Marine Microbial Fuel Cells (MMFC) as remote power generator

Microbial fuel cells (MFC) are fuel cells able to use electrons generated by electron-transport chain of bacteria, adhering on electrodes surface, as electrical energy. Microorganisms contained in different natural environments such as marine sediments, waste water, and soils at the anode of a MFC, oxidize the dissolved organic matter contained in the environment, use the electron and give it to the electrode surface as the final electron acceptor. MFC present promising advantages with respect to the standard abiotic fuel cells. They offer the possibility of harvesting electricity from organic waste and renewable biomass because the as bacteria consortia can adapt to different organic matters contained in a large variety of ‘dirty’ environments such as wastewaters or sediments. Therefore, the expensive catalyst such as Pt, which is required in abiotic fuel cells (PEM fuel cells for instance) is replaced by naturally growing microorganisms. Marine MFC have been investigated in the recent years with the end to operate low-power of requiring: marine instrumentations, such as oceanographic sensors, monitoring devices and telemetry systems. The purpose of this work was to check the effectiveness of electricity production by an MFC prototype where bacteria were growing in the anode of MFC cell, producing and releasing electrons to the electrode surface. MFC device consists of two circular chambers in Plexiglas with internal diameter of 12 cm and 1.5 cm of thickness (internal volume for each chamber ~170 ml) separated by a cation exchange membrane (CEM, CMI 7000, Membranes International Inc.). In each chamber there is a carbon conductive sheet (Carolina, USA) with a graphite rod of diameter 2 mm to ensure an effective current carrying out. Experiments were conducted in continuous mode at room temperature (22±2ºC) using mixed population naturally present in sea water as active microorganisms previously enriched by repeated fed-batch growth. Either the anodic or cathodic solution were constituted by a buffer solution of minerals salts Na2HPO4 and NaH2PO4, the cathodic reaction was assured by potassium ferricyanide (6.58 g/L). All electrochemical experiments were performed on a multi-channel VSP potentiostat (BioLogic) and a Data Acquisition Unit (Agilent 34972A) in order to acquire Current and Voltage under an external resistance of 1000 _. Results shown that marine water, could be a suitable source of bacteria under a continuous feeding of organic substrate, of giving about 4W/m2 at anode surface. It provides sufficiently energy supplying an acceptable monitoring capability to the remote sensor nodes, where the possibility to connect at the electrical grid is forbidden or in such situations where the substitution of traditional battery occurs with difficulties.