2-34: Evaluating the consistency of digestibility and fermentability of corn stover and switchgrass harvested in multiple years

Corn stover and switchgrass are two promising feedstocks considered for cellulosic biofuel fermentation.  Both feedstocks have been studied extensively and their susceptibility to enzymes and fermentability into biofuels have been demonstrated.  However, variability of composition and digestibility can occur among different farms and across different seasons, which can impact downstream processing and resulting ethanol yields.  Such variability can significantly impact the profitability of a biorefinery, and thus should be minimized through careful crop management. To assess the variability of feedstocks across multiple years, corn stover and switchgrass were harvested from the same location in 2008, 2009, and 2010.  Compositional analysis of all samples revealed that significant differences in glucan, lignin, and extractive content between the three years for both corn stover and switchgrass.  For corn stover, the 2010 harvest required a more severe AFEX^TM pretreatment than the previous harvests to achieve similar sugar yields.  For switchgrass, the 2008 harvest was more immature than the other harvests, which inhibited xylose fermentation.  Optimal enzyme mixtures for each feedstock harvest were also determined.  These results suggest that further improvements in feedstock quality control are needed to insure a consistent feedstock supply to a biorefinery.