Production Of Bioethanol Onto Enhanced The Fermentation Performance Of Immobilized Yeast

The Burning and disposal of straw lead to serious secondary contamination and waste ofresources. The conversion from straw into fuel ethanol could not only avoid the secondarypollution, but also utilize this kind of biomass energy. However, traditional biologicalfermentation process mainly used free saccharonyces cerevisiae, which resulted in suchproblems as high cost of yeast cultivation, lower utilization efficiency of equipment, and highpotential of bacterial contamination. A method of cell embedding technology was used toimmobilize Saccharomy cescerevisiae and the immobilized yeast was used in the fermentationprocess of making fuel ethanol from straw.Firstly, Saccharomyces cerevisiae BY4742was embedded by dropping the mixture into2%(w/v) calcium chloride, and the mixture contained2.5%(w/v) sodium alginate and2%(w/v) yeast dry cells. Yeast embedded in sodium-alginate was adopted to ferment ethanolfrom glucose continuously. In order to research the fermentation capability of immobilizedyeast in repeated batch fermentation, a experiment was conducted at the condition of80g/Lglucose，pH4.0and10%(v/v) immobilized yeast, and each experiment was carried out in atriplicate fermentation with a reaction time of72h. The experiments showed thatfermentation time was reduced from72h to48h in comparison with the fermentation usingfree yeast cells. The maximum ethanol yield can respectively reach82%，62%and35%infirst，second and third batch，and the mean value of ethanol volumetric productivity was0.30g/(L·h) in three sequential fermentation cycles. These results indicated that the fermentationperformance of immobilized yeast gradually decline during the reuse of embedded yeast.Secondly, in order to slow down the performance decay of immobilized yeast cells,regulation and optimization of cells’ fermentation capability was conducted throughcultivation in Yeast Extract Peptone Dextrose (YEPD) medium, repeated batch fermentationwith less reaction time and parameter adjusting. After the optimization, the decreasing offermentation performance of immobilized cells was delayed while the fermentation efficiencywas comparatively enhanced. The best performance of the immobilized cells were found atthe condition of110g/L glucose, pH4.0,30%(v/v) immobilized cells and the temperature of35℃, under which, the ethanol yield was respectively81%,80%,73%,61%and59%in thefive repeated fermentation cycles with a fermentation of12h for each. The mean value ofethanol volumetric productivity was3.44g/(L·h). The unsatisfactory performance ofimmobilized yeast could be recovered through the cultivation and activation in the break of two repeated batch fermentation sequence. Ethanol yield of the fourth fermentationexperiment could still reach84%after immobilized yeast was activated for10h.Finally, simultaneously saccharification and fermentation (SSF) using immobilized yeastwas performed to produce bio-ethanol from straw. This series of SSF was carried out underthe temperature of38℃,16.0%(w/v) straw solid content，35FPU/g enzyme loading, and8g/L dry yeast cells. And it demonstrated that after120h of SSF reaction, the ethanolconcentration and ethanol yield reached28.94g/L and76%, respectively.