Photochemical degradation of iodate by UV/H 2 O 2 process: Kinetics, parameters and enhanced formation of iodo-trihalomethanes during chloramination.

In this paper, it was demonstrated that UV/H2O2 process can not only obviously promote the degradation rate of IO3−, but also greatly enhance iodo-trihalomethanes (I-THMs) formation in sequential chloramination. UV/H2O2 exhibited much faster IO3− decomposition than either UV or H2O2 treatment alone due to the contribution of highly reactive species including O−, OH and eaq−. The degradation rate of IO3− was affected by H2O2 dosages, pH, UV intensity as well as the presence of natural organic matter (NOM). The calculated pseudo-first order rate constant gradually increased with H2O2 dosages and solution pH, but behaved directly proportional to the UV intensity. Although NOM remarkably reduced the degradation rate of IO3− in UV/H2O2 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/H2O2 was proved to be more capable on the evolution of IO3− 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 IO3− as the emerging iodine precursor to form I-THMs via diverse advanced oxidation process technologies like UV/H2O2.