高速公路路面径流沉降过程中重金属去除特性

在对南京机场高速公路令桥段2008年2月~2009年2月15场降雨事件初期路面径流进行自由沉降试验的基础上，考察了自由沉降过程中Cu、Zn、Cd、Pb 4种重金属的去除率随时间的变化特征.同时，重点分析了重金属去除与截留沉速和悬浮固体(SS)去除的关系，并探讨了降雨特征和径流pH值对重金属去除特性的影响.结果表明，沉降开始30min内Cu、Zn、Cd、Pb去除率增长迅速，30min去除率均占2h总去除率的60%以上.Pb的2h平均去除率最高，可达25.62％，Cu、Cd和Zn的2h平均去除率分别为21.20%、19.97%和19.10%.同一重金属的沉降去除率每提高10%，截留沉速范围及上限值减少5倍左右.截留沉速相同时，Pb的去除效果最好，Cd、Cu、Zn的去除效果相差不大.SS与Cu、Zn、Cd、Pb沉降去除率之间的相关性存在差异，Pb多数以颗粒态形式存在，因而SS与Pb沉降去除率相关系数最大，其相关系数为0.8126(p=0.0002）；SS与Cd、Cu、Zn沉降去除率的相关系数分别为0.6871、0.6804、0.7653.路面径流pH值对重金属去除特性的影响显著，与4种重金属沉降去除率均呈正相关，且与Zn、Cd、Pb的相关系数均大于0.5；Zn主要以溶解态形式存在，因而Zn沉降去除率受pH值影响最明显，两者在0.05水平上显著相关(p=0.029).

Characteristics of heavy metal removal during highway runoff sedimentation

The removal rates of four heavy metals(Cu,Zn,Cd and Pb)during free sedimentation of runoff were investigated based on test results on the initial road surface runoff after 15 rainfall events from February 2008 to February 2009 on the Lingqiao section of the Nanjing Airport Expressway.The emphasis was placed on the relationship between the heavy metal removal and the settlement rate,as well as the relationship between the heavy metal removal and SS removal,and the effects of precipitation features and runoff pH values on the removal rates of heavy metals were explored.The removal rates of Cu,Zn,Cd and Pb increased rapidly during the first 30 minutes of settling,accounting for over 60% of the total removal rates of the four heavy metals in 2 hours.Pb had the highest 2 h mean removal rate(25.62%) and the 2 h mean removal rates of Cu,Cd and Zn were 21.20%,19.97% and 19.10%,respectively.With every 10% increase of settling removal rate of the same heavy metal,the range and maximum value of settling velocity decreased by around 5 times.Under the same settling velocity,the removal efficiency of Pb is best while those of Cd,Cu and Zn showed little difference.The linear correlations of the settling removal rate between Cu,Zn,Cd,Pb and SS were different.Since Pb existed mostly in particulate form,the correlation of settling removal rate between Pb and SS was the highest,with a correlation coefficient of 0.8126(p=0.0002).The correlation coefficients of settling removal rate between Cd,Cu,Zn and SS were 0.6871,0.6804 and 0.7653 respectively.The runoff pH value had significant impact on the removal features of heavy metals,maintaining a positive relationship with the settling removal of the four heavy metals,and the correlation coefficients between runoff pH value and Zn,Cd and Pb were all higher than 0.5.Since Zn was mostly dissolved,its settling removal was most significantly impacted by the runoff pH value,and they were significantly related(p=0.029).