1a. Objectives (from AD-416)
The overall objectives of this project are to develop economically viable technology to allow production of fuel ethanol from "Generation 1.5" regional non-corn feedstocks such as winter barley, that are grown outside the Corn Belt on fallow land or land that does not compete with food production. Evolve these ethanol plants into multiple product biorefineries, producing high value food and feeds and then into multi-feedstock biorefineries that can accept fermentable sugars from local lignocellulosic feedstock to produce additional ethanol and valuable coproducts. 1. In conjunction with CRADA partners and other collaborators, develop technologies that enable (1) commercially-preferred processes for converting winter barley into fuel ethanol in ways that significantly reduce biorefinery water usage and (2) commercially-viable, value-added co-products from barley-based biorefineries. 1a: Develop commercially-preferred processes for converting winter barley into fuel ethanol and improved DDGS in ways that increase ethanol yield and significantly reduce biorefinery water usage. 1b: Develop commercially-viable, value-added carbohydrate based co-products from barley kernels, hulls, and/or straw in barley-based biorefineries. 1c: Develop commercially-viable, value-added lipid based co-products from barley kernels, hulls, and/or straw in barley-based biorefineries. 2. In collaboration with NCAUR, develop technologies that enable the commercially-preferred conversion of barley hulls and/or straw into sugar-containing make-up water, allowing the production of ethanol from both starch and cellulose in a barley grain-based biorefinery.
1b. Approach (from AD-416)
In conjunction with CRADA partners and other collaborators, develop technologies that enable commercially-preferred processes for converting winter barley into fuel ethanol and improved DDGS in ways that increase ethanol yield and significantly reduce biorefinery water usage. Develop commercially-viable, value-added carbohydrate based co-products from barley kernels, hulls, and/or straw in barley-based biorefineries. Develop commercially-viable, value-added lipid based co-products from barley kernels, hulls, and/or straw in barley-based biorefineries. In collaboration with NCAUR and other partners, develop technologies that enable the commercially-preferred conversion of barley hulls and/or straw into sugar-containing make-up water, allowing the production of ethanol from both starch and cellulose in a barley grain-based biorefinery.
3. Progress Report
We worked with our CRADA partner to conduct research to support the new Appomattox Bio Energy Barley ethanol plant being built in Hopewell Virginia. Our work focused on improving our previously developed barley EDGE ethanol process so that it is optimized for a 60 million gallon per year commercial plant. To do this, several modifications must be made to our lab/pilot scale process. One aspect we focused on was to develop a pre-incubation process that would optimize use of enzymes and lead to higher ethanol yields. Preliminary studies show that of the 5 classes of enzymes being used in the process, one enzyme, beta-glucosidase, is critical for producing the highest ethanol yields. It was found that use of a pre-incubation stage for the barley mash before the liquefaction step may result in lower cost and higher yields. Progress was made on the extraction of all constituents including arabinoxylan and cellulose rich fractions from several varieties of barley hulls and straws from different sources. Organic solvent-soluble components of barley hulls and straws obtained were dried and their percentage yields calculated. The water soluble components, starch, Hemi. A, Hemi. B (arabinoxylan), oligosaccharides, acid insoluble lignin, acid soluble lignin and cellulosic residue from all these barley hulls and straws were also extracted, dried and their percent yields were calculated. As part of our effort to identify and quantify co-products in barley and in barley processing fractions, ten new barley cultivars were obtained from ARS barley breeders in Aberdeen, Idaho. One of these, Clearwater, is an important new cultivar developed to have enhanced feed value, because it contains very low levels of phytate. Kernel samples were extracted and quantitatively analyzed for total oil, the four common barley tocopherols and the four common barley tocotrienols. One cultivar was found to contain about 30% more oil than the others. We previously reported that barley oil contains the higher levels of health-promoting tocotrienols than any other common seed oil. As with older barley cultivars, the barley oil from these ten new cultivars contained consistently high levels of tocotrienols. We are collaborating with engineers at Iowa State University with experience in cellulosic ethanol pretreatment, saccharification, and fermentation to migrate cellulosic ethanol technology into barley (starch) ethanol plants. Biomass feedstocks including corn stover and barley hull were treated with the Iowa State SAA cellulosic ethanol pretreatment technology. The treated materials were first hydrolyzed with Multifect Xylanase to generate a xylose-rich stream. The residual sold is then hydrolyzed with Accellerase cellulase to generate a glucose-rich stream. Thus the two main carbohydrate fractions of the biomass were fractionated into two separate fermentable sugar solutions, which could be used with suitable microorganisms for production of value-added co-products and ethanol.
1. Two-Phase Simultaneous Saccharification and Fermentation (TPSSF) process improves yield of ethanol from corn stover. The production of bioethanol from lignocellulosic feedstock is much more difficult than starch-based ethanol production for several reasons. For one, lignocellulose contains both hexoses, such as glucose, and also pentoses, such as xylose. Brewers yeast can easily convert glucose to ethanol but cannot convert pentoses, such as xylose into ethanol. Commercial bioconversion of lignocellulose to ethanol requires efficient fermentation of all the sugars. If this cannot be achieved, the ethanol yield will be too low to make the lignocellulosic ethanol cost-competitive. Currently, researchers are trying to develop new microorganisms that can convert both hexoses and pentoses to ethanol simultaneously. One of the major problems with these recombinant organisms is they ferment glucose preferentially and do not begin to metabolize xylose until low glucose concentrations have been reached. This results in very long fermentations times and incomplete conversion of xylose in mixed sugar solutions obtained from lignocellulosic biomass. To overcome this hurdle, ARS researchers have developed a Two-Phase Simultaneous Saccharification and Fermentation (TPSSF) process in which xylose is preferentially released from a pretreated biomass and simultaneously fermented to ethanol first using an organism capable of highly efficient xylose metabolism, followed by release of glucose and its simultaneous conversion to ethanol by the yeast Saccharomyces cerevisiae, which has been known for high ethanol yields. We used this new process on corn stover. The results were outstanding as an ethanol yield of 84% of theoretical value was achieved with E coli KO11 (a xylose-fermenting bacterium) and subsequently with S cerevisiae D5A (a glucose-fermenting yeast). This high level of sugar conversion will be of value in improving the economics of lignocellulosic ethanol production.
Li, X., Kim, T., Nghiem, N.P. 2010. Bioethanol production from corn stover using aqueous ammonia pretreatment and two-phase simultaneouos saccharification and fermentation (TPSSF). Bioresource Technology. 101:5910-5916.