471752 Understanding the Influence of Hemicellulose and Lignin Removal on Deconstruction of Switchgrass By Clostridium Thermocellum Consolidated Bioprocessing Vs. Conventional Fungal Enzymatic Hydrolysis

Thursday, November 17, 2016: 5:20 PM
Union Square 17 & 18 (Hilton San Francisco Union Square)
Ninad D. Kothari1,2,3, Charles M. Cai2,3, Rajeev Kumar2,3 and Charles E. Wyman1,2,3, (1)Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, Riverside, CA, (2)Center for Environmental Research and Technology (CE-CERT), University of California, Riverside, Riverside, CA, (3)BioEnergy Science Center (BESC), Oak Ridge National Laboratory (ORNL), Oak Ridge, TN

Low cost sustainable fuels are urgently needed to support human prosperity. Currently, almost all liquid fuels are derived from petroleum that is finite in quantity and contributes significantly to climate change. According to the US Energy Information Administration, transportation accounts for about 70% of the total US oil consumption and about 95% of which is from fossil fuels consumption. Alternatively, biofuels would provide a sustainable energy source and help reduce our dependence on imported petroleum. Ethanol made from corn starch and cane sugar is presently the largest biotechnology-based product and commands a large market share of the alternative fuels market. However, currently the trend is to produce ethanol from lignocellulosic biomass that, unlike corn starch and cane sugar, does not directly compete with our food infrastructure. Ethanol is a high octane, cleaner burning fuel that, when made from lignocellulosic biomass, offers a low carbon footprint and the potential to be further upgraded to other drop-in fuels, such as butanol, jet fuel, gasoline, and diesel. Ethanol production from lignocellulosic biomass involves numerous important operations including size reduction, pretreatment, enzyme production, enzymatic hydrolysis, fermentation, and product recovery. The production of cellulolytic enzymes, typically from a fungus such as Trichoderma reesei, is one of the most expensive steps because of the high concentrations of enzymes needed to achieve economically attractive ethanol yields from recalcitrant lignocellulosic biomass. Consolidated bioprocessing (CBP) is a simplified, integrated bioprocess for directly converting lignocellulosic biomass into ethanol by utilizing thermophilic anaerobes that can produce their own enzyme consortium to hydrolyze biomass polysaccharide chains into fermentable sugars after which the same organism metabolizes the sugars to produce ethanol and other products. Clostridium thermocellum, in particular, is a very promising CBP organism. However, pretreatment may still be required to assist C. thermocellum in biomass deconstruction for high yields. Dilute acid and hydrothermal are leading pretreatment technologies that reduce biomass recalcitrance by removing some of the lignin and most of the hemicellulose. Alkali pretreatments, on the other hand, remove some hemicellulose and a lot of the lignin. By comparison, co-solvent enhanced lignocellulosic fractionation (CELF), a novel pretreatment technology recently invented at the University of California, Riverside, which makes use of tetrahydrofuran (THF) as a co-solvent in water, enhances the solubilization and recovery of both hemicellulose sugars and lignin from lignocellulosic biomass beyond that of conventional pretreatment technologies. Because different pretreatment technologies produce solids with different physical and compositional characteristics, it is important to evaluate how these features impact CBP performance. This study, therefore, compared the effects of CELF pretreatment combined with C. thermocellum CBP on total sugar release from switchgrass to those of hydrothermal, dilute acid, and alkali pretreatments. The objective was to identify pretreatment conditions that give the highest possible sugar release in pretreatment (Stage 1) and biological conversion (Stage 2) steps combined for each pretreatment technology. The pretreatments were performed over a range of temperatures and times, and the resulting washed solids were then subjected to C. thermocellum CBP at 5 g/L glucan loading in 50 mL bottle reactors incubated at 60˚C with a shaking speed of 180 rpm and fungal enzymes mediated enzymatic hydrolysis at 50˚C and 150 rpm with the same solids loading to establish overall switchgrass deconstruction and sugar recovery.

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