Ozonation of waters containing bromide ion leads to the formation of organic and inorganic by‐products. By‐product formation is influenced by bromide ion concentration, the source and concentration of organic precursors, pH, ozone dosage, temperature, and alkalinity. Both organic and inorganic by‐products increased when bromide ion concentration increased but decreased with an increase in alkalinity. Organic by‐products were found to increase with a decrease in pH, whereas bromate formation was favored by a high pH. In general, bromoform concentration first increased, then diminished, as the dosage of ozone was increased. Both ozonation and incubation temperatures had a positive effect on the formation of bromoform and bromate. PEROXONE appears to favor bromate formation over organic by‐product formation, whereas the addition of ammonia reduces both bromate and organic by‐products.
Bromate, which forms upon ozonation of water containing bromide ion, can be minimized before production by chemical or physical–hydrodynamic factors or after its formation by removal techniques.
As utilities consider changing their primary disinfection practices from free chlorine to ozone in order to minimize the formation of chlorinated disinfection by‐products (DBPs), the potential for producing ozonation DBPs such as bromate ion must be addressed. Important research findings of bromate ion formation studies over the past five years, which have resulted in substantial understanding of ozone‐bromide ion interactions, are summarized. Areas of incomplete information are identified, and a complete list of references is provided.
For all the potential bromate removal processes evaluated, analysis of the treated water showed the formation of bromide ion, indicating that chemical reduction of the bromate is the primary removal mechanism.
Stage 1 of the Disinfectants–Disinfection By‐Products Rule specifies a maximum contaminant level of 10 μg/L for bromate ion, a by‐product of the ozonation of natural water containing bromide ion. Several options for removing bromate after its formation are evaluated: reduction with ferrous iron (Fe2+), reduction on the surface of activated carbon, ultraviolet irradiation, and high‐energy electron beam irradiation. For all the processes, bromide was found in the treated water, which indicates that the dominating mechanism of bromate removal is chemical reduction. If Fe2+ is introduced after preozonation, it may function both as a reducing agent for bromate and as a coagulant for dissolved organic carbon removal.
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