Reductive Hexachloroethane Degradation by S2O8•– with Thermal Activation of Persulfate under Anaerobic Conditions

Despite that persulfate radical (S2O8•–) is an important radical species formed from the persulfate (PS) activation process, its reactivity toward contaminant degradation has rarely been explored. In this study, we found that S2O8•– efficiently degrades the contaminant hexachloroethane (HCA) under anaerobic conditions, whereas HCA degradation is negligible in the presence of oxygen. We observed dechlorination products such as pentachloroethane, tetrachloroethylene, and Cl– during HCA degradation, which suggest that HCA degradation is mainly a reductive process under anaerobic conditions. Using free radical quenching and electron paramagnetic resonance (EPR) experiments, we confirmed that S2O8•– forms from the reaction between sulfate radical (SO4•–) and S2O82–, which are the dominant reactive species in HCA degradation. Density functional theory (DFT) calculations were used to elucidate the pathways of HCA degradation and S2O8•– radical decomposition. Further investigation showed that S2O8•– can efficiently degrade HCA and DDTs in soil via reduction during the thermal activation of PS under anaerobic conditions. The finding of this study provide a novel strategy for the reductive degradation of contaminant when PS-based in situ chemical oxidation used in the remediation of soil and groundwater, particularly those contaminated with highly halogenated compounds.