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Understanding Substrate Features Influenced by Pretreatments that Limit Biomass Deconstruction by Enzymes


Conflict between dwindling reserves of fossil energy and growing consumption presents significant challenges to our society. To shift society's dependence away from petroleum to renewable energy, biorefineries are needed that employ advances in genetics, biotechnology, process chemistry, and engineering to convert biomass to valuable fuels and other products. Lignocellulosic biomass is the only sufficiently abundant source of renewable carbon that can support large-scale sustainable and economic production of transportation fuels and industrial chemicals. However, lignocellulosic biomass is naturally resistant to microbial or enzymatic deconstruction, a characteristic collectively termed "biomass recalcitrance," and overcoming this resistance is the main hurdle to realizing low costs. A better understanding of relationships among biomass recalcitrance, pretreatment, and enzymatic hydrolysis can accelerate this quest.

Against this background, this thesis seeks to understand the influence of pretreatment on substrate features and how such features affect subsequent enzymatic hydrolysis. First, application of a high throughput pretreatment and co-hydrolysis system (HTPH) was extended to dilute acid pretreatment to facilitate development of a novel two-stage pretreatment strategy that sought to achieve high cellulose digestibility and total sugar yields while keeping hemicellulose degradation low. Along with this, the feasibility of recycling liquid for low temperature pretreatment was demonstrated. Inspired by the HTPH screening results, a new method was developed for simple and rapid quantification of the hemicellulose sugar content in biomass. Finally, compositional and structural features of solids produced by application of two-stage pretreatment to switchgrass and three leading pretreatment technologies to corn stover were compared to provide new insights into control of biomass recalcitrance, as well as how pretreatments with much different deconstruction patterns impact enzymatic hydrolysis.

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