Efficient destruction of emerging contaminants in water by UV/S(IV) process with natural reoxygenation: Effect of pH on reactive species

UV/sulfite systems with oxygen have recently been considered as advanced oxidation processes in view of the participation of oxysulfur radicals. However, the contribution of center dot OH and the efficiency of destructing emerging contaminants (ECs) in water remain largely unclear. Here, the UV/S(IV) process was applied with natural reoxygenation to degrade two typical ECs, diethyl phthalate (DEP) and bisphenol A (BPA) showing different properties. Solution pH played the key role in determining the reactive species, and both DEP and BPA were more favorably degraded at more alkaline conditions with higher utilization efficiency of SO32-. Specifically, the H center dot, O-2(center dot-), center dot OH and SO3 center dot- were identified at acidic condition, but the amount of center dot OH accumulated significantly with the elevation of pH. Competitive quenching experiments showed that e(aq)(-) and center dot OH dominated the degradation of DEP and BPA at alkaline condition, respectively. Besides, DEP showed higher quantum efficiency for the indirect photolysis and mineralization degree than that of BPA at pH 9.2 mainly due to the direct use of the primary photoproduct. The possible transformation mechanisms of S(IV) and mineralization routes of both pollutants were proposed. This study may provide new insights into the mechanisms involved in UV/S(IV) process and a promising alternative for efficient removal of ECs in water. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The UV/S(IV) process with natural reoxygenation was applied to degrade DEP and BPA, showing that solution pH played a key role in determining reactive species. DEP and BPA were more favorably degraded at more alkaline conditions with higher utilization efficiency of SO32-. The study proposed possible transformation mechanisms of S(IV) and mineralization routes of both pollutants.