Syngas biomethanation and upgrading mediated by different microbial consortia

Syngas biomethanation is a promising technology for energy recovery from non-degradable organic wastes. In the present study, anaerobic sludges from three thermophilic biogas reactors were applied as inocula for syngas biomethanation at 55 degree. The inocula presented different abiotic and biotic properties, as they were retrieved from different biogas reactors fed with cattle manure (CS), sewage sludge (SS) and H2/CO2 (GS). The results showed that the microbial community composition could significantly affect CO conversion and syngas biomethanation. CS presented the highest CO consumption rate due to its higher relative abundance of CO consuming bacteria. In cultures inoculated with CS and SS, CO was mainly converted to acetate following syntrophic acetate oxidization (SAO) to produce H2 CO2 for methane generation via hydrogenotrophic methanogenesis. However, acetate was accumulated in GS due to the lack of acetoclastic methanogens and SAO bacteria. In addition, the CO and CO2 were converted to pure methane (higher than 95% in methane content) via adding H2. However, H2 addition reduced the CO consumption rate due to its preference reacting with biocarbonate in inoculum leading to increase of pH. Moreover, addition of H2 resulted in different conversion efficiencies to methane in the three inocula, exposing different microbial activity and thermodynamic equilibrium of reactions. The results present novel insights into syngas biomethanation process and pave the way to recover energy from recalcitrant biomass.