Experimental and simulation investigations of UV/persulfate treatment in presence of bromide: Effects on degradation kinetics, formation of brominated disinfection byproducts and bromate

Bromide (Br − ), which is omnipresent in water bodies, can not only affect the degradation kinetics of target pollutants but may also form undesired byproducts (such as bromate ( BrO 3 - ${\text{BrO}}_{\text{3}}^{-}$ ) and brominated disinfection byproducts (Br-DBPs)) through sulfate radical ( SO 4 ∙ - ${\text{SO}}_{\text{4}}^{\bullet -}$ )-based advanced oxidation processes (AOPs). This study found that Br − significantly suppressed the degradation of diethyl phthalate (DEP) based on the ultraviolet (UV)/persulfate (PS) treatment and was efficiently converted into reactive species (radicals and free bromine) by the SO 4 ∙ - ${\text{SO}}_{\text{4}}^{\bullet -}$ or hydroxyl radical (HO ) generated in the UV/PS system. These reactive bromine species could, in turn, brominate the phenolic degradation intermediates of DEP as well as natural organic matter (NOM), yielding Br-DBPs, including tribromomethane (TBM), which was observed when Br − , DEP and/or NOM coexisted in this UV/PS system. However, the Br-DBPs were a short-lived form of bromine during the transformation of Br – and were degraded by the excessive oxidants (e.g., S O 4 ∙ - $\text{S}{\text{O}}_{\text{4}}^{\bullet -}$ and HO ). Instead, Br − was eventually transformed into BrO 3 - ${\text{BrO}}_{\text{3}}^{-}$ , with free bromine acting as the requisite intermediate. The BrO 3 - ${\text{BrO}}_{\text{3}}^{-}$ formation initially showed a delay before increasing monotonically. In general, raising the PS dosage and the initial Br − concentrations enhanced both the maximum concentration of TBM and the formation of BrO 3 - ${\text{BrO}}_{\text{3}}^{-}$ , while increasing the amounts of DEP and NOM facilitated the former and inhibited the latter. The maximum concentration of TBM increased while the formation of BrO 3 - ${\text{BrO}}_{\text{3}}^{-}$ was suppressed with increasing pH from 5.0 to 8.0. In addition, through simulating the steady-state concentration of radicals, it was found that the contribution of bromine atom radical (Br ) towards oxidizing free bromine to BrO 3 - ${\text{BrO}}_{\text{3}}^{-}$ was far greater than those of S O 4 ∙ - $\text{S}{\text{O}}_{\text{4}}^{\bullet -}$ and HO . The findings demonstrate the potential negative effects of Br − on SO 4 ∙ - ${\text{SO}}_{\text{4}}^{\bullet -}$ -based AOPs, which need to be considered when this technology is applied in practice.