State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, 430072, China; Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering of the Ministry of Education, Wuhan University, Wuhan, 430072, China.
State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, 430072, China; Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering of the Ministry of Education, Wuhan University, Wuhan, 430072, China.
Chemosphere. 2023 Nov;341:140071. doi: 10.1016/j.chemosphere.2023.140071. Epub 2023 Sep 4.
Surfactant-enhanced aquifer remediation has been proved successful to remove dense non-aqueous phase liquids (DNAPLs) from contaminated sites. However, the underlying mechanisms of the DNAPL mobilization and solubilization at the pore scale remains to be addressed for efficient application to the field remediation system. In this work, the emerging microfluidic and imaging technologies are applied to investigate the dynamics of DNAPL remediation. Visualized experiments of the evolution of DNAPL remediation are performed to study the role of surfactant type, concentration and injection rate. The DNAPL remediation is dominated by mobilization followed by solubilization for most surfactants. Mobilization occurs as soon as surfactants and DNAPL are in contact until forming a new stable phase structure, and the solubilization continues until the end of injection. We observe the breakup behavior of long droplets and ganglia during the mobilization, which is attributed to the surfactant-reduced interfacial tension and thus expedites DNAPL mobilization and redistribution. During the solubilization, the formation of micelles incorporating DNAPL fractions increases the DNAPL concentration gradient and thus enhances the mass transfer, but the rate-limited diffusion of micelles reduces the mass transfer rate coefficient. Increasing the surfactant content and decreasing the injection rate can promote mobilization and solubilization. The DNAPL mobilization ability of the surfactants SDS and SDBS is stronger than SAOS and Tween 80 regardless of the injection rates. Tween 80 may be considered an ideal surfactant of only solubilization but not mobilization is desired. This work elucidates the pore-scale mechanisms during surfactant-enhanced DNAPL remediation, which are beneficial for upscaling studies, predictive modeling, and operation optimization of DNAPL remediation in the field.
表面活性剂强化含水层修复已被证明可成功去除受污染场地中的致密非水相液体 (DNAPL)。然而，为了将其有效地应用于现场修复系统，仍需要解决 DNAPL 在孔隙尺度上的迁移和增溶的基本机制。在这项工作中，新兴的微流控和成像技术被应用于研究 DNAPL 修复的动力学。进行了 DNAPL 修复演化的可视化实验，以研究表面活性剂类型、浓度和注入速率的作用。对于大多数表面活性剂，DNAPL 修复主要由迁移 followed 增溶作用主导。只要表面活性剂和 DNAPL 接触，就会发生迁移，直到形成新的稳定相结构，并且增溶作用会持续到注入结束。我们观察到在迁移过程中长液滴和液滴聚集体的断裂行为，这归因于表面活性剂降低的界面张力，从而加速了 DNAPL 的迁移和重新分布。在增溶过程中，包含 DNAPL 部分的胶束的形成增加了 DNAPL 浓度梯度，从而增强了传质，但胶束的受限扩散降低了传质速率系数。增加表面活性剂含量和降低注入速率可以促进迁移和增溶作用。无论注入速率如何，SDS 和 SDBS 这两种表面活性剂的 DNAPL 迁移能力都强于 SAOS 和 Tween 80。如果不希望发生迁移而只希望发生增溶作用，则可以考虑使用 Tween 80。这项工作阐明了表面活性剂强化 DNAPL 修复过程中的孔隙尺度机制，这有利于对现场 DNAPL 修复的放大研究、预测建模和操作优化。
