Degradation of sulfadiazine in water by a UV/O3 process: performance and degradation pathway

Abstract

In this study, the performance of a combined UV/O₃ process for aquatic sulfadiazine (SDZ) removal was investigated. By comparing with UV irradiation or ozonation, the UV/O₃ process showed excellent performance for SDZ removal, particularly on the mineralization of SDZ. The degradation rate of SDZ by UV/O₃ increased with the increment of O₃ gas concentration and UV intensity. Meanwhile, initial solution pH also played an important role in the UV/O₃ process. The pH increment of solutions (3.0–9.0) could promote the SDZ degradation rate which was mainly ascribed to the generation of ˙OH by O₃ self-decomposition and the dissociation of SDZ. But this phenomenon was seriously reversed for the production of more free radical scavengers like CO₃²⁻ as initial pH increased from 9.0 to 11.0. Two different degradation pathways of SDZ by UV/O₃ were proposed based on the combination of theoretical calculations and experimental intermediate identification. Pathway I was initiated by hydroxyl radicals which involved oxidative cleavage of the S–N bond and pathway II was induced by direct UV irradiation which involved the opening of the pyrimidine ring. According to the results obtained in this work, UV/O₃ was recommended as an effective method to remove SDZ.