Formation of Iodinated Disinfection Byproducts in Periodate-Based Advanced Oxidation Processes: The Self-Supplying Iodine Mechanism

Periodate-based advanced oxidation processes (IO₄^--based AOPs) have attracted significant interest for degrading organic micropollutants due to their high efficiency and ease of use. However, the formation risk of iodinated disinfection byproducts (I-DBPs) during these processes has long been overlooked. At pH = 3.0-9.0, I-DBPs including iodophenols and triiodomethane were formed in the ultraviolet (UV)/IO₄^-/phenol system, and the total iodine concentration in I-DBPs ranged from 4.8 to 451.3 nM. In this system, the conversion of IO₄^- to hypoiodous acid (HOI) proceeded in two stages: (1) a rapid HOI generation phase, where IO₄^- first transformed into an iodine-containing intermediate followed by its subsequent transformation to HOI, and (2) a slow HOI generation phase, where iodate (the primary product of IO₄^-) was photoreduced to HOI. The established kinetic model successfully simulated the two-phase formation of HOI. Treatments of the simulated source water samples with hydroxylamine, hydrogen peroxide, Mn²⁺, Fe²⁺, nanoscale zerovalent iron, UV, and vacuum ultraviolet (VUV)-activated IO₄^- processes all resulted in the formation of I-DBPs. The fact that the iodine source of these I-DBPs was IO₄^- confirmed the self-supplying iodine mechanism of IO₄^-. Future research should develop technologies that efficiently degrade micropollutants while minimizing I-DBP formation.