地下水循环井强化过硫酸盐在低渗透含水层中的方向性迁移

Groundwater circulation wells enhance the directional delivery of persulfate in low-permeability aquifers

原位化学修复技术在地下水环境中存在注入困难、扩散速度缓慢、扩散范围有限、扩散方向性不明等问题,很大程度上限制了其在实际修复工程中的效能。地下水循环井(GCW)作为一种人为水力调控技术在耦合强化原位化学注入技术的修复效率方面具有潜力。采用一维砂柱实验、二维砂箱实验和数值模拟相结合的方法,探讨了GCW驱动下修复剂的迁移过程。选用过硫酸盐(PS)作为修复剂,研究了修复剂浓度和循环井工艺参数(循环模式和循环流速)、低渗透介质(高岭石和伊利石)对GCW增强修复剂迁移的影响。结果表明,正向循环模式有利于PS实现均匀分布,能显著提升PS的迁移速率,而逆向循环模式能使PS相对集中于靠近循环井的位置;提升循环流速有助于提升PS在横向及垂向上的迁移速率,但高循环流速会导致PS浓度分布变化幅度较大,也增加了修复过程的不稳定性;初始浓度越高,有效扩散系数越大,越有利于过硫酸盐由高浓度向低浓度扩散;循环井能形成一个与低渗透区域正交的水力梯度以减弱低渗透介质对PS迁移的阻碍,其产生的流量能促使PS沿垂直于低渗透介质的方向发生垂向迁移。研究成果为受污染低渗透区域的原位高效修复提供了新的解决方案。

In situ chemical remediation technology has many problems in groundwater environment,such as difficult injection,slow diffusion speed,limited diffusion range and unclear diffusion direction,etc.,to a great extent,it has limited its effectiveness in actual restoration projects.Groundwater circulating wells(GCW),as a kind of artificial hydraulic control technology,have potential in the remediation efficiency of coupling enhanced in situ chemical injection technology.One-dimensional sand column experiment,two-dimensional sandbox experiment and numerical simulation were used to investigate the delivery process of GCW-driven reagent.Persulfate(PS)was selected as the repairing agent,the effects of the concentration of GCW reinforcements and the process parameters of circulating wells(circulation mode and flow rate)and low permeability media(kaolinite and illite)on the migration of GCW reinforcements were studied.The results showed that the forward circulation mode was beneficial to the uniform distribution of PS and can significantly increase the delivery rate of PS,while the reverse circulation mode can make PS relatively concentrated near the circulation wells.However,the higher the circulating velocity,the greater the variation of PS concentration distribution and the instability of the repair process.The higher the initial concentration,the greater the effective diffusion coefficient,which was more conducive to the diffusion of persulfate from high concentration to low concentration.GCW can form a hydraulic gradient with orthogonal to the low permeability zone to weaken the obstruction of PS delivery.The research results provide a new solution for in situ high-efficiency remediation of contaminated low permeability areas.