Oxidation of 2,4-bromophenol by UV/PDS and formation of bromate and brominated products: A comparison to UV/H2O2.

Graphical abstract Highlights • UV/PDS is proposed to be unsuitable for treatment of bromophenols compared to UV/H 2 O 2. • Brominated polymeric products can be formed in UV-based oxidation process. • BrO 3 − evolution in the degradation of 2,4-DBP by UV/PDS exhibited biphasic kinetics. Abstract The sustained massive use of bromophenols in industrial products leads to their especially pernicious in aquatic environments. This study explored the oxidation kinetics of 2,4-bromophenol (2,4-DBP) and formation potential of bromate (BrO 3 −) and brominated polymeric products of concern during water treatment by UV/persulfate (PDS) and UV/hydrogen peroxide (H 2 O 2). 2,4-DBP exhibited appreciable reactivity toward sulfate radical (SO 4 −) and hydroxyl radical (HO). The second-order rate constants of SO 4 − and/or HO with 2,4-DBP at pH 9 were higher than those at pH 5 and 7. It is mainly due to the deprotonation of the hydroxyl group in 2,4-DBP when pH > pKa (pKa = 7.79). The chloride ions (Cl−) significantly inhibited 2,4-DBP degradation in UV/PDS process, which showed little inhibition in the UV/H 2 O 2 process. Carbonate/bicarbonate (CO 3 2−/HCO 3 −) and natural organic matters (NOM) significantly retarded 2,4-DBP degradation in both processes. BrO 3 − formation in UV/PDS process in the presence of 2,4-DBP (as organic carbon model compound) exhibited biphasic kinetics, i.e., BrO 3 − was undetectable in the lag phase and rapid generated in the secondary rapid phase. However, BrO 3 − was not detected throughout UV/H 2 O 2 process. According to the analysis by electrospray ionization-triple quadruple mass spectrometry, tentative oxidation pathway was proposed. The results showed that brominated polymeric products in the reaction of 2,4-DBP with SO 4 − and/or HO were readily produced by electrophilic addition and coupling reactions. Given the enhanced toxicological effects of these BrO 3 − and brominated polymeric products compared with the bromophenols precursors, it is important to better understand their reactivities and fates when UV/PDS or UV/H 2 O 2 is applied for the oxidative treatment of bromophenols-containing waters. [ABSTRACT FROM AUTHOR]