Study On Runoff Pollution And Control Of Rainfall At Different Underlying Surfaces In Urban Residential Area Of Chongqing

Urban storm-water runoff is referred as non-point source pollution. Researchers have found that the load and concentration of suspended solid, nutrient, heavy metals and organic pollutants discharge from urban storm-water runoff are higher than that in untreated polluted and rural areas. These contaminants may lead to deterioration of water quality and degradation of steam habitats in urban areas. But till now, there are few reports about runoff pollution and control of rainfall at different underlying surfaces in urban residential area of Chongqing.The objective of this study was to investigate the characteristic of storm-water runoff from different underlying surfaces in a residential area called Shuizhuyuan in Yubei district of Chongqing, based on the analysis of major pollutants from storm-water runoff, hydrographs and pollutographs analysis, correlation analysis between water quality parameters, and first flush phenomenon analysis. At last, the effect of the runoff pollution compared with green roof and other 3 roofs with different materials is studied. The major conclusions are as follows:1. The results showed that the event-mean concentrations of total suspended substances (TSS), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) from the runoff on asphalt pavement were 451.1 mg/L,169.3 mg/L, 5.15 mg/L,0.85 mg/L, as well as 271.85 mg/L,89.55 mg/L,6.91 mg/L,0.51 mg/L respectively on concrete pavement. The concentrations of TSS, COD and TP from the runoff on asphalt pavement were 2.05,1.35 and 1.27 times higher than that on concrete pavement respectively when samples were collected at the same time from the two roads in 3 rainfall events. The initial concentrations of pollutants on asphalt pavement were higher than those on concrete pavement, and the maximum concentrations of TSS and TP on asphalt pavement appeared later than those on concrete pavement, the average values of the ratios of 30% runoff amount to the concentration of the pollutant in runoff (FF30) on asphalt pavement were 1.26,1.07 and 1.32 times that on concrete pavement, respectively. Differences in number of dents and chemical compositions of the pavements were the two major causes for the differences of runoff pollution. To improve street sweeping practice is firstly implemented as the most effective measure to reducing the urban storm-water runoff pollution loads in residential areas. Storage of the first 30% runoff for treatment could reduce 30%-70% of the total suspended solids load in combined flow.2. By investigating surface runoff from urban roofs in Chongqing, we assessed the variations of pollutants concentrations in the runoff and the first flush phenomenon of the concrete roof and tile roof, and analyzed the effect of rainfall characteristics on runoff water quality using multivariate statistical analysis. The results indicated that COD and TN in the runoff on both kinds roof were of high concentrations. The concentrations of COD, TN, TSS, Cu and Zn on the concrete roof were significantly higher than those on the tile roof, and were 1.63,1.57,1.15,1.70,1.65 and 2.05 times higher, respectively. On the concrete roof, the COD, TN, TP and TSS concentrations changed more greatly than the tile roof, and the peaks were behind or synchronous with the peak of the maximum rainfall intensity. Meanwhile, the COD, TN, TP and TSS concentrations peaks on the tile roof were ahead of or synchronous with the peak of the maximum rainfall intensity. The average FF30 of all the pollutants on the tile roof was higher than the concrete roof. On the concrete roof, except for Zn and Cd, the FF30 of each pollutant of standard deviation showed larger variation than tile roof. The values of EMCs were negatively correlated with precipitation, runoff volume and rainfall intensity. The concentrations of dissolved heavy metals were negatively correlated with the dry weather deposits, but the concentrations of the other pollutants showed positive correlation with the dry weather deposits.3. Compared with the bare asphalt roof, green roof has obvious interception effect to rainfall runoff as only 28.4%, and it slows the pressure of the peak of the experiment site from the rainstorm apparently. Although some pollutant concentrations are higher than the bare asphalt roof, because of the significant reduced runoff volume, except for TN, the total output of pollutants all decreased significantly, the removal rates of COD, TSS, and TP are 68.2%,94.8%, and 74.2%, respectively. Therefore, the green roof reduced the total output of pollutants.