裂隙地下水中残留LNAPL物理驱替冲洗实验

利用透明复制裂隙模型,选择两种典型LNAPL（轻非水相液体）-邻二甲苯和十二烷残留体,开展一系列水流驱替冲刷和SDS（十二烷基磺酸钠）表面活性剂增强驱替实验,直接获取了裂隙内部LNAPL残留体几何形状与分布情况,结果表明：水流驱替冲刷和SDS驱替裂隙内残留体的去除率分别为8.3%~12.3%和65.9%~82.1%.残留体累积去除率随着驱替流体雷诺数的增加而增加.水流驱替冲刷条件下,残留体离散为小液滴,数量比初始残留状态增加1.3~2.2倍.SDS表面活性剂降低了"LNAPL-水"间的界面张力,能够有效去除裂隙内较大残留体,驱替后仅残余单个面积为1mm²左右的微小液滴.由于粗糙裂隙的非均质性,水流冲刷易导致系统内的"LNAPL-水"有效界面面积增加,对LNAPL污染修复不利,表面活性剂增强修复是一种更有效的方法.

Physical displacement and flush of entrapped LNAPL in fractured media groundwater

With the transparent replica fracture model, two typical LNAPL (light non-aqueous phase liquid) pollutants o-xylene and dodecane) were selected to be flushed by water and the SDS (sodium dodecyl sulfonate) solution. The geometry and distribution of the entrapped LNAPL were obtained directly in a series of experiments. The results showed that the removal percentage of the entrapped LNAPL flushed by water and the SDS solution were in the ranges of 8.3%~12.3% and 65.9%~82.1%, respectively. The cumulative removal percentage were increased with increasing Reynolds number of the flushing fluids. Under the water flushing condition, the entrapped blobs were dispersed into smaller droplets, and the droplet numbers were increased by 1.3~2.2times compared with the initial states. SDS surfactant reduced the interfacial tension between LNAPL and water, thus it can effectively remove the larger entrapped blobs in the fracture. After SDS displacement, only small droplets with a single area of about 1mm² remained. Because of the heterogeneity of variable-aperture fractures, water flush was demonstrated to result in the increase of the effective interface area of ‘LNAPL-water’ in the system, which was disadvantageous to the remediation of LNAPL pollutants. Surfactant enhanced displacement could be a more effective method for LNAPL removal.