Formation of iodinated trihalomethanes during UV/chloramination with iodate as the iodine source

• IO3− is a new iodine source of I-THM formation during UV/chloramination.
• I-THMs increased with the increase of UV dose, IO3− and NH2Cl concentrations.
• High Br− level enhanced I-THM formation from IO3− during UV/chloramination.
• NOM species affect I− production and I-THM formation during UV/chloramination.

Iodinated trihalomethanes (I-THMs) are a group of emerging disinfection by-products with high toxicity, and iodide (I−) as well as iodinated organic compounds are expected to be their iodine sources. Nevertheless, in this study, iodate (IO3−) was proven to be a new iodine source of I-THM formation during UV/chloramination. In the iodate-containing waters (without any other iodine sources), I-THM formation increased with the increase of UV dose, IO3− and NH2Cl concentrations. With the increase of Br−/IO3− molar ratio, I-THM formation (especially for the brominated species) increased. Besides, NOM species could affect I-THM formation from IO3− during UV/chloramination. Fulvic acid could promote IO3− phototransformation to I− but humic acid impeded the production of I− during UV irradiation. Under realistic drinking water treatment conditions (DOC = 5.0 mg-C/L, IO3− = 12.7 μg-I/L, UV dose = 50 mJ/cm2, NH2Cl = 5 mg-Cl2/L), CHCl2I was detected as 0.17 μg/L using solid-phase microextraction method, and the production rate of I-THMs from IO3− was about 7% of that from I−.

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