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 (KMnO(4)), chlorine dioxide (ClO(2)), or hydrogen peroxide (H(2)O(2))] before preformed monochloramine (NH(2)Cl) 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 KMnO(4) increased I-THM formation due to an increase in iodoform (CHI(3)) and brominated I-THM (CHBrClI, CHBrI(2), CHBr(2)I) formation. In contrast, preoxidation with ClO(2) sometimes reduced I-THM formation, primarily due to a reduction in CHI(3) formation. Preoxidation with H(2)O(2) had no effect on I-THM formation or speciation. I-THM formation from each preoxidant alone was considerably less than the formation from NH(2)Cl. 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.