Overlooked Role of Sulfur-Centered Radicals During Bromate Reduction by Sulfite

• Published in: Environmental science & technology 2019-09, Vol.53 (17), p.10320-10328
• Main Authors: Qiao, Junlian, Feng, Liying, Dong, Hongyu, Zhao, Zhiwei, Guan, Xiaohong
• Format: Article
• Language: English
• Subjects: Atmosphere; Bromates; Contaminants; Dissolved oxygen; Organic contaminants; Oxidation; Oxidizing agents; Reaction kinetics; Reduction; Stoichiometry; Sulfite; Sulfur; Sulfur trioxide; Water treatment
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.9b01783

In this work, the kinetics and mechanisms of the reductive removal of BrO3 – by sulfite in air atmosphere were determined. BrO3 – could be effectively reduced by sulfite at pHini 3.0–6.0, and the reduction rate of BrO3 – increased with decreasing pH. The coexisting organic contaminants with electron-rich moieties could be degraded, accompanied with BrO3 – reduction by sulfite. The reaction stoichiometries of −Δ­[sulfite]/Δ­[bromate] were determined to be 3.33 and 15.63 in the absence and presence of O2, respectively. Many lines of evidence verified that the main reactions in the BrO3 –/sulfite system in air atmosphere included the reduction of BrO3 – to HOBr and its further reduction to Br–, as well as the oxidation of H2SO3 by BrO3 – to form SO3 · – and its further transformation to SO4 · –. Moreover, SO4 · – rather than HOBr was determined to be the major active oxidant in the BrO3 –/sulfite system. SO3 · – played a key role in the over-stoichiometric sulfite consumption because of its rapid reaction with dissolved oxygen. However, the formed SO3 · – was further oxidized by BrO3 – in the N2 atmosphere. BrO3 – reduction by sulfite is an alternative for controlling BrO3 – in water treatment because it was effective in real water at pHini ≤ 6.0.