| This research investigated the overflows of combined sewer systemby on-site monitoring in Changzhou, southern of Jiangsu province, together with wastewater,runoff and sewer sediments, which are associated with CSO. And then discussed the water quality and operation low of pollution load of CSO. Additionally, a device named ―suspended rapid filter‖ was designed and undertook for the treatment of CSO at the end of the pipe networks.It is found that the pollutions were in high concentrations and large variable ranges, according to the result of water quality analysis. Among the monitored outfall, the EMC of COD, TN, TP, NH3-N and SSwere 33~649mg/L, 6~30mg/L, 0.18~2.09mg/L, 3~22mg/L and 23~366mg/L respectively, both were worse than the quality specified in the V class of surface water quality standard(GB3838-2002). Different type of rainfall has different influence on pollution, such as high intensity rainfall has a significant influence on COD and SS, and because of flush and dilution in work in turn, the water quality were in high polarization. NH3-N was in dominance at low intensity rainfall. The concentration of pollutions were staying in medle or high level because of sustainable impact of flush effect in moderate rainfall event. Drought period is another factor of water quality, long drought may lead to high accumulation and serious pollution.Sewer sediment was the primary source of the pollution load of CSO, based on the result of load analysis, and made a contribution of 53%~68%,43%~56%,42%~62%,23%~46%and 57%~67%, respectively for COD,TN,TP,NH3-N and SS. Runoff was the second source, contributed 17%~36%,8%~33%,10%~26%,11%~30%,18%~36% load for different pollution. Wastewater was the least one, took an apportionment of 9%~24%,18%~35%,19%~47%,27%~52%,5%~25%, respectively. The contribution percentage of different source were effected by rainfall intensity. Different surface condition also made a different contribution to runoff pollution load, among which the runoff on road contributed the most and roof followed, runoff on courtyard contributed the least. Turn the capacity of the river pumping station into rainfall equivalent, and took intercepting ratio into account, we can get the critical value of the pumping station, which can be used to judge or predict the happening of overflows. The MV carve analysis also found that combined sewer system show different action at different rainfall intensity. It shows up non-flush phenomenon, first flush phenomenon and intermediate flush phenomenon, respectively in low rainfall intensity, moderate rainfall intensity and high rainfall intensity conditions.This research also designed a device namedsuspended rapid filter for CSO immediate processing at the end of the pipe, which mainly removed SS and pollution associated by physical entrapment and absorption. The result showed that the filter can remove SS for more than 45% percent at high velocity. The analysis of removal efficiency at different range of particle diameter also showed that when the particle was bigger than 90μm, it can be removed more than 50%, while when it’s larger than 150μm, it can be almost removed totally. |
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