Syngas biomethanation in a semi-continuous reverse membrane bioreactor (RMBR)

Abstract

Syngas biomethanation is a potent bio-conversion route, utilizing microorganisms to assimilate intermediate gases to produce methane. However, since methanogens have a long doubling time, the reactor works best at a low dilution rate; otherwise, the cells can be washed out during the continuous fermentation process. In this study, the performance of a practical reverse membrane bioreactor (RMBR) with high cell density for rapid syngas biomethanation as well as a co-substrate of syngas and organic substances was examined in a long-term fermentation process of 154 days and compared with the reactors of the free cells (FCBR). The RMBR reached maximum capacities of H 2 , CO, and CO 2 conversion of 7.0, 15.2, and 4.0 mmol/L reactor .day, respectively, at the organic loading rate of 3.40 gCOD/L.day. The highest methane production rate from the RMBR was 186.0 mL/L reactor .day on the 147th day, compared to the highest rate in the FCBR, 106.3 mL/L reactor .day, on the 58th day. The RMBR had the ability to maintain a high methanation capacity by retaining the microbial cells, which were at a high risk for cell wash out. Consequently, the system was able to convert more syngas simultaneously with the organic compounds into methane compared to the FCBR.