Enrichment of syngas‐converting communities from a multi‐orifice baffled bioreactor

Abstract

SummaryThe substitution of natural gas by renewable biomethane is an interesting option to reduce global carbon footprint. Syngas fermentation has potential in this context, as a diverse range of low‐biodegradable materials that can be used. In this study, anaerobic sludge acclimatized to syngas in a multi‐orifice baffled bioreactor (MOBB) was used to start enrichments with CO. The main goals were to identify the key players in CO conversion and evaluate potential interspecies metabolic interactions conferring robustness to the process. Anaerobic sludge incubated with 0.7 × 105 Pa CO produced methane and acetate. When the antibiotics vancomycin and/or erythromycin were added, no methane was produced, indicating that direct methanogenesis from CO did not occur. Acetobacterium and Sporomusa were the predominant bacterial species in CO‐converting enrichments, together with methanogens from the genera Methanobacterium and Methanospirillum. Subsequently, a highly enriched culture mainly composed of a Sporomusa sp. was obtained that could convert up to 1.7 × 105 Pa CO to hydrogen and acetate. These results attest the role of Sporomusa species in the enrichment as primary CO utilizers and show their importance for methane production as conveyers of hydrogen to methanogens present in the culture.

Enrichment of Mesophilic and Thermophilic Mixed Microbial Consortia for Syngas Biomethanation: The Role of Kinetic and Thermodynamic Competition

“…Overall, the microbial composition found was in agreement with the catabolic routes identified for each enriched consortium in section 3.2 as most of the dominant genera identified could be associated with a specific microbial activity. Additionally, the results obtained here were highly consistent with other batch enrichment studies performed at similar conditions as the genera Acetobacterium and Methanospirillum were also found to be predominant by Arantes et al [16] at mesophilic conditions and the genus Thermincola by Alves et al [15] at thermophilic conditions. This indicates that the microbial selection process is somewhat independent of the inoculum used for the enrichment and shows high reproducibility, since microbial communities with very different initial microbial composition converged towards enriched cultures with high similarity as a result of the microbial selection driven by the operating conditions used.…”

“…In the present study, the initial PCO was kept constant at 0.4 atm along the whole thermophilic microbial enrichment, which probably favored the prompt selection of hydrogenotrophic methanogenic species with higher tolerance to CO, allowing a complete conversion of syngas into CH4. Similarly, recent work on the enrichment of mesophilic mixed cultures using a multi-orifice baffled bioreactor (MOBB) sludge as initial inoculum reported a partial conversion of syngas into CH4 with acetate accumulation in the fermentation broth, which was attributed to a possible inhibition of aceticlastic methanogens due to the toxicity of CO [16].…”

“…Studying changes in the microbial community structure and activity when exposed to different operating conditions is thus fundamental for understanding the population dynamics determining the outcome of microbial conversion processes. The evolution of the activity and composition of syngas-converting methanogenic microbial communities upon exposure to syngas as the sole carbon and energy source using mesophilic and thermophilic anaerobic sludges has been recently studied through microbial enrichments in batch mode [15,16]. However, both of these enrichment studies resulted in the development of enriched cultures with limited methanogenic potential, as significant amounts of acetate remained unconverted in the fermentation broth due to the absence of certain methanogenic microbial groups in the mixed cultures.…”

Influence of Liquid-to-Gas Ratio on the Syngas Fermentation Efficiency: An Experimental Approach

“…In a previous study, a complete CO consumption at nine days was shown, but not at four days [ 14 ]. Another study showed a complete CO consumption at 10 days [ 16 ]. Both studies exhibited similar mesophilic conditions and a headspace containing a volumetric CO concentration of 23.3% and 40% CO, respectively.…”

Biomethanation of Syngas by Enriched Mixed Anaerobic Consortia in Trickle Bed Reactors

“…Improved methane productivity rates were reported by Strübing et al [34,35] when H2/CO2 methanation was performed under thermophilic conditions with mixed microbial consortia. Alternative reactor configurations reported in literature for syngas biomethanation are reverse membrane bioreactors [36,37] and multi-orifice baffled bioreactors [38].…”