Integration of electrokinetics and chemical oxidation for the remediation of creosote-contaminated clay

Remediation of clayey soils that are contaminated with polycyclic aromatic hydrocarbons (PAHs) is a challenging task that may require integration of several technologies. The benefits of integrating in situ electrokinetic remediation with chemical oxidation were evaluated in laboratory-scale experiments lasting for 8 weeks. A voltage gradient of 48 V/m of direct current and 4.7 V/m of alternating current and periodic additions of chemical oxidants were applied to creosote-contaminated soil. Electrokinetically enhanced oxidation with sodium persulphate resulted in better PAH removal (35%) than either electrokinetics (24%) or persulphate oxidation (12%) alone. However, the improvement was shown only within 1/3 (5 cm) of the soil compartment. Electrokinetics did not improve the performance of Fenton oxidation. Both chemical oxidants created more positive oxidation–reduction potential than electrokinetic treatment alone. On the other hand, persulphate treatment impaired the electroosmotic flow rate. Elemental analyses showed reduction in the natural Al and Ca concentrations, increase in Zn, Cu, P and S concentrations and transfer of several metal cations towards the cathode. In conclusion, the results encourage to further optimisation of an integrated remediation technology that combines the beneficial effects of electrokinetics, persulphate oxidation and Fenton oxidation.