Electricity generation by living plants in a plant microbial fuel cell

Society is facing local and global challenges to secure needs of people. One of those needs is the increasing demand of energy. Currently most energy is generated by conversion of fossil fuels. The major drawback of using fossil fuels is pollution of the environment by emission of carbon dioxide, nitrogen oxides, sulfur dioxide, volatile organic compounds, heavy metals, and fine particles. Furthermore fossil fuels are not renewable in a time scale in the order of decades. The microbial solar cell (MSC) is a new collective name of biotechnological systems that integrate photosynthetic and electrochemically active organisms to generate electricity in a clean and renewable manner. Among the MSCs, the plant microbial fuel cell (PMFC) that employs higher plants, is the most promising MSCs. In PMFCs, plant roots provide substrate for electrochemically active bacteria in the anode by the loss of organic compounds. In natural environments plant roots loose organic compound by diffusion through the cell membrane, or release organic compounds in order to acquire necessary nutrient. In both cases these organic compounds are an energy source for micro-organisms. In the PMFC these lost or released organic compounds are partly utilized by electrochemically active bacteria. During the oxidation of these organic compounds s electrochemically active bacteria transfer electrons to the anode electrode and produce protons and carbon dioxide. The electrons flow via a power harvester to the cathode compartment where the electrons are consumed by typically oxygen reduction. The aim of this thesis was to characterize the PMFC biologically and electrochemically and to improve the design towards higher applicable power outputs. The approach of this thesis was to understand processes in the PMFC which limit electrical power generation and use these findings to improve electrical power generation and the applicability of the PMFC design.