Effects of Periodic Electric Potential and Electrolyte Recirculation on Electrochemical Remediation of Contaminant Mixtures in Clayey Soils

This paper investigates the operational factors that affect an integrated electrochemical remediation (IECR) process for the degradation and removal of both organic and heavy metal contaminants in low permeability soils. IECR aims to degrade the organic contaminants through chemical oxidation process and at the same time remove the heavy metals through electromigration. Hydrogen peroxide is used as an oxidant which is transported into the soil by the electroosmotic flow. The natural iron in the soil acts as a catalyst for the decomposition of hydrogen peroxide in a Fenton-like process. Kaolin soil was used as model low permeability soil. Soil was polluted with phenanthrene and nickel at concentrations of 500 mg/kg each. Experiments were carried out at a constant voltage gradient of 1 VDC/cm using 10 % H2O2 as a flushing solution at the anode. The use of periodic voltage gradient and the recirculation of the cathodic solution to the anode favored the electroosmotic flow and the contaminant removal. Phenanthrene was eliminated from the soil in an average value of 30%. Though electroosmotic flow was registered in all the experiments, negligible amount of phenanthrene was detected in the electrode solutions, confirming that the removal of phenanthrene is due to chemical oxidation. Nickel was solubilized and transported towards the cathode, but it was accumulated in the close vicinity of the cathode due to the high pH. Overall, this study showed that IECR has potential to remediate soils contaminated by both organic compounds and heavy metals.