Simultaneous Biogas Upgrading and Valuable Chemical Production Using Homoacetogens in a Membrane Biofilm Reactor

Biogas produced from anaerobic digestion usually contains impurities, particularly with a high content of CO₂ (15-60%), thus decreasing its caloric value and limiting its application as an energy source. H₂-driven biogas upgrading using homoacetogens is a promising approach for upgrading biogas to biomethane and converting CO₂ to acetate simultaneously. Herein, we developed a novel membrane biofilm reactor (MBfR) with H₂ and biogas separately supplied via bubbleless hollow fiber membranes. The gas-permeable hollow fibers of the MBfR enabled high H₂ and CO₂ utilization efficiencies (∼98% and ∼97%, respectively) and achieved concurrent biomethane (∼94%) and acetate (∼450 mg/L/d) production. High-throughput 16S rRNA gene amplicon sequencing suggested that enriched microbial communities were dominated by Acetobacterium (38-48% relative abundance). In addition, reverse transcription quantitative PCR of the functional marker gene formyltetrahydrofolate synthetase showed that its expression level increased with increasing H₂ and CO₂ utilization efficiencies. These results indicate that Acetobacterium plays a key role in CO₂ to acetate conversion. These findings are expected to facilitate energy-positive wastewater treatment and contribute to the development of a new solution to biogas upgrading.