The Study Of Production Of Ethanol By Co-fermenting Of Cellulose And Hemicellulose From Sugarcane Bagasse Using Multi-mocroorganisms

Sugarcane bagasse, which is the main by-product of sugar industry, is composed mainly of cellulose and hemicellulose. Sugarcane bagasse is considered as one of the most important renewable resources and raw materials of cellulosic ethanol fuel. At present, however, the conversion rate of sugarcane bagasse to ethanol is still very low. One important reason is the utilization of sugarcane bagasse hemicellulose is very low. In order to improve the conversion rate of sugarcane bagasse to fuel ethanol, especially the utilization of hemicellulose, four pretreatment methods, i.e. sodium hydroxide, sulfuric acid, hydrogen peroxide and steam explosion, were explored in this study. The component changes of sugarcane bagasse after pretreatments and the synergistic effect between cellulose hydrolases were investigated. Different strains of microorganisms were used alone or in mixed culture to ferment the alkali pretreated sugarcane bagasse and the optimization of fermentation process were also studied.The results showed that the best hydrolysis performance was obtained from sugarcane bagasse pretreated by sodium hydroxide, of which the glucose yield reached 12.76 g/L, and the cellulose conversion rate was 100.4% of theoretical yield, followed by steam explosion. The glucose yield from peroxide pretreated sugarcane bagasse was lowest, of which the cellulose conversion rate was only 23.47% of the theoretical value. According to the results of synergistic analyses between cellulase and pectinase or xylanase, the synergy degree between cellulase and xylanase was related to the chemical composition of substrate and the way of pretreatment. Synergism between pectinase and cellulase was not observed in this study, which may because the pectin component in sugarcane bagasse is too little. Synergistic analysis results showed that the optimal combination of enzymes was 3.17, 1.63 and 1.2 mg of Celluclast1.5L, Novozym 188 and xylanase per gram substrate respectively.The alkali pretreated sugarcane bagasse was hydrolyzed using the optimal combination of enzymes for 60 h. Fermentation experiments of the hydrolysate were carried out using different fermentation microbial strains, including glucose utilizing and pentose utilizing microorganisms, to investigate the fermentation performance of these organisms. The best one of the glucose utilizing microorganisms was Saccharomyces cerevisiae 1445, of which the glucose consuming rate was faster than the other strains, and the rate was 4.53 g/L*h, the highest ethanol yield was found after 24 h of fermentation(22.10 g/L). The fermentation performance of Candida shehatae is better than that of Pichia stipitis in the pentose utilizing microorganisms and the highest ethanol yield was 15.15 g/L. Saccharomyces cerevisiae 1445 were co-cultured with Candida shehatae or Pichia stipitis respectively to ferment the hydrolysis of sugarcane bagasse. The result showed that the ethanol yield of the combination of Candida shehatae and Saccharomyces cerevisiae 1445 was relatively higher(the highest yield of ethanol is 22.82 g/L) than that of the combination of Pichia stipites and Saccharomyces cerevisiae 1445..Finally, single factor method was used in this study to optimiz the fermentation conditions of the co-culture of Candida shehatae and Saccharomyces cerevisiae 1445 on the amount of inoculation, the proportion of two strains, the time of enzymatic hydrolysis and the way of fermentation etc. The results suggested that the optimal fermentation system condition was: the inoculation amount of the two strains was 2.0 g/L in total dry weight; the ratio between the two strains was 1:1, and simultaneous saccharification and fermentation without pre-saccharificationshould be adopted. Under this condition, the ethanol rate and yield reached 15.73 g/L and 0.2622 g/g dry weight of alkali pretreated bagasse respectively, achieving theoretical value(0.4825 g/g)of 54.34%.Based on the above, besides the use of Candida shehatae and Saccharomyces cerevisiae 1445 in mixed to co-fermentation cellulose and hemicellulose of sugarcane bagasse to ethanol was feasible, as raw material for production of fuel ethanol, sugarcane bagasse was also feasible.