New prototypes for the isolation of the anodic chambers in microbial fuel cells

• The influence of the cell construction over the performance of a MFC was studied.
• A cathode, facing both MFC compartments, isolated anodic and cathodic reactions.
• The cathode facing both compartments keeps ionic and electric conductivity.
• Anodic and cathodic separation with a PEM membrane yielded the highest efficiency.
• Unbalanced electron exchanges indicate the existence of complex processes.

This work has been focused on the assessment of new prototypes of MFC in which a more strict separation of the anode and cathode compartments is looked for, in order to attain strict anaerobic conditions in the anode chamber and hence, avoid lack of efficiency due to the prevalence of non-electrogenic competing microorganisms and to optimize composition of the anolyte and catholyte. A cylinder reactor with an inner chamber with graphite bars acting as anodes and the outer one with a stainless steel tube acting as cathode was used in three different configurations and results obtained during lifetests are compared in terms of electricity production, cathode oxygen consumption and anode COD depletion. Separation between compartments was obtained by (a) a two faces cathode (prototype R1, in which the cathode faces both compartments of the MFC), (b) a single cathode (prototype R2, in which the surface facing the anode compartment is electrically isolated and the ionic circuit is virtually detached) and (c) a conventional PEM membrane (prototype R3). Results show that the three prototypes perform as MFC from the electric point of view and they are efficient in the degradation of the COD contained in wastewater. However, the efficiencies in the production of electricity are very different and the greater the isolation of the anodic compartment, the lower are the current intensities produced. These results are explained because of the higher resulting ohmic loses. This large increase in the cell potential mask the potential benefits searched for with the isolation of the anode chamber but, at the same time, it gives significant information about performance of MFC that can be used for future MFC miniaturization studies.