Formation of Iodo-Trihalomethanes during Disinfection and Oxidation of Iodide-Containing Waters

The formation of iodo-trihalomethanes (I-THMs) such as iodoform (CHI 3 ) during oxidative treatment of iodide-containing drinking waters can be responsible for taste and odor problems. I-THMs are formed by reactions of hypoiodous acid (HOI) with natural organic matter. HOI is quickly formed from naturally occurring iodide (I - ) by oxidation with ozone, chlorine, or chloramine. The kinetics of reactions of HOI with organic model compounds as well as the resulting CHI 3 formation were measured. Substituted phenols, phenol, and, to a smaller extent, α-methyl carbonyl compounds were found to be reactive toward HOI and also to yield CHI 3 . Resorcinol ( m -hydroxyphenol) had the highest yield of CHI 3 . The kinetics of I-THM formation were also measured in natural waters which were oxidatively treated with ozone, chlorine, or chloramine. When ozone was used, no I-THMs were detected and ≥90% of I - was transformed to IO 3 - . Chlorine led to the formation of both IO 3 - and I-THMs. With increasing chlorine doses, the CHI 3 formation decreased, whereas IO 3 - formation, as well as the formation of classical THMs such as chloroform, increased. In chloramination processes, I-THMs (especially CHI 3 ) were the main products. The CHI 3 formation in the oxidation of natural waters increased in the order O 3 < Cl 2 < NH 2 Cl.