Oxidation of tetrabromobisphenol A (TBBPA) by peroxymonosulfate: The role of in-situ formed HOBr.

The degradation of tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardant, was evaluated during peroxymonosulfate (PMS) oxidation. TBBPA degradation was pH-dependent, with peak degradation rate constants occurring at pH 8.0-9.0, which was distinct from some other phenolic compounds. Singlet oxygen and radicals were found to play negligible roles in TBBPA degradation. TBBPA oxidation by PMS mainly proceeded via a direct oxidation pathway and the in-situ formed HOBr was found to greatly accelerate its degradation rates. The values of species-specific second-order rate constants for the reactions of PMS with the TBBPA kHSO5-+TBBPA, kHSO5-+TBBPA- and kHSO5-+TBBPA2- were determined to be (1.11 ± 0.84) × 10-2, (8.05 ± 2.31) × 10-2, and (1.34 ± 0.25) × 10-1 M-1 s-1, respectively, while the reaction rate constants for HOBr/OBr- with TBBPA kHOBr+TBBPA, kHOBr+TBBPA-, kHOBr+TBBPA2-and kOBr-+TBBPA2- were determined to be (9.38 ± 2.10) × 103, (1.59 ± 0.56) × 105, (8.22 ± 0.41) × 106, and (1.81 ± 0.12) × 106 M-1 s-1, respectively. The bromine mass balance analysis showed that bromide ion and HOBr/OBr- occupied 19.5% of total Br and brominated organic compounds accounted for the remaining percentages at pH 7.0. No formation of bromate was observed. Based on the identified products, a reaction pathway was proposed, which included oxidation, β-scission, hydroxylation, and dimerization reaction pathways. The results indicate that unactivated PMS is useful for the remediation of TBBPA contaminated water.