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 (ClO2) and (bi)sulfite/ClO2 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 ClO2 and S(IV)/ClO2 process regarding the degradation performance of contaminant, generation of reactive species, transformation of products and toxicity variation. Both ClO2 and S(IV)/ClO2 can degrade BPA within 3 min. The BPA degradation mechanism was mainly based on direct oxidation in ClO2 process while it was attributed to radicals (especially SO4 & sdot;-) generation in S(IV)/ClO2 process. Meanwhile, the effect of pH and coexisting substances (Cl-, Br-, HCO3- and HA) were evaluated. It was found that ClO2 preferred the neutral and alkaline condition and S(IV)/ClO2 preferred the acidic condition for BPA degradation. An unexpected speed-up of BPA degradation was observed in ClO2 process in the presence of Br-, HCO3- and HA. In addition, the intermediate products in BPA degradation were identified. Three exclusive products were found in ClO2 process, in which p-benzoquinone was considered to be the reason of the acute toxicity increase in ClO2 process.

Automated summary

This study investigated the differences in degradation performance and product transformation between ClO2 and (bi)sulfite/ClO2 processes for BPA removal. The results showed that ClO2 process mainly relied on direct oxidation, while S(IV)/ClO2 process involved the generation of radicals. The pH and coexisting substances also had an influence on the degradation of BPA.