Location: Bioenergy ResearchTitle: Effect of compositional variability of Distillers' Grains on cellulosic ethanol production) Author
Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2010
Publication Date: 6/1/2010
Citation: Kim, Y., Hendrickson, R., Mosier, N.S., Ladisch, M.R., Bals, B., Balan, V., Dale, B.E., Dien, B.S., Cotta, M.A. 2010. Effect of compositional variability of Distillers' Grains on cellulosic ethanol production. Bioresource Technology. 101(14):5385-5393. Interpretive Summary: Distillers’ grains (DG) is a co-product of corn ethanol from plants that directly process ground corn (dry grind). If DG were converted into ethanol, it would increase the amount of ethanol obtained from a bushel of corn. Earlier, we had demonstrated that pretreatment of DG by liquid hot-water (LHW) or ammonia fiber expansion (AFEX), followed by enzymatic digestion and fermentation by yeast is sufficient to obtain good ethanol yields. However, DG composition and physical properties vary among ethanol plants. To study the effect of this variability, we evaluated four samples of DG, selected from unique plants, and picked the two most different for further processing by LHW and AFEX. Despite the differences, we were able to convert the samples to ethanol with efficiencies of 70-80% based upon the maximum possible yields. Incorporation of cellulose conversion technology into existing ethanol plants could serve as a first step in the development of the biomass to ethanol industry.
Technical Abstract: In a dry grind ethanol plant, approximately 0.84 kg of dried distillers’ grains with solubles (DDGS) is produced per liter of ethanol. The distillers’ grains contain the unhydrolyzed and unprocessed cellulosic fraction of corn kernels, which could be further converted to ethanol or other valuable bioproducts by applying cellulose conversion technology. Its compositional variability is one of the factors that could affect the overall process design and economics. In this study, we present compositional variability of distillers’ grains collected from four different dry grind ethanol plants and its effect on enzymatic digestibility and fermentability. We then selected two sources of distillers' grains based on their distinctive compositional difference. These were pretreated by either controlled pH liquid hot water (LHW) or ammonia fiber expansion (AFEX) and subjected to enzymatic hydrolysis and fermentation. Fermentation of the pretreated distillers’ grains using either industrial yeast or genetically engineered glucose and xylose co-fermenting yeast, yielded 70–80% of theoretical maximum ethanol concentration, which varied depending on the batch of distillers’ grains used. Results show that cellulose conversion and ethanol fermentation yields are affected by the compositions of distillers’ grains. Distillers’ grains with a high extractives content exhibit a lower enzymatic digestibility but a higher fermentability.