Thermal assisted heterogeneous activation of peroxymonosulfate by activated carbon to degrade perfluorooctanoic acid in soil

Abstract

The chemical degradation of perfluorooctanoic acid (PFOA), an –environmentally persistent contaminant, has recently attracted much attention. Still, very few reports have focused on the degradation of PFOA in soil due to the process’s non-liquid, complex system and uneasy operation. In this study, thermal treatment was applied in the remediation of PFOA contaminated soil. Complementary to thermal activation of peroxymonosulfate (PMS), fresh activated carbon (FAC) and modified activated carbon (NAC), which were used as heterogeneous catalysts, were incorporated into the system to promote the production of sulfate radicals (SO4•−) and the diminution of PFOA in soil. Two portions of soils, both homogenous but one with and the other without natural organic carbon (OC), were provided to study the impact of OC on the elimination of PFOA in soil. The degradation of PFOA was initiated using the combined methods in cohesion with heat activation. During the process, the effect of temperature, the dosing amount of catalyst and oxidant, the reaction time and the volume ratio between soil and solution on the degradation of PFOA in soil were fully studied and optimized. The results showed that over a 12 h period, a PFOA (1.0 mg/kg) removal of 76% and 70% by using FAC/PMS and NAC/PMS respectively could be achieved at 60 °C. Furthermore, density functional theory (DFT) calculations were combined with experimental data and verify that the adsorption ability of both FAC and NAC for PFOA are 3 times stronger than that of soil grain. This greater adsorption can attract PFOA molecules from within soil and provide opportunities for interactions with oxidative radicals. This work sheds light on a much over-looked aspect of advanced oxidation of PFOA in soil systems, which might provide a potential option for the in-situ remediation of PFOA contaminated soil in the future.