Evaluation of Simultaneous Saccharification and Ethanol Fermentation of Undetoxified Steam-Exploded Corn Stover by Sacch
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Evaluation of Simultaneous Saccharification and Ethanol Fermentation of Undetoxified Steam-Exploded Corn Stover by Saccharomyces cerevisiae Y5 Shen Tian & Yun Li & Zhen Wang & Xiushan Yang
# Springer Science+Business Media New York 2013
Abstract Toxin-tolerant yeast strains that produce high ethanol yield are inevitably requited for cost-effective ethanol production from undetoxified steam-exploded corn stover. To verify the ethanol-producing capability of the strain Saccharomyces cerevisiae Y5 developed in our laboratory, simultaneous saccharification and fermentation of undetoxified steam-exploded corn stover with solids loading of 30 % (w/v) was carried out in different-sized flasks and an automatic fermenter. After 96 h, the ethanol concentrations had reached 50, 47.8, and 47.5 g/L in the 100-mL flask, 3,000mL flask, and 5-L automatic fermenter, respectively. The experiment demonstrates that ethanol production from undetoxified steam-exploded corn stover using S. cerevisiae Y5 simplifies the production process, reduces equipment investment and water consumption, and generates highly concentrated ethanol. S. cerevisiae Y5 is a promising strain that could reduce the cost of producing ethanol from steamexploded corn stover. Keywords Steam-exploded corn stover . Undetoxification . Simultaneous saccharification and fermentation (SSF) . Fermenter . Ethanol concentration
Introduction Producing ethanol from lignocellulose has the potential to alleviate the energy crisis and protect the environment; therefore, it is an important direction for energy development [1, 2]. Steam explosion of stover is one of the pretreatment methods Shen Tian and Yun Li contributed equally to this work. S. Tian : Y. Li : Z. Wang : X. Yang (*) College of Life Science, Capital Normal University, Beijing 100048, China e-mail: [email protected]
of lignocellulose that has been developed in many countries [3–7], but steam explosion also produces toxic substances, such as acetic acid, furfural, and 5-HMF that greatly inhibit yeast growth and fermentation [8]. Thus, before enzymatic hydrolysis and fermentation, material obtained from steam explosion must be washed and detoxified, which increases equipment cost and consumes large amounts of water. Therefore, direct enzymatic hydrolysis and fermentation of the substrate from steam-exploded stover without washing and detoxification is critical to reducing the cost of cellulosic ethanol production. Increasing the ethanol concentration in the fermentation broth to reduce the energy requirement for ethanol distillation is another important cost-saving measure. A final ethanol titer of 40 g/L is the benchmark concentration for commercial cellulosic ethanol production [9, 10]. A higher ethanol concentration in the fermentation broth requires increased substrate loading during simultaneous saccharification and fermentation (SSF). This further reduces water consumption and water treatment cost. But the hydrolysate from 30 % substrate concentration of undetoxified steamexploded corn stover was unable to
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