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

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 mg/L), 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 mgC/L). The second-order reaction rate constant of hydroxyl radical with bromide ion, of 1.7 × 10 9 (M −1 s −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.hile ozonation and advanced oxidation processes are widely recognized to be efficient water treatment processes to improve tastes and odors, and to remove pathogenic organisms and micropollutants, concern over bromate ion formation during ozonation of water containing bromide ion has arisen. The maximum k HO,Br − W

Formation and inhibition of bromate during ferrate(VI) – Ozone oxidation process

“…2, the concentration of bromate formed in ozonation process was respectively about 12.90 lg/L and 28.44 lg/L with and without t-BuOH addition. As estimated, bromate generated by hydoxyl radical oxidation was about 54.64%, suggesting that the hydroxyl free radical pathway played a significant role on bromate formation, and the finding in our experiments was consistent with other studies [6,32].…”

A Simple Model to Predict Formation of Bromate Ion and Hypobromous Acid/Hypobromite Ion through Hydroxyl Radical Pathway during Ozonation

“…The contribution of ozone and hydroxyl radicals on the formation of bromate ion was well studied based on the equilibrium state of hypobromous acid/hypobromite ion and the ratio of ozone and hydroxyl radical from the aspect of chemical reactions in previous research von Gunten, 1999, 2001). In addition to the kinetic approach for individual reactions, the significant role of hydroxyl radical to bromate ion formation for the overall reaction was reported from a numerical modeling approach and an empirical approach in previous research (Westerhoff et al, 1998;Mizuno et al, 2005). In this research, the contribution of hydroxyl radical to bromate ion formation was estimated to be 70% and almost 100%, respectively.…”

“…The values of reaction rate constants k 4 (=4.5 · 10 9 M À1 s À1 ) and k 5 (=2.0 · 10 9 M À1 s À1 ) for reactions on R 4 and R 5 , which were proposed as direct reactions, were obtained from the literature (Buxton et al, 1988). Because the accumulation of intermediate compounds was not found except for hypobromous acid/hypobromite ion (Mizuno et al, 2005), R 2 and R 3 (k 2 and k 3 ) were treated with introducing the fast reaction rate constants whose values are much higher by 10 2 -10 3 times than k 4 and k 5 . The dissociation reaction between hypobromous acid and hypobromite ion (R 6 and R 7 ) was represented by the equilibrium constant, pKa = 8.8 under the assumption that this reversible conversion reaction is considered much faster than any other reactions.…”

“…In the latter combination reaction, several oxy-bromine radical species are also included besides hypobromous acid/hypobromite ion and bromite ion, which are the main intermediate compounds in the direct ozone pathway. In addition to these two pathways, it has been shown that bromate ion is formed through the only hydroxyl radical pathway (Mizuno et al, 2005). In both ozone and hydroxyl radical reactions, hypobromous acid and hypobromite ion are considered key compounds because their equilibrium state (pKa = 8.8) affects the formation of bromate ion.…”

“…The purpose of this study is to establish a simple model to predict the formation of bromate ion as well as hypobromous acid/hypobromite ion through the hydroxyl radical pathway based on the previous research (Mizuno et al, 2005). In this model, the difference of bromate ion concentration formed under the different pH conditions is exclusively derived from the different concentration of hydroxyl radical.…”