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

In this study, the performance of a combined UV/O-3 process for aquatic sulfadiazine (SDZ) removal was investigated. By comparing with UV irradiation or ozonation, the UV/O-3 process showed excellent performance for SDZ removal, particularly on the mineralization of SDZ. The degradation rate of SDZ by UV/O-3 increased with the increment of O-3 gas concentration and UV intensity. Meanwhile, initial solution pH also played an important role in the UV/O-3 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)-O-center dot by O-3 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/O-3 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/O-3 was recommended as an effective method to remove SDZ.