Bioelectrochemical Systems for Energy and Biocommodity Production

Timothy David Harrington

The objective of this dissertation is to present data and conclusions about bioelectrochemical systems using whole-cell bacteria to perform anodic and cathodic biotransformations with a variety of bacteria and reactors. Chapter 1 provides an overview of the field of bioelectrochemical systems, and the relevant background information for the two parts of the dissertation. The first part of this dissertation describes studies on bioelectrochemical systems where Geobacter sulfurreducens was grown on advective, flow-through anodes. Chapter 2 explores the effect of NaCl concentration on electricity production in flow-through anodes modified with Geobacter sulfurreducens biofilms. Chapter 3 describes studies performed on Geobacter sulfurreducens in the same systems with a focus on the modeling of biofilm growth and attachment kinetics. The role of ion transport and the kinetics of bacterial growth are evaluated, and conclusions are reached that bioelectrochemical systems with flow-through anodes lead to very fast current-development kinetics after inoculation, that NaCl concentration in the biofilm alters the biofilm kinetics, and that when excess surface area is present, the biofilms grow at an arithmetic rate. The second part of this dissertation explores the use of neutral red as a redox mediator during electro-fermentation, in which cells are grown planktonically in a cathode chamber polarized to deliver electrons to the medium. Chapter 4 describes the various effects of neutral red electro-fermentation with the bacteria Escherichia coli, Zymomonas mobilis, and Klebsiella pneumoniae in electro-fermentation cells with no electron acceptors present. Chapter 5 delineates the mechanism of action of neutral red in bacterial membranes during electro-fermentation with and without the presence of terminal electron acceptors. The main conclusions reached are that reduced neutral red reduces menaquinone species in the inner bacterial membrane, which can alter some cells' sensing of their redox environment, and that reduced neutral red can drive anaerobic respiration in the presence of the anaerobic terminal electron acceptors fumarate, DMSO, and nitrate. Chapter 6 describes a bioelectrochemical system using similar reactors in which genetically modified Shewanella oneidensis biofilms were subjected to cathodic potentials in order to cause the reduction of carbon dioxide to formate. Chapter 7 consists of concluding remarks that discuss the future of bioelectrochemical systems research.

Bioelectrochemical Systems for Energy and Biocommodity Production

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