Progress and development of syngas fermentation processes toward commercial bioethanol production

Syngas is created through the thermochemical conversion of biomass using gasification or pyrolysis and from CO-rich off-gases obtained from industries such as steel mills. The Wood–Ljungdahl metabolic pathway, or one of its variations, is used by acetogenic bacteria to convert syngas components (CO, H₂, and CO₂) to alcohols and other compounds. Many factors affect how well syngas is fermented, including the bacteria species used, syngas composition, medium components, bioreactor type, operational parameters used and the gas–liquid mass transfer rate. These parameters impact carbon and electron flow in the bacteria, influencing the distribution, concentration and metabolic end-product yield, which determines process feasibility. This article focuses on gas composition, microorganisms, gas–liquid mass transfer fermentation strategies, medium design and commercialization activities to develop the syngas fermentation processes.