Evaluation for biological reduction of nitrate and perchlorate in brine water using the hydrogen-based membrane biofilm reactor

Whereas ion exchange is an attractive technology for treating perchlorate and nitrate in drinking water, a major disadvantage is that the resin must be regenerated using a brine, producing wastes with high concentrations of nitrate, perchlorate, and salt. This study investigates the potential for simultaneous nitrate and perchlorate reductions in high-salt conditions using the H-2-based membrane biofilm reactor (MBfR). The autotrophic biological reductions produce harmless N-2 and Cl-, making the brine safe for reuse or disposal. A very high-strength brine (similar to 15% salt) from a commercial ion-exchange membrane, Purolite, supported biofilm accumulation and allowed slow reduction rates for nitrate and perchlorate. Reduction rates increased significantly when the Purolite brine was diluted by 50% or more. A synthetic high-strength salt medium containing nitrate, perchlorate, or both supported more rapid reduction rates for as high as 20 g/L (similar to 2%) NaCl, while 40 g/L NaCl slowed reduction by 40% or more, confirming that the microorganisms in the MBIR were inhibited by high salt content. An increase of H-2 pressure gave higher fluxes for 20 g/L NaCl, demonstrating that H-2 availability controlled the reduction kinetics when the system was not salt-inhibited.