Field productivities of Napier grass for production of sugars and ethanol

Authors: Dien, Bruce; Anderson, William - Bill; CHENG, MING-HSUN - University Of Illinois; Knoll, Joseph - Joe; Lamb, Marshall; O Bryan, Patricia; SINGH, VIJAY - University Of Illinois; Sorensen, Ronald - Ron; Strickland, Timothy; Slininger, Patricia - Pat

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2020
Publication Date: 1/8/2020
Citation: Dien, B.S., Anderson, W.F., Cheng, M., Knoll, J.E., Lamb, M., O Bryan, P.J., Singh, V., Sorensen, R.B., Strickland, T.C., Slininger, P.J. 2020. Field productivities of Napier grass for production of sugars and ethanol. ACS Sustainable Chemistry & Engineering. 8(4):2052-2060. https://dx.doi.org/10.1021/acssuschemeng.9b06637.
DOI: https://doi.org/10.1021/acssuschemeng.9b06637

Interpretive Summary: Napier grass has the highest biomass productivity of any grass for cropping in southeastern United States. This is a case study using Napier grass for production of bioethanol. Napier grass was grown for 5 years using low-input systems on fields in the Southeast. As long as the crop was fertilized (May) and harvested (December) production was consistent. In contrast, two cutting systems led to dramatic declines in production beginning in year 3. The 2nd and 4th year samples were analyzed for chemical composition and processed to ethanol using an ARS developed yeast suitable for this purpose. The ethanol yield per hectare was 9.0 and 12.8 cubic meters in the 2nd and 4th growing season, respectively. This estimated to out yield a corn production field at 180 bu/acre by a considerable margin. As such, this manuscript demonstrates that Napier grass cropped with low-input system is suitable for production of advanced ethanol fuel. This work will be of interest to the bioethanol producers and farmers located in the Southeast.

Technical Abstract: Napier grass (Pennisetum purpureum (L) Schum) is being developed as a bioenergy crop for production in the southeastern United States. Important criteria for selecting a feedstock are cost, consistent biomass production, composition, and process related quality. In this study, we considered the effects of fertilizer application and cutting regimes on production yield, chemical composition, and process yields. Napier grass was grown for 4 years in field plots (Shellman, GA) with three treatments, which were selected to maximize production yields, and replicated in four sub-plots. It was observed that multiple seasonal cuts negatively impacted production yield by 21% over the total 4 years. Samples from years 2 and 4 were analyzed for composition. Glucan, xylan, and acid insoluble lignin differed among the samples. Carbohydrate yields were 11.1 – 25.7 Mg/ha. Samples were pretreated with low moisture ammonia hydroxide (110°C, 2 days) and evaluated for conversion to sugars using commercial cellulases as well as to ethanol using separate hydrolysis and fermentation with Scheffersomyces stipitis. Glucose and xylose yields were 317-379 kg/Mg and 141 – 164 kg/Mg, respectively for years 2 and 4. Ethanol yields were 268 – 313 L/Mg or 61.3 – 79.3% of maximum. Ethanol yields were 5.9 – 12.8 m3/ha. Ethanol yields for year 4 were over 50% higher for the crop harvested in winter versus the crops harvested in summer and winter. Ethanol production per hectare from winter harvested Napier grass is comparable to grain-based biofuel crops.