有机污染物在含土工膜复合隔离墙和含水层系统的运移半解析模型

A semi-analytical model for analyzing the transport of organic pollutants through the geomembrane composite cut-off wall and aquifer system

为评估土工膜与土-膨润土组成的复合隔离墙对有机污染物的防污性能,建立了污染物在源区域发生降解扩散时透过复合隔离墙的一维瞬态扩散模型。通过拉普拉斯变换和Talbot数值反演获得了模型解。第3类入流边界条件下,考虑源区的扩散和降解时,第1类隔离墙(土工膜/土-膨润土)和第2类隔离墙(土-膨润土/土工膜/土-膨润土)100 a的击穿浓度分别较源浓度恒定时减少了59%和53%。由于假设土工膜渗透系数高于10^(–12) m/s,污染物在复合隔离墙中的对流作用不能忽略,因此,采用第2类复合隔离墙使土-膨润土能更好地发挥主导隔离作用。将土工膜的渗透系数从10^(–10) m/s减少到10^(–16) m/s,第1类复合隔离墙的击穿时间从26 a增加到188 a,第2类复合隔离墙的击穿时间从32 a增加到81 a。利用抽水井调整墙体内外为负水头差及提高源区的污染物降解能力,可使隔离墙的防污性能得到较大提升。

In order to evaluate the antifouling performance of the composite cut-off wall composed of geomembrane and soil-bentonite to the organic pollutants,a one-dimensional transient diffusion model was established to describe the diffusion behavior of pollutants through the composite cut-off wall when the pollutants were degraded in the source region.The solution of the analytical model was calculated by the Laplace transform and the Talbot numerical inversion.When the effects of pollutant diffusion and degradation were considered under the 3^(rd) type inlet boundary condition,the 100-year breakthrough concentration of the type I(geomembrane/soil-bentonite)and type II(soil-bentonite/geomembrane/soil-bentonite)composite cut-off walls decreased by 59%and 53%than that under the 1^(st) type inlet boundary condition,respectively.Since the permeability coefficient of geomembrane was assumed to be higher than 10^(–12) m/s,the convection of pollutants in the composite cut-off wall cannot be ignored.Thus,the type II composite cut-off wall enabled the soil-bentonite to play a dominant role in isolating the organic pollutants better.By reducing the permeability coefficient of geomembrane from 10^(–10) m/s to 10^(–16) m/s,the breakthrough time of type I composite cut-off wall was increased from 26 years to 188 years,and that of type II composite cut-off wall was increased from 32 years to 81 years,correspondingly.The antifouling performance of the composite cut-off wall can be effectively increased by adopting the methods,such as adjusting the negative head loss inside and outside the wall by a pumping well,and increasing the degradation capacity of pollutants in the source region.