Ecology and technology of microbial fuel cells

The global demand for energy is predicted to increase by as much as 50% by 2050. With increased demands for energy there will also be increased amounts of wastewater being produced. The treatment of wastewater is expensive, and in the UK, demands 1% of the daily energy consumption across the nation. However, the associated cost and energy that wastewater demands could be reduced using Microbial Fuel Cells (MFC's). MFC's produce energy by utilising electrons that have been derived from microbes (known as exoelectrogens) anaerobically oxidising organic substrates. These electrons are then transferred from the microorganisms to an anode where they flow to a cathode, separated by a proton exchange membrane. Estimates suggest that wastewater contains between three and ten times the amount of energy that is necessary to treat it. In domestic wastewater, approximately 26% of the locked energy is in the form of carbon and previous studies have demonstrated that MFC's are able to remove over 90% of this available carbon via microbial oxidation in a fuel cell. The technology behind MFC's was first postulated over 100 years ago by Michael Potters. Despite the age of MFC technology, improvements to electrodes and membranes have made MFC's more feasible as a method of energy production today. However, investigations into microbial composition within a fuel cell and its impact on energy production and efficiency are dated. Currently, the efficiency of energy production by MFC's is approximately 30%, but they are predicted to be capable of exceeding an efficiency of 50%. This PhD project therefore investigates the impact that different, engineered microbial communities have on the overall production of energy, and to identify ways of increasing energy yields and efficiency in MFC's. Exoelectrogenic microbes are well documented, however, the interactions between them are not. An example of an exoelectrogenic bacterium is Pseudomonas aeruginosa which, in a monomicrobial culture can produce 28mW/m2, relative to Shewanella putrefaciens which can only produce 10.2mW/m2. P. aeruginosa produces pyocyanin, a phenazine which is highly valuable in energy production for its role as an electron mediator and ability to promote biofilm formation. However, pyocyanin has antimicrobial properties which could drastically hinder energy production, especially as energy yields in MFC's are greater in polymicrobial biofilms rather than planktonic cultures. Using experimental techniques (such as qPCR), the abundance of each species within the MFC can be monitored over time, enabling us to identify any dominant species and/or dysbiosis that occurs in the microbial community that my impact energy production. By incorporating different types of MFC, organic substrate and anodic materials into this research, we will be able to optimise the efficiency of MFC's, aiding in the development of a sustainable and environmentally friendly mode of energy production.