The Treatment And Recycling Of City Rainwater By Coagulation-Sedimentation-Sand Filtration-Ultrafiltration Process

At present, China’s urbanization process is spending up. The urbanization plays a great impact on water resources which is related to people’s lives. Urban residential rainwater utilization can solve the contradiction between the urbanized areas of economic growth and the changes in the water environment in the city. Therefore, treatment and reuse of urban residential rainwater is a promising technology.According to the water quality of the urban residential rainwater and stormwater reuse purposes, the process for treatment of municipal city rainwater is reasonably integrated, namely coagulation-sedimentation-sand filtration-ultrafiltration process. At first, the subject malces the preferred experiment on coagulation on simulated rain. Secondly modifing quartz sand and determining the optimal modification conditions by CODcr removal in simulated rain as evaluation criteria. The subject malces sand filter filtration speed selected experiments by simulated rain are made coagulation precipitation supernatant water. Finally, the subject studies removal effect of process to turbidity, CODcr, ammonia nitrogen, total phosphorus in simulated rain and rain.In coagulation the preferred experiment, the subject determines coagulant for urban rainwater and its optimum dosage, the optimal pH of the water and the best slow stirring time by coagulation fractal dimension. The experimental results show that PAC is the optimum coagulantand its optimum dosage is30mg/L from the economic point view and coagulation effect. In the conditions of PAC dosage of30mg/L, best raw water pH range which PAC deals with urban stormwater is6to8. In the conditions of PAC dosage of30mg/L and the water pH value of7, slow stirring10min floe fractal dimension.In modifing quartz sand experiments, the subject determines the optimal modification conditions by CODcr removal in simulated rain as evaluation criteria. The experimental results show that optimum modification conditions for the ferric chloride concentration is2mol/L, stirring number is0, the calcination temperature is550℃and the modified time is3hours. Modified quartz sand is higher than quartz sand though modifing quartz sand and quartz sand removal rate of CODcr.In sand filter filtration speed selected experiments,when the filtration rate is6m/h, the cycle water yield is maximum and FN value is minimum. Therefore6m/h is test optimal filtration rate.The experiment of coagulation-sedimentation-sand filtration-ultrafiltration to simulated rain shows that the process has a good removal effect on the turbidity in simulated rain and the removal rate is stable over99%. After ultrafiltration effluent turbidity decreases to between0.1NTU-0.25NTU; The process has a better removal effect on CODcr in simulated rain and removal is stable over65%. After ultrafiltration effluent CODcr decreases to between30mg/L～35mg/L; The process has an effect on ammonia nitrogen in simulated rain and removal stable at between35%and38%. After ultrafiltration effluent ammonia nitrogen decreases to between3.3mg/L～4.4mg/L; The process has an effect on total phosphorus in simulated rain and removal stabilizes at between35%and40%, after ultrafiltration effluent total phosphorus decreased to between2.57mg/L～3.13mg/L.The coagulation-sedimentation-sand filtration-ultrafiltration process has a good effect on turbidity, CODcr, ammonia nitrogen, total phosphorus in rain. The ultrafiltration water quality can reach the flushing and urban greening standard in Urban miscellaneous water quality standards.