地下水中Tween80对DNAPL运移和分布的影响

选用地下环境中普遍存在的四氯乙烯（PCE）为典型DNAPLs污染物，建立二维砂箱模型，研究一种人为引入表面活性剂Tween 80对粗砂介质中DNAPLs迁移和分布的影响.测定了含不同浓度Tween 80水溶液/石英砂/PCE三相体系下的液/液界面张力及PCE在石英介质表面的接触角，结果表明PCE在石英砂表面的接触角随着Tween 80浓度的增大而增大，PCE/水的界面张力随着Tween 80浓度的增大而减小，Tween 80浓度在CMC值附近时变化急剧.随后的二维砂箱实验定量描述地下水中表面活性剂Tween 80对PCE的迁移和最终形态的影响.由于Tween 80可以使石英砂介质由水相润湿转变为中间润湿或油相润湿态，相应地在20~30目的粗砂均质介质中Tween 80对DNAPLs迁移存在明显影响.背景溶液中表面活性剂的存在使得DNAPL的垂直运移速度减小，垂向迁移距离减小，最终使得被截留在运移路径上的残留PCE增加.和纯水流情况下相比，地下水中含有表面活性物剂Tween 80时，使得DNPAL污染羽向水流方向偏移减弱，污染羽展布面积与纯水情形下相比，在垂向上均明显减小，并且以较大饱和度残留的DNAPL量增加.

Effects of Tween 80 in groundwater on DNAPL migration and distribution

How artificial surfactant Tween 80 in groundwater affect ubiquitous tetrachloroethylene (PCE) migration and distribution in coarse porous media was investigated in this work. Batch experiments were first conducted to measure the contact angles and interfacial tensions (IFT) between PCE and quartz surface in water containing different amount of Tween 80. Results showed that the contact angle increased and IFT decreased with the increased concentration of Tween 80, and the effects were more obvious near the CMC value. Three 2-D sandboxexperiments were then conducted.Correspondingly, Tween 80 showed strong effects on the migration and distribution of PCE in the coarse porous media due to its ability to change the medium wettability from water-wet into intermediate/NAPL-wet. The presence of surfactant in the background solution decreased the vertical migration rate of DNAPL, decreased the vertical migration distance, and eventually increased the residual PCE trapped in the migration path. Compared with the situation without surfactant, the Tween 80 in groundwater weakened the tendency of PCE plumes deflect to the direction of water flow. Compared with the water-only case, the distribution area of PCE plumes decreased significantly in the vertical direction, but the amount of DNAPL residues with greater saturation increased.