Photochemical degradation of iodate by UV/HO process: Kinetics, parameters and enhanced formation of iodo-trihalomethanes during chloramination.

In this paper, it was demonstrated that UV/HO process can not only obviously promote the degradation rate of IO, but also greatly enhance iodo-trihalomethanes (I-THMs) formation in sequential chloramination. UV/HO exhibited much faster IO decomposition than either UV or HO treatment alone due to the contribution of highly reactive species including O, OH and e. The degradation rate of IO was affected by HO dosages, pH, UV intensity as well as the presence of natural organic matter (NOM). The calculated pseudo-first order rate constant gradually increased with HO dosages and solution pH, but behaved directly proportional to the UV intensity. Although NOM remarkably reduced the degradation rate of IO in UV/HO process, their presence greatly enhanced the formation of I-THMs during subsequent chloramination. The overwhelming majority of iodoform at high UV fluences was also observed, which indicated improved iodination degrees of the detected I-THMs. UV/HO was proved to be more capable on the evolution of IO to I as well as I-THMs than UV and thereby enhanced the toxicity of disinfected waters in the following chloramination process. This study was among the first to provide a comprehensive understanding on the transformation of IO as the emerging iodine precursor to form I-THMs via diverse advanced oxidation process technologies like UV/HO.