Overlooked Role of Iodate in Micropollutant Degradation by UV/Periodate: Kinetic Modeling and Mechanism

The periodate (PI, IO4-) is known as an emerging oxidant and disinfectant in water treatment with iodate (IO3-) as the benign end product. However, new results herein strongly suggest that IO3- could contribute to pollutant degradation and trigger disinfection byproduct (DBP) formation in the UV/IO4- process. The degradation of micropollutants, e.g., 17α-ethinylestradiol (EE2), followed two-stage pseudo-first-order kinetics along with the conversion of IO4- (stage I) to IO3- (stage II) in the UV/IO4- process. The radical scavenging experiments and electron spin resonance technique confirmed both reactive oxygen species (e.g., •OH and O3) and reactive iodine species (RIS) (e.g., IO3•), contributing to contaminant degradation in the UV/IO4- system. A kinetic model based on first-principles was further developed to simulate reaction kinetics, revealing that •OH was the primary reactive species responsible for EE2 degradation in stage I, while RIS, especially IO3•, played major contributions in stage II. The photolysis of IO3- in stage II could increase the risk of iodinated DBP (I-DBP) formation, especially under acidic conditions. The new findings of this work broaden the mechanistic knowledge on the UV/IO4- process and highlight the overlooked role of IO3- in the worrisome I-DPB formation in the wastewater treatment.