Location: Sustainable Biofuels and Co-products Research
2017 Annual Report
Objectives
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.
Approach
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.
Progress Report
Progress was made on all objectives, all of which fall under NP 213 (Biorefining), Problem Statement 1.1 – “Technologies for producing advanced biofuels or other marketable biobased products”; Problem Statement 1.2 - “Technologies that reduce risks and increase profitability in existing industrial biorefineries”; and Problem Statement 1.3 - “Accurately estimate the economic value of biochemical technologies”.
Objective 1a: The Eastern Regional Research Center (ERRC) corn dry grind process model has been updated with current economic and processing data. The process model now includes distillers corn oil recovery, which is currently being used in the majority of corn ethanol facilities.
Objective 1b: Utilization of sweet sorghum juice for the production of ethanol and for value-added products is ongoing. Incorporation of the sugar rich juice from sweet sorghum into existing corn ethanol facilities has been tested on a small scale in the lab. Results clearly show that the juice can be incorporated into the ethanol process; however, alterations to the co-product yield and water balances are significant. A process model is being developed to investigate alternative approaches to solving these significant problems in an economically viable manner.
Objective 1c: Shake-flasks fermentations have been used to thoroughly study production of astaxanthin by the yeast Phaffia rhodozyma strain ATCC 74219. Synthetic media were prepared to mimic the expected sugar concentrations in sweet sorghum juice to assess yeast growth and astaxanthin production with different sources and levels of nitrogen supplementation. Preliminary fermentations in synthetic media showed best growth and astaxanthin production with yeast extract and urea supplementation. Similar results were obtained when sweet sorghum juice was fermented with P. rhodozyma. Supplementation with yeast extract and urea produced cell productivities of about 1500 and 800 mg of astaxanthin per kg of dry cells, respectively. It is expected that a greater amount of astaxanthin will be produced in larger scale fermentations whereby variables such as pH or nitrogen supplementation can be controlled during the entire fermentation process. Currently, experiments are being developed to test astaxanthin production in fermenters with P. rhodozyma and sweet sorghum juice. The obtained results will identify fermentation process parameters that give the best yields of astaxanthin.
Objective 2b: Sweet sorghum bagasse was washed to extract residual sugars. The washed bagasse then was subjected to low moisture anhydrous ammonia (LMAA) pretreatment and subsequently hydrolyzed with commercial xylanases to produce a 5-carbon sugar-rich solution from the hemicellulose fraction with little hydrolysis of the cellulose fraction. The remaining cellulose-rich solids then were hydrolyzed with commercial cellulases to produce a 6-carbon sugar-rich solution. The feasibility of this process has been demonstrated. Work is being continued to produce larger quantities of 6-carbon sugar-rich solution for use in fermentation experiments to demonstrate fermentability of this sugar solution.
Objective 2c: The remaining solids obtained after hydrolysis of the sweet sorghum bagasse with cellulases as described in Objective 2b were rich in lignin. The lignin was extracted with sodium hydroxide solution and purified by precipitation with ethanol. The conditions for lignin extraction and recovery had previously been determined with corn stover and will be used in lignin extraction and recovery from sweet sorghum bagasse. The recovered lignin will be characterized using standard procedures.
Objective 3a: Itaconic acid production using the microorganism Aspergillus terreus has been demonstrated with solutions containing glucose (a 6-carbon sugar), xylose (a 5-carbon sugar) and mixture of the two sugars in shake-flasks. The experiments have been successfully scaled up in 2-liter fermentors using glucose media and the effects of pH and dissolved oxygen (DO) levels will be studied under controlled conditions. Experiments are now being performed with 5-carbon sugar-rich solutions obtained from sweet sorghum bagasse as described under Objective 2b.
Objective 3b: Washed and unwashed sweet sorghum bagasse were pretreated by the low moisture anhydrous ammonia (LMAA) method. The pretreated materials then were combined with sweet sorghum juice for ethanol fermentation. Commercial cellulases were added to generate glucose for additional ethanol production. To attempt to enhance ethanol production from sorghum grains, the grains were de-waxed with boiling ethanol under reflux conditions to recover wax as a value-added co-product and improve enzymatic starch hydrolysis. 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.
Accomplishments
1. Production of wax and ethanol from sorghum grains. Some sorghum contains wax that negatively affects enzymatic hydrolysis of starch during ethanol fermentation. Removal of wax by ethanol extraction, which resulted in more efficient starch hydrolysis to glucose and subsequently better ethanol yield. Following wax extraction the grains were treated with dilute sulfuric acid under mild conditions and commercial cellulase was added during fermentation to produce more ethanol from the additional sugar coming from the hulls. An integrated process for production of wax as a value-added co-product and ethanol at higher yields using sorghum grains as feedstock.
Review Publications
Nghiem, N.P., Ellis, C.W., Montanti, J.M. 2016. The effects of ethanol on hydrolysis of cellulose and pretreated barley straw by some commercial cellulolytic enzyme products. AIMS Bioengineering. 3(4):441-453.
Challi, R.K., Zhang, Y.B., Johnston, D., Singh, V., Engeseth, N.J., Tumbleson, M., Rausch, K.D. 2017. Evaporator fouling tendencies of thin stillage and concentrates from the dry grind process. Heat Transfer Engineering. 38(7-8):743-752.
Johnston, D., Moreau, R.A. 2017. A comparison between corn and grain sorghum fermentation rates, distillers dried grains with solubles composition, and lipid profiles. Bioresource Technology. 226:118-124.
Nghiem, N.P., Montanti, J., Tae, H. 2016. Pretreatment of dried distillers grains with solubles by soaking in aqueous ammonia and subsequent enzymatic/dilute acid hydrolysis to produce fermentable sugars. Applied Biochemistry and Biotechnology. 179(2):237-250.
Nghiem, N.P., Senske, G.E., Kim, T.H. 2016. Pretreatment of corn stover by low moisture anhydrous ammonia (LMMA) in a pilot-scale reactor and bioconversion to fuel ethanol and industrial chemicals. Applied Biochemistry and Biotechnology. 179(1):111-125.
Nghiem, N.P., Brooks, W.S., Griffey, C.A., Toht, M.J. 2017. Production of ethanol from newly developed and improved winter barley cultivars. Applied Biochemistry and Biotechnology. 182:400-410.
Yoo, C., Nghiem, N.P., Kim, T. 2016. Production of fermentable sugars from corn fiber using soaking in aqueous ammonia (saa) pretreatment and fermentation to succinic acid by Escherichia coli afp184. Korean Journal of Chemical Engineering. 33(10):2863-2868.
Nghiem, N.P., Kleff, S., Schegmann, S. 2017. Succinic acid: technology development and commercialization. Fermentation. 3(26):1-14.
