Exploring the Biomass Recalcitrance of Douglas Fir for Improving Bioproducts and Biofuels Production

Thesis (Ph.D.), Chemical Engineering, Washington State UniversityForestry residuals can potentially provide an abundant source of biomass feedstock for an emerging renewable chemicals and fuels industry, particularly in the Pacific Northwest region of the United States. Although Douglas fir is a major part of the forestry industry due to its favorable growth and lumber properties, it exhibits high levels of biomass recalcitrance. Biomass recalcitrance is a naturally complex phenomenon that poses a challenge to the development of an economically viable biorefinery concept by increasing biomass conversion costs and reducing product yield. One potential solution to improve the viability of Douglas fir as a bioconversion feedstock by reducing biomass recalcitrance would be the application of selective breeding in forestry practices. Tree improvement programs have successfully improved desirable traits for Douglas fir in the past, although their application toward a biorefinery industry is largely unexplored. In this project, variations between individual trees in Douglas fir populations were examined. A method was designed to screen for various traits related to recalcitrance, including chemical composition, pretreatment solids yield, holocellulose after pretreatment, and enzymatic hydrolysis of pretreated biomass. A “recalcitrance factor” was calculated and used to characterize the differences in sugar yield between trees. This screening method is applied to estimate the heritability and genetic correlations of these factors for one population, showing good potential for improvement of biomass recalcitrance through selective breeding and tree improvement. Further examination of structural differences between individual trees is also conducted to examine the underlying factors leading to the considerable variations in biomass recalcitrance of Douglas fir individuals, and their implications on refining biomass screening and selection for recalcitrance is discussed.Washington State University, Chemical Engineerin