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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #319574
Title: Switchgrass (Panicum virgatum) fermentation by Clostridium thermocellum and Clostridium saccharoperbutylacetonicum sequential culture in a continuous flow reactor

Author
item ELIA, NOELIA - University Of Kentucky
item NOKES, SUE - University Of Kentucky
item Flythe, Michael

Submitted to: AIMS Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2016
Publication Date: 1/19/2016
Citation: Elia, N.M., Nokes, S.E., Flythe, M.D. 2016. Switchgrass (Panicum virgatum) fermentation by Clostridium thermocellum and Clostridium saccharoperbutylacetonicum sequential culture in a continuous flow reactor. AIMS Energy. 4(1):95-103.

Interpretive Summary: Alcohols for fuel can be produced from food crops like corn or from lignocellulosic biomass (like grasses), which are not used for human food. Either food crops or biomass can be converted to alcohols by bacteria or yeasts. However, grasses can be very difficult to convert because bacteria that convert them are very sensitive to the alcohol that they make. When too much alcohol accumulates, the bacteria stop producing alcohol. The goal of these experiments was to develop a system for real-time separation, that is, a system that continually washes the alcohol from the grass as the alcohol is produced. The alcohol is then collected in a reservoir away from the bacteria that make it. Two bacteria were used: one digested the grass into component sugars; the other converted the sugars to alcohols and other products. The biomass tested was switchgrass, which is very difficult to digest without chemical steps. The bacteria were able to survive in the continuous flow reactor and their products were collected in the reservoir for 9 days. Three flow rates were tested, but none was better than the others, which is beneficial because the lowest flow rate can be used, saving energy and water. The impact of this research is to introduce a way to improve conversion of grass to alcohols and other products, even when the bacteria are very sensitive to the products.

Technical Abstract: The study was conducted to evaluate fermentation by Clostridium thermocellum and C. saccharoperbutylacetonicum in a continuous-flow, high-solids reactor. Liquid medium was continuously flowed through switchgrass (2 mm particle size) at one of three flow rates: 83.33 mL h-1 (2 L d-1), 41.66 mL h-1(1 L d-1), and 20.833 mL h-1(0.5 L d-1). The cellulolytic phase was initiated by culturing C. thermocellum (63 ºC, 24 h). The temperature was decreased (35 ºC) and C. saccharoperbutylacetonicum was inoculated. When metabolism decreased (96 h), the temperature was increased (63 ºC; 24 h) to permit cellulosome production by C. thermocellum. The C. saccharoperbutylacetonicum was re-inoculated and the temperature returned to 35 ºC. The average gross production over 9 d was 1480 mg total acids (formic, acetic lactic butyric), 207 mg total solvents (acetone, butanol, ethanol), and average dry matter disappearance was 2.8 g from 25 g non-pretreated switchgrass. There was no effect of flow rate on the product formation. These results indicate that C. thermocellum can survive and produce cellulases with C. saccharoperbutylacetonicum in a continuous-flow, high-solids reactor temperature with temperature cycling.