Abstract
Syngas – a gas mixture of CO, CO2, and H2 – can be produced by gasification of C-based streams (e.g. biomass, plastics). It is as a cost-effective substrate for the production of numerous valuable products. Some microorganisms can thrive using CO or syngas as carbon and energy source, and just a few strains are able to converting CO/syngas into biofuels. Clostridium carboxidivorans is a microorganism known for its ability to produce short- and long-chain acids and alcohols, including acetic acid, butyric acid, hexanoic acid, ethanol, butanol and hexanol.
This contribution focuses on characterizing CO fermentation by C. carboxidivorans in a continuous gas-fed bioreactor. The bioreactor was continuously supplied with a 100% CO stream at a flow rate of 0.6 L/h. Fermentation tests were carried out at constant temperature with an without pH control. The fermentation process was characterized in terms of metabolites and cell production, CO conversion, specific rate of cells/metabolite production and yields. Ethanol was the primary solvent produced and a shift towards longer-chain alcohols was observed under constant pH. The maximum cell concentration was 0.56 gDM/L with and without pH control. The highest solvent concentrations was 1820 mg/L of ethanol without pH control, and 330 mg/L of butanol and 20 mg/L of hexanol with pH control.
The study highlithed the role of the substrate composition and the operating conditions on syngas. The reported results provides a first guidline for syngas fermentation for the production of biofuels and chemicals.
