Overlooked Role of Iodate in Micropollutant Degradation by UV/Periodate: Kinetic Modeling and Mechanism
Shirong Zhao, Shaoze Xiao, Yajie Qian, Ching‐Hua Huang, Urszula Aleksander-Kwaterczak, Tongcai Liu, Ziyu Zou, Jiabin Chen
Abstract
The periodate (PI, IO 4 – ) is known as an emerging oxidant and disinfectant in water treatment with iodate (IO 3 – ) as the benign end product. However, new results herein strongly suggest that IO 3 – could contribute to pollutant degradation and trigger disinfection byproduct (DBP) formation in the UV/IO 4 – process. The degradation of micropollutants, e.g., 17α-ethinylestradiol (EE2), followed two-stage pseudo-first-order kinetics along with the conversion of IO 4 – (stage I) to IO 3 – (stage II) in the UV/IO 4 – process. The radical scavenging experiments and electron spin resonance technique confirmed both reactive oxygen species (e.g., • OH and O 3 ) and reactive iodine species (RIS) (e.g., IO 3 • ), contributing to contaminant degradation in the UV/IO 4 – 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 IO 3 •, played major contributions in stage II. The photolysis of IO 3 – 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/IO 4 – process and highlight the overlooked role of IO 3 – in the worrisome I-DPB formation in the wastewater treatment.