Method for design of production medium for fermentation of synthesis gas to ethanol by acetogenic bacteria.

Abstract. Biomass and waste materials are converted to ethanol by gasification followed by fermentation of the synthesis gas using acetogenic bacteria such as Clostridium ragsdalei. Fuel ethanol is a high-volume, low-cost commodity, so capital and operating expenses must be very low to achieve profitable operation. The fermentation medium supplies minerals, metals, and organic co-factors needed to build cell biomass and the functional enzyme platform that conducts the conversion reactions. Research directed toward commercial deployment of synthesis gas (syngas) fermentation processes must consider cost and availability of medium components, and use economically viable medium. A method based on elemental accounting of cell composition was developed to assess the cost and function of fermentation media and their potential for commercial use for syngas fermentation to produce ethanol using C. ragsdalei. Cost of medium was reduced from $9.87 L -1 to $0.26 L -1 . Additional cost reduction can be achieved by eliminating components that are not required, using commercial components purchased at bulk commodity prices, using H 2 S and NH 3 from the syngas production in lieu of purchased sodium sulfide and ammonium chloride, and retaining the acetate buffer from ethanol distillation. These savings can reduce the medium cost below $0.01 L -1 .