An Analysis of Anaerobic Dual-Anode Chambered Microbial Fuel Cell (MFC) Performance

Microbial Fuel Cell (MFC) technology utilizes bacterial growth in carbon-containing solutions to generate electricity or hydrogen. For the direct production of electricity, an MFC operates aerobically at the cathode and anaerobically at the anodes. The same basic design can be used with minor changes to produce hydrogen at the cathode by applying an additional overpotential and omitting oxygen from the cathode. In this configuration, the device is called an MEC (Microbial Electrolysis Cell). However, the term “MFC” is frequently used to describe both devices. The primary objectives of this study were to determine optimal operating conditions and to minimize the internal resistance in the MFC in order to improve the reactor performance for power generation or hydrogen production using the organism Shewanella oneidesis MR-1. In this study, MFC performance was evaluated under various operating conditions with a modified MFC system architecture called a “Dual-Anode Chambered MFC” which incorporates two anode chambers flanking a single cathode chamber. This design leads to improvements in reactor performance and reduced internal resistance by minimizing electrode separation and providing parallel electrical connectivity, which increases the maximum current the MFC can supply for a given time (mA). These improvements lead to increased maximum specific power output (W/m³), volumetric hydrogen production rate (m³-H₂/m³-substrate/day), and hydrogen yield on substrate (mol-H₂/mol-substrate). An analysis of reactor performance using the new MFC reactor system included as system variables the size of the electrode surface area, substrate (lactate) concentration (5mM, 10mM, 20mM), substrate flow rate (1ml/min, 3ml/min, 5ml/min), and internal resistance (Ohms) for electricity production. The maximum volumetric power density of 23.6 W/m³ (standard deviation: 2.25, error: 1.3) and hydrogen yield of 0.438 mol-H₂/mol-substrate were obtained under optimized conditions; these conditions were then used to compare the reactor performance to that of a single-anode chambered MFC. Results indicated that the dual-anode MFC produced power per unit anode volume of 23.6 W/m³, about 1.2 times the power of a single-anode MFC (20.2 W/m³). This was due to the reduction of internal resistance within the dual-anode MFCs. The internal resistance was reduced by 45 %, from 106 Ohms (single-anode) to 58.3 Ohms (dual-anode).