Development of a scalable microbial electrolysis cell and investigations of exoelectrogenic pure and mixed communities

Bioelectrochemical systems (BESs) combine the fields of microbiology and electrochemistry for the production of electricity, gaseous fuels, or chemicals from biodegradable material. The work described in this dissertation addresses these areas through the development of a scalable microbial electrolysis cell (MEC), characterization of exoelectrogenic biofilms using the molecular technique fluorescent in-situ hybridization (FISH), and investigation into the current-producing and substrate-utilizing capabilities of the exoelectrogenic bacterium Geobacter sulfurreducens.;Stainless Steel Brush Cathodes. MECs are a promising alternative method for producing hydrogen (H2) from biomass, yet they have been limited to the lab scale due in part to the inherent non-scalability and costs of electrodes. I examined high surface area stainless steel (SS) brushes as cathodes in MECs. A brush cathode with graphite instead of SS and a specific surface area of 4600 m2/ m3 generated substantially less current (1.7 ± 0.0 A/ m3), and a flat SS cathode (25 m2/ m3) produced 64 ± 1 A/ m3, demonstrating that both the SS and the large surface area contributed to high current densities. These results demonstrated for the first time that H2 production can be achieved at rates comparable to those with precious metal catalysts in MECs.;Small-Scale MECs. Membrane-free MECs employing SS cathodes provide a model for building larger scale reactors, but I also investigated if this simplified design could be scaled down to allow for an improved method of conducting lab scale research. I developed a new method based on using two electrodes placed ca. 0.5-cm apart in small (5 mL) serum bottles, with multiple reactors operated in parallel using a single power supply. Several anode and cathode materials were examined, with the highest current production and most robust design consisting of graphite plate anodes and SS mesh cathodes.;Microbial Ecology of Exoelectrogenic Biofilms. The bacteria that compose anodic biofilms are critical components of BESs, functioning as converters of chemical to electrical energy. To characterize exoelectrogenic biofilms, I used the molecular technique fluorescent in-situ hybridization (FISH), which involves fluorescently labeling bacteria for visual identification and quantification. In both microbial fuel cells (MFCs) and MECs, a strong correlation between the presence of the exoelectrogen G. sulfurreducens and reactor performance was apparent from FISH analysis targeting this bacterium.;Geobacter vs. Mixed-Culture MECs. Since G. sulfurreducens was found to be a predominant exoelectrogen based on FISH analysis of mixed communities, I examined if this bacterium could perform comparably to a mixed community in an MEC supplied acetate. Reactors with G. metallireducens, a non-H2 oxidizing exoelectrogen, were also included to better understand the role of H 2 recycling in membrane-free MECs. At an applied voltage of 0.7 V, G. sulfurreducens initially produced higher current densities than a mixed consortium, but both cultures converged to roughly 160 A/ m 3 after several fed-batch cycles, while G. metallireducens produced substantially less current.;Lactate Oxidation by Geobacter sulfurreducens . Using the serum bottle based MEC method, I examined if G. sulfurreducens could oxidize lactate. Current densities of ca. 0.8 A/ m2 were produced at an applied voltage of 0.7 V indicating that this bacterium was capable of lactate oxidation. In tests with Fe(III) as the terminal electron acceptor, it was discovered that complete lactate oxidation occurred, with the concurrent production and consumption of both acetate and pyruvate. The ability of G. sulfurreducens to oxidize lactate will allow for better comparative studies with the Fe(III)-reducing bacteria of the Shewanella genus, as these bacteria can oxidize lactate, but not acetate, under anaerobic conditions. (Abstract shortened by UMI.).