Generation, activation, and recycling of ammonium persulfate for the remediation of organic-contaminated soil: System construction, process, and mechanisms

Persulfate advanced oxidation processes (PS-AOPs) are among the most promising methods of remediating organic-contaminated soil. However, the application of this technology is restricted by high costs associated with the single use of large amounts of PS and great environmental risks associated with the accumulation of sulphate in the soil after remediation. Therefore, in this study, we proposed and tested a circulation system for soil remediation that more efficiently activates and regenerates PS. By using porous carbon felts as ‘flow-though’ electrodes, a high concentration of PS was generated in the carbon anode and then co-activated by electrons and carbon in the carbon cathode. In this process, electron transfer, rather than mass transport, was revealed as the rate-controlling step. Soil remediation experiments indicated that non-radical oxidation with carbon-activated, transition-state PS* and radical oxidation with SO4−∙ and ∙OH collectively contribute to the degradation of naphthalene in organic-contaminated soil. By analysing the mechanism of competition between PS regeneration and reactions involving soil impurities in the carbon anode, it was found that leached organic pollutants were degraded in a timely manner when passing through the carbon anode, with negligible impact on PS regeneration. Finally, this system demonstrated high stability and wide applicability, based on the characterisation of electrodes and evaluation of environmental impact parameters. These findings provide a theoretical and practical basis for reducing the application cost and ecological risk of PS-AOPs in the remediation of organic-contaminated soil.