Accelerated degradation of micro-pollutant by combined UV and chlorine dioxide: Unexpected inhibition of chlorite formation

Yan Wang; Wenyu Sun; Huiyu Dong; Zhimin Qiang

doi:10.1016/j.envpol.2023.122600

Accelerated degradation of micro-pollutant by combined UV and chlorine dioxide: Unexpected inhibition of chlorite formation

Environ Pollut. 2023 Nov 15:337:122600. doi: 10.1016/j.envpol.2023.122600. Epub 2023 Sep 20.

Authors

Yan Wang¹, Wenyu Sun², Huiyu Dong³, Zhimin Qiang¹

Affiliations

¹ Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing, 100085, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
² Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing, 100085, China; Sino-Danish College, University of Chinese Academy of Sciences, Beijing, 100101, China.
³ Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing, 100085, China; University of Chinese Academy of Sciences, Beijing, 100049, China. Electronic address: hydong@rcees.ac.cn.

PMID: 37739255
DOI: 10.1016/j.envpol.2023.122600

Abstract

UV/chlorine dioxide (ClO₂) process can be intentionally or accidently conducted and is potentially effective in micro-pollutants degradation. UV irradiation can promote ClO₂ decay and subsequently result in the formation of reactive radicals. Hence, the co-exposure of ClO₂ and UV exhibited a synergetic effect on metribuzin (MET) degradation. The MET degradation was promoted by UV/ClO₂ with a rate of 0.089 min^-1 at pH 7.5, which was around 2.4 folds the total of rates caused by single ClO₂ (0.004 min^-1) and single UV (0.033 min^-1). Reactive radicals mainly HO^• and reactive chlorine species were involved in the acceleration effect, and contributed to 59%-67% of the total degradation rate of MET during UV/ClO₂ under pHs 5.5-7.5. Among them, HO^• was the predominant contributor and the contribution rate gradually rose under higher pH. Chlorite (ClO₂^-) and chlorate (ClO₃^-) formation has been the major concern of ClO₂ oxidation. However, a comparison of their formation during UV/ClO₂ and ClO₂ oxidation is rarely reported. Herein, during MET degradation by ClO₂, only ClO₂^- was identified with the highest amount of 1.17 mg L^-1. Conversely, during MET degradation by UV/ClO₂, only ClO₃^- was identified with the highest amount of 0.68 mg L^-1, showing an upward trend with prolonging treatment time. Furthermore, organic halogenated DBPs formation after 24 h post-chlorination with UV/ClO₂ and ClO₂ pre-treatments was comparatively evaluated. Organic DBPs formation after post-chlorination was higher with UV/ClO₂ pre-treatment compared to ClO₂ pre-treatment. The overall concentration of DBPs produced with 30 min UV/ClO₂ pre-treatment was about 4.5 times that with 1min UV/ClO₂ pre-treatment. This study provided useful reference for the application of UV/ClO₂ in micro-pollutants degradation.

Keywords: Degradation kinetics; Degradation mechanism; Disinfection by-products; Metribuzin; UV/Chlorine dioxide.

MeSH terms

Chlorine / pharmacology
Disinfectants*
Disinfection
Halogenation
Oxidation-Reduction
Oxides / pharmacology
Water Pollutants, Chemical* / analysis
Water Purification*

Substances

chlorine dioxide
chlorite
Disinfectants
Oxides
Chlorine
Water Pollutants, Chemical