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Rational design and novel bioprocesses for low-carbon biofuels and bioproducts

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dc.contributor.authorBartholet, Danielle, author
dc.contributor.authorReardon, Kenneth, advisor
dc.contributor.authorFoust, Thomas, advisor
dc.contributor.authorDe Long, Susan, committee member
dc.contributor.authorPeebles, Christie, committee member
dc.contributor.authorWindom, Bret, committee member
dc.date.accessioned2024-01-01T11:25:12Z
dc.date.available2025-01-31T11:25:12Z
dc.date.issued2023
dc.description.abstractThe reduction of fossil fuel consumption and carbon emissions is one of the greatest challenges of our time, and innovative solutions are necessary to prevent climate catastrophe while maintaining economic development and modern ways of life. Biofuels and bioproducts can provide low-carbon alternatives to petroleum fuels and petroleum-based chemical processes. However, several limitations have impeded the wide-scale implementation of bio-based technologies. Biologically derived chemicals frequently do not possess ideal fuel properties due to high oxygen content and lower energy density. Furthermore, petroleum processes remain economically favorable to biological alternatives due to the high costs and low yields associated with bioprocesses. Rational design approaches to the development of new fuels and chemicals combined with improved bioconversion processes are strategies that address multiple aspects of sustainable development for a circular carbon economy. The broad purpose of this work was to explore and develop low-carbon alternatives to petrochemical products and processes. We begin by proposing a group of novel fuel additive molecules, then explore alternative technologies for their production. In Chapter 2 of this work, a rational design approach was used to identify "ideal" diesel fuel additive molecules. The desired characteristics of a liquid transportation fuel include high efficiency and engine performance, low particulate emissions, compatibility with current engines and infrastructure, and low risk of environmental contamination. In this work, we use computational tools to propose structures for diesel fuel additives that meet these criteria. Starting with the chemical structure of dimethoxymethane (DMM), a class of oxygenated molecules, called polyoxymethylene ethers (POMEs) is proposed by varying oxygen content in the backbone length and carbon content in the end group length. Additional structural variations, including iso-alkyl end groups and tertiary branches, are considered here for the first time. The ten candidate molecules identified consist largely of butyl-terminated POMEs. Synthesis chemistry for butyl-terminated POMEs was developed, utilizing an acid-catalyzed transacetalization reaction of butanol with methyl-terminated POMEs. To improve the sustainability of POME production, it is desirable to produce precursors from biomass using bioconversion processes. Therefore, the focus of this work pivoted to bioprocess technologies for improved production of butanol and other fuel precursor molecules. Butanol and other molecules of interest are highly reduced metabolic products, requiring the input of electrons through intracellular reducing equivalents. Frequently, the yields of these reduced products are limited due to redox constraints of metabolic pathways. Electro-enhancement, which refers to the direct supplementation of electrons from solid electrodes, may overcome redox constraints by enabling "unbalanced fermentations". While electro-enhancement of processes like fermentation (electro-fermentation) and anaerobic digestion (electro-AD) has been reported to successfully induce metabolic shifts and alter product profiles, much remains unknown about the mechanisms leading to observed shifts. Chapter 3 provides a detailed review of the literature in this field, highlighting the challenges and shortcomings of electro-enhancement research. Methods developed to improve the study of bioelectrochemical systems are also presented here. In Chapter 4, we apply these methods to pure culture electro-fermentations of Clostridium pasteurianum with the objective of increasing butanol production. Our results indicate that applied potentials may affect metabolite profiles through redox control but did not provide sufficient evidence for direct bacterial/electrode interaction. In Chapter 5, these methods are applied to electro-AD of food waste inoculated with wastewater sludge. Applied potentials are shown to have a wide range of effects on product profile and microbial communities. These results suggest that electro-enhancement may provide a method for fine-tuning product profiles in heterogeneous, mixed culture systems. However, further experiments are required in both pure and mixed culture systems to fully elucidate the effect of electro-enhancement on cellular processes. Through this work, new methods were developed to facilitate future research in bioelectrochemical systems and enable the design of improved electro-enhanced bioprocesses.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.identifierBartholet_colostate_0053A_18015.pdf
dc.identifier.urihttps://hdl.handle.net/10217/237402
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2020-
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.rights.accessEmbargo expires: 1/31/2025.
dc.titleRational design and novel bioprocesses for low-carbon biofuels and bioproducts
dc.typeText
dcterms.embargo.expires2025-01-31
dcterms.embargo.terms2025-01-31
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineChemical and Biological Engineering
thesis.degree.grantorColorado State University
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy (Ph.D.)

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