Formation of Bromate Ion Through a Radical Pathway in a Continuous Flow Reactor

Abstract

ABSTRACT The contribution of ozone and hydroxyl radical to the formation of bromate ion was investigated in a continuous flow reactor. Experiments were conducted under a wide range of ozone dose (0.7 ∼ 3.8 mgL), pH (6.5 ∼ 8.5), and t-butanol concentration (0 ∼ 0.5 mM). The formation of bromate ion was found to depend on radical reaction pathway, because the amount of bromate ion formed increased with pH and decreased with t-butanol, a radical scavenger, even when dissolved ozone concentrations were almost the same. In fact, the amount of bromate ion formed was reduced by 90% in the presence of t-butanol. Furthermore, the formation of bromate ion occurred even when dissolved ozone was not significantly detected in the presence of organic matter (TOC of 1 mgCL). The second-order reaction rate constant of hydroxyl radical with bromide ion, k HO,Br− of 1.7 × 109 (M−1s−1), was obtained on the assumption that the reactions of bromide ion and t-butanol with hydroxyl radical were competitive with each other in the presence of t-butanol and that the formation of bromate ion depended on the reaction of bromide ion with hydroxyl radical. Therefore, it is concluded that the reaction of bromide ion with hydroxyl radical dominated in the overall reaction from bromide ion to bromate ion in the continuous flow reactor.