A novel integrated biological process for cellulosic ethanol production featuring high ethanol productivity, enzyme recycling and yeast cells reuse

High enzyme loading requirements, slow xylose fermentation and low ethanol productivity are three of the major issues impeding commercial biochemical production of cellulosic ethanol. We report here a novel integrated biological process to overcome these problems. Enzymatic hydrolysis was performed for only 24 h to avoid the slow rate period which begins at about that time. Unhydrolyzed recalcitrant solids with adsorbed enzymes were recycled to the subsequent cycles. By this approach, easily digestible biomass was processed first and recalcitrant biomass was given enough residence time to get hydrolyzed during subsequent processing steps. Fermentation was conducted using a high yeast inoculation level and was also completed in 24 h. The yeast cells were then recycled. With this novel processing approach, the enzyme loading was reduced from 36 to 22.3 and 25.8 mg protein per gram glucan, respectively, for separate hydrolysis and fermentation (SHF) and for simultaneous saccharification and co-fermentation (SSCF) on AFEX (TM) pretreated corn stover. The process ethanol productivity was enhanced by 2 to 3 fold due to both fast enzymatic hydrolysis and fast fermentation.