Mechanistic insights into chlorinated hydrocarbons degradation with bromide ion presence in hydrogen peroxide and persulfate-based systems

In this work, the effect of bromide ion (Br–) on 1,2,3-trichloropropane (TCP) and trichloroethylene (TCE) degradation in hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and peroxydisulfate (PDS) oxidation processes was investigated. In ultrapure water, 100 %, 90 %, and 47.2 % TCE could be removed in H2O2/Fe(II), PMS/Fe(II), and PDS/Fe(II) systems within 60 min at selected dosages, respectively, while only H2O2/Fe(II) system was efficient for TCP removal (82.5 %). Compared with TCE, the negative effect of Br– on TCP removal was more obvious due to the poor TCP degradation by reactive halogen species. Besides, hydroxy radical (HO•)-based system (H2O2/Fe(II)) was more sensitive to Br– than sulfate radical (SO4–•)-based systems (PMS/Fe(II) and PDS/Fe(II)), because HO• was prone to react with Br– with a greater reaction rate constant. In the presence of Br–, the addition of citric acid or zero-valent iron (ZVI) promoted TCP and TCE degradation in SO4–•-mediated systems, while TCP and TCE removal in HO•-based system could be slightly enhanced by ZVI. In actual groundwater tests, both pre-adjusting solution pH to acidity for TCE removal in HO•-driven system and increasing chemical dosages in SO4–•-based systems could effectively degrade the target pollutants in the presence of Br–.