Effect of addition of ammonia on the bromate formation during ozonation

Continuous ozonation experiments of bromide solutions have been conducted in the presence of ammonia. Solutions were prepared with phosphate-buffered NOM-free water (pH=8) spiked with high levels of bromide and ammonium ions according variable molar ratio R=NH4+/Br-. Our results have shown that in the presence of tert-butanol, the bromate formation presents a delay increasing with the value of R. Bromate formation occurs when total bromine measured by the DPD colorimetric method presents a minimum level and when total bromine measured by the DPD+KI colorimetric method reaches a maximum level. The hypothesis that dibromamine was not quantitatively measured by DPD alone was first made, but unconfirmed, by complementary experiments. So we assumed that, in our experimental conditions, an unknown by-product measured by DPD+KI could be formed by ozonation of bromide in the presence of ammonia. The nitrate formation was found to be lower than expected, probably due to autonomous bromamine decomposition into nitrogen.