Insights into carbon isotope fractionation on trichloroethene degradation in base activated persulfate process: The role of multiple reactive oxygen species

Highlights: • The ε values of TCE were found to be dependent of the base:persulfate molar ratios. • Carbon isotope fractionation characterized TCE degradation by O₂⁻. • HO and O₂⁻ were the predominant ROS for TCE degradation in base activated PS. • CSIA offers an alternative to evaluate roles of ROS for contaminants degradation. Understanding the role of reactive oxygen species (ROS) is essential to elucidate the mechanism of contaminants degradation in in-situ chemical oxidation (ISCO). In this study, compound specific isotope analysis (CSIA) and radicals quenching methods were integrated to investigate the roles of hydroxyl radical (HO), sulfate radical (SO₄⁻), and superoxide radical (O₂⁻) on trichloroethene (TCE) degradation during persulfate (PS) activated with base. The carbon isotope fractionation of TCE was found to be dependent of the base:PS ratios, yielding carbon enrichment factors (ε values) from −9.8 ± 0.5‰ to −16.7 ± 1.0‰ at base:PS molar ratios between 0.5:1 and 10:1, which was attributed to multi-pathways degradation of TCE by multiple ROS. The expected ε value (−31.6 ± 1.6‰) for TCE degradation via O₂⁻ attacking pathway, was more negative than those values via SO₄⁻ or HO pathways. The relative contributions of HO, SO₄⁻ and O₂⁻ for TCE degradation during base activated PS were estimated with observed ε values. HO and O₂⁻ were the predominant ROS for TCE degradation (with the relative contribution of 55–69% and 22–45%, respectively) in base activated PS. This work highlights the prospect of CSIA application for identifying degradation pathways of contaminants with ROS in environment.