(755e) Enhancement of Clostridium Thermocellum Consolidated Bioprocessing (CBP) of Switchgrass By Co-Solvent Enhanced Lignocellulosic Fractionation (CELF) Compared to Dilute Acid and Hydrothermal Pretreatments

Consolidated bioprocessing (CBP) of lignocellulosic biomass into fuels offers the potential for considerable cost savings by eliminating separate enzyme production and combining enzyme production, biomass saccharification, and carbohydrates fermentation in a single vessel.  Clostridium thermocellum, a thermophilic anaerobe, in particular, is a very promising CBP organism, but pretreatment may still be desirable to achieve high product yields.  Leading pretreatments, such as dilute acid, hydrothermal, and others, developed to date remove/relocate different amounts of lignin and/or hemicelluloses, whereas co-solvent enhanced lignocellulosic fractionation (CELF), a novel pretreatment technology recently developed at University of California, Riverside, removes majority of hemicelluloses and lignin from lignocellulosic biomass. However, it is not known how CBP performance is impacted by the physical and compositional characteristics of solids produced by these different kinds of pretreatment. Hence, this project varied operating conditions of CELF pretreatment to determine the effect of high removal of both hemicellulose and lignin together on biomass deconstruction by conventional enzymes and C. thermocellum and compared these effects to those of high removal of just hemicellulose from switchgrass by dilute acid and hydrothermal pretreatments. Hydrolysis performance of conventional enzymes and C. thermocellum were both measured in terms of the time required for release of sugars from solids produced by pretreatments at different severities (i.e., combined time, temperature, and acid concentration). CELF pretreatment conditions were 0.5 to 1.0 wt% sulfuric acid in a 1:1 by volume ratio of tetrahydrofuran (THF) in water at 140-180°C for 10-30 minutes, hydrothermal pretreatment was operated at 160-200°C for 10-30 min, and the dilute acid pretreatment was run at 140-180°C for 10-30 min in 0.5% and 1.0 wt% sulfuric acid to prepare pretreated solids for biological conversion.  The resulting washed solids were then employed in C. thermocellum fermentations at 5 g/L glucan loadings in 50 mL bottle reactors incubated at 60˚C with a shaking speed of 180 rpm, and fungal enzymes mediated enzymatic hydrolysis was performed at low to high enzyme protein loadings at 50°C, pH 5.0, and 150 rpm.  From this data, pretreatment conditions were identified to give the highest possible sugar release in pretreatment (Stage 1) and biological conversion (Stage 2) steps for both free fungal enzymes and C. thermocellum CBP systems.