Hydrogenotrophic denitrification in a microporous membrane bioreactor

Hydrogenotrophic denitrification of nitrate contaminated groundwater in a bench-scale microporous membrane bioreactor has been investigated. To prevent microbial contamination of the effluent from the reactor the nitrate-laden water treated was separated from the denitrifying culture with a 0.02 μm pore diameter membrane. Equal pressure was maintained across the membrane and nitrate was removed by molecular diffusion through the membrane and into the denitrifying culture. The system was operated with a hydrogenotrophic denitrification culture to circumvent the addition of an organic substrate to the water. Removal efficiencies ranging from 96% to 92% were achieved at influent concentrations ranging from 20 to 40 mg/L NO3−-N. The flux values achieved in this study were 2.7–5.3 g NO3−-N m−2 d−1. The microporous membrane served as an effective barrier for preventing microbial contamination of the product water as evidenced by the effluent heterotrophic plate count of 9 (±3.5) CFU/mL. The hydrogenotrophic culture was analyzed using available 16S and 23S rRNA-targeted oligonucleotide probes. It was determined that the enrichment process selected for organisms belonging to the beta subclass of Proteobacteria. Further analysis of the hydrogenotrophic culture indicated that the organisms may belong to the β-3 subgroup of Proteobacteria and have yet to be identified as hydrogenotrophic denitrifiers.