Rapid bio-methanation of syngas: efficiency of a reverse membrane bioreactor (RMBR) in a semi-continuous fermentation process

There are many promising routes to convert feed-stocks into renewable energy. Gasification is a thermal process used to convert a carbon containing-feedstock to a mixture of gases called syngas. Syngas contains primarily CO, H₂ and CO₂. Since methane (CH₄) is a preferred energy gas, fermentation of the syngas to methane is extensively studied. High loading of bacterial cells in the digester plays an important role to keep the process stable and increase the methane productivity, due to the long retention time required, high sensitivity and easy wash out of cells. The current work focused on the development of the syngas bio-conversion process to methane by using a reverse membrane bioreactor (RMBR), microorganisms encased in membrane under the long term anaerobic fermentation process. In this experiment, an active inoculum was used and syngas containing CO, H₂ and CO₂ and organic medium was provided as carbon and energy source. Polymeric membranes (PVDF) were used to encase the methanogens in the RMBR. Thermophilic anaerobic conditions were performed and compared to the controls (free cells) in the same conditions. Results show that the bio-conversion of syngas to methane using RMBR under anaerobic bioprocess was performed smoothly. The RMBR was able to retain the cells and consequently increased the methane productivity, with decreasing of syngas and maintained low levels of total volatile fatty acid. This result indicates that the RMBR is a useful technique for retaining the cells and increase the efficiency of syngas bio-methanation process.