Converting CO2 from biogas with H2 into acetic acid in a trickle bed bioreactor with Moorella thermoacetica or a homoacetogenic mixed culture.

Gaseous fermentation for converting carbon-dioxide (CO2) from biogas with H2 into value-added chemicals such as acetic acid offers a sustainable solution compared to chemical upgradation. In this study we compare the performance of Moorella thermoacetica, a thermophilic homoacetogen employing the Wood-Ljungdahl pathway, with a mixed rumen culture enriched for homoacetogenic activity. Both cultures were evaluated for CO2/H2 conversion efficiency, acetic acid production, and upgrading of biogas and added H2 to renewable natural gas (RNG) using a trickle bed reactor (TBR). The mixed culture achieved high hydrogen (H2) conversion (99.4 %), and carbon-dioxide (CO2) conversion 95.1 %, significantly outperforming M. thermoacetica in process stability and volumetric productivity, with acetic acid yields reaching 22.3 g/L and biomass productivity of 1.8 g/L/day. Output methane composition of the TBR reached 99.1 %. This work highlights the trade-offs between pure and mixed cultures during gas fermentation, emphasizing the mixed culture's enhanced productivity and superior stability under fluctuating process conditions of importance for a scalable industrial application.