SIMULTANEOUS SACCHARIFICATION AND FERMENTATION OF CELLULOSE TO ETHANOL

Simultaneous saccharification and fermentation (SSF) of cellulose (untreated BW-200 Solka Floc) to ethanol utilizing the cellulase enzyme complex of Trichoderma reesei Rut C-30 and the yeast Saccharomyces cerevisiae QM 8226, has resulted in increased rates and longer times of hydrolysis when compared to simple saccharifications. Additionally, two schemes for ethanol removal during hydrolysis, nitrogen sparging and vacuum operation, have also shown increased rates and longer times of saccharification of cellulose when compared to the simple SSF. Yeast inoculums of 15 v/v% and 5 x 10(\u277) cells/ml have resulted in quick conversion of glucose within the SSF reactor. Early yeast addition (less than 10 hours) for long SSF operation (more than 100 hours) and delayed yeast addition (about 20 hours) for shorter SSF (less than 100 hours) have been observed to be best for cellulose utilization. This is due to the competing combination of high saccharification temperature and enzyme deactivation. Early nitrogen sparging and a high rate of sparge (1 v/v/m) have been observed to slow the growth of the yeast inoculum. Delayed sparge (10 hours after yeast addition) or a low rate (.2 v/v/m) permitted yeast growth. The cellobiose level within the SSF reactor was reduced to 4-5 mg/ml at the end of the run by the action of the beta-glucosidase fraction of the T. reesei Rut C-30 cellulase enzyme system. Thus this enzyme system was able to convert cellobiose to glucose in the presence of ethyl alcohol eliminating the strong inhibition of cellobiose on cellulase while the yeast converted glucose to ethanol by glycolysis eliminating the inhibition of glucose on beta-glucosidase. The hydrolysis curves did not fit either simple or competitive product inhibition Michaelis - Menten type kinetic analysis. An enzyme deactivation-inhibition model seems necessary to fit the data. The yield parameter for ethanol/substrate (Yp/s) varied from .42 g/g to .47 g/g (theoretical .51 g/g) with the majority of glucose being converted to ethanol in less than 15 hours