Inhibition effect of chlorine ion on hydroxyl radical generation in UV-H₂O₂ process

UV-H₂O₂ process is widely used as an advanced oxidation process (AOP) for the treatment of chlorine volatile organic compounds (CVOCs) such as dichloromethane (DCM) with strong oxidativity of hydroxyl radical generated from photolysis of H₂O₂. The result of DCM degradation rate at different initial concentrations in UV-H₂O₂ processes indicated the inhibition effect of produced chlorine ions on DCM oxidation processes, because the first-order degradation rate constant increased with lower initial concentrations. A spin trapping adduct of hydroxyl radical with 5,5-dimethyl-1-pyrroline-n-oxide (DMPO) was quantified by ESR spectrometer after UV irradiation in the presence of different amounts of chlorine ion, and as a result, the chlorine ion was found to act as a hydroxyl radical scavenger, which resulted in decreasing DCM degradation rate. An UV-H₂O₂ reactor equipped with ion exchangers for removing chlorine ion achieved higher DCM degradation rate than that without ion exchangers.