Towards syngas biorefineries: The potential of microbial consortia for syngas valorisation.

Gasification has emerged as a promising platform to cope with recalcitrant organic waste within the framework of biomass-based biorefineries, producing syngas that can be fermented into valuable bioproducts. Despite its potential, syngas fermentation is based predominantly on pure cultures, which faces significant challenges, including the limited portfolio of generated compounds (primarily acetate and ethanol) and their low productivity. To address these bottlenecks, the potential of microbial consortia as effective platforms for syngas conversion has been evaluated. Syngas biomethanation using mixed cultures is a well-established process, with pilot-scale implementations yielding promising results. Alternatively, the production of carboxylic acids has emerged as an interesting option compared to pure cultures, as comparable acetate productivities can be achieved along with the possibility for chain elongation to butyrate or caproate. However, the feasibility of using mixed cultures to produce alcohols and other high-value compounds from syngas remains underexplored. Advancing the field will also require the development of innovative technologies to overcome inherent barriers and fully unlock the potential of syngas-based bioprocesses. Key challenges include the presence of impurities and variability in syngas composition, mass transfer limitations in bioreactors, and the need for efficient downstream effluent purification. In this context, mixed cultures emerge as a robust approach capable of buffering syngas fluctuations and tolerating certain impurities. At the same time, the development of novel gas phase bioreactors and innovative membrane-based systems for effluent purification is crucial for enhancing CO and H mass transfer and improving products titers, respectively.