The bromate formation accompanied by the degradation of 2,4-bromophenol in UV/peroxymonosulfate

This study explored the degradation kinetics of 2,4-bromophenol (2,4-DBP) and the fate of bromine affected by different water matrix (i.e., dissolved organic matter (DOC), chloride ions (Cl⁻)) and operation conditions (i.e., peroxymonosulfate (HSO₅⁻) dosage, 2,4-DBP concentration, and solution pH) in UV/HSO₅⁻ process. Results showed that there was a linear positive correlation between the apparent pseudo-first order rate constant of 2,4-DBP degradation (k_obs) and HSO₅⁻ dosage. The k_obs decreased as the initial 2,4-DBP concentrations increased, and significantly increased by raising the pH value from 5 to 9. The presence of Cl⁻ had negligible effect on the degradation of 2,4-DBP in UV/HSO₅⁻ process, while DOC showed the remarkable inhibitory effect. In addition, results indicated that the formation of bromate (BrO₃⁻) from 2,4-DBP oxidation exhibited biphasic kinetics under various conditions (i.e., BrO₃⁻ was undetectable in the lag phase and rapidly generated in the secondary phase). The yield of BrO₃⁻ increased up to 100% when HSO₅⁻ dosage was higher than 500 μM. The longer lag-phase of BrO₃⁻ formation was observed when the initial 2,4-DBP concentration increased from 1 μM to 10 μΜ, while the formation rate and concentration of BrO₃⁻ were promoted. The lag phase of BrO₃⁻ formation at pH 5 was shorter than that at pH 7 (i.e., 0 min vs 5 min), while no BrO₃⁻ was detected at pH 9. The presence of Cl⁻ (1–5 mM) suppressed BrO₃⁻ formation significantly. DOC could scavenge the generated HOBr/OBr⁻ and bromine atom (Br·) to inhibit the yield of BrO₃⁻. This study suggested that bromophenols could be degraded effectively by UV/HSO₅⁻ process, whereas the great potential of BrO₃⁻ formation should be paid attention to during advanced oxidation of bromine-containing aromatic compounds.