Enzymatic Hydrolysis of Steam-Exploded Hardwood Using Short Processing Times

Woody materials are generally resistant to enzymatic saccharification unless they undergo harsh fiber disrupting pre-treatments such as steam explosion. In this study, enzymatic hydrolysis of steam-exploded hardwood was investigated using various conditions and commercial cellulase preparations. Hydrolysis times were kept below 24h in order to approach industrially realistic conditions. The optimal conditions for enzymatic hydrolysis were found to be 55 degrees C and a pH of about 4.5. During enzymatic hydrolysis, acetate was released from the hemicellulose fraction. Increasing the dry matter concentration had a negative effect on glucose yields. Using fermentors with pH control, 66% of the cellulose in steam-exploded hardwood could be hydrolyzed to glucose within 12 h using an enzyme dose of 25 filter paper units (FPU)/g of dry matter. For 24 h hydrolysis maximum cellulose saccharification (71%) was observed at 25 FPU/g, and increasing the enzyme dose further did not increase the sugar yield.