Initial rainwater pollutant reduction practice of urban drainage system in Shanghai city

The main current concepts of initial rainwater pollution reduction were to use engineering and non-engineering technical measures to cut-off the higher pollution concentration part of the rainwater. Among the initial rainwater pollution reduction practices, the urban rainwater detention tank (RDT) was a useful measure. During the 2nd stage Suzhou comprehensive environmental treatment project, five RDTs were first constructed and used to control initial rainwater pollution of the combined sewerage system (CSS) along Suzhou Creek in central Shanghai of China. In order to comprehensive assess the environmental benefits of the Chengdulu RDT, the first running RDT in China, the precipitation, discharge and pollutant concentration of the Chendulu CSS were measured over 40 times from 2006 to 2010. The results show that the Chengdulu RDT has better environmental benefits in reducing initial rainwater pollution of CSS: (1) firstly, the RDT could reduce initial rainwater pollution of the Chengdulu CSS effectively, the mean annual initial rainwater reduction and reduction rate were 8.95 ×10⁴ m³ and 8.84% from 2006 to 2010, respectively. (2) secondly, the initial rainwater pollutants could also been reduced efficiently by the Chengdulu RDT, the initial rainwater pollutants decrease rate of COD, SS, NH₄⁺-N and TP were 11.34%, 12.65%, 15.23% and 12.49%, respectively, and those pollutants decrease 40.52 t, 49.26 t, 2.08 t and 0.29 t annually from 2006 to 2010, respectively. (3) thirdly, the Chengdulu RDT could improve the CSS discharge capacity effectively with promoted interception ratio from 3.16 to 7.35 during the RDT running time, and from 3.16 to 3.55 during the precipitation time. (4) fourthly, the Chengdulu RDT could delay the runoff peak 1 h or 0.5 h in the CSS pipe with two different pump running models.