Roles of hydroxyl and sulfate radicals in degradation of trichloroethene by persulfate activated with Fe2+ and zero-valent iron: Insights from carbon isotope fractionation

Abstract

Active species including hydroxyl (HO) and sulfate radicals (SO4−) play important roles in contaminant degradation during the persulfate based in-situ chemical oxidation (ISCO) process. The generation and contribution of active species are critical and can potentially be evaluated using compound specific isotope analysis (CSIA). However, the evaluation of stable isotope fractionation (or isotope enrichment factor ε values) for contaminants degraded by individual active species of concern is required but lacking. This study firstly determined the carbon isotope fractionation of trichloroethene (TCE) degradation by SO4·− with chemical probe methods to obtain ε values from −6.4±0.7 to −6.9±0.5‰. The ε values were significantly different from those reported for TCE degradation by HO, which could be used to identify the competing TCE degradation by HO and SO4−. Relying on the observed ε values and the extended Rayleigh-type equation, the contributions of SO4− and HO to TCE degradation were evaluated in persulfate activated by Fe0 or Fe(II). This study provides an illuminating idea to determine stable isotope fractionation for contaminant degradation by individual active species, which is crucial for the application of CSIA in relevant environments.