Parameters Affecting the Formation of Bromate Ion During Ozonation

Batch type ozone experiments conducted on aquatic humic substances solutions spiked with bromide ion were developed to evaluate the importance of various parameters that may affect the formation of bromate ion during ozonation. The nature of the NOM, the alkalinity, the bromide ion content and the presence of ammonia were found to significantly affect the bromate ion production. Temperature and pH can be considered as minor factors. The ozonation of a clarified surface water using a continuous flow ozone contactor have shown that the addition of a low quantity of ammonia (0.05 to 0.1 mg/L NNH₄ ⁺) appeared to be an interesting option for controlling the bromate formation. On the contrary, the addition of hydrogen peroxide may enhance or reduce the bromate ion production, depending on the applied hydrogen peroxide/ozone ratio.     

The Measurement Of Very Low Level Bromate Ion

The potential to form BrO₃ ^? as a byproduct during ozone treatment of raw water containing bromide ion is a major concern for utilities planning to use ozone. The proposed BrO₃ ^? Maximum Contaminant Level (MCL) of 10 μg/L in the USA has been established largely by using ion chromatography. A spectrophotometric method based on the oxidation of chlorpromazine in the presence of BrO₃ ^? has been developed. The method detection limit (MDL) in reagent water is 0.8 μg/L BrO₃ ^? The procedure has an operating range of 1 to 40 μg/L BrO₃. The precision of the method is calculated to be better than 2.5% with an accuracy within ± 1 μg/L BrO₃ ^?. Details of the method are presented along with data gathered by ion chromatography using borate and carbonate eluants; chlorpromazine post column studies; and low level capillary electrophoresis studies.     

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

A simple model is developed to predict the formation of bromate ion as well as hypobromous acid/hypobromite ion through the hydroxyl radical pathway. For simplicity of the model, hydroxyl radical concentrations are represented by the concentration ratio of hydroxyl radical to dissolved ozone under the different pH conditions. A kinetic analysis is conducted to evaluate the ratio under the different pH conditions based on the experimental data. The different extent of the ratio by one pH unit is found to be 3–4 times. This model can favorably simulate the formations of bromate ion as well as hypobromous acid/hypobromite ion in spite of the simplicity of the model. So it is likely that this model will be applicable to the prediction of bromate ion formation in water purification process such as drinking water treatment by introducing the concentration ratio of hydroxyl radical to dissolved ozone.     

Pilot-Scale and Full-Scale Evaluation of the Chlorine-Ammonia Process for Bromate Control During Ozonation

An innovative approach to minimize bromate formation using sequential chlorine and ammonia (Cl₂-NH₃ process) was developed at pilot scale and validated in a full-scale drinking water facility. Pilot-scale results showed the Cl₂-NH₃ process minimized bromate formation by 65–95% compared to 40–70% using ammonia only. A 90-day full-scale evaluation confirmed the Cl₂-NH₃ process could prevent bromate concentrations from exceeding 10 μg/L. Full-scale implementation of the Cl₂-NH₃ process allowed an increase in ozone exposure level from 3.0 mg-min/L to 8.6 mg-min/L at 15.1°C. The increased exposure level is important as drinking water utilities strive to meet more stringent drinking water regulations such as Cryptosporidium inactivation.     

The Effect of Bromide Ion on the Formation of Organohalogen Disinfection By-products During Ozonation

Ozonation of water containing bromide ion (Br^?) leads to the formation of brominated disinfection byproducts (DBPs). The purpose of this study was to examine the influence of bromide ion upon the distribution and variation of organohalogen DBPs. Bromide ion concentration had a negative effect on chloroform formation as opposed to increased formation of brominated trihalomethanes (THMs). The results of factor analysis lead clearly to the interpretation that the bromide ion was strongly correlated with brominated THMs and less strongly with brominated HANs (haloacetonitriles). Compared to THMs and HANs, brominated HAAs (haloacetic acids) demonstrated a relatively weak correlation to bromide ion concentration. The addition of alkalinity enhanced the formation of chloroform when ozonation time was 10 to 30 minutes, while concentrations of other bromide ion-containing THMs decreased with increasing alkalinity.