Long-term performance of a microbial electrolysis cell operated with periodic disconnection of power supply

This study describes a new approach for achieving stable long-term performance and maximizing the removal of chemical oxygen demand (COD) in a Microbial Electrolysis Cell (MEC). In the proposed approach, the MEC power supply is periodically disconnected, e.g. at a frequency of 0.1–0.5 Hz and a duty cycle of 90–95%. To evaluate the impact of such periodic power supply disconnection (on/off mode) on MEC performance, experiments were carried out in two flow-through MECs with activated granular carbon electrodes. The on/off operating strategy was applied to one MEC, while the other one was operated at a fixed voltage (control MEC). Long-term on/off operation resulted in progressive increase in COD removal efficiency (from 80% to 90%) and MEC current over time, while the control MEC showed stable but inferior performance. Furthermore, by changing the operating strategies and applying the on/off approach to the control MEC, its COD removal was increased from 78% to 83% and internal resistance decreased. The proposed on/off mode of operation can be used to develop a high-rate MEC-based wastewater treatment system

Maximizing power production in a stack of microbial fuel cells using multiunit optimization method

This study demonstrates real-time maximization of power production in a stack of two continuous flow microbial fuel cells (MFCs). To maximize power output, external resistances of two air\u2013cathode membraneless MFCs were controlled by a multiunit optimization algorithm. Multiunit optimization is a recently proposed method that uses multiple similar units to optimize process performance. The experiment demonstrated fast convergence toward optimal external resistance and algorithm stability during external perturbations (e.g., temperature variations). Rate of the algorithm convergence was much faster than in traditional maximum power point tracking algorithms (MPPT), which are based on temporal perturbations. A power output of 81\u201384 mW/LA (A = anode volume) was achieved in each MFC.NRC publication: Ye

On-line Monitoring and Parameter Estimation of a Microbial Fuel Cell Operated with Intermittent Connection of the External Resistor

This study describes on-line monitoring and parameter estimation during Microbial Fuel Cell operation with a pulse-width modulated connection of the external resistor (R-PWM mode) at low and high frequencies. Analysis of the output voltage profiles acquired during R-PWM tests showed the presence of slow and fast dynamic components, which can be described by an equivalent circuit model suitable for process monitoring and control applications. To demonstrate the proposed monitoring and parameter estimation procedure, the MFC was operated at several influent concentrations of acetate (carbon source) and an on-line parameter estimation procedure was used for estimating internal resistance and internal capacitance. Furthermore, these parameters were re-estimated at the end of each test yielding similar results. The proposed on-line procedure can be used for real-time process optimization.Peer reviewed: YesNRC publication: Ye

Real-Time Performance Optimization and Diagnostics during Long-Term Operation of a Solid Anolyte Microbial Fuel Cell Biobattery

This study describes a novel approach for real-time energy harvesting and performance diagnostics of a solid anolyte microbial fuel cell (SA-MFC) representing a prototype smart biobattery. The biobattery power output was maximized in real time by combining intermittent power generation with a Perturbation-and-Observation algorithm for maximum power point tracking. The proposed approach was validated by operating the biobattery under a broad range of environmental conditions affecting power production, such as temperature (4–25 °C), NaCl concentration (up to 2 g L−1), and carbon source concentration. Real-time biobattery performance diagnostics was achieved by estimating key internal parameters (resistance, capacitance, open circuit voltage) using an equivalent electrical circuit model. The real time optimization approach ensured maximum power production during 388 days of biobattery operation under varying environmental conditions, thus confirming the feasibility of biobattery application for powering small electronic devices in field applications

A comparison of simultaneous organic carbon and nitrogen removal in microbial fuel cells and microbial electrolysis cells

This study demonstrates simultaneous carbon and nitrogen removal in laboratory-scale continuous flow microbial fuel cell (MFC) and microbial electrolysis cell (MEC) and provides side-by side comparison of these bioelectrochemical systems. The maximum organic carbon removal rates in MFC and MEC tests were similar at 5.1 g L 121 d 121 and 4.16 g L 121 d 121, respectively, with a near 100% carbon removal efficiency at an organic load of 3.3 g L 121 d 121. An ammonium removal efficiency of 30\u201355% with near-zero nitrite and nitrate concentrations was observed in the MFC operated at an optimal external resistance, while open-circuit MFC operation resulted in a reduced carbon and ammonium removal of 53% and 21%, respectively. In the MEC ammonium removal was limited to 7\u201312% under anaerobic conditions, while micro-aerobic conditions increased the removal efficiency to 31%. Also, at zero applied voltage both carbon and ammonium removal efficiencies were reduced to 42% and 4%, respectively. Based on the observed performance under different operating conditions, it was concluded that simultaneous carbon and nitrogen removal was facilitated by concurrent anaerobic and aerobic biotransformation pathways at the anode and cathode, which balanced bioelectrochemical nitrification and denitrification reactions.Peer reviewed: YesNRC publication: Ye

Cathode materials evaluation in microbial fuel cells : a comparison of carbon, Mn2O3, Fe2O3 and platinum materials

In this work the oxygen reduction reaction (ORR) electro catalytic activity of Fe\u2082O\u2083 and Mn\u2082O\u2083 nanopowders, and carbon black powder was compared and evaluated against that of a Pt-cathode in an air-cathode microbial fuel cell (MFC) using several electrochemical techniques. The total resistance of the cathode electrode determined by impedance spectroscopy was 9.6, 7.8, 7.6 and 21.6\u3a9 for Pt, Mn\u2082O\u2083, Fe\u2082O\u2083 and C, respectively. Although the Mn2O3 cathode had the lowest resistance, the highest power output in polarization tests was observed for Pt, followed by Mn\u2082O\u2083, Fe\u2082O\u2083 and C. The corresponding volumetric power outputs were 90, 32, 15 and 8 W m\u207b\ub3. The ORR onset potentials determined using cyclic voltammetry have shown values of 783, 844, 696 and 562 mV vs Ag/AgCl for Pt, Mn\u2082O\u2083, Fe\u2082O\u2083 and C, respectively. Therefore, Mn\u2082O\u2083 exhibited the best ORR potential, whereas Pt exhibited the best volumetric power output. The MFCs based on these cathodes showed a performance decline with time, most likely due to the loss of the catalyst, catalyst deactivation, or parasitic reactions. The MFC based on carbon cathode showed the most stable behavior. In all tests, biofilms were, of course, formed at the various cathodes, but a microbially catalyzed ORR (biocathode) or a biofilm catalytically active for the ORR was not observed. The Mn\u2082O\u2083 electrode appeared to be the most promising non-noble electro catalyst cathode; however its high overpotential (activation loss) should be improved in order to increase significantly the power generation. \ua9 2011 Elsevier Ltd. All rights reserved.Peer reviewed: YesNRC publication: Ye