| Urban rainwater resource utilization, as an effective method to solve water scarcity, reduce the possibility of flood, control the rainfall runoff pollution and improve ecological environment in the city, has much significance. Taking rainwater from road and parking areas in Lingang, Shanghai city as the research object, complying with the principle of ecological engineering and with the purpose of collecting, purifying and utilizing rainwater runoff, two pilot scale projects are established. In this paper, operation efficiency of two projects is attached much emphasis on. To sum up, the main research contents and conclusion are as follows:1. Through the analysis of rainwater runoff characteristics and determination of rainwater quality in the selected areas, the study shows that TN, CODcr and SS are the main contaminants in the rainwater runoff. Specifically, average contaminant range of are TN2.41-6.04mg/L, CODcr80.0～98.8mg/L and SS66.0-144.0mg/L in parking runoff. They are1.51-2.72mg/L,72.7～119.6mg/L and69.1～182.0mg/L respectively in road runoff. The maximum values of them are far more than that of Class V of the National Surface Water Quality Standards. Meanwhile, the results indicate that road runoff quality varies more than that of parking runoff.2. Combined with the characteristics of rainwater distribution and catchment in Lingang city, the knowledge of foreign advanced technology and taking economic principles into account, two pilot scale research projects of rainwater resource utilization are established. They are located in the near of Hucheng Ring Road and Guzong Road in Lingang city. According to the storm water intensity formula of Shanghai (parameters such as annual rainfall and the runoff coefficient are included). The total scale of both projects is750m3/d, with150m3/d and600m3/d respectively. Covering the area of60,000square meters, the two projects include parking, road and surrounding catchment areas. In terms of rainwater utilization technology, the infiltration ditch, constructed wetland and ecological pond are arranged to treat parking runoff, while sand and microorganism filtration,"ladder type" ecological purification ditch are arranged to treat road runoff.3. Evaluate the operation efficiency of two projects. Firstly, select sampling sites and detect the contaminant concentration of CODcr, NH3-N, TP, TN and SS in the two processes. Site A1stands for rainwater inlet, Site B1for infiltration ditch outlet and Site C1for compound ecological pond outlet in parking area, while Site A2stands for rainwater inlet, Site B2for hydrophyte pond and Site C2for submerged plant pond in the road area. The experiments demonstrate that two pilot scale projects both operate well and parking purification project can remove more contaminants than the road project in CODcr, NH3-N, TP and TN, while SS removal rate amounts to63.5%in the road project. In addition, through the designed processes, runoff water quality in the two areas can meet Class V of the National Surface Water Quality Standards.(GB3838-2002) and The Use of Urban Recycling Water—Water Quality Standard for Urban Miscellaneous Water Consumption(GB/T18920-2002).Secondly, study on the species diversity in the two projects in order to explain their functions in the perspective of biology. The acquisition of rainwater samples from compound ecological pond, hydrophyte pond, submerged plant ponds and two blank rainwater samples is prior to the identification of phytoplankton species. Then, the Shannon-Wiener diversity index H’, Margalef index d and Pielou index J are calculated respectively. The experimental data display that the water quality after our purification projects is obviously better than blank ones.4. Estimate the economic and environmental benefits of two rainwater ecological purification projects due to the decrease of surface runoff and runoff contaminant concentration. |
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