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水消毒的目的是解决水中生物污染的问题。生活污水经过二级处理后，水质改善，细菌含量大幅度减少，但细菌的绝对值仍很客观，并存在病原菌的可能，为防止对人类健康产生危害和对生态造成污染，在污水排入水体前应进行消毒。目前常用的污水消毒剂是液氯，其次是漂白粉、臭氧、次氯酸钠、氯片、氯氨、二氧化氯和紫外线等。其中液氯效果可靠、投资设备简单、投量准确、价格便宜。漂白粉投量不准确，溶解调制不便。臭氧投资大，成本高，设备管理复杂，其他几种消毒剂也有明显的缺点，所以目前液氯仍然是消毒剂首选。本设计采用液氯消毒,并使用真空转子加氯机加氯，使得处理污水与消毒液充分接触混合以处理水中的微生物，尽量避免造成二次污染。本设计采用隔板式接触反应池。
降低污泥中的含水率，可以采用污泥浓缩的方法来降低污泥中的孔隙水，通过降低污泥的含水率，减少污泥的体积，能减少池容积和处理所需的投药量，缩小用于输送污泥的管道和泵类的尺寸。污泥脱水的主要目的在于实现有效减容。。本设计采用卧螺式浓缩脱水一体机，近远期共设置三台，两用一备。
毕业论文关键词： 城市污水，CAST工艺，设计
Urban Sewage Denitrification and Dephosphorization
Process Design
General Information of Design
Water is not only the source of human life, but also the most important supporting factor of the social and economic development. In recent years, as China's rapid economic development and social rapid urbanization, drinking water safety and water quality requirements continue to increase, at the same time, domestic sewage and wastewater emissions increased significantly, rising emissions of various pollutants, water resources and water environment is facing serious challenges. Therefore, accelerating the sewage treatment rate to protect the limited water resources has become an urgent task for Chinese environmental protection work.
This design topic is “Urban Sewage Denitrification and Dephosphorization Process Design”. This topic is the purpose of through the sewage treatment process design, so that the students can learn knowledge to apply to the actual design for water and wastewater treatment, improve the comprehensive ability to solve practical problems. This topic has practical application value, its requirement is: the sewage treatment process design independently, and draw process flow diagram, layout, etc.
Some urban residents, about 250000 people in the sewage treatment plant mainly acceptance of urban sewage and drainage to factory. Daily average sewage 50000 m3, scale of design for sewage accounted for about 70%.Treatment of water quality in accordance with the following concerns: CODcr: ~ 260 mg/L, BOD5: ~ 120 mg/L, SS: ~ 220 mg/L, NH3 - N: ~ 30 mg/L, P: ~ 3 mg/L.
Processing technology and economy are feasible, treated wastewater into a nearby river, the water quality to perform the urban sewage treatment plant pollutant discharge standard "(GB 18918-2002) in the level 1 B standard specific for: CODcr: 60 mg/L, or less BOD5:20 mg/L, or less SS: 20 mg/L, or less NH3 - N: 15 mg/L, or less pH: 6 ~ 9, P: 1 mg/L or less.
This design uses the CAST process as a best process, its process is: The sewage treatment plant process: from the pumping station to the grit chamber, into the CAST reactor, contact disinfection tank, the final effluent; sludge process: from the CAST reactor sludge discharged from into the sludge thickening tank for pollution soil enrichment, and then sent to the belt filter press, and further dehydrated, transported for burning. The process has the advantages of high resistance to shock loading, small area, low cost, flexible operation and other advantages.