A novel hollow-fiber membrane biofilm reactor (HFMBR) was developed to remove nitrate from contaminated drinking water using molecular hydrogen as a clean electron-donor substrate. The hollow fibers were sealed on one end and were pressurized with hydrogen on the other end. The counter-diffusion transfer of nitrate and hydrogen allowed 100% hydrogen transfer efficiency into the biofilm and achieved up to 99.9% hydrogen-utilization efficiency for denitrification. Partial denitrification met regulatory standards for nitrate and nitrite at the same time that relatively high steady-state nitrate fluxes (0.08 and 0.1 mg N/cm2−d) were achieved with liquid-phase hydrogen concentrations (0.009 and 0.07 mg H2/l) magnitudes lower than in previous studies. The low frequency of fiber-to-fiber contact in the upflowing liquid established good biofilm accumulation. The specific biofilm detachment rates were between 0.015 and 0.017 day−1, which attained biofilm thickness up to 179 μm. Finally, DOC and BDOC analyses showed that the DOC was increased, while the effluent BDOC was 0.5 mg/l.

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