Rapid DDTs degradation by thermally activated persulfate in soil under aerobic and anaerobic conditions: Reductive radicals vs. oxidative radicals.

Persulfate (PS)-based oxidation technologies have been extensively employed for contaminant remediation, but the mechanisms of PS-mediated pollutant removal in soil under anaerobic conditions have not been fully explored. In this study, the degradation of DDTs (DDT and DDE) by thermally activated PS in a real contaminated soil was investigated. It was found that DDTs degradation could be achieved under both aerobic and anaerobic conditions, and anaerobic conditions were comparatively more efficient. Further analyses based on electron paramagnetic resonance (EPR), free radical quenching studies and degradation product identification showed that, oxidative radicals (SO/OH) were the major species responsible for DDTs degradation under aerobic conditions, while both reductive (persulfate radical SO) and oxidative radicals were involved under anaerobic conditions. Furthermore, reductive degradation of DDT could also be observed in the presence of ethanol (EtOH) due to the formation of EtOH radical. In addition, DDT degradation was hardly affected by anions such as HCO and Cl at anaerobic conditions while its degradation was greatly inhibited by these anions under aerobic conditions. This study significantly improved our knowledge of PS-mediated degradation processes of DDTs and provided new insight into soil remediation by in-situ chemical oxidation at different oxygen status.