Improving Cellulosic Ethanol Production

摘要

As bioengineers seek to amplify production of cellulosic ethanol from benchtop to industrial scale, economic factors become impor-rntant, several steps that are common in laboratory work, such as washing of the pre-treated feedstock and supplementing nutrients during fermentation, loom as being prohibitively expensive in large-scale production. To develop a prototype for industrial fermentation, Ming Lau and Bruce Dale integrated and optimized some of the most effective techniques. The authors obtainedrncorn "stover"-stalks and husks that are normally discarded-rnthat had been milled into fragments to increase its surface area. The stover was then treated with ammonia to open the fibers, mixed with enzymes to break down cellulose into its component sugars, and fermented with an engineered strain of Saccharomyces cerevisiae. The authors searched for the optimal mixture of pH and temperature to maximize yield and explored the properties of the rinsewater left over after washing. Lau and Dale suggest that rinsing should be avoided because it removes nutrients as well as degradation products that are important to increase fermentation yield. If the feedstock is treated with ammonia, the most important bottleneck is the efficiency of the enzymes that digest cellulose, according to the authors.