Factors affecting the formation of iodo-trihalomethanes during oxidation with chlorine dioxide

•Factors affecting I-THM formation during oxidation using ClO2 were evaluated.•CHI3 yields correlated moderately with SUVA values (R2 = 0.79).•CHI3 yields were the highest at I−/ClO2 molar ratio of 1–2.•CHI3 was predominant even in the presence of high concentrations of bromide.•CHI3 yields were the highest at pH 8.

Effects of water characteristics, reaction time, temperature, bromide and iodide ion concentrations, oxidant doses, and pH on formation of iodinated trihalomethanes (I-THM) during oxidation of iodide-containing water with chlorine dioxide (ClO2) were investigated. Among the water samples collected from ten water sources, iodoform (CHI3) was the predominant I-THM and trace amount of chlorodiiodomethane (CHClI2) was occasionally found. CHI3 yields correlated moderately with specific UV absorbance (SUVA) (R2 = 0.79), indicating that hydrophobic aromatic content were important precursors. Longer reaction time led to continued formation of CHI3. I-THM containing bromide was also found in waters containing both bromide and iodide, but CHI3 was dominant. The formation of CHI3 was higher at 25 °C than 5 °C and 35 °C. CHI3 formation showed an increase followed by a decrease trend with increasing ClO2 doses and iodide concentrations and the highest yields occurred at iodide to ClO2 molar ratios of 1–2. pH 8 resulted in the highest CHI3 formation. It should be noted that a high iodide concentration was spiked to waters before adding ClO2 and the results may not reflect the formation yields of iodinated THMs in real conditions, but they provide information about formation trend of I-THM during oxidation of ClO2.

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