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

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 (BrO₃⁻) and brominated polymeric products of concern during water treatment by UV/persulfate (PDS) and UV/hydrogen peroxide (H₂O₂). 2,4-DBP exhibited appreciable reactivity toward sulfate radical (SO₄⁻[rad]) and hydroxyl radical (HO[rad]). The second-order rate constants of SO₄⁻[rad] and/or HO[rad] 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/H₂O₂ process. Carbonate/bicarbonate (CO₃²⁻/HCO₃⁻) and natural organic matters (NOM) significantly retarded 2,4-DBP degradation in both processes. BrO₃⁻ formation in UV/PDS process in the presence of 2,4-DBP (as organic carbon model compound) exhibited biphasic kinetics, i.e., BrO₃⁻ was undetectable in the lag phase and rapid generated in the secondary rapid phase. However, BrO₃⁻ was not detected throughout UV/H₂O₂ 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 SO₄⁻[rad] and/or HO[rad] were readily produced by electrophilic addition and coupling reactions. Given the enhanced toxicological effects of these BrO₃⁻ and brominated polymeric products compared with the bromophenols precursors, it is important to better understand their reactivities and fates when UV/PDS or UV/H₂O₂ is applied for the oxidative treatment of bromophenols-containing waters.