Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2010
Publication Date: 2/1/2011
Citation: Weimer, P.J. 2011. End product yields from the extraruminal fermentation of various polysaccharide, protein and nucleic acid components of biofuels feedstocks. Bioresource Technology. 102:3254-3259.
Interpretive Summary: The complex assemblage of bacteria from the bovine rumen can be used for in vitro fermentations to generate mixtures of volatile fatty acids (VFA) and methane that can be chemically converted to hydrocarbon fuels. We have quantified yields of VFA and methane from a wide variety of biomass components, including carbohydrates, proteins and nucleic acid bases. The data will be of use to bioenergy researchers for calculating the potential for chemical conversion of these compounds to fuels.
Technical Abstract: “Extraruminal” fermentations, employing mixed ruminal bacterial consortia incubated in vitro, are capable of fermenting a complex array of biomass materials to mixtures of volatile fatty acids (VFA), methane, and carbon dioxide. Most of the potential energy in the biomass feedstock is retained in the VFA products, which are known substrates for electrochemical conversion to hydrocarbon fuels. Estimating the fuel potential of extraruminal fermentations requires measurements of the yield and distribution of VFA products from different substrates, but such measurements have not been systematically reported. VFA yields by weight were shown to range from 53 to 66% for various carbohydrates, primarily in the form of acetic and propionic acids. Proteins produced lower VFA yields (20 to 52% by weight), but a more desirable mixture of VFAs (longer average chain length, and both straight- and branched-chain isomers). Nucleic acids were also fermented, but at lower yield (15% by weight for DNA), due in part to poor fermentability of adenine and cytosine bases. Addition of certain co-substrates (e.g., glycerol, an abundant co-product of biodiesel production) favorably improved the VFA product mix. The results have implications for hydrocarbon fuel generation from biomass materials by hybrid fermentation/electrochemical processes.