Bruce S. Dien, Patricia J. O'Byran, Ronald Hector, Loren B. Iten, and Michael A. Cotta. National Center for Agricultural Utilization Research, USDA-ARS, Midwest Area, 1815 N. University Street, Peoria, IL 61604
There has been growing interest in producing switchgrass as an energy crop because as a perennial it can be grown on erosion-prone land, has low energy/water requirements, and is a native species of the with much genetic variability. However, further conversion research is needed to realize its potential as a feedstock for ethanol production. In this study, switchgrass was converted to ethanol by Saccharomyces cerevisiae following dilute ammonium hydroxide pretreatment. Switchgrass was treated at various ammonium hydroxide loadings and reaction temperatures and times. Following pretreatment, the ammonium was removed by evaporation and the samples evaluated for release of glucose when digested with GC220 cellulase (30/g glucan), Novo188 b-glucosidase (40 U/g glucan), and Multifect Pectinase (50 ul/g). When ammonium hydroxide loadings were varied between 4–10%, pretreatment with 8% w/v was determined to be sufficient to maximize glucose yields (78% of max). Samples were subsequently treated for up to 20 min at 160, 170, and 180°C. The highest glucose yields were observed when treated at 180°C for 10 and 20 min (78 and 81% of max). Switchgrass treated at optimal conditions was evaluated for fermentability using S. cerevisiase D5A in a simultaneous saccharification and fermentation culture. No lag phase was observed and the fermentation efficiency, based upon glucose conversion to ethanol, was 70% after 48 h. Further work is in progress to evaluate the effect of harvest maturity on yield and to characterize the effect of enzyme loadings on final ethanol yields
