CSO Pollutants Reduction Effects of Two Different Stormwater Detention Tanks in Central Shanghai

The stormwater detention tank (SDT) was a useful facility to reduce combined sewer overflow (CSO) pollutants during wet season. The study was carried out in the Chendulu combined sewer system (CSS) and the Xinchangping CSS with two different SDTs. The Chengdulu SDT was the first running SDT in China, and the Xinchangping SDT had the best environmental effects in China. The CSO pollutants reduction effects of the two SDTs which serviced the Chendulu CSS and the Xinchangping CSS along the Suzhou Creek in central Shanghai were studied based on the precipitation, discharge, pollutants concentrations and running data measured over 10 times in 2011. The results show that: (1) The Chengdulu SDT and the Xinchangping SDT could reduce CSO pollutants effectively. In 2011, the annual CSO volume reduction rate were 5.7% and 63.6%, respectively, and the annual chemical oxygen demand (COD) of CSO reduction rate were 8.1% and 78.8%, respectively. (2) Under the given conditions, such as service area, underground type and precipitation, design method and design standard of SDT volume, stormwater inlet and emptying modes of SDT were the important impact factors to the pollutants reduction rate of CSO. (3) According to the local physiogeographic conditions listed above, the proper volume design standard and stormwater inlet and emptying mode should be chosen to make full use of the CSO pollutants reduction effects of SDT.