Dilute Acid Pretreatment of Douglas Fir Forest Residues: Pretreatment Yield, Hemicellulose Degradation, and Enzymatic Hydrolysability

Two Douglas fir (D. fir) forest residues were evaluated for fermentable sugar production by dilute acid pretreatment and subsequent enzymatic hydrolysis in comparison with a clean D. fir wood chip sample. Detailed mass balances of cellulose, hemicellulose, and lignin fractions presented in D. fir samples during pretreatment and enzyme hydrolysis processes were determined. The presence of higher bark and lignin content in D. fir forest residues lowered substrate hydrolysability by 25-36 % compared to clean D. fir wood chips. A significant variation in biomass recalcitrance between the two forest residues toward biomass pretreatment and enzymatic hydrolysis was also found and reflected by a significant difference in final glucose yield (by similar to 20 %). Applying ball-milling treatment of pretreated D. fir residues prior to enzyme hydrolysis can significantly enhance their hydrolysability. Both chemical composition and physical property factors (i.e., bulk density) contributed to the recalcitrant nature of forest residues.