Simultaneous biogas upgrading and medium-chain fatty acids production using a dual membrane biofilm reactor

Utilizing H₂-assisted ex-situ biogas upgrading and acetate recovery holds great promise for achieving high value utilization of biogas. However, it faces a significant challenge due to acetate's high solubility and limited economic value. To address this challenge, we propose an innovative strategy for simultaneous upgrading of biogas and the production of medium-chain fatty acids (MCFAs). A series of batch tests evaluated the strategy's efficiency under varying initial gas ratios (v/v) of H₂, CH₄, CO₂, along with varying ethanol concentrations. The results identified the optimal conditions as initial gas ratios of 3H₂:3CH₄:2CO₂ and an ethanol concentration of 241.2 mmol L^-1, leading to maximum CH₄ purity (97.2 %), MCFAs yield (54.2 ± 2.1 mmol L^-1), and MCFAs carbon-flow distribution (62.3 %). Additionally, an analysis of the microbial community's response to varying conditions highlighted the crucial roles played by microorganisms such as Clostridium, Proteiniphilum, Sporanaerobacter, and Bacteroides in synergistically assimilating H₂ and CO₂ for MCFAs production. Furthermore, a 160-day continuous operation using a dual-membrane aerated biofilm reactor (dMBfR) was conducted. Remarkable achievements were made at a hydraulic retention time of 2 days, including an upgraded CH₄ content of 96.4 ± 0.3 %, ethanol utilization ratio (URethanol) of 95.7 %, MCFAs production rate of 28.8 ± 0.3 mmol L^-1 d^-1, and MCFAs carbon-flow distribution of 70 ± 0.8 %. This enhancement is proved to be an efficient in biogas upgrading and MCFAs production. These results lay the foundation for maximizing the value of biogas, reducing CO₂ emissions, and providing valuable insights into resource recovery.