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

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