Simultaneous Saccharification And Fermentation For Ethanol And Single Cell Protein From Corn Stover By The Recombinant Saccharomyces Cerevisiae Strain 14

Lignocellulose is one of the most abundant global renewable source. Making full use of agro stovers for useful products such as fuel ethanol and single cell protein has great significance to solve energy limit, food shortness and environment pollutions caused by the growth of population and the development of economic. Recently our group screened several new xylose utilizable strains through genome shuffling, and in this study we tested the ethanol fermentation ability of these strains and selected the best one which was named as Saccharomyces cerevisiae Str. 14. Then a feasible process was developed to produce ethanol and single cell protein from agro stover with high efficiency. The main results of this study are included below:1. Str. 14 and two parent strains were tested by fermentations carried out in hexose(glucose, mannose, galactose), pentose(xylose and arabinose) and disaccharide(sucrose and cellobiose) media. The result indicated that Str. 14 gained the excellent traits of both two parents and all these sugars can be utilized efficiently, especially in the experiments using cellobiose and two pentose which cannot be used by S.cerevisiae.2. Fermentations of Str. 14 in high concentration glucose under anaerobic and aerobic conditions were conducted separately in 5-L bioreactor, resulting in a biomass yield of 0.47 g/g in aerobic and an ethanol yield of 0.50 g/g in anaerobic conditions.Similar fermentations of high level xylose under anaerobic, aerobic and micro-aerobic were achieved and showed a biomass yield of 0.46 g/g in aerobic and a xylitol yield of 0.31 g/g in micro-aerobic conditions. These results indicated that Str.14 acquired outstanding capability to utilize glucose and xylose.3. A series of fermentations with mixed sugar medium mimicking the corn stover hydrolysate were conducted, and the influence of ethanol on xylose aerobic utilization was studied. It was suggested that 2-3% ethanol can inhibit the cell growth,and ethanol titer above 4% can prevent xylose utilization. The fermentations with mix sugar mimicking the stover hydrolysate was separated to an initial anaerobic fermentation and following aerobic fermentation after a distilling process. Ethanol yield on glucose reached 0.46 g/g in anaerobic, and the productivity is 1.14 g/L/h. In aerobic stage, it showed a biomass yield on xylose of 0.29 g/g, with xylitol yield of0.17 g/g and glycerol yield of 0.06 g/g.4. A feasible process was built for comprehensive utilization of corn stover:pretreatment by Na OH solution with sequential washing, and anaerobic fermentation with sequential aerobic fermentation of pretreated stover after distillation by fed-batch simultaneous saccharification and fermentation(SSF). In the first fed-batch SSF, ethanol titer at anaerobic stage reached 35.83 g/L, the biomass titer at aerobic stage reached 23.63 g/L, with product(ethanol and biomass) yield on corn stover of0.45 g/g stover from 133 g/L pretreated corn stover. In the second fed-batch with a high solid loading, ethanol titer reached 64.07 g/L at anaerobic stage and dry biomass reached 50.67 g/L from 250 g/L pretreated corn stover in a 5-L bioreactor. Finally, the ethanol and biomass yield reached of 0.46 g/g stover together, which was one of the best result in this field until now.