(420b) Redox Control During Producer Gas Fermentation

The fermentation of biomass-generated producer gas (primarily CO, CO2, H2, and N2) to fuel ethanol and other useful products at economically competitive prices is the prime research focus of our multi-disciplinary, multi-institutional research team. The research is comprised of the holistic process starting from biomass growth to production of ethanol and is driven by a need for a low-cost sustainable, renewable energy source that would be beneficial both economically as well as environmentally.

Many enzymatic reactions in converting producer gas into ethanol are oxidation-reduction reactions where one substance is oxidized in order to reduce another substance. The fermentation process is non-typical since the carbon source for ethanol is obtained from the producer gas containing both oxidized (CO2) and reduced (CO) carbon. It is therefore important to understand the culture redox potential (CRP) in order to determine the ability of the bacteria to perform the oxidation/reduction reactions.

A component of the current research involves fermentation of synthetic producer gas using Clostridium Carboxidivorans P7. As pH manipulation has not been found to control product distribution, current studies are assessing the CRP. In several unrelated studies, CRP has been shown to control product distributions in other bacterium.

Variables being addressed that affect the CRP are feed gas composition and media in the presence and absence of cells. Results of how these variables affect CRP and how the CRP effects the product distribution will be presented. In addition, results will be presented regarding CRP control, optimal CRP levels, and the effect of CRP on the ability of the bacteria to switch from acetogenesis (acetic acid production) to solventogenesis (ethanol production).