北京城市典型下垫面降雨径流污染初始冲刷效应分析

Analysis of First Flush Effect of Typical Underlying Surface Runoff in Beijing Urban City

城市硬化地表的迅速增加使得降雨径流量增加,屋面和路面等下垫面上污染物的大量累积并随径流进入城市排水系统,对城市水环境造成威胁.为了解径流污染过程和给径流污染控制提供科学依据,于2004～2006年选取典型屋面和路面对径流污染过程进行了监测和分析,计算了两种径流的次降雨平均浓度(EMC)水平,发现两类径流的COD和TN污染较为严重;屋面径流的化学需氧量(COD)、总氮(TN)分别超标(地表水环境质量标准GB 3838-2002 V类)3.64和4.80倍;路面径流的COD、TN分别超标3.73和1.07倍.利用M(V)曲线,判断径流量同径流污染负荷的关系,发现屋面径流污染物总悬浮颗粒物(TSS)、COD、TN和总磷(TP)发生了不同程度的初始冲刷现象;路面初始冲刷现象主要表现为TSS和TP,总体上初始冲刷效应不明显.汇水面性质、降雨强度、污染物累积状况等都是影响屋面和路面径流污染物排放特征的重要影响因素.

Rapid increase of the urban impervious underlying surfaces causes a great increase of urban runoff and the accumulation of pollutants on the roof and road surfaces brings many pollutants into the drainage system with the runoff,and it thus becomes a great threat to the urban water environment.To know the runoff pollution process and to build scientific basis for pollutant control,runoff processes from the roof and road surfaces were monitored and analyzed from 2004 to 2006,and the runoff EMC（Event Mean Concentration） was calculated.It was found that two types of runoff were seriously polluted by COD and TN.The COD and TN of roof runoff exceeded the fifth level of the surface water environmental quality standard（GB 3838-2002） by 3.64 and 4.80 times,respectively,and the COD and TN of road runoff exceeded by 3.73 and 1.07 times,respectively.M（V） curve was used to determine the relation between runoff volume and runoff pollution load.Various degrees of the first flush phenomenon were found for TSS,COD,TN and TP in roof runoff.But this phenomenon occurred only for TSS and TP of the road runoff,and on the whole it was not obvious.Properties of the underlying surfaces,rainfall intensity,and pollutant accumulation are all important factors affecting the roof and road runoff pollutant emission characteristics.