Degradation of bisphenol A by UV/persulfate process in the presence of bromide: Role of reactive bromine

Bromide (Br-), a ubiquitous species in natural water, is capable of reacting with sulfate radical (SO4∙-) and hydroxyl radical (∙OH) to form secondary reactive bromine species (RBS). The reaction routes can influence the degradation mechanisms and performance of these radicals for removal of target pollutants and may also form harmful bromine-containing disinfection by-products (Br-DBPs) during subsequent chlorination. In the present research, the UV-activated persulfate (PS) degradation of bisphenol A (BPA) was systematically examined in the presence of Br-. Results indicated that the presence of Br-enhanced the BPA degradation and both UV/PS and UV/PS/Br- processes followed the pseudo-first-order kinetics. At 0-0.8 mM Br-, 0.2 mM Br- exerted the best enhanced effect on BPA degradation, while RBS functioned as the major contributor in the presence of 0.05-0.5 mM Br-. Solution pH (6.0-8.0) barely affected the BPA degradation in the UV/PS system, but the introduction of Br- augmented the pH dependence. In the UV/PS/Br-system, the reaction rate constant of BPA increased/decreased with increasing PS/HA dosage, and was affected slightly in the presence of bicarbonate and chloride. According to the quantum chemical calculation, the second-order rate constants of BPA with ∙OH, SO4∙-, Br∙ and Br2∙- were calculated as 7.65 × 1010, 1.67 × 109, 1.77 × 108 and 2.83 × 102 M-1 s-1, respectively. Additionally, three degradation pathways of BPA were proposed based on DFT calculation and HPLC/MS analysis, and the formed bromine-containing products exhibited higher toxicity than BPA. Br-DBPs, particularly tribromomethane and tribromoacetic acid, generated from UV/PS/Br-pre-oxidation during BPA chlorination significantly increased the toxicity of total DBPs.