降雨特征及污染物赋存类型对路面径流污染排放的影响

Impacts of Rainfall Characteristics and Occurrence of Pollutant on Effluent Characteristics of Road Runoff Pollution

在西安市城市主干道南二环路太白立交高架段设置路面径流采样点,采用人工时间间隔采样法对2014年7月~2015年9月的13场径流事件全程采样,共获得样品207个,测试径流过程SS、COD、溶解态COD、Cu、溶解态Cu、Pb、溶解态Pb、Cr、溶解态Cr、Cd、溶解态Cd的质量浓度变化,研究降雨特征及污染物赋存类型对路面径流污染质量浓度变化和负荷排放的影响.结果表明,西安市城市道路径流SS、COD污染严重,是径流的主要污染物,重金属Pb、Cr污染水平亦较高;径流过程中污染物质量浓度变化与降雨特征及污染物赋存状态密切相关,溶解态污染物排放不受降雨特征影响,均在径流初期达到质量浓度峰值随即持续降低,颗粒态污染物的质量浓度峰值出现在足够大的降雨强度峰值之后,径流过程随雨强变化波动显著,且受降雨历时和降雨量等因素的共同影响;降雨特征对溶解态污染物负荷排放的影响较小,但对颗粒态污染物具有显著影响.Ⅰ、Ⅱ型降雨事件较之Ⅲ型降雨,SS、COD、Cu、Pb、Cr、Cd的负荷初期冲刷效应更明显;路面径流的负荷初期冲刷效应并非普遍存在,所监测径流场次所有污染指标均未出现强烈的负荷初期冲刷,各污染物的负荷初期冲刷程度排序为COD>SS>溶COD>Cu>Pb>Cr>溶Cu>Cd>溶Pb>溶Cr>溶Cd.

Urban road runoff contains pollutants such as particulate matters, organic chemicals, heavy metals, nutrients, oil and grease that can cause significant degradation of receiving water quality. Eliminating the pollutant mass loading of road runoff and protecting the receiving water bodies have been the focuses in environmental field in recent years. To accomplish pollutant reduction and develop a cost-effective treatment method, knowledge of water quality characteristics, as well as the pollutant effluent characteristics of road runoff is required. In order to investigate the impacts of rainfall characteristics and occurrence of pollutant on the variation of pollutant concentrations during the duration of runoff events and pollutant load effluent characteristics of road runoff, 207 road runoff samples in the durations of 13 storm events occurred at Taibai Interchange of the south second-ring road in Xi＇an, Shaanxi province from July 2014 to September 2015 were collected by the manual time-interval sampling method, and concentrations of SS, COD, dissolved COD, Cu, dissolved Cu, Pb, dissolved Pb, Cr, dissolved Cr, Cd and dissolved Cd of the samples were determined. The results indicated that, the road runoff of Xi＇an city was seriously polluted by SS and COD, which were the main contaminants in road runoff. Meanwhile, concentrations of Pb and Cr in road runoff were also at a high level. The variation of pollutant concentrations during the duration of runoff was closely related to rainfall characteristics and occurrence states of the pollutants. Emission of the dissolved pollutants was not affected by the type of rainfall. The concentration of the dissolved pollutants in the runoff reached a peak in the initial duration of runoff, and then, decreased continuously. However, the peak concentration of particulate pollutants in the runoff only occurred after the peak of sufficiently large rainfall intensity. The concentration of particulate pollutants in the runoff fluctuated sharply with the variation of rainfall intensity, and impacted by the rainfall duration and rainfall depth as well. Rainfall characteristics didn＇t have a great impact on the load emission of the dissolved pollutants, therefore, had a significant influence on the load emission of the particulate pollutants. Compared with the rainfall type Ⅲ, first flush effects of pollutant loads of SS, COD, Cu, Pb, Cr, Cd in rainfall type Ⅰand type Ⅱ were more obvious. Besides, first flush effect of pollutant loads was not ubiquitous. All the pollutants in the monitoring 13 runoff events didn＇t exhibit an obvious first flush effect. The descending order of the first flush effect of those pollutants was COD, SS, dissolved COD, Cu, Pb, Cr, dissolved Cu, Cd, dissolved Pb, dissolved Cr, dissolved Cd.