Degradation of benzophenone-8 in UV/oxidation processes: Comparison of UV/H2O2, UV/persulfate, UV/chlorine processes

Abstract

Benzopenone-8 (BP8) is an ultraviolet (UV) filter commonly used in sunscreen and plastic products. BP8 can cause acute and chronic toxicity in living organisms because it is biologically toxic and bioaccumulates. Advanced oxidation processes (AOPs) are widely used to treat contaminated water using powerful radical species. In this study, we compared the degradation kinetics and mechanisms of BP8 under UV/H2O2, UV/persulfate (PS), and UV/chlorine processes. BP8 reacts quickly with reactive oxidants following pseudo-first-order kinetics. At an oxidant concentration of 12.5 μM within the pH range of 6–10, the degradation rate constant (kobs) was the highest for the UV/chlorine ((5.29–14.2) ×10−3 s−1), followed by UV/PS ((1.38–2.90) ×10−3 s−1) and UV/H2O2 ((0.79–2.41) ×10−3 s−1). kobs increased linearly with increasing oxidant dosage, with the highest value at pH 6 in the UV/H2O2 and UV/PS and pH 8 in the UV/chlorine process. At the pH with the highest kobs, hydroxyl radicals (∙OH), sulfate radicals (∙SO4–), and reactive chlorine species played significant roles in removing 99.7 %, 82.3 %, and 56.2 % of BP8 in the UV/H2O2, UV/PS, and UV/chlorine processes, respectively. Humic acids significantly inhibited BP8 degradation, whereas NO3– ions promoted BP8 degradation in UV/H2O2 process, NO3– and Cl– ions promoted BP8 degradation in UV/PS process and Br– ions promoted BP8 degradation in UV/chlorine process. The electricity consumption (EE/O) in various water matrices was in the order of UV/H2O2 > UV/PS >> UV/chlorine process; however, the chlorinated transformation products (TPs) produced in the UV/chlorine process were more toxic than the hydroxylated TPs from the UV/H2O2 and UV/PS processes, implying that the UV/PS process was most suitable for removing BP8 while controlling the formation of toxic products.