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Understanding Synergies Between Pretreatment, Feedstock, and Consolidated Bioprocessing for Lignocellulosic Biomass Conversion

  • Author(s): Thomas, Vanessa Ann
  • Advisor(s): Wyman, Charles E
  • et al.
Abstract

Renewable fuels are essential to environmental sustainability, economic competitiveness, air and water quality, and national energy security for a transportation sector that is almost totally dependent on petroleum. Cellulosic biomass is the only natural resource from which liquid organic fuels can be made sustainably on a large scale due to its abundance, widespread geographic availability, and low cost. In order to reduce the capital and operating costs of cellulosic biorefineries, consolidated bioprocessing (CBP) has been identified as a powerful biotechnology platform that combines enzyme production, saccharification, and fermentation, into a single unit operation using microorganisms capable of enzyme production and sugar-to-fuel fermentation. Although much research has been devoted to obtaining microorganisms able to achieve high sugar conversion, conservation of the available sugars proves to be an equal challenge in light of the preceding pretreatment step where the greatest sugar losses may occur. However, research devoted to the study of pretreatment with organism-free enzyme systems may not be applicable to CBP as organism-mediated hydrolysis operates by a different mechanism than free enzyme cocktails. Thus, studies which combine real biomass, pretreatment, and CBP are vital to establishing commercially successful bioconversion systems. In order to determine synergies between pretreatment, feedstock, and CBP, various studies were expounded through a diversity of feedstocks, pretreatment methods, and biocatalysts. These studies included: (1) sugar release optimization for C. thermocellum CBP and free, fungal enzymes across hydrothermal pretreatment severity for Populus, (2) characterization of Populus natural variants by comparing biological catalysts while applying a suite of characterization techniques to the biomass, and (3) evaluation of a newly developed pretreatment method, co-solvent enhanced lignocellulosic fractionation (CELF), through comparison with dilute sulfuric acid pretreatment across multiple feedstocks and biological catalysts while aligning our results with insights from ultrastructure characterization. Contrasting sugar release from pretreated biomass by C. thermocellum CBP and fungal enzymes was used as a means of evaluating synergy resulting in reduced recalcitrance while biomass characterization informed of structural properties potentially indicative of low recalcitrance. By considering real biomass under industrially relevant process scenarios, we develop fundamental knowledge towards the design of superior bioconversion systems and improved sugar yields.

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