危险废物填埋场复合衬层渗漏分析与污染物运移预测

Predicting leakage and contaminant transport through composite liners in hazardous waste landfill

以我国危险废物填埋场次防渗层采用1 mm高密度聚乙烯(HDPE)土工膜和0.5 m压实粘土衬垫(CCL)组成的复合衬层为研究对象,采用经验公式以及解析方法计算了不同缺陷条件下复合衬层的渗漏率.在此基础上,采用一维污染物对流扩散运移方程对重金属Cd^(2+)、Zn^(2+)、Cu^(2+)、Pb^(2+)击穿复合衬层的时间进行了计算和分析.结果表明:复合衬层渗漏率主要受到复合衬垫界面接触条件,渗滤液水位以及缺陷类型的影响;当复合衬层的漏洞密度为20个·hm^(-2)时,半径为5.64 mm的圆孔型缺陷其最大渗漏率为22.7 m^3·a^(-1)·hm^(-2);当单位面积裂缝长度为200m·hm^(-2)时,宽度为2 mm长度为1 m的裂缝型缺陷其最大渗漏率为42.5 m^3·a^(-1)·hm^(-2);Cd^(2+)可作为重金属污染物击穿复合衬层的指示性污染物,其击穿时间最长为2.74 a,最短为1.38 a;通过改变土工膜下伏土壤衬层的性能或增加土壤衬层厚度可延缓污染物击穿时间.

Composite liners consisting of a 1 mm thick HDPE geomembrane overlaying a 0.5 m thick compacted clay liner（CCL） are commonly used in the secondary barrier system of hazardous waste landfill in China. By taking the typical composite liners as the research object, leakage through composite liners with different defects was analysed using existing empirical equations and analytical solutions., the breakthrough time of composite liners for contaminant Cd^2＋, Zn^2＋, Cu^2＋ and Pb^2＋ was calculated using one-dimensional convection-diffusion equation. The results show that the leakage rate may be influenced by the interface properties, the leachate level and the defect types. When the hole density of composite liners is 20 holes·hm^-2, the maximum leakage rate through composite liners with circle defect having a radius of 5.6 mm is 22.7 m3·a^-1·hm^-2 When the length of defective seam on unit area is 200 m·hm-2, the maximum leakage rate through composite liners with defective seam is 42.5 m3^·a^-1·hm^-2. The longest and shortest breakthrough time of composite liners with defects for Cd^2＋, which is taken as contaminantion indicator of heavy metal, are 2.74 a and 1.38 a respectively. By changing the properties of the underlying soil layer or increasing the thickness of the soil layer, the breakthrough time of contaminant can be delayed.