Bisphenol A degradation by chlorine dioxide (ClO2) and S(IV)/ClO2 process: Mechanism, degradation pathways and toxicity assessment

Recently, it has been reported that chlorine dioxide (ClO 2 ) and (bi)sulfite/ClO 2 showed excellent performance in micropollutant removal from water; however, the degradation mechanisms and application boundaries of the two system have not been identified. In this study, bisphenol A (BPA) was chosen as the target contaminant to give multiple comparisons of ClO 2 and S(IV)/ClO 2 process regarding the degradation performance of contaminant, generation of reactive species, transformation of products and toxicity variation. Both ClO 2 and S(IV)/ClO 2 can degrade BPA within 3 min. The BPA degradation mechanism was mainly based on direct oxidation in ClO 2 process while it was attributed to radicals (especially SO 4 · - ) generation in S(IV)/ClO 2 process. Meanwhile, the effect of pH and coexisting substances (Cl − , Br − , HCO 3 − and HA) were evaluated. It was found that ClO 2 preferred the neutral and alkaline condition and S(IV)/ClO 2 preferred the acidic condition for BPA degradation. An unexpected speed-up of BPA degradation was observed in ClO 2 process in the presence of Br − , HCO 3 − and HA . In addition, the intermediate products in BPA degradation were identified. Three exclusive products were found in ClO 2 process, in which p-benzoquinone was considered to be the reason of the acute toxicity increase in ClO 2 process.