The Applied Research On The Treatment Of Sewer Overflow By High-rate Clarifier

In recent years, the pollution of water resources is increasingly serious, especially the urban waters, of which the overflow pollution in rainy days has already been one of the main factors leading to water pollution. As a major urban water system in Hefei, Nanfei River seems gloomy in its pollution at present. According to the preliminary survey of water quality and the overflow sewage from Nanfei River’s QingChong Ⅰ/Ⅱ section, this thesis designed a set of high-efficiency clarification processing devices, and gave a series of examination on its operation. The treatment effect was analyzed when the devices worked in dry season, light rain, moderate rain and storm. And a research about the influence factors like the operation flow rate, start-up mode, sludge recirculation, etc... The results of the study showed that:(l)The overflow sewage from Nanfei River’s QingChong Ⅰ/Ⅱ section had an average pollution concentration of SS:800～1000mg/L, COD:300～600mg/L. During the earlier rainfall course, the concentration was high which then fell off quickly as time went by.(2)The sewage treatment efficiency in dry season was poor with removal rate of about55%on SS and about50%on COD. The effluent had a good quality with removal rate up to89.6%on SS and61.5%on COD.(3)Under the condition of flow speed at60m3/h, the devices worked steadily and had good effluent quality. It took55min from start-up to stable operation in dry mode, while only15-20min in wet mode. The wet mode start-up had a better effluent quality, a stronger resistance to impact load, and when the device was in stable operation and the sludge was recirculated, reducing coagulation dosage by30%still could keep the device in good treatment efficiency.