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

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 (O-2 .-) 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 (e 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 e value (-31.6 +/- 1.6%) for TCE degradation via O-2.- attacking pathway, was more negative than those values via SO4.- or HO. pathways. The relative contributions of HO., SO4.- and O-2.- for TCE degradation during base activated PS were estimated with observed e values. HO. and O-2.- 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. (C) 2021 Elsevier B.V. All rights reserved.