Formation of iodinated products in Fe (II)/peroxydisulfate (PDS) system

The transformation of iodide (I − ) and hypoiodous acid (IO − ) by Fe (II)-activated peroxydisulfate (PDS) in the presence of natural organic matter (NOM) was investigated. In the water of a reservoir in Shenzhen, four kinds of organic matter were detected: iodoform > diiodo-bromomethane > dibromo-iodomethane > dichloromethane. As pH increased from 3 to 10, I − conversion rate decreased from 31.0% to 11.0%. There is basically no iodic acid ( ⁠ ⁠ ) generated under alkaline conditions, probably due to these organic matters. When PDS concentration is low, PDS can oxidize part of I − to IO − , and the oxidation of I − into reaction and continued oxidation reaction exist at the same time, so some is generated in the system. As the proportion of Fe (II) increases, the generation rate of gradually increases. When Fe 2+ /PDS is 1:5, 2:5, and 3:5, the conversion rates of are 4.7%, 6.5%, and 8.4%, respectively. There are two main reasons for this: (i) the reaction of IO − produced in the system with humic acid (HA) inhibits the further conversion of IO − to ⁠ ; (ii) both HA and I- in the system can react with PDS, resulting in a reduction in the oxidation rate of I − . Formation of I-DBPs by Fe (II)/PDS process in real water was evaluated. I-DBPs generation in various reaction conditions was examined. Existence of HA showed apparent inhibition on IO 3 − generation.