Fate and transformation of iodine species during Mn(VII)/sulfite treatment in iodide-containing water

During oxidative treatment of iodide (I-)-containing waters, I- is easy to be oxidized into hypoiodous acid (HOI) by various oxidants and the further reaction of HOI with organic compounds can lead to the formation of iodinated disinfection by-products (I-DBPs). Oxidation of HOI to iodate (IO3-) or reduction of HOI to I- has been proposed to reduce the formation of I-DBPs. Because the reaction of HOI with sulfite proceeds rapidly, this study examined the fate of iodine and the formation of I-DBPs in Mn(VII)/sulfite process. Results showed that I- was oxidized to HOI but the further formation of IO3- was suppressed due to the fast reduction of HOI to I- by sulfite. The reactions of HOI with SO32- and IO- with SO32- are the major pathways with species-specific second-order rate constants determined to be 1.12 x 10(5) M-1 s(-1) and 9.43 x 10(7) M-1 s(-1), respectively. The rapid reaction of HOI with sulfite plays an essential role in minimizing the formation of iodinated products in HOI- and phenol-containing solutions. The toxic risk analysis showed that the toxicity of the generated DBPs from Mn(VII)/sulfite pre-oxidation followed by chlorination only changed slightly. Practitioner Points The decay of I- was negligible in Mn(VII)/sulfite process. The rapid reaction of HOI with SO32- resulted in the negligible generation of IO3-. Mn(VII)/sulfite process exerted slight influence on the formation of I-DBPs. Mn(VII)/sulfite process is promising for the pretreatment of I--containing water.