State of the Art

Bio-electrochemical systems (BESs) have emerged as a promising and yet exciting technology. In a BES, bacteria interact with electrodes using electrons, which are either removed or supplied through an electric circuit. The most-described type of BES is the microbial fuel cell (MFC), in which power is generated from
electron donors, such as organic compounds present in wastewater. MFC is considered to be a technology for sustainable bioenergy production, due to the ability of the system to generate electricity from wastewaters, while simultaneously treating them.
Microbes in the anodic chamber of an MFC oxidize added substrates and generate electrons and protons in the process. Carbon dioxide is produced as an oxidation product. However there is no net carbon emission because the carbon dioxide in the renewable biomass originally comes from the atmosphere in the photosynthesis process. Unlike in a direct combustion process, the electrons are absorbed by the anode and are transported to the cathode through an external circuit. After crossing a PEM or a salt bridge, the protons enter the cathodic chamber where they combine with oxygen to form water. Microbes in the anodic
chamber extract electrons and protons in the dissimilative process of oxidizing organic substrates. Electric current generation is made possible by keeping microbes separated from oxygen or any other end terminal acceptor other than the anode and this requires an anaerobic anodic chamber.

Typical electrode reactions are shown below, using glucose as an example substrate and oxygen as the final electron acceptor: