本次毕业设计包括了每个构筑物各部分的尺寸计算，以及管道布置。同时，根据计算好的尺寸绘制构筑物的图纸，根据厂区平面布置原则绘制平面图，根据高程计算结果绘制高程图。

毕业论文关键词： 生活污水；城市污水处理厂；生物处理；倒置A2/O

Optimized design of a municipal sewage treatment plant＇s process

General description of design： With the development of the economy, it is common to use detergents containing nitrogen and phosphorus, such as washing powder, and the domestic sewage produced during the process contains high concentrations of nitrogen and phosphorus, which makes the content of nitrogen and phosphorus in the current domestic sewage high. This also has increased the difficulty of sewage treatment and brought challenges for the old process of urban sewage treatment.

The treatment of urban domestic sewage has been paid more and more attention in recent years.This kind of sewage is characterized by stable water quality and good biodegradability. It is suitable for biological treatment. As emission requirement is becoming more stringent, people must develop new processes or optimize the original process.

The graduation project is a optimized design of a municipal sewage treatment plant＇s process，and the design scale is 100,000 tons per day. This design is mainly for the treatment of domestic sewage.I chose oxidation ditch process, A+A2/O process and reversed A2/O process according to the given water quality.Based on the above analysis of the advantages and disadvantages of the three processes, this design chose the reversed A2/O process. Compared to the other two processes, the oxidation ditch process covers a large area.Because the sewage treatment plant is located in the urban area, the price is more expensive. And the aeration equipment investment is high,so this process is not selected based on the economic point of view . The allocation of carbon sources is unreasonable, so A+A2/O process is not a good choice. The reversed A2/O process is an optimization of the A/O process for sewage treatment plants, which can enhance nitrogen and phosphorus removal capacity. The most important thing is that this process has been put into operation in many cities of the country. If the process is operated properly,the quality of the treated water can achieve grade A standard, which is more strict than the comprehensive sewage discharge standard of Shanghai. Therefore, I chose the reversed A2/O process as the design as the main processing technology.

 The water quality of the design was BOD5:180mg /L,COD:360mg/L,SS:180mg/L,NH4-N:30mg/L,TP:6.7mg/L,TN:45mg/L.The ratio of BOD5 to COD is 0.5.It is generally considered that the wastewater has a good biodegradability when the ratio is more than 0.3.According to the design requirements, the design of the effluent quality needs to meet the comprehensive sewage discharge standard of Shanghai, that is, BOD5≤20mg/L, SS≤20mg/L,COD≤60mg/L,NH4-N≤10mg/L,TP≤0.5mg/L,TN≤15 mg/L.

The calculation part of this design refers to the "water supply and drainage design manual", and the calculation of A2/O reaction pool refers to the "urban sewage treatment plant design and calculation."

The main process of this design is that after the grille,the sewage is pumped to ascend into the aeration grit chamber and the initial settling tank. After the initial treatment,the sewage flows into the reversed A2/O reaction tank and the second settling tank, and then into the disinfection tank and finally flows out. A part of the sludge from the second settling tank is returned to the reaction tank while the other part of the excess sludge and the primary settling tank sludge are transported through the pipeline to the sludge treatment structure like the sludge concentrate tank, and finally the sludge will be transported for sinotrans disposal.

The pretreatment of sewage in this design consists of three parts: grille, grit chamber and primary settling tank.The grille is used to intercept large suspended solids and floats in the effluent. Aeration grit chamber is pided into two cells, which are used to precipitate large inorganic particles by gravity. The primary settling tank mainly reduces the concentration of suspended solids in the sewage, and it also can reduce a little part of BOD5.I chose four radial-flow sedimentation tanks as the first sedimentation tank. The main process is reversed A2/O process.A reaction pool has six corridors, the first two corridors for the anoxic section and anaerobic section,and the other four corridors for the aerobic section. Four secondary sedimentation tanks are also radial-flow,which chose the centre-inflow and surrounding-outflow type. The main function of the secondary settling tank is to carry out solid-liquid separation, as well as the role of concentrating sludge. To ensure the quality of the treated water,chlorine is used to disinfect in the effluent from the secondary sedimentation tank. Due to the need for heating and other equipment, and increasing investment and operating costs ,digestion process is not considered in this design. The sludge is directly concentrated by gravity and dehydrated by a belt filter press. After dehydration, the sludge will be transported through the truck to the designated area outside the plant for disposal.