Efficient chlorinated alkanes degradation in soil by combining alkali hydrolysis with thermally activated persulfate

Alkali activation is the most commonly used activation method for persulfate (PS) in in-situ remediation. However, the role of alkali in pollutant degradation is still elusive, limiting the optimization of relevant remediation strategies. In this study, we found that chlorinated alkanes (e.g., tetrachloroethane (TeCA)) could be efficiently degraded by thermal-alkali activation of PS. The main role of alkali was not activating PS but hydrolyzing the chlorinated alkanes, which was evidenced by the immediate conversion of TeCA into trichloroethylene (TCE) with NaOH and PS or with sole NaOH solution. Electron paramagnetic resonance analysis also showed that with a high NaOH/PS molar ratio (4:1) the intensity of oxidative radicals decreased, implying that high levels of alkali did not favor the formation of free radicals. Interestingly, better degradation of TeCA and its product TCE was observed by the combination of alkaline hydrolysis and thermal activation of PS (where alkali was added 6 h before PS rather than simultaneously) in comparison to thermal-alkali activation of PS. This study provides new insights into the remediation of chlorinated alkane-contaminated soils by in-situ chemical oxidation.