Rapid autohydrogenotrophic denitrification by a membrane biofilm reactor equipped with a fibrous support around a gas-permeable membrane

A hydrogen-based membrane biofilm reactor (MBfR), employing fibrous slag as a bacterial carrier, was developed for rapid and stable autohydrogenotrophic denitrification. This reactor allows hydrogen to be supplied through a gas-permeable membrane to the biofilm supported by fibrous slag. The estimation of hydrogen supply rate clearly demonstrated that hydrogen flux (JH2JH2) is dependent on the gas pressure, leading to a possibility to control JH2JH2 by adjusting the pressure. A startup experiment to investigate denitrification rate with time clarified that denitrification rate of 4.35 g N/m2/day was achieved on day 10, exhibiting rapid startup for autohydrogenotrophic denitrification. Continuous denitrification experiment obviously indicated the effectiveness of the fibrous slag as a bacterial support; concretely, mean denitrification efficiency and rate after 70-days operation reached 99% and 6.58 g N/m2/day at a hydrogen pressure of 50 kPa, respectively, which results in the accomplishment of stable and high-speed denitrification. However, hydrogen utilization efficiency (HUE) was approximately 40%. This low efficiency allowed autotrophic sulfate-reducing bacteria (SRB) to grow in the fibrous-membrane matrix; eventually the HUE for sulfate reduction increased up to 28% on day 74. This result clearly indicates the significance of JH2JH2 control through the gas-permeable membrane for suppressing the occurrence of sulfate reduction.