William Mitch, Postdoctoral Faculty Sponsor
Reactivity of Bromine Radical with Dissolved Organic Matter Moieties and Monochloramine: Effect on Bromate Formation during Ozonation
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Bromine radical (Br•) has been hypothesized to be a key intermediate of bromate formation during ozonation. Once formed, Br• further reacts with ozone to eventually form bromate. However, this reaction competes with the reaction of Br• with dissolved organic matter (DOM), of which reactivity and reaction mechanisms are less studied to date. To fill this gap, this study determined the second-order rate constant (k) of the reactions of selected organic model compounds, a DOM isolate, and monochloramine (NH2Cl) with Br• using γ-radiolysis. The kBr• of all model compounds were high (kBr• > 108 M-1 s-1) and well correlated with quantum-chemically computed free energies of activation, indicating a selectivity of Br• toward electron-rich compounds, governed by electron transfer. The reaction of phenol (a representative DOM moiety) with Br• yielded p-benzoquinone as a major product with a yield of 59% per consumed phenol, suggesting an electron transfer mechanism. Finally, the potential of NH2Cl to quench Br• was tested based on the fast reaction (kBr•, NH2Cl = 4.4 × 109 M-1 s-1, this study), resulting in reduced bromate formation of up to 77% during ozonation of bromide-containing lake water. Overall, our study demonstrated that Br• quenching by NH2Cl can substantially suppress bromate formation, especially in waters containing low DOC concentrations (1-2 mgC/L).
View details for DOI 10.1021/acs.est.2c07694
View details for Web of Science ID 000963569000001
View details for PubMedID 36706342