污染源区结构特征对Tween 80去除DNAPL效果的影响

The influence of source-zone architecture on DNAPL removal by Tween 80 flushing

选择四氯乙烯(PCE)作为特征污染物,通过二维砂箱实验探究3种介质情景中,污染源区结构特征对Tween 80冲洗去除PCE的影响.采用透射光法监测PCE的运移及去除过程,定量测定PCE的饱和度.进而采用不连续的离散状与连续的池状PCE体积比(GTP)定量表征污染源区结构特征.结果表明,PCE在含透镜体介质中运移时,运移路径延长,离散状PCE增多.离散状PCE与Tween 80溶液的有效接触面积较大,被优先溶解去除,而细砂层上部的污染池的比表面积和接触面积较小,溶解能力有限,远比运移路径上的PCE难以去除.此外,初始离散状PCE较多,GTP较大,有利于池状PCE溶解转变为离散状PCE,PCE去除率增大.因此对于实际污染场地,需要详细分析DNAPLs污染源区结构特征,以助于评估表面活性剂冲洗技术的修复效率及试剂消耗.

The PCE was selected as representative DNAPLs. Three 2-D sandbox experiments were conducted to investigate the effect of source-zone architecture on the PCE by Tween 80flushing. The light transmission method was used to monitor the migration and remediation processes of PCE within the sandboxes, and quantitatively measure PCE saturation distribution. The ratio of volume of PCE ganglia to the volume of pools （GTP） was used to quantify source-zone architecture, and the effect of GTP on the PCE removal was evaluated. Experimental results showed that when PCE migrated in the porous media containing lenses, the percolation paths extended, and PCE ganglia increased. PCE ganglia was preferentially solubilized by micelles due to a larger contact area with Tween 80 solution. While PCE pool on the fine-sand layer was much more difficult to remove due to a smaller contact area and limited solubilization capacity. The larger initial PCE ganglia promoted pool on migration path to rapidly transform into ganglia, and hence increased cumulative PCE removal, indicating that GTP significantly influenced the remediation effectiveness of surfactant flushing. Therefore, detailed source-zone architecture characterization is needed to evaluate the remediation efficiency and dose of flushing agent during in-situ surfactant flushing process.