1: Develop technologies that enable the integrated processing of sorghum grains and sweet sorghum juice at existing biofuels production facilities and that enable the commercial production of new co-products at sorghum-based biorefineries. 1A: Develop technologies that enable the integrated processing of sorghum grains at existing biofuels production facilities. 1B: Develop technologies that enable the integrated processing of sweet sorghum juice at existing biofuels production facilities. 1C: Develop technologies that enable the commercial production of new co-products at sorghum-based biorefineries. 2: Develop technologies that enable the commercial production of marketable C5-rich and C6-rich sugar streams from sorghum lignocellulosic components. 2A: Develop technologies that enable the commercial production of marketable C5-rich sugar streams from sorghum lignocellulosic components. 2B: Develop technologies that enable the commercial production of marketable C6-rich sugar streams from sorghum lignocellulosic components. 3: Develop technologies that enable the commercial conversion of sorghum lignocellulosic components into fuels and industrial chemicals. 3A: Develop technologies that enable the commercial production of industrial chemicals from the C5-rich sugar stream obtained from the enzymatic hydrolysis of pretreated sorghum cellulosic components. 3B: Develop technologies that enable the commercial production of additional ethanol and industrial chemicals from the C6-rich sugar stream obtained from the enzymatic hydrolysis of the cellulose-enriched residue. 3C: Develop technologies that enable the use of byproducts and wastes generated in ethanol and other fermentation processes in the sorghum biorefinery for production of energy and chemicals.
In conjunction with collaborators, develop technologies that enable commercially-preferred bio/chemical processes for converting all components of sorghum plants, including grains, juice, and bagasse, into fuels, industrial chemicals and consumer products. Develop commercially viable processes for incorporation of sorghum grains into existing commercial corn-based ethanol plants and evaluate the effects of this process modification on overall water balances in the existing plants. Develop commercially viable technologies for using sweet sorghum juice and sorghum biomass, including both carbohydrates and lignin, for the production of important platform chemicals, i.e. chemicals that can be used as precursors for production of a wide range of industrial chemicals and consumer products. Develop technologies for capturing the carbon dioxide gas generated in ethanol fermentation for use in other fermentation processes that requires CO2 as a secondary feedstock in addition to fermentable sugars. Develop technologies for conversion of the wastes generated in cellulosic ethanol and industrial fermentation processes into methane for internal use as an energy source. Develop an integrated process combining the aforementioned process components for a sorghum-based biorefinery.
Considerable progress was made on all objectives, all of which fall under National Program 306 – Product Quality and Uses, Component 3 - Biorefining. Objective 1a: We have adapted our existing corn to ethanol model developed at the Eastern Regional Research Center (ERRC) to utilize grain sorghum. This model has been further adapted to include mixtures of corn with grain sorghum. These models will be utilized for economic and production comparison with the base case corn-to-ethanol model. The comparison will help determine the impact on ethanol and coproduct yields as well as the potential benefits of grain sorghum utilization. Objective 1b: Fermentations utilizing sweet sorghum juice mixed with corn were conducted. Sufficient quantities of modified distillers dried grains with solubles (DDGS) were produced during these fermentations for detailed compositional analysis. Important animal nutrient profiles of the DDGS were measured and evaluated. Results indicated that the modified DDGS composition changed little from the base case (i.e. corn-to-ethanol). However, the overall DDGS yields were reduced that could potentially decrease coproduct revenue. Objective 1c: A simple process using boiling ethanol under reflux conditions to extract wax from sorghum grains was developed. The extracted wax was recovered as a value-added co-product. Wax removal was found to improve enzymatic starch hydrolysis and subsequent ethanol yield. The de-waxed grains then were treated with dilute sulfuric acid (1 and 2 wt %) and subjected to mashing for ethanol fermentation. Commercial cellulases were added to the mash to hydrolyze the cellulose fraction of the hulls to produce glucose for additional ethanol production. A net improvement of 36.8 % in ethanol production over the raw grains was obtained. This work was completed and previously reported in the 2017 annual report. Objective 2c: Lignin has been isolated from sorghum bagasse insoluble residue obtained after enzymatic hydrolysis. Initial characterization by analytical pyrolysis GC/MS has indicated it was enriched in G and H-type lignin monomers such as phenol, o-cresol, guaiacol, and vanillin. Currently, sorghum bagasse lignin is being extracted and recovered in larger quantities to perform pyrolysis at larger scale to generate a representative sample of bio-oil. This substance will be characterized for chemical composition and overall water content. Additionally, a lignin sample will be characterized by an outside collaborator to determine if this lignin type is a good material candidate to be used as a replacement for bisphenol-A in epoxy resins. Objective 3b: Pretreated sweet sorghum bagasse by the low moisture anhydrous ammonia (LMAA) process has been hydrolyzed to generate a sugar hydrolysate enriched in both glucose and xylose. This hydrolysate will form the primary substrate in which the microorganisms Clostridium acetobutylicum ATCC 824 and C. beijerinckii ATCC 55025 will be cultivated to determine butanol production titers. C. tyrobutyricum ATCC 25755 will be another strain investigated, but this strain produces butyric acid instead of butanol. Different fermentation processing schemes will be investigated to determine if the butyric acid produced from C. tyrobutyricum can be fermented downstream by the other two organisms to butanol. Objective 3c: Cellulosic ethanol stillage has been collected after ethanol fermentation for utilization as a substrate for anaerobic digestion. Local farms are being contacted to provide a sample of cow manure to be used as a starter inoculum for anerobic digestion. The cellulosic ethanol stillage will be inoculated with bacteria from the starter inoculum to determine production rates of biogas (e.g. methane, carbon dioxide, and other gases).
Norvell, K.L., Nghiem, N.P. 2018. Soaking in aqueous ammonia (SAA) pretreatment of whole corn kernels for cellulosic ethanol production from the fiber fractions. Fermentation. 4(87):1-10. https://doi.org/10.3390/fermentation4040087.
Stoklosa, R.J., Johnston, D., Nghiem, N.P. 2019. Phaffia rhodozyma cultivation on structural and non-structural sugars from sweet sorghum for astaxanthin generation. Process Biochemistry. 83:9-17. https://doi.org/10.1016/j.procbio.2019.04.005.