[Environmental effects of combined sewage detention tank in central Shanghai]

Through measuring the processes of precipitation, discharge and pollutant concentration over 20 times from 2006 to 2008 in Chendulu combined sewerage system (CSS) along Suzhou Creek in central Shanghai, the environmental effects of Chendulu combined sewage detention tank (CSDT), the first running CSDT in China, were studied. The results show that CSDT could improve CSS discharge capacity effectively with promoted interception ratio from 3.87 to 6.90-9.92. The mean annual combined sewer overflow (CSO) reduction and reduction rate are 9.10 x 10(4) m3 and 9.00%, respectively, and those of sanitary waste discharged directly to Suzhou Creek in non-rain-weather are 8.37 x 10(4) m(3) and 100% , respectively. The mean annual pollutants decrease rate of COD, BOD5, SS, NH4+ -N and TP of CSO are 13.76%, 19.69%, 15.29%, 18.24% and 15.10%, respectively, and those CSO pollutants decrease 41.21 t, 12.37 t, 50.10 t, 2.12 t and 0.29 t annually, respectively. The CSDT also could decrease sanitary waste discharged to Suzhou Creek totally, and those decreased pollutants are 20.75 t, 4.87 t, 14.90 t, 4.49 t and 0.30 t annually, respectively. The analysis shows that the CSDT design standard, running models and rainfall characteristics are the important influencing factors to realize the environmental effects of CSDT.