Biomass gasification-fermentation is a process that involves the partial oxidation of biomass to synthesis gas or syngas, primarily containing CO, CO2, and H2, which is then fermented to ethanol and other co-products. The advantage of gasification-fermentation over the saccharification-fermentation process is that gasification utilizes all lignocellulosic components (cellulose, lignin and hemicellulose) in the biomass, leading to a greater potential for ethanol production from the same quantity of biomass.
Syngas fermentation using “Alkalibaculum bacchi” a new alkaliphilic acetogen strain CP11 was studied in 250-mL bottles containing 100 mL of yeast extract medium at 37°C and pH 8.0. The new strain CP11 was able to convert CO and H2 present in modeled syngas (from bottled gases) and producer syngas (obtained from gasifying switchgrass) to ethanol and acetic acid. The modeled syngas was composed of 40% CO, 30% CO2, and 30% H2 (by volume). The producer gas was made of 13.4% CO, 16.4% CO2, 11.1% H2, 2.8% methane, 0.4% acetone, and 54.5% N2 (by volume).
Products formed and conversion efficiencies of syngas components during the fermentation were determined. Preliminary results showed that strain CP11 grew faster and produced more ethanol in the medium with modeled syngas compared to producer syngas. However, two times more acetic acid formation was measured in the medium with producer syngas. This showed that the presence of more CO in the syngas favored ethanol formation. The CO and H2 conversion efficiencies were 28.1% and 6.4%, respectively, with modeled syngas compared to 49.2% and 37.1% with the producer syngas. These results showed the potential of “Alkalibaculum bacchi” strain CP11 use in ethanol and acetic acid production from syngas.