A generalized mathematic model for microbial fuel cells

Microbial fuel cells (MFCs) can convert the energy content of organic substrates directly to electricity through microbial reactions. Optimal performance of microbial fuel cells (MFCs) depends on the reactor configuration, materials of construction, and the operating conditions. In this study, three different MFC design configurations were evaluated in batch mode: single compartment combined membrane-electrodes (SCME); single compartment brush-type anode electrode (SBE); and twin-compartment brush-type anode electrodes (TBE) design (reversed T-shape MFC with two-air cathode). The following alternate materials were examined: carbon anode and cathode electrode assembled with proton exchange membrane (PEM) in SCME system; and brush-type anode fabricated with carbon fibers and carbon cloth cathode electrodes coated with platinum (Pt) and ionomer in SBE and TBE MFCs. The following substrates were evaluated in this study: glucose, cattle manure leachate, solid cattle manure, and sucrose at different concentrations with phosphate buffer solution (PBS) of 200mM to increase the conductivity, thereby reducing the internal resistance.;The peak power densities produced from the SCME and SBE systems were 36.6mW/m2, fed with cattle manure as a substrate, and 209mW/m 2 (0.58V), fed with glucose, respectively. The TBE system was tested with and without a mediator to identify effect of mediator (2-hydroxy-1, 4-naphthoquinone) for effective MFC performance; the corresponding power densities (P) were Pmax 115mW/m2 (47O) with sucrose media at a concentration of 5g COD/L, with a mediator, and Ppeak=23.3mW/m 2 with sucrose at a concentration of 12g COD/L, without any mediators, respectively. The maximum power density produced from the TBE MFC was P max 67mW/m2 (220O) with solid cattle manure, and Pmax 93mW/m2 (220O) with solid cattle manure and humic acid salt as a mediator.;A simplified mathematical model for microbial fuel cell (MFC) was developed to predict the current-voltage-power generation as a function of time, under batch mode. The current generation model consisted of: the mediator-biocatalyst enzyme redox reaction kinetics in the electroactive bacteria within the biofilm; and the potential between overpotentials such as activation and Ohmic and electromotive force potential of the mediator. Mediator kinetics was related to the substrate utilization kinetics. The activation overpotential could be calculated using Tafel equation from the observed current generation data. Finally, the cell voltage and power density were calculated based on Ohm's law. The generalized model of an MFC for wider application was validated with experimental data from the three MFC designs tested in this study. Key factors in current production were identified as presence of a mediator with low overpotentials and a low external resistor. Model predictions of voltage agreed well with the experimental results (r2 > 0.99) in MFCs that were dosed with a mediator.