Reduction of Bromate Source Contamination

A potential source remediation technique for an aquifer contaminated by bromate has been investigated, utilising biological bromate reduction to bromide by augmentation of indigenous microbial populations. This technique, involving addition of a carbon source to contaminated groundwater, is analogous to the methodology used in commercial denitrification systems. Experimental work is aimed at development of an ex-situ pump-to-waste or pump, treat-and-reinject strategy, but the technique may also have in-situ applications. Trials initially focussed on a laboratory-scale anaerobic suspended growth chemostat system, investigating glucose addition to real groundwater supplies. Following targeted enrichment of the microbial population, reduction of 32 mgl-1 bromate within a 40 hour residence time was obtained with specific reduction rates of up to 160.48 µmol Br.g dry wt-1.hr-1, which suggested the presence of high-rate bromate reducing bacterial strains. Use of a pilot-scale fixed-film upflow bioreactor seeded with enriched chemostat biomass subsequently confirmed stoichiometric bromate reduction to bromide with 87-90% bromate reduced from an influent concentration of 1.08 mgL-1 over retention times of 40-80 hours. Nitrate reduction of 97-99% from a 30.7 mgL-1 nitrate (as NO3-) influent also occurred at retention times of 10-80 hours, although an increase in nitrite production to 2.7 mgL-1 was observed with a 10 hour retention time. A period of batch operation during the startup phase was shown to be critical to stable operation, but backwashing was not required during the timescale of the experimental run. Further process optimisation will be required, but this study has demonstrated the potential of biological bromate reduction for remediation of a bromate contaminated groundwater source