Investigation of Chemical Enhancers and Physical Constraints in Electrokinetic Remediation of Low-Permeability Soil Contaminated by PAHs and TPH

The remediation of low-permeability clay soils co-contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) and Total Petroleum Hydrocarbons (TPH) remains a significant environmental challenge. Traditional Electrokinetic Remediation (EKR) is fundamentally constrained by the high hydrophobicity of these contaminants and strong matrix adsorption, which severely limit their aqueous solubility and mobility. This study systematically investigated the combined effects of critical operating parameters, chemical amendments, and physical constraints on the efficiency of Surfactant-Enhanced EKR (SE-EKR) for a highly contaminated clay matrix. A suite of batch tests was performed to optimize EKR conditions. Key findings demonstrated that operating parameters exert a crucial influence on both current dynamics and contaminant removal. Acidic conditions (pH 4.5) were optimal, yielding the highest average removal rate of 70.97% for 12 target contaminants, primarily driven by the high mobility of H<sup>+</sup> ions which significantly boosted electrical current. This elevated current led to increased Joule heating (accelerating VOC volatilization) and enhanced oxidative capacity (improving PAH degradation). The use of the composite electrolyte EDTA further improved performance, achieving 69.29% removal by increasing overall conductivity and effectively solubilizing and desorbing highly adsorbed SVOCs (e.g., Benzo[a]anthracene removal reached 82.41%). Furthermore, increasing the voltage gradient to 2.0 V/cm maximized removal at 73.42%, confirming the importance of electromigration and electrochemical oxidation for persistent pollutants. The incorporation of Activated Carbon (AC) increased the system current by 14.3% and enhanced PAH removal, functioning as a 3D particulate electrode that established internal electron conduction pathways and localized redox reaction sites within the low-conductivity clay. Comparing chemical enhancers, SDBS demonstrated superior solubilization and removal efficiency over Alpha Olefin Sulfonate (AOS), likely due to favorable π-π stacking interactions with PAHs. Finally, the simulation of non-conductive subsurface infrastructure demonstrated its role as a physical constraint, disrupting electroosmotic flow pathways, reducing current, and successfully preventing the severe local contaminant accumulation observed in the EKR control. This research provides essential insights into developing robust, field-applicable strategies for EKR by emphasizing the combined necessity of optimized chemical control and mitigation of physical constraints.