The Impact of Ammonia Photo-Oxidation Under UV Light from Low Pressure Mercury Lamps on Bromate Decay in Water

This research examines the influence of ammonia photo-oxidation on the reduction of the water contaminant, bromate (BrO₃^-) as a potential removal strategy. It has long been recognized that aqueous ammonia (NH₃) has the potential to accelerate the photodecomposition of bromate. This phenomenon has never been studied in dilute solutions whereby its impact during water treatment with UV low-pressure lamps may be used advantageously. It is hypothesized that the accelerated rate of BrO₃^- photodecomposition in the presence of NH₃ is attributed to the generation of an additional supply of electrons as ammonia photo-oxidation occurs. The findings revealed that the rate of bromate photo-decay is increased in the presence of ammonia even in dilute ammonia and BrO3- solutions and the reaction is further accelerated in basic solutions and solutions containing chloride ions. Nitrate is the final stable reaction product formed with prolonged irradiation, followed by a depression of pH. Hypobromous acid was undetected at these concentrations. It was also found that ammonia oxidation occurred in the presence of bromide ions even in acidic solution. The hypothesis that electrons are made available for electron scavengers when ammonia oxidation occurs was verified using sulphur hexafluoride as an electron scavenger.