表面活性剂强化抽出处理含水层中DNAPL污染物的去除特征

为明确表面活性剂强化抽出处理含水层中DNAPL污染物过程中表面活性剂的增强修复效果,及DNAPL自身理化性质和介质孔径的影响,利用数码图像分析技术对1,2-二氯乙烷和四氯乙烯2种DNAPL在石英砂填充的二维砂箱中的抽取迁移过程进行了实验模拟研究,并对抽出水样中DNAPL的浓度进行了测试分析。结果表明,实验条件下加入低浓度(0.18%)的十二烷基苯磺酸钠(SDBS)大幅提高了对弱透水层截留的2种DNAPL聚集体的抽出处理效率。1,2-二氯乙烷在该表面活性剂溶液中的表观溶解度远高于四氯乙烯,因此其短时间内的绝对去除率更高。SDBS强化抽出处理DNAPL的作用机理以增溶作用为主,而其增流作用使DNAPL迁移流动后分布面积增大,增加了与表面活性剂溶液接触的面积,对增溶作用起到促进效果。细粒介质中DNAPL迁移后的最大分布面积较大,因此体系中DNAPL的溶解速率较高。在DNAPL聚集体质量与水力梯度固定的条件下,油水界面张力越低,DNAPL的密度越大,DNAPL垂向迁移的风险就越大。本研究为修复工程中如何依据DNAPL种类与场地多孔介质的情况选择表面活性剂提供了参考。

Removal characteristic of DNAPL contaminants in surfactant enhanced equifer remediation

The extraction and migration process of 1, 2-dichloroethane and tetrachlorethylene upon low permeability lenses in aquifer were studied in a two-dimensional sand box packed by two kinds of silica sand to determine the remediation efficiency of surfactant at low concentration and the impact of physicochemical properties of DNAPLs and pore sizes of porous media to the mechanism of surfactant enhanced remediation. Results indicated that the add of sodium dodecyl benzene sulfonate (SDBS) in the concentration of 0.18% substantially increased the extraction rates of the two DNAPLs. 1, 2-dichloroethane exhibited higher removal rates compared to tetrachlorethylene because of its higher observed solubility in the surfactant solution. Solubility improvement was demonstrated to be the major mechanism of SDBS enhanced remediation, while fluidity improvement promoted solubilization by making the DNAPL remove from original pools so that the contact areas between DNAPL and surfactant increased. The largest contact areas were larger in the fine sand than in the coarse sand, which explained why the solubilization rates of DNAPL were higher in the fine sand. It was observed that the smaller the interfacial tension and the heavier the DNAPL, the greater the risk of the vertical migration of the DNAPL under the experimental conditions. This research could provide a basis to the practical remediation engineering on how to select appropriate surfactant according to the variety of DNAPL and field conditions.