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A, the process and measures of sewage treatment plant
The process of urban sewage plant is determined according to the required treatment degree and economic analysis. Usually divided into three levels: ① Primary treatment. By precipitation method, the removal rates of suspended solids and five-day biochemical oxygen demand can generally reach about 60% and 30% respectively. ② Secondary treatment. The removal rate of suspended solids and five-day biochemical oxygen demand by biological treatment of water can generally reach about 90%, and the removal rate of five-day biochemical oxygen demand by high-load activated sludge method is about 60%. ③ Three-stage treatment. Further remove the untreated substances in the secondary treatment.
The main treatment structure of the first-class sewage treatment plant is sedimentation tank. The secondary sewage plant will be equipped with biological devices (aeration tank, biological filter, biological turntable or biological aerated filter, etc.). ) and post-sedimentation tank. Because there are sedimentation tanks before and after and their functions are different, the former is often called primary sedimentation tank and the latter is called secondary sedimentation tank. There are also auxiliary facilities and facilities for sludge treatment in sedimentation tanks. Auxiliary facilities are generally grids and grit chambers (also known as impurity chambers). Remove the grating of rags, etc. The grit chamber removes the easy-to-settle substances, so as to avoid accumulation in the subsequent deep grooves and affect the operation. Sludge treatment equipment is usually digester and dehydration equipment (drying bed or dehydrator). Sewage treatment plant buildings usually include pump house, laboratory, sludge dewatering machine room, maintenance workshop, etc. Activated sludge wastewater treatment plant usually has blower or air compressor room. In order to control operation, economic dispatch and improve management level, sewage treatment plants began to adopt automation devices and computer control, including: ① remote communication, telemetry, recording and alarm of operation parameters such as water quality, water quantity and power supply voltage; ② Automatic control and remote control of valve opening and closing and water pump unit scheduling; ③ Three-stage treatment. The effluent quality of secondary treatment sometimes fails to meet the discharge requirements, so further treatment (or advanced treatment) is needed. The effluent from biological treatment is generally rich in ammonia nitrogen, nitrate and phosphate, and when it is discharged into gurgling water (such as lakes and bays), the water body is often eutrophic. At this time, it is often necessary to increase nitrogen and phosphorus removal facilities. When the effluent is discharged into water bodies with high water quality requirements or irrigated grasslands, stadiums and recreational green spaces, and the water quality needs to be comprehensively improved, double filter beds are often added. There are also biological ponds and land treatment.
Second, the sewage treatment plant site selection
The site selection of sewage treatment plant should match the wastewater outlet, consider the needs of the phased construction of the whole drainage system, and obey the urban land use planning. Sewage treatment plants, especially those with sludge treatment and dehydration equipment, have a certain impact on the environmental quality of surrounding houses, and should be properly isolated with green belts. Developed computing technology makes the economic analysis of drainage system planning more and more perfect, and the choice of sewage plant site is often solved at the same time as the planning of the whole system.