Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, Duebendorf 8600, Switzerland.
Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, Michigan 49931, United States.
Environ Sci Technol. 2023 Nov 28;57(47):18658-18667. doi: 10.1021/acs.est.2c07694. Epub 2023 Jan 27.
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 () of the reactions of selected organic model compounds, a DOM isolate, and monochloramine (NHCl) with Br using γ-radiolysis. The of all model compounds were high ( > 10 M s) 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 -benzoquinone as a major product with a yield of 59% per consumed phenol, suggesting an electron transfer mechanism. Finally, the potential of NHCl to quench Br was tested based on the fast reaction ( = 4.4 × 10 M s, 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 NHCl can substantially suppress bromate formation, especially in waters containing low DOC concentrations (1-2 mgC/L).
溴自由基 (Br) 被假设为臭氧化过程中溴酸盐形成的关键中间体。一旦形成，Br 会进一步与臭氧反应，最终形成溴酸盐。然而，这种反应与 Br 与溶解有机物 (DOM) 的反应竞争，目前对后者的反应性和反应机制研究较少。为了填补这一空白，本研究使用γ辐照法确定了选定有机模型化合物、DOM 分离物和一氯胺 (NHCl) 与 Br 的反应的二级速率常数 (k)。所有模型化合物的 k 值都很高 (>10 M s)，与通过量子化学计算得到的活化自由能很好地相关，表明 Br 对富电子化合物具有选择性，这是由电子转移决定的。Br 与苯酚（一种代表性的 DOM 部分）的反应生成了 - 苯醌，其产率为每消耗一个苯酚生成 59%，表明存在电子转移机制。最后，根据快速反应（k = 4.4 × 10 M s，本研究），测试了 NHCl 淬灭 Br 的潜力，导致含溴湖水臭氧化过程中溴酸盐的形成减少了高达 77%。总体而言，我们的研究表明，NHCl 对 Br 的猝灭可以显著抑制溴酸盐的形成，特别是在含有低 DOC 浓度（1-2 mgC/L）的水中。
