Accelerated oxidation of iopamidol by ozone/peroxymonosulfate (O3/PMS) process: Kinetics, mechanism, and simultaneous reduction of iodinated disinfection by-product formation potential

Iopamidol (IPM) is a potential source of toxic iodinated byproducts (I-DBPs) during water disinfection. In this work, we determined the kinetics and mechanism of degradation of IPM by a combination of ozone (O-3) and peroxymonosulfate (PMS, HSO5-), and assessed its effect on the formation of iodinated trihalomethanes (I-THMs) during chlorination treatment. The degradation of IPM was accelerated by the O-3 /PMS process, and the hydroxyl (HO center dot) and sulfate (SO4 center dot-) radicals were major contributors to the degradation. Using identification of the second order reaction rate between SO4 center dot- and IPM (k(SO4)(center dot-)ipm = 1.6 x 10(9) M-1 s(-1)), the contribution of HO center dot to the degradation was determined to be 78.3%. The degradation of IPM was facilitated by pH > 7, and natural organic matter (NOM) and alkalinity had limited effects on the degradation of IPM in the O-3/PMS process. The transformation products of IPM were determined and inferred by QTOF-MS/MS, and the degradation pathways were elucidated. These include amide hydrolysis, amino oxidation, hydrogen abstraction, deiodination, and hydroxyl radical addition. Interestingly, oxidation of IPM by O-3/PMS also decreased its potential for formation of I-THMs. After oxidation of IPM, the I-THMs formed from 5-mu M IPM decreased from 14.7 mu g L-1 to 3.3 mu g L-1 during chlorination. Although the presence of NOM provided the precursor of I-THMs during chlorination of IPM, the O-3/PMS process decreased I-THMs formation by 71%, because oxidation of released iodide into iodate effectively inhibited I-THMs formation. This study provides a new approach for the accelerated degradation of IPM and control of the formation of I-DBPs. (C) 2020 Elsevier Ltd. All rights reserved.