Field test of electrokinetically-delivered thermally activated persulfate for remediation of chlorinated solvents in clay

Ahmed, S., Gerhard, J.I., Inglis, A.M., Nunez Garcia, A., Chowdhury, A.I.A., Reynolds, D.A., de Boer, C.V., Sidebottom, A., Austrins, L.M., Eimers, J., O'Carroll, D.M

Published in ‘Water Research’

Abstract

In situ chemical oxidation (ISCO) has demonstrated success in remediating soil and groundwater contaminated with chlorinated volatile organic compounds (CVOCs). However, its performance is often hindered in low-permeability or heterogeneous media due to an inability to effectively deliver the oxidants. This field-scale study investigated the novel approach of applying electrokinetics (EK) to enhance the delivery of persulfate in a low-permeability media and the ability of electrical resistance heating (ERH) to thermally activate the delivered persulfate. Results showed that 40% of the mass of total sulfur delivered was due to EK mechanisms, demonstrating that EK has the potential to enhance oxidant delivery. ERH may have activated some of the persulfate, but catalytic reactions with reduced forms of iron likely resulted in appreciable persulfate decomposition prior to ERH. Significant decreases (>80%) in the aqueous concentration of CVOCs was observed before and after ERH initiation, attributed to in situ transformation and physical processes (e.g., dilution). In situ transformation of CVOCs was assessed by compound-specific isotope analysis (CSIA) of 1,2-dichloroethane (1,2-DCA) samples collected after ERH application. Enrichment of 13C was only measured in the well with appreciable persulfate breakthrough, confirming dechlorination of 1,2-DCA. Results from this field study demonstrate that EK and ERH can be used for persulfate delivery and activation for remediation of CVOCs in low-permeability media.