(27ba) Continuous Production of Acetic Acid By Eubacterium Limosum KIST612 Using an External Membrane Module

The emission of waste gases from fossil fuel-based industries is a major contributor to environmental issues, including global warming. As a result, numerous studies are being conducted to find solutions, and one effective method is the gas fermentation process that utilizes acetogenic bacteria to convert industrial waste gas (e.g., steel mill gas) into valuable products. Additionally, this biological conversion process can contribute to the circular carbon economy by capturing and recycling carbon-rich waste gases that would otherwise be released into the atmosphere. Eubacterium limosum KIST612, an anaerobic acetogen, is capable of converting carbon monoxide (CO) into organic acids such as acetate and butyrate using the Wood-Ljungdahl pathway. However, the low gas-liquid mass transfer limitation of CO gas can make it challenging to achieve high biomass and acetate concentrations with E. limosum KIST612. Therefore, alternative methods are needed to overcome this limitation. In this study, continuous gas fermentation with hollow fiber membrane-based cell recycle systems was employed to achieve high cell density. And various gas (40% CO and 60% N₂) flow rates were implemented to increase cell growth and acetate production through the conversion of carbon monoxide (CO). Furthermore, the trace metal concentration, known to enhance enzyme activity in the Wood-Ljungdahl pathway responsible for the conversion of CO to organic acids, was optimized to increase acetate production. A maximum of 28.8 g/L acetate was observed, which is a 4-fold increase compared to the previous results. Therefore, the cell-recycled fermentation strategy, involving two stages of cell concentration and acetate production, is considered more effective than the conventional continuous culture.