Date of Award

Spring 6-9-2023

Document Type

Thesis (Ph.D.)

Department or Program

Engineering Sciences

First Advisor

Lee R. Lynd

Abstract

Efficient deconstruction and conversion of inedible plant biomass, i.e., lignocellulose, is critical to decarbonizing the energy system in order to meet climate stabilization objectives. However, lignocellulose biomass is recalcitrant to deconstruction, and is often augmented by energy and capital intensive thermochemical pretreatment. Alternatively, Clostridium thermocellum is a thermophilic anaerobe capable of both deconstruction and conversion of lignocellulose without pretreatment. This thesis seeks to inform the deployment of cellulosic ethanol production by furthering our understanding of C. thermocellum mediated deconstruction, especially at industrially relevant conditions, i.e., solid loadings exceeding 100 g/L. In batch fermentations, it was observed that fractional deconstruction declines as solid loadings increase, which prompted diagnostic experiments and the inclusion of a second bacterium, Thermoanaerobacterium thermosaccharolyticum, to improve deconstruction. Ultimately, the bioreactors used to characterize this were unsuitable for work above 100 g/L, which necessitated a novel bioreactor system capable of high solids, semi-continuous fermentations. To our knowledge, this first-of-its-kind bioreactor will enable lab-scale characterization of lignocellulose deconstruction at high solid loadings not yet reported in literature. Lastly, a technoeconomic analysis adds another component to the thesis describing project economics and relative greenhouse gas (GHG) emissions for a 60-million gallon per year biorefinery. The impact of adopting emerging technologies such as carbon capture and storage (CCS) and biogas upgrading were evaluated in this context. Results indicate there are significant, i.e., up to 8-fold improvement, in net GHG benefits by adopting this approach, while simultaneously improving project economics.

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