Probing the role of BrCl in benzotriazole transformation during seawater chlorination

Yongjie Fan; Jing Yang; Kunde Lin

doi:10.1016/j.watres.2024.122609

Probing the role of BrCl in benzotriazole transformation during seawater chlorination

Water Res. 2024 Oct 10;268(Pt A):122609. doi: 10.1016/j.watres.2024.122609. Online ahead of print.

Authors

Yongjie Fan¹, Jing Yang¹, Kunde Lin²

Affiliations

¹ Fujian Provincial Key Laboratory for Coast Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China.
² Fujian Provincial Key Laboratory for Coast Ecology and Environmental Studies, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China. Electronic address: link@xmu.edu.cn.

PMID: 39413710
DOI: 10.1016/j.watres.2024.122609

Abstract

A common understanding attributes the formation of brominated disinfection by-products (Br-DBPs) in seawater chlorination to the conversion of hypochlorous acid to hypobromous acid (HOBr) by bromide. In this study, we reveal that bromine chloride (BrCl), mediated by both chloride and bromide in seawater, plays a dominant role in the transformation of 1H-benzotriazole (BTA) and 5-methyl-1H-benzotriazole (MBTA) and in the formation of brominated DBPs. Using anisole as a reference compound, the second-order rate constant for the reaction of BrCl with BTA was determined to be (2.65 ± 0.13) × 10⁵ L mol^-1 s^-1, which is over 30,000 times higher than that for the reaction between HOBr and BTA. Ten brominated products were identified and showed a successive bromination pattern. The bromination reaction mechanism was elucidated through theoretical calculations, and the pathways were proposed. The concentrations of brominated BTA and MBTA in seawater were 5.7 and 7.9 times higher than in bromide-only solutions, respectively. BrCl significantly promoted brominated product generation and increased the toxicity of blended DBPs. These results suggest that focusing solely on bromide's effect on brominated product generation may significantly underestimate the potential for DBP formation during seawater chlorination.

Keywords: Bromine chloride; Disinfection by-products; Emerging contaminants; Reactive halogen species; Seawater chlorination.