Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2011
Publication Date: 11/8/2011
Citation: Nghiem, N.P., Taylor, F., Hicks, K.B., Johnston, D., Shetty, J. 2011. Scale-up of ethanol production from winter barley by the EDGE (enhanced dry grind enzymatic) process in fermentors up to 300 liters. Applied Biochemistry and Biotechnology. 165:870-882. Interpretive Summary: The inevitable depletion of fossil energy sources has stimulated worldwide interest in alternative and renewable fuels. In the U.S., the 2007 Energy Independence and Security Act (EISA) mandated production of 36 billion gallons of renewable fuels by 2022, of which 22 billion gallons must be "Advanced Biofuels" made from non-corn feedstocks. Ethanol production from corn in the U.S. has steadily increased during the last 15 years to reach 10.6 billion gallons in 2009. The increase in corn ethanol production is expected to continue. However, the 2007 EISA also limited the quantity of ethanol that can be produced from corn in the U.S. at 15 billion gallons per year to avoid negative impacts on feed and food markets. Thus, production of ethanol from renewable feedstocks other than corn is needed. Ethanol produced from lignocellulosic biomass can help meet the stated goal of the 2007 EISA but the technology is not quite ready for commercialization. The main problem of cellulosic biomass ethanol production is the difficulty in feedstock conversion that results in uneconomical production cost. Starch conversion technology, on the other hand, has been successfully used for commercial production of ethanol for many years. Thus, a process for ethanol production that can use starch-based feedstocks other than corn is of great interest. A process, which was designated the barley EDGE (enhanced dry grind enzymatic) process, has recently been developed in our laboratory for barley ethanol production. The EDGE process was developed with Thoroughbred, a winter hulled barley variety, using a shake-flask model. Under the optimum conditions, 30 percent of total dry solids could be used to produce 15 percent (v/v) ethanol, which gave a yield of 402 liters/metric ton (dry basis) or 2.17 gallons/53 lb bushel of barley with 15 percent moisture. After development of the EDGE process, our next objective was to test its scalability and also its suitability for other barley varieties. We have successfully scaled up the EDGE process using Thoroughbred and Eve, a winter hull-less barley variety, in fermentors up to 300 liters in size.
Technical Abstract: A fermentation process, which was designated the EDGE (enhanced dry grind enzymatic) process, has recently been developed for barley ethanol production. In the EDGE process, in addition to the enzymes normally required for starch hydrolysis, commercial Beta-glucanases were used to hydrolyze (1,3)(1,4)-Beta-D-glucans to smaller molecules, thus reducing the viscosity of the mash to levels sufficiently low to allow transport and mixing in commercial equipment. Another enzyme, a developmental Beta-glucosidase, then was used to hydrolyze the resulting oligomers to glucose, which subsequently was fermented to produce additional ethanol. The EDGE process was developed with Thoroughbred, a winter hulled barley, using a shake-flask model. To move toward commercialization it is necessary to prove that the developed process would be applicable to other barley varieties and also to demonstrate its scalability. Experiments were performed in 7.5, 70, and 300-liter fermentors using Thoroughbred, a winter hulled barley, and Eve, a winter hull-less barley. It was shown that the process was scalable for both barley varieties. Low levels of glucose throughout the course of the fermentations demonstrated the high efficiency of the SSF process. Final ethanol concentrations of 14 percent v/v were achieved for initial total solids of 28.5-30 percent w/w, which gave an ethanol yield of 83 percent-87 percent of the theoretical values. The DDGS co-products contained very low levels of Beta-glucans and thus were suitable for use in feed formulations for all animal species.