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Bromate reduction by ultraviolet light irradiation using medium pressure lamp

Bromate reduction in water by ultraviolet irradiation using medium-pressure lamps (UV-M) emitting light in the range of 200–600 nm has been investigated. Effects of certain experimental parameters including the initial bromate concentration, UV light intensity, initial pH, and presence of dissolved organic and inorganic carbon and nitrate on the kinetics and efficiency of UV irradiation for bromate reduction were evaluated. Experimental results showed that UV-M irradiation achieved complete destruction of bromate and almost total conversion of bromate into bromide for the initial bromate concentrations ranging from 10 to 1000 μg/L under different pH conditions. A simple kinetic model for bromate destruction was developed. Bromate decay with time during UV-M irradiation follows pseudo-first-order kinetics. The observed rate constant (kobs) decreased with increasing bromate concentrations upto 100 μg/L and then it becomes constant at 0.058 min−1 for higher bromate concentrations. Increasing the UV light intensity resulted in the increase of the rate of bromate destruction. The kobs increased linearly with increasing light intensity. A UV dose of 1000 mJ/cm2 was sufficient to reduce the bromate concentration to less than 10 μg/L within 10 min. The presence of dissolved organic carbon or carbonate/bicarbonate slowed the bromate reduction rate due to absorption of non-negligible fraction of UV light by these compounds. Presence of nitrate affects both the kinetics and efficiency of bromate reduction.