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

Abstract

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.

Keywords: Compound specific isotope analysis (CSIA); In-situ chemical oxidation (ISCO); Persulfate; Reactive oxygen species (ROS); Superoxide radical.