Technical and Cost Assessment of Electrocatalytic Bromate Removal from Drinking Water

Bromate is a potential human carcinogen and is commonly found in water and wastewater after ozonation. Electrocatalytically, Pd has shown good activity in reducing bromate to bromide; however, the energy efficiency and cost of this technology in a realistic treatment system remain unknown. A custom filter-press reactor with minimal mass-transfer limitations was used to test the kinetics and energy consumption for bromate reduction using Pd, Ru, or Cu on activated carbon cloth as the cathode. In phosphate-buffered nanopure water at circumneutral pH, 95% of bromate was reduced to bromide (from 200 to 10 mu g/L) in 1 h with a normalized activity of 2136 mL min(-1) g(Pd)(-1). The total energy consumption was 0.576 kW h per gram of bromate removed, which is 9 to 43 times lower than that in reported studies. In Austin tap water (TW) at pH 9.5, the normalized activity dropped to 544 mL min(-1) g(Pd)(-1), and the total energy consumption increased to 2.198 kW h per gram of bromate removed, still an improvement over all values reported in the literature despite the latter using synthetic waters. This superior performance is due to the design of the filter-press reactor that minimizes mass-transfer limitations as well as solution resistance compared to reactors evaluated in the literature, such as batch and three-dimensional electrochemical reactors. We note that any lost activity due to catalyst oxidation and poisonings in TW can be electrochemically regenerated by briefly applying a positive and strongly negative potential. This electrocatalytic treatment has estimated costs of $1.41 per 1000 gal (91% capital costs and 9% O&M costs) and is comparable to ion exchange, granular activated carbon, and reverse osmosis, yet benefits from no waste stream generation, indicating that this technology is ready for evaluation at the pilot scale.