|dc.description.abstract||Bioelectrochemical systems, such as microbial fuel cells (MFCs), are a specialized branch of biotechnology which aims to use the diversity of microbial metabolism for industrial applications including: the treatment of wastewater coupled with the production of electricity; the production of high value compounds (e.g. hydrogen); and biosensing applications. MFC technologies use exoelectrogenic bacteria such as Geobacter sp. These bacteria possess a particular metabolism that allows them to exchange electrons with solid surfaces like electrodes. One major parameter that can limit efficient electron transfer from biofilms to the electrode is the metabolic capability and microbial composition of the biofilm. Consequently, a main focus of this research was to determine if it is possible to select and maintain stable electrode biofilm communities that have efficient electron transfer properties and are suitable for specific functions such as biological oxygen demand (BOD) biosensing and electricity production. To achieve this objective, the influence of four parameters including the anode potential, the inoculum source, the substrate and the electrode surface properties, was tested on the selection of exoelectrogenic biofilms. The differences in community structures and electrochemical properties of the different biofilms selected were investigated using population profiling (e.g. SSCP, ARISA, RFLP), cloning and electrochemical analysis (e.g. cyclic voltammetry, power curves). Here, I present evidence that these four parameters altered the dominant community of the selected biofilms, with the anode potential and the substrate having the most effects. These results enrich an ongoing controversy in the literature as to whether electrode potential can influence the composition of anode-respiring biofilms or if they physiologically adapt to different potentials. In this study, I proved that the anode potential affects the composition of Geobacter-dominated biofilms at a strain level. My results imply that it is possible to select for high current-producing biofilms using specific anode potentials.
In addition to microbial composition, operational stability of anode-respiring biofilm communities is also of importance for electricity production and the development of biosensors. In this study, I explored the use of a biosensor based on an exoelectrogenic biofilm for the real-time monitoring of BOD, as a fast alternative to the conventional 5-day BOD assay. A Geobacter-dominated biofilm was selected at an anode potential of -0.36 V vs Ag/AgCl with ethanol as the sole carbon source. The biofilm had a broad metabolic capability and accurately quantified the BOD of complex media, opening the way to a new generation of biosensors.
Although MFCs are mainly limited by the efficiency of electron transfer at the anode, processes such as the reduction of oxygen at the cathode can also alter the current output of these systems. In this work, I demonstrated that photosynthetic cathodic biofilms enhance the power output of microbial fuel cells by saturating the catholyte in oxygen under illumination.
This project contributes significant knowledge to the parameters affecting the formation of anode- respiring biofilms, especially those dominated by Geobacter sp., the dynamics of their community structures, their operational stability and their potential use as BOD biosensors. It also provides evidence of the utility of photosynthetic biofilms to overcome cathodic limitations caused by low rates of the oxygen reduction reaction. The combination of my key research findings provides substantial opportunities to enhance the reliable use and implementation of MFC technologies for environmental monitoring and energy production applications.||en