表面流人工湿地对城市径流水质的净化研究

Experimental Study on the City Runoff Pollutant Reduction by Multi-Series Surface Flow Constructed Wetland

城市径流水质已经成为农业面源污染的主要来源之一,根据武汉市径流的水质和水量特征,采用多级串联的表面流人工湿地系统对其进行了径流净化研究。对人工湿地不同运行阶段模拟径流的净化效果进行了对比,分析化学耗氧量COD_(Cr),生物耗氧量BOD_5,固态悬浮物SS,总氮TN,总磷TP,铵氮NH^+_4-N在湿地系统中的沿程变化,探讨人工湿地对城市径流污染的去除效应。结果表明:各指标在人工湿地中的去除效应大小依次为NH^+_4-N>COD_(Cr)>BOD_5>TN>SS>TP,其中对NH^+_4-N的去除效应显著高于其他指标的去除效应(p<0.05),对TP的去除效应最弱(p<0.05);人工湿地对COD_(Cr),BOD_5,SS,TN,TP,NH^+_4-N的去除效应在1—7月呈逐渐增加趋势,局部有所波动,9月达到最大值,9月以后去除效应趋于平稳;除了TN外,人工湿地系统出水各指标均达到《地表水环境质量标准—GB》质量标准,其中TN达Ⅳ类标准。径流各指标主要在人工湿地的第1格被去除,随着人工湿地沿程进水浓度的增加,其去除效应逐渐下降。相关性分析表明,各径流各指标之间存在一定的相关性,而TP与各指标之间没有相关性(p>0.05)。通过对湿地系统沿程氮磷浓度衰减的拟合及回归分析,建立了与湿地系统进口浓度有关的COD_(Cr),BOD_5,SS,TN,TP,NH^+_4-N浓度的沿程衰减模型,相关分析表明其最佳的拟合模型均为指数衰减模型。该湿地系统在整个试验时期内均表现出了良好的净化效果,有效地减轻了城市径流水质对外界水环境的破坏,可用于城市地面径流污染的控制和利用,指数衰减模型的建立也为后续湿地设计及排水水质预测提供了理论分析依据。

Rural domestic sewage has become one of the main sources of agricultural non-point source pollution. According to water characteristics of the runoff in Wuhan City, multi-series surface flow constructed wetland was used for purification experiment study on simulated and on-the-spot runoff. The purification effects of simulated runoff were compared in different operated phases of multi-series surface flow constructed wetland. Meanwhile, the variation of the pollutants(CODCr, SS, TN, TP, NH+4-N) along the constructed wetland and their removal mechanism were analyzed and discussed, respectively. In the purification study of on-the-spot runoff, removal rates of CODCr, SS, TN, TP, NH+4-N decreased in the order: NH+4-N>CODCr>BOD5>TN>SS>TP in which the effluent met the grade Ⅲ of water. In the simulated experiment, the effluent water quality of BCW system met the needs of Environmental Quality Standard for Surface Water(GB 3838—2002) Ⅲ, besides TN met Ⅳ, most of the pollutants were removed in the front of the constructed wetland. The removal rate gradually decreased with the units. Correlation analysis showed that TP had no significant difference with the other pollution parameters(p>0.05). We established the exponential, the linear, and the quadratic polynomial model which were related to the inlet concentration of the wetland system through the monadic linear regression analysis of model coefficients. Then these three models were used for prediction and evaluation on the basis of the other four groups of testing data. Correlation analysis revealed that exponential decay model had a smaller relative root-square-error value with the best performance. The wetland system showed good purification effect during the whole test period, reducing the discharge of nitrogen and phosphorus of rural domestic sewage greatly, and mitigating the damage of domestic sewage to freshwater environment. The establishment of exponential attenuation model provided reference for the prediction of concentration changing along the multistage tandem constructed wetland system. The model can be used to easily predict nutrient concentration in any wetland subsystem when the influent concentration of the system is known. In total, there was remarkable treatment performance of the runoff when constructed wetland system was used, which also can withstand strong shock load. Moreover, it can be used to control urban surface runoff pollution.