Hollow fiber membrane based H2 diffusion for efficient in situ biogas upgrading in an anaerobic reactor

Bubbleless gas transfer through a hollow fiber membrane (HFM) module was used to supply H₂ to an anaerobic reactor for in situ biogas upgrading, and it creates a novel system that could achieve a CH₄ content higher than 90 % in the biogas. The increase of CH₄ content and pH, and the decrease of bicarbonate concentration were related with the increase of the H₂ flow rate. The CH₄ content increased from 78.4 % to 90.2 % with the increase of the H₂ flow rate from 930 to 1,440 ml/(l?day), while the pH in the reactor remained below 8.0. An even higher CH₄ content (96.1 %) was achieved when the H₂ flow rate was increased to 1,760 ml/(l?day); however, the pH increased to around 8.3 due to bicarbonate consumption which hampered the anaerobic process. The biofilm formed on the HFM was found not to be beneficial for the process since it increased the resistance of H₂ diffusion to the liquid. The study also demonstrated that the biofilm formed on the membrane only contributed 22–36 % to the H₂ consumption, while most of the H₂ was consumed by the microorganisms in the liquid phase.