Critical Review on Bromate Formation during Ozonation and Control Options for Its Minimization

Ozone is a commonly applied disinfectant and oxidantin drinkingwater and has more recently been implemented for enhanced municipalwastewater treatment for potable reuse and ecosystem protection. Onedrawback is the potential formation of bromate, a possible human carcinogenwith a strict drinking water standard of 10 & mu;g/L. The formationof bromate from bromide during ozonation is complex and involves reactionswith both ozone and secondary oxidants formed from ozone decomposition,i.e., hydroxyl radical. The underlying mechanism has been elucidatedover the past several decades, and the extent of many parallel reactionsoccurring with either ozone or hydroxyl radicals depends stronglyon the concentration, type of dissolved organic matter (DOM), andcarbonate. On the basis of mechanistic considerations, several approachesminimizing bromate formation during ozonation can be applied. Removalof bromate after ozonation is less feasible. We recommend that bromatecontrol strategies be prioritized in the following order: (1) controlbromide discharge at the source and ensure optimal ozone mass-transferdesign to minimize bromate formation, (2) minimize bromate formationduring ozonation by chemical control strategies, such as ammoniumwith or without chlorine addition or hydrogen peroxide addition, whichinterfere with specific bromate formation steps and/or mask bromide,(3) implement a pretreatment strategy to reduce bromide and/or DOMprior to ozonation, and (4) assess the suitability of ozonation altogetheror utilize a downstream treatment process that may already be in place,such as reverse osmosis, for post-ozone bromate abatement. A one-size-fits-allapproach to bromate control does not exist, and treatment objectives,such as disinfection and micropollutant abatement, must also be considered.