Tuesday, April 30, 2013
Exhibit Hall
Developing an understanding of the interactions between pretreatment and CBP mediated hydrolysis and fermentation is vital to advancing a conversion system that reduces biomass recalcitrance at a low cost. With advances in transgenic materials and the systemic synergies of CBP, low severity pretreatments may be optimal for downstream biomass deconstruction and sugar conversion. Although recent efforts have been devoted to developing CBP organisms which can synthesize the appropriate enzymes, effectively release sugars from carbohydrates, and ferment sugars with high ethanol yields, comparatively little has been done on investigating how successful these organisms are in hydrolyzing highly non-ideal, real pretreated substrates. This factor is essential to determine CBP feasibility, improve its performance, and apply it commercially. Therefore, the influences of severity and pretreatment method are being explored in terms of CBP performance through organism and substrate characterizations. In this study, poplar (Populous trichocarpa) and switchgrass (Panicum virgatum) were pretreated under hydrothermal and dilute acid conditions over a range of severities. The pretreated solids were separated from the liquid hydrolysate and used as feedstocks for the CBP system. Both untreated and pretreated solids were tested at a constant solids loading of 5 g glucan/L. For fermentation, 50 mL bottle reactors were incubated with wild type Clostridium thermocellum for up to 7 days at 60°C and 180 rpm. Biomass solubilization, solids composition, and aqueous phase concentrations of metabolites and soluble sugars were determined to measure performance against pretreatment method, severity, and feedstock type.