Biomethanation of Biomass-Derived Syngas by Enriched Microbial Consortia

The current increasing trend in worldwide gasification capacity anticipates that thermochemical biomass conversion methods will play a significant role in the transition to a future bio-based economy. However, the development of more efficient syngas conversion processes to produce biofuels and chemicals is still needed. In this context, the process of syngas biomethanation is currently being considered as an alternative to the catalytic syngas methanation process. This biological process presents a number of inherent benefits such as the use of inexpensive biocatalysts, milder conditions of operation and higher tolerance to the impurities of the raw syngas, which may result in a more cost-effective process [1]. Nevertheless, a thorough understanding of the biological processes that prevail during the biomethanation of syngas is fundamental for the control and optimization of this process.
This work focuses on the study of methanogenic syngas-converting microbial consortia, with the ultimate objective of enhancing the efficiency of the biomethanation of syngas in terms of yield and rate of conversion. A series of enrichment experiments were performed in order to generate two different microbial consortia, one of them enriched at mesophilic conditions and the other at thermophilic conditions. Subsequently, these enriched consortia were kinetically characterized in order to study their patterns of activity and determine the main syntrophic interactions present in each of the consortia. The results showed a significant increase in the conversion efficiency of syngas by the enriched consortia due to the selection and adaptation of the most efficient microbial groups. The maximum methane yields obtained at the end of the enrichment corresponded to 82,4% and 92,7% of the stoichiometric yield for the mesophilic and the thermophilic consortium, respectively. Additionally, the kinetic studies revealed significant differences between the patterns of activity of the mesophilic and the thermophilic consortia. Overall, the thermophilic consortium presented higher conversion rates along with a less complex microbial structure, both of which would ultimately favor a much higher methane productivity in a continuous syngas biomethanation process.