Insight into the degradation mechanism of peroxyacetic acid for pentachlorophenol by thermal activation in soil system

In this study, inorganic and organic radicals generated from a thermally activated peroxyacetic acid (PAA) system were used to degrade pentachlorophenol (PCP) in contaminated soils. In addition, the effects of various operating parameters on PCP removal were fully considered, including reaction temperature, PAA dosage, initial pH and natural organic matter (NOM). The experimental results showed that PCP was more easily degraded under the conditions that temperature was higher than 40 °C and near neutral pH, and PAA dosage was more than 750 mM/kg. In contrast, humic acid (HA) exhibited a significant inhibitory impact on PCP degradation. The results from the chemical quenching and electron para-magnetic resonance (EPR) experiments further indicated that in the PAA system, HO• has much better degradation ability for PCP than 1O2. Moreover, the degradation of PCP was dominated by R-O• radicals, including CH3C(O)O• and CH3C(O)OO•. Besides, the potential degradation pathways of PCP by PAA system were investigated, based on the degradation intermediates and the density functional theory (DFT) calculation. The present study results indicated that the combined process of PAA and heat treatment has a significantly high efficiency in the degradation of chlorobenzenes in soils. This study is the first to use thermally activated PAA for soil remediation without the use of other chemicals as activators, and provides a novel, efficient and economical technique for the remediation of actual chlorinated hydrocarbon contaminated sites.