Enhanced Carbon Monoxide Bioconversion Through Adaptation of Mixed Microbial Consortia in Trickle Bed Reactors

Syngas, mainly including CO, H₂ and CO₂, generated from biomass gasification can be used to produce a wide range of commodity chemicals and fuels. However, its biological conversion is still challenging since most microorganisms are sensitive to high CO gas content, resulting in low growth and production rates. In this study, adaptation of mixed microbial consortia to high CO gas content was investigated in trickle bed reactors, TBR, operated in continuous mode under mesophilic (37 ºC) conditions and ambient pressure. Initially, artificial syngas mixture including 20% CO was supplied followed by an incremental increase in CO gas content as 40%, 60% and 90%. The results revealed that the gradual increase of CO concentration led to the successful adaptation of CO-consuming microbial consortia. Enriched consortia exhibited efficient CO conversion primarily to acetic acid, with high consumption rates and product selectivity. The highest CO consumption rates achieved were 21.7 mmol·l_bed⁻¹·h⁻¹ for TBR1 and 22.3 mmol·l_bed⁻¹·h⁻¹ for TBR2 supplied by 90% CO at a gas inflow rate of 28.84 mmol·l_bed⁻¹·h⁻¹. Up to 40% CO in the inflow gas, the dominant product was acetic acid (89 mol %); further increase in CO gas content resulted in increased butyric acid production up to 19 mol %. 16S rRNA analysis revealed an important change in the microbial community during the adaptation process, pointing at Acetobacterium and Sporomusa as key genera for an efficient process at high CO gas content.