Effect of mixing sweetgum and oak on sugar yields using dilute acid pretreatment and enzymatic hydrolysis

Due to their heterogeneous nature, forest residues may not be used to their full potential as biorefinery feedstocks. This work investigated the effect of mixing biomass species from the hardwood understory on xylose and glucose yields obtained from dilute acid pretreatment and enzymatic hydrolysis. The mixed biomass samples consisted of: 70% sweetgum wood + 30% sweetgum bark, 70% sweetgum wood + 30% oak bark, and 70% sweetgum wood + 30% oak wood. A feedstock of 100% sweetgum wood was used as the control. Samples were pretreated with 0.98% (v/v) sulfuric acid at 160°C for 20 min, followed by hydrolysis with a cellulase enzyme cocktail. Resulting sugars from hydrolysis of the mixed samples were statistically compared to the sugar yield of the control; experimental and predicted sugar yields for the mixed samples were also compared to each other. Results showed that mixing biomass species did not negatively affect sugar yields. There were positive interactions between sweetgum wood and sweetgum bark during hydrolysis, as indicated by an increase of experimental xylose and glucose yields by 25% and 12%, respectively. However, the mixture with sweet-gum bark increased formic acid concentration by 70% when compared to the control. In conclusion, the heterogeneous nature of forest residues would not prevent their use as a feedstock in biochemical biorefineries, as far as sugar yields are concerned, but inclusion of bark biomass in forest residues could reduce the quality of the sugar stream, which could cause some processing challenges. © 2014 American Society of Agricultural and Biological Engineers.