Fermentation of synthesis gas to fuel ethanol

The fermentation of biomass-generated synthesis gas (syngas) was studied. Switchgrass and bermudagrass were gasified using three reactor operating conditions: air gasification, near pyrolysis, and steam. For switchgrass, the average CO concentration increased from 20 % with air to 47% with steam, while the H2 concentration increased from 6% to 18%. For bermudagrass, the CO concentration increased from 16% with air to 34% with steam, while the H2 concentration increased from 6% to 28%.
The syngas generated from air gasification was bubbled into a 3-liter bioreactor containing Strain P7. P7 was isolated froman agricultural lagoon and is a new species of Clostridium closely related to Clostridium scatologenes. Important characteristics of P7 include excellent culture stability, tolerance to oxygen, tolerance to high concentrations of ethanol, and an ability to grow in defined medium. Syngas fermentation caused an increase in ethanol production compared to bottled gases of similar composition. However,
exposure to the gas also resulted in cell dormancy and inhibition of hydrogen consumption. The cell dormancy was circumvented by additional cleaning of the gas using acetone scrubbing and a 0.025 µm filter. Gases known to cause hydrogenase inhibition, such as nitric oxide and acetylene, were evaluated with regards to hydrogenase activity.