1a. Objectives (from AD-416)
Develop pretreatment and fermentation processes to convert lignocellulosic materials such as barley straw, barley hulls, DDGS, and other crop biomass into fuel ethanol and value-added coproducts. This work complements present ARS work to develop advanced bioconversion process for production of cellulosic ethanol and value-added co-products that can be integrated into an existing fuel ethanol plant. The first step in a lignocellulosic biomass bioconversion process normally is pretreatment to open up the structure and subsequently allow increased enzymatic hydrolysis. Soaking in aqueous ammonia (SAA) has been proven to be effective as a pretreatment method of agricultural residues, such as corn stover, corn fiber, barley hull, switchgrass, etc. In this study, SAA will be employed for the pretreatment step and subsequent conversion of SAA pretreated biomass will be investigated.
1b. Approach (from AD-416)
The composition of specific types of biomass studied in this project will be determined using standard procedures for biomass analysis. Then, pre-treatment processes based upon Soaking in Aqueous Ammonia (SAA) technology will be developed and optimized for each biomass source. SAA will open up the structure of the biomass and subsequently allow increased enzymatic hydrolysis. This pretreated biomass will be subject to saccharification using commercial cellulases with xylanase supplements. The conversion of biomass to free sugars will be monitored by HPLC and standard methods of analysis. Once saccharified, the sugars will be fermented by traditional brewers yeast. In other studies, pre-treated biomass will be simultaneously saccharified and fermented to directly produce ethanol from the pretreated biomass in one step.
3. Progress Report
In this specific cooperative agreement, engineers at ISU with experience in cellulosic ethanol pretreatment, saccharification, and fermentation are collaborating with us 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. We also developed a Two-phase Simultaneous Saccharification and Fermentation (TPSSF) process for production of ethanol from corn stover. 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). A journal article was published on this work and is included in the parent list of publications. Communication with collaborators was through emails and conference calls.