The effects of selected preoxidation strategies on I-THM formation and speciation

In this study, the impacts of three preoxidation strategies [i.e., using potassium permanganate (KMnO4), chlorine dioxide (ClO2), or hydrogen peroxide (H2O2)] before preformed monochloramine (NH2Cl) addition on the formation and speciation of iodinated trihalomethanes (I-THMs) were evaluated at the Br−/I− mass ratio of 10 in two natural waters. The effects of preoxidant dose, Br−/DOC, and I−/DOC ratio were investigated. Preoxidation with KMnO4 increased I-THM formation due to an increase in iodoform (CHI3) and brominated I-THM (CHBrClI, CHBrI2, CHBr2I) formation. In contrast, preoxidation with ClO2 sometimes reduced I-THM formation, primarily due to a reduction in CHI3 formation. Preoxidation with H2O2 had no effect on I-THM formation or speciation. I-THM formation from each preoxidant alone was considerably less than the formation from NH2Cl. Overall, preoxidant type, preoxidant/DOC, preoxidant/I−, and I−/DOC ratios are the important factors that water utilities should evaluate when assessing the impact of preoxidation for controlling I-THM formation.

► Br−/I− concentrations and ratio play a key role in I-THM formation.
► Preoxidation with KMnO4 increased I-THM formation due to an increase in iodoform and brominated I-THMs.
► Preoxidation with ClO2 sometimes reduced I-THM formation, primarily due to a reduction in iodoform.
► Preoxidation with H2O2 had no effect on I-THM formation or speciation.