Bromate requires one further step of oxidaton. Hypobromite can react again with ozone if it is thermodynamically possible to produce Bromate, which is BrO3- (aq)
The level of bromate that may form in water depends on the concentration of bromide in the source water (60 mg / l in seawater, which is very high when comparied to tapwater), the amount of ozone contact time, and a variety of water chemistry factors including pH, organic material, hardness and alkalinity. Ozone reacts directly with the bromide ion to form hypobromite and oxygen.
O3 + Br - 1/2 O2 + OBr -
Two ozone molecules then react directly with the hypobromite to form bromate and oxygen. Alternatively, the hypobromite can react with multiple hydroxyl radicals created by the destruction of ozone.
2O3 (or OH*) + OBr - 1/2 2O2 + BrO3 -
Bromate can also be converted to Bromide ;
BrO3- (aq) + 5 Br- (aq) + 6 H+ (aq) 3 Br2 (aq) + 3 H2O (l)
In seawater with ozone the kinetics just doesn't do much, as there are other things being oxidized, not to mention Iodide @ < 1 mg / l, then there is the chloride ion @ 19,000 mg / l but very, very unfavorable kinetically. The reason behind GAC with ozone is mainly for Hypobromite, but it will also take out Bromate. Finally Bromate is also a function of pH, as pH increases there will be more Bromate.
Also
EFFECTS OF PH AND ALKALINITY ON OZONATION OF BROMIDE AND CHLORIDE IN SEAWATER
A series of laboratory experiments were performed in which unbuffered and buffered solutions of NaBr and NaCl were exhaustively ozonated. The production patterns and relative abundances of the products were compared in order to quantify the roles of pH, carbonate system and borate system in ozone reactions with these two halides in seawater. Concentrations of hypohalites in solutions where pH was buffered in the range 8.6-8.8 were consistently lower than those in the equivalent unbuffered solutions. Bromate production rates in unbuffered NaBr solution, NaBr solution buffered with 3 meq/L carbonate alkalinity, and that buffered with 3 meq/L borate alkalinity were, respectively, 1.30 mM/min, 1.58 ìM/min and 0.83 mM/min.
Our finding that, relative to carbonate alkalinity, borate alkalinity enhances the production of hypobromite while simultaneously depressing bromate formation, may have important consequences for seawater facilities such as aquaria and mariculture that use borate buffers. Hypobromite produced during ozonation in such systems is a desired secondary disinfectant, due to the very short half-life of dissolved ozone in seawater. The use of borate buffers may thus serve to enhance the potential for disinfection while simultaneously diminishing the unwanted bromate accumulation in these environments.
