Kinetics of Oxidation of Iodide (I^-) and Hypoiodous Acid (HOI) by Peroxymonosulfate (PMS) and Formation of Iodinated Products in the PMS/I^-/NOM System

In this work, the kinetics of transformation of iodide (I^-) and hypoiodous acid (HOI) by peroxymonosulfate (PMS) and potential formation of worrisome iodinated products in the presence of natural organic matter (NOM) were investigated. As the pH increased from 5 to 10, the apparent second-order rate constants of reaction of PMS with I^- gradually decreased from 1.01 × 10³ to 3.86 × 10² M^-1 s^-1, while those for HOI increased dramatically from 1.08 × 10² to 7.90 × 10⁴ M^-1 s^-1. The obtained pH-dependent rate profiles were explained well by the effects of pH-affected speciation of PMS and/or HOI. Considerable amounts of total organic iodine (TOI) could be formed in the PMS/I^-/NOM system over a wide pH range. Under similar conditions, the TOI levels formed in the PMS/I^-/NOM system were generally higher than those formed in the case of HOCl but much lower than those formed in the case of NH₂Cl. Also, specific iodoform (IF) and monoiodoacetic acid (MIAA) were detected in both simulated and authentic waters during treatment with PMS. This work for the first time demonstrates the potential formation of worrisome iodinated products during water treatment with PMS, and this has important implications for its application.