Implications of hydrogen peroxide on bromate depression during seawater ozonation. (October 2021)

• Record Type: Journal Article
• Authors: Yu, Yixuan; Zhao, Yingping; Wang, Haonan; Tao, Ping; Zhang, Xinmin; Shao, Mihua; Sun, Tianjun
• Is Part Of: Chemosphere. Volume 280(2021)
• Publication Date: 2021-10
• Subjects: Bromate depression -- Ozonation -- Hydrogen peroxide -- Seawater treatment -- Chain reactions; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2021.130669
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: The presence of hydrogen peroxide (H2 O2 ) in ozonation process can resist the formation of carcinogenic bromate (BrO3 ¯) efficiently, and the bromate depression is closely related with background water qualities, especially in high bromide-containing seawater. In this study, the freshwater and seawater were selected to investigate the effects of H2 O2 on ozone (O3 ) decomposition kinetics, bromide transformation and bromate depression, and the evolutions of BrO3 ¯ under different scavengers were explored to speculate the primary bromate formation pathways. The results showed that the initial O3 half-live period (t1/2 -O3 ) in seawater was only one-sixth of that in freshwater, and its attenuation rate increased analogously with the increase of H2 O2 concentration in both freshwater and seawater. The H2 O2 could promote the formation of BrO3 ¯ via hydroxyl radical (OH) based bromate pathways, nevertheless higher concentration of H2 O2 facilitated the reduction of HOBr/OBr¯ back to Br¯, resulting in 87.0% and 73.2% of BrO3 ¯ retardment in freshwater and seawater, respectively. The suppression ratios of BrO3 ¯ were up to 48.4% and 35.3% in freshwater with the addition of OH and O2 ¯ scavengers, and the corresponding depressions in seawater decreased to 35.3% and 12.7%, indicating that OH was dominant on bromate formation when the concentration of residual ozone was adequate to generate some bromine intermediates, meanwhile H2 O2 and O2 ¯ functioned as the key reductants for bromate depression. Based on these results, the Br¯ transformation mechanisms via O3, OH, H2 O2, and O2 ¯ reactions were speculated, and the feasibility of H2 O2 -ozonation was verified for the treatment of high Br¯-containing seawater. Highlights: Abundant organic groups in seawater led to lower BrO3 ¯/Br¯ ratio in ozonation. H2 O2 facilitated the reduction of HOBr/OBr¯, resulting in the retardment of BrO3 ¯. .OH was dominant on BrO3 ¯ formation when residual O3 was adequate to form bromides. The inhibition effect of H2 O2 on BrO3 ¯ formation was enhanced in seawater. H2 O2 and.O2 ¯ functioned as the key reductants for bromate depression.