CCL非线性平衡吸附条件下填埋场渗滤液运移过程数值分析

Numerical analysis of landfill leachate migration processes considering nonlinear equilibrium sorption behaviour of CCL

采用Langmuir等温吸附方程表示黏土对渗滤液中某种污染物的非线性吸附,依据污染物在多孔介质中运移机理,建立了渗滤液在饱和多孔介质运移的一维数学模型。在考虑填埋场采用压实黏土衬里防渗层、垃圾生物降解生成污染物的特性、在填埋场下含有一定厚度含水层等实际情况下,采用有限差分法求解控制方程。通过参数对比计算与分析表明,与线性吸附相比,非线性吸附使得污染物的穿透能力增强,污染物浓度随时间变化曲线尖锐而狭窄、峰值浓度出现时间提前、曲线有尾部拖长现象。组合参数Sl对污染物运移影响较大,当Sl取值较大时,可降低污染物浓度,"挫峰"能力增强,污染物浓度随时间变化曲线表现出线性吸附性质。参数K1对污染物运移影响较参数Sl小。压实黏土衬里的渗透系数较低时,弥散控制污染物运移,且弥散系数较大和较小时,穿透曲线分别表现出线性吸附性质和非线性性质。

While Langmuir＇s isotherm equation is employed to describe nonlinear equilibrium sorption behavior of some contaminant compound in leachate sorption onto particles of clay material and the migration mechanism of pollutants in porous medium, one-dimensional mathematical model of contaminant migration in saturated porous medium is developed. Considering the actual landfill profile which generally underlies the compacted clay liner （CCL） and an aquifer layer with a finite thickness and waste biodegradation effect,the governing equations are numerically solved by finite difference method. Through parametric analyses based on numerical computations,the effect of nonlinear sorption of CCL on contaminant migration is examined. Compared with the case of linear sorption of CCL,non-linear sorption displays a more considerable effect on the contaminant transport which will induce a bigger break-through capacity of contaminant and a sharper front in the contaminant concentration curve,an earlier shift of peak concentration and a longer tailing. The combined parameter,St ,shows a heavier effect on the contaminant migration. As Sl increases,the contaminant concentration with time displays linear sorption behavior,the contaminant concentration is reduced and corresponding peak is shifted backward. Compared with the combined parameter of Sl ,the effect of the sorption intensity of K1 on the contaminant migration is relatively not appreciable. For the compacted clay liner with a lower hydraulic conductivity,the mechanism of hydrodynamic dispersion will dominate contaminant migration process. Therefore,when hydrodynamic dispersion coefficient is high, the break-through curve will display the nonlinear sorption characteristics while the break-through curve will exhibit the linear sorption feature when hydrodynamic dispersion coefficient is low.