Comparison of batch and fed-batch fermentations using corncob hydrolysate for bioethanol production

The optimal conditions for the maximum production of ethanol from cellulosic hydrolysate in batch and fed-batch cultures were investigated and compared. The pretreated corncob could be converted into reducing sugar with maximal yields after the enzyme mixtures were fed. After 48 h of hydrolytic reaction, overall reducing sugar and glucose concentrations reached 0.61 and 0.36 g/g dried substrate, respectively. Further batch fermentation of cellulosic hydrolysate was performed using batch cultures of Saccharomyces cerevisiae BCRC 21812, 23.3–41.1 g/l biomass and 6.9–23.0 g/l ethanol was obtained. For the fed-batch fermentation, the effects of feeding glucose concentrations on ethanol fermentation were studied. The feeding glucose concentration of 30 g/l resulted in a higher ethanol yield than that of 20 g/l and 10 g/l did. The cell biomass, ethanol yields, and ethanol conversion rate for the fed-batch fermentation, feeding at 30 g/l glucose concentration, were 44.5 g/l, 32.3 g/l and 0.64 g ethanol/g glucose, respectively. The results indicate that the fed-batch fermentation had a higher ethanol yield than that of the batch fermentation.