ARS | Publication request: Quantifying actual and theoretical ethanol yields for switchgrass strains using NIRS analyses

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 2010
Publication Date: April 10, 2011
Citation: Vogel, K.P., Dien, B.S., Jung, H.G., Casler, M.D., Masterson, S.D., Mitchell, R. 2011. Quantifying actual and theoretical ethanol yields for switchgrass strains using NIRS analyses. BioEnergy Research. 4(2):96-110. DOI: 10.1007/s12155-010-9104-4.

Interpretive Summary: Quantifying actual and theoretical ethanol yields from biomass conversion processes requires expensive, complex fermentation tests and extensive laboratory analyses of the biomass sample with costs exceeding $300 per sample. Near infrared reflectance spectroscopy (NIRS) is a non-destructive technology that can be used to obtain accurate estimates of agricultural product composition based on differential absorbance and reflectance of light at specific wave lengths. NIRS calibrations were developed for switchgrass biomass that can be used to estimate over 20 components including cell wall and soluble sugars and also ethanol production as measured using a laboratory conversion and fermentation procedure. With this information, an additional 13 complex biomass feedstock traits can be determined including theoretical and actual ethanol yields. These NIRS calibrations were used to estimate feedstock composition and conversion information for biomass samples from a multi-year switchgrass biomass cultivar trial. There were significant differences among switchgrass strains for all biomass conversion and composition traits including actual ethanol yields and theoretical ethanol yields per ton and acre. Conventional analyses costs for this study would have exceeded $100,000 but with NIRS the costs of the analyses were approximately $3000 or about $10 per sample. It should be feasible to improve ethanol yields per acre by improving both biomass yield and conversion efficiency by using NIRS analyses to quantify differences among cultivars and management practices.

Technical Abstract: Quantifying actual and theoretical ethanol yields from biomass conversion processes such as simultanteous saccharification and fermentation (SSF) requires expensive, complex fermentation assays and extensive compositional analyses of the biomass sample. Near infrared reflectance spectroscopy (NIRS) is a non-destructive technology that can be used to obtain accurate estimates of agricultural product composition. In this study, broad based NIRS calibrations were developed for switchgrass biomass that can be used to estimate over 20 components including cell wall and soluble sugars and also ethanol production and pentose sugars released as measured using a laboratory SSF (procedure. With this information, an additional 13 complex feedstock traits can be determined including theoretical and actual ethanol yields from hexose fermentation. The NIRS calibrations were used to estimate feedstock composition and conversion information for biomass samples from a multi-year switchgrass (Panicum virgatum L.) biomass cultivar evaluation trial. There were significant differences among switchgrass strains for all biomass conversion and composition traits including actual ethanol yields, ETOHL (L Mg-1) and theoretical ethanol yields, ETOHTL (L Mg-1), based on cell wall and non-cell wall composition NIRS analyses. ETOHTL means ranged from 98 to 115 L Mg-1 while ETOHTL means ranged from 203 to 222 L Mg-1. Because of differences in both biomass yields and conversion efficiency, there were significant differences among strains for both actual (2534 to 3720 L ha-1) and theoretical (4878 to 7888 L ha-1 ) ethanol production per hectare. It should be feasible to improve ethanol yields per hectare by improving both biomass yield and conversion efficiency by using NIRS analyses to quantify differences among cultivars and management practices.