| This study focuses on nitrate removal from drinking water by a novel hollow-fiber membrane biofilm reactor using hydrogen as the electron-donor substrate. With the biofilm growing directly on the surface of the hollow fiber, the hydrogen-transfer efficiency to the biofilm was virtually 100%, and the biofilm achieved a high nitrate flux without the need for a high H 2 concentration in the bulk liquid. These factors dramatically reduce the size of the reactor and loss of hydrogen in the effluent and to the atmosphere, making the hollow-fiber membrane biofilm reactor an economically favorable and safe process.; Short-term pseudo-steady-state experiments achieved a range of maximum nitrate fluxes between 0.042 and 0.16 mg N/cm2-d, which correspond to maximum H2 utilization fluxes between 0.014 and 0.055 mg H 2/cm2-d with PH2 between 0.2 and 0.56 atm. The H2 utilization fluxes in this study are significantly higher than the hydrogen fluxes in previously published autohydrogenotrophic denitrification studies. The experimentally determined fluxes and concentrations for hydrogen, nitrate, and nitrite can be used as practical guidelines for system design.; The optimum pH for denitrification was between 7.7 and 8.6, with the maximum efficiency at pH 8.4. Increasing the pH over 9 caused a decrease in nitrate-removal efficiency and an increase of nitrite accumulation. Precipitation of hardness occurred in all runs. Denitrification increased alkalinity and elevated the pH significantly when the systems contained a low buffer intensity.; Dissolved organic carbon was greater in the effluent than in the influent, with 22% of the effluent DOC being biodegradable. Thus, the denitrification reactor should be followed by a process that removes biological instability.; Modeling analyses defined the conditions for which H2 or NO 3-- was the limiting substrate. The analyses also showed that high hydrogen pressures dramatically increased the maximum specific nitrate and nitrite reduction rates, which suggests an up-regulation of nitrate and nitrite reductases by a higher H2 concentration in the biofilm. |
