Sunday, May 3, 2009
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Development and scale-up of xylose-rich hydrolysate fermentation process for lignocellulosic ethanol production
Ting-Hsiang Lin, Chiung-Fang Huang, Wen-Hua Chen, and Jia-Baau Wang. Cellulosic Ethanol Program, Institute of Nuclear Energy Research, No. 1000, Wenhua Road, Jiaan Village, Longtan, Taoyuan, 32546, Taiwan
Pichia stipitis is widely used in pentose fermentation because of high ethanol productivity. However, the yeast is sensitive to some inhibitors, such as acetic acid and furfural in xylose-rich hydrolysate. Thus, the capability of hydrolysate fermentation by Pichia stipitis was often neglected in the lignocellulosic ethanol production process. The study was aimed to investigate the scale-up of rice straw hydrolysate fermentation process. Adaptive evolution of Pichia stipitis was first performed to enhance the tolerance of yeast to inhibitors in rice straw hydrolysate. Microarray analysis has been demonstrated the expression levels of alcohol dehydrogenase (ADH), pyruvate decarboxylase and several sugar transports from adapted yeast were up-regulated in comparison of parental yeast. The optimization of fermentation conditions and detoxification procedure were then carried out to enhance the ethanol conversion during the fermentation of hydrolysate. The maximal ethanol yield of total sugars was achieved to 0.44g/g at 5L scale fermentation when rice straw hydrolysate was prepared by a twin-screw extrusion pretreatment with dilute acid hydrolysis. Recently, 100L fermentation experiments were further conducted to optimize scale-up of rice straw hydrolysate fermentation for ethanol production. An ethanol yield 0.43 g/g was obtained by controls of dissolved oxygen in hydrolysate. Thus, the fermentation of xylose-rich hydrolysate by adapted Pichia stipitis was shown potential for further scale-up experiment.