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. 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.