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ARS Home » Southeast Area » Tifton, Georgia » Crop Genetics and Breeding Research » Research » Publications at this Location » Publication #267775

Title: Ethanol and co-product generation from pressurized batch hot water pretreated T85 bermudagrass and Merkeron napiergrass using recombinant Escherichia coli as biocatalyst

Author
item BRANDON, SARAH - University Of Georgia
item SHARMA, LEKH - University Of Georgia
item HAWKINS, GARY - University Of Georgia
item Anderson, William - Bill
item CHAMBLISS, KEVIN - Baylor University
item DORAN-PETERSON, JOY - University Of Georgia

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2011
Publication Date: 7/18/2011
Citation: Brandon, S.K., Sharma, L.N., Hawkins, G.M., Anderson, W.F., Chambliss, K., Doran-Peterson, J. 2011. Ethanol and co-product generation from pressurized batch hot water pretreated T85 bermudagrass and Merkeron napiergrass using recombinant Escherichia coli as biocatalyst. Biomass and Bioenergy. 35:3667-3673. DOI: 10.1016/j.biombioe.2011.05.021.

Interpretive Summary: Various warm-season grasses have been proposed as good biomass sources for conversion to ethanol or petroleum replacement fuels. Due to the fact that only cellulose and hemi-cellulose can be converted and presence of lignin with cell wall of these plants, pretreatment of the grasses is required to maximize ethanol yield during fermentation. T85 bermudagrass and Merkeron napiergrass (Pennisetum purpureum Schumach.) samples were either left untreated or were pretreated with pressurized batch hot water (PBHW) for 2 minutes at 230°C at 5% w/v whole grass solids loading. Theoretically, this pretreatment would break the cell wall apart to make cellulose and hemi-cellulose available for enzymatic conversion to sugars for subsequent fermentation. Following a 24 h enzymatic digestion, untreated and PBHW pretreated grasses were evaluated for ethanol production and co-product generation including potential fermentation inhibitors. Fermentations of PBHW pretreated grasses with Escherichia coli LY01 produced twice the ethanol of their untreated counterparts. PBHW pretreated Merkeron napiergrass produced 224.5 mg/g grass ethanol (73% maximum theoretical yield) and PBHW pretreated T85 bermudagrass reached 213.0 mg/g grass (70% maximum theoretical ethanol yield). PBHW pretreatment produced potential fermentation inhibitors such as acetic acid, formic, cinnamic acids, and aldehydes. Despite some of these inhibitors remaining with the solids after PBHW pretreatment, there was greater reduction of cellulose and hemicellulose to sugars during the enzymatic digestion of the grasses prior to fermentation when compared to the untreated grasses. This resulted in increased ethanol yields during fermentation with bacteria as the catalyst.

Technical Abstract: Pretreatment of grasses is required to maximize ethanol yield during fermentation. T85 bermudagrass and Merkeron napiergrass (Pennisetum purpureum Schumach.) were either left untreated or were pressurized batch hot water (PBHW) pretreated for 2 minutes at 230°C at 5% w/v whole grass solids loading. Following a 24 h enzymatic digestion, untreated and PBHW pretreated grasses were evaluated for ethanol production and co-product generation including potential fermentation inhibitors. Fermentations of PBHW pretreated grasses with Escherichia coli LY01 produced twice the ethanol of their untreated counterparts. PBHW pretreated Merkeron napiergrass produced 224.5 mg/g grass ethanol (73% maximum theoretical yield) and PBHW pretreated T85 bermudagrass reached 213.0 mg/g grass (70% maximum theoretical ethanol yield). Pretreatment by PBHW resulted in increased solubilization of hemicelluloses. PBHW pretreatment also produced potential fermentation inhibitors such as acetic acid, formic, cinnamic acids, and aldehydes. Despite some of these inhibitors remaining with the solids after PBHW pretreatment, there was more efficient hydrolysis of the cellulose and remaining hemicellulose during the enzymatic digestion of the grasses prior to fermentation when compared to the untreated grasses. This increase in digestibility observed with enzymes prior to fermentation resulted in increased ethanol yields during bioconversion using E.coli LY01 as the biocatalyst.