Promoting uniform distribution of persulfate and surfactant via electrokinetic delivery for remediation of low-permeability PAHs-contaminated soil: Critical importance of reverse electroosmotic flow and soil Joule heating

During conventional electrokinetic remediation, the decay, stagnation, and partial reversal of electroosmotic flow (EOF) caused non-uniform delivery of persulfate (PS), resulting in high-concentration residual of PAHs in localized regions. Simultaneously, controlled in-situ activation of PS and limited mixing with soil-adsorbed PAHs hindered the remediation efficacy. Herein, we proposed an innovative strategy that inducing complete reverse electroosmotic flow (REOF) to enhance electrokinetic co-delivery of PS and surfactant, coupled with subsequently in-situ thermal activation via heating tubes for remediating PAHs-contaminated soil. This strategy facilitated severe soil Joule heating, concurrently transported and activated PS during electrokinetic delivery, which ensured the acidification of the pore solution to induce complete REOF. More stable REOF made PS distribution uniform and high-concentration in contaminated regions after electrokinetic delivery. Following in-situ thermal activation of PS by soil Joule heating and rod-shaped heating tubes, the total removal of phenanthrene (PHE, 500 mg/kg) reached 96%. Batch degradation experiments demonstrated that SDBS promoted the mixing of soil-adsorbed PHE with thermally activated PS or derived reactive oxygen species (ROS) through solubilization and mobilization, thereby enhancing PHE degradation. Hence, the addition of SDBS in electrolytes promoted the desorption of soil-adsorbed PHE, elevating the total removal to 98.80%. Lastly, the efficiency of the proposed remediation strategy was validated on historically multicomponent PAHs-contaminated soil (349.95 mg/kg), achieving a satisfactory removal of 62.54%. • OH, SO 4 •− and 1 O 2 derived from PS activation were identified as dominant reactive oxygen species for degrading PAHs. This work presents considerable potential for site-scale remediation of PAHs-contaminated soils with low permeability.