Bromate can come from the ...
Published by Joseph Cotruvo, President at Joseph Cotruvo & Associates, Water , Environment and Public Health
Bromate can come from the original hypochlorite solution (not chlorine gas) or it can be formed by oxidation processes during water treatment. Bromate does not continue to form in hypochlorite like chlorate does.
It would be necessary to know more about your process water and the oxidation processes before anyone can provide sensible advice on post treatment formation.
You should also know that the current drinking water standards and guidelines for bromate are not scientifically valid, and lower than necessary to protect health. . They are extrapolated from the very high dose feeding studies from about 25 years ago. The risk assessors assume that effects at high doses can be extrapolated to low doses. They cannot be extrapolated because normal low doses (even higher than drinking water levels ) are metabolized mostly to bromide after ingestion so the human is not exposed to bromate in vivo, but just microgram amounts of bromide.
See Non-genotoxic Mechanisms Involved in Bromate-induced Cancer in Rats. R.J. Bull and Joseph Cotruvo, Journal AWWA Summary 105:12, pp 47-48, December 2013.