Remediation of an aged PCP-contaminated soil by chemical oxidation under flow-through conditions

In this study the oxidation of pentachlorophenol (PCP) in an aged contaminated soil was performed under both water-unsaturated and water-saturated conditions using potassium permanganate (PM), potassium persulfate (PS) and hydrogen peroxide (HP). Overall, the results of PCP removal extent and oxidant decomposition indicated that the water content in column has no significant impact on the oxidation performance. The increase in flow rate from 0.025 to 2.5 mL min−1 decreased the oxidant decomposition as well as the PCP degradation extent, except for HP that is highly reactive. Kinetic limitations in column may explain the effect of residence time of oxidant on the degradation performance. Consistently, re-circulation of oxidant solutions in a closed loop system improved the oxidation efficiency and oxidant decomposition extents in case of PS and PM, but not for HP. Surprisingly, attempts to enhance the PCP availability in soil by using solubility agents or by heating did not improve the degradation efficiency in soil. The presence of methyl-β-cyclodextrin (M-β-CD) affects only the decomposition rate of HP, which is positively correlated with M-β-CD concentration. High persistence of HP could be advantageous where delivery of oxidants to zone-source of contamination can be limited by their high reactivity. Collectively, these results may have strong implications for the application of chemical oxidation under field conditions, particularly where oxidant injection mode in saturated or unsaturated zones is crucial in determining the remediation performance.