Research with a laboratory prototype and at the pilot scale documents that the hydrogen-based hollow-fiber Membrane-Biofilm Reactor (MBfR) is technically and economically feasible for reduction of nitrate and perchlorate. In the MBfR, H2 gas diffuses through the wall of a composite membrane, and an autotrophic biofilm naturally develops on the outside of the membrane, where the bacteria's electron acceptor is an oxidized contaminant (e.g., NO3 or ClO4) supplied from the water. The hydrogen pressure to the hollow fibers is a key control parameter that can be adjusted rapidly and easily. For denitrification, partial nitrate removal often is acceptable, and the hydrogen pressure can be low to minimize the costs of H2 supply and the concentration of H2 in the effluent. When perchlorate must be reduced, full nitrate removal is essential, since NO3-N above about 0.2 mg/L slows perchlorate reduction. Perchlorate reduction is sensitive to the hydrogen pressure, which underscores the critical role of H2 pressure for controlling process performance. Given that H2-oxidizing microorganisms have the potential to reduce many oxidized contaminants, we hypothesize that and are beginning to test how well the MBfR reduces bromate, selenate, chlorinated solvents, and other oxidized contaminants.

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