A comparison of iodinated trihalomethane formation from chlorine, chlorine dioxide and potassium permanganate oxidation processes

This study compared the formation of iodinated trihalomethanes (I-THMs) from iodide-containing raw waters oxidized by chlorine, chlorine dioxide (ClO₂) and potassium permanganate (KMnO₄) at different oxidant concentrations, reaction times, pHs, initial iodide concentrations and bromide to iodide mass ratios. Among the six investigated I-THMs, iodoform was the major species formed during the oxidation using chlorine, ClO₂ and KMnO₄. When oxidant concentration increased from 0.1 to 3.0mg/L, the formation of I-THMs increased and then decreased for chlorine and ClO₂, but kept increasing for KMnO₄. As the reaction time went by, I-THM concentration increased to a plateau within 10h (ClO₂ within only 1h, especially) for all the three oxidants. I-THM formation gradually increased from pH 3.0 to 9.0 and remained stable at pH values higher than 7.5 for chlorine however, for ClO₂ and KMnO₄ the highest I-THM formation showed at pH 7.0 and 7.5, respectively. As initial iodide concentration increased from 20 to 800μg/L, the total amount and species of I-THMs increased for the three oxidants. Iodide contributed to I-THM formation much more significantly than bromide.