Large-scale Microbial Fuel Cells Research Articles

Development of a 3D-printed spongy electrode design for microbial fuel cell (MFC) using gyroid lattice

Microbial fuel cell technology addresses both issues in finding new ways to clean water systems while harnessing electricity. Several studies suggest that a single large-scale MFC is proven to be inefficient and expensive. Therefore, producing small-scale MFCs is focused on investigation to provide an efficient system and cost-effective approach. This study used 3D-printed MFCs using a spongy electrode design to produce a modern approach to modifying electrode capacity in energy generation. Furthermore, the study identifies the electrical conductivity of the spongy electrode by determining the voltage generated and power density by stacked MFCs in series, parallel, and hybrid configurations. The MFCs generate a maximum voltage of 633 mV and a current of 14.22 . One way to reduce the effects of voltage reversal in the MFC system is the application of hybrid connection circuits. Parallel-series hybrid connection possesses stable voltage generation of 250−300 𝑚𝑉 with the highest current generation of 115.20 𝜇𝐴. At the same time, the Series-Parallel Connection generates the highest voltage and current of 259 mV and 30 , respectively. The spongy electrode design and hybrid connection produced a maximum power and current density of 29.30 μW⁄m2 and 279.41 μA⁄m2 obtained from a different connection of pure parallel and 28P-2S hybrid connection. Furthermore, water quality parameters were examined (pH, TDS, ORP, and COD), that the MFCs design is efficient in wastewater treatment, with a %COD removal of 95.24% efficiency, reduced ORP from +48.00 mV to -7.00 mV, and the TDS concentration from 270 ppm to 239 ppm.

Untreated vs. Treated Carbon Felt Anodes: Impacts on Power Generation in Microbial Fuel Cells.

This research sought to enhance the efficiency and biocompatibility of anodes in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), with an aim toward large-scale, real-world applications. The study focused on the effects of acid-heat treatment and chemical modification of three-dimensional porous pristine carbon felt (CF) on power generation. Different treatments were applied to the pristine CF, including coating with carbon nanofibers (CNFs) dispersed using dodecylbenzene sulfonate (SDBS) surfactant and biopolymer chitosan (CS). These processes were expected to improve the hydrophilicity, reduce the internal resistance, and increase the electrochemically active surface area of CF anodes. A high-resolution scanning electron microscopy (HR-SEM) analysis confirmed successful CNF coating. An electrochemical analysis showed improved conductivity and charge transfer toward [Fe(CN)6]3-/4- redox probe with treated anodes. When used in an air cathode single-chamber MFC system, the untreated CF facilitated quicker electroactive biofilm growth and reached a maximum power output density of 3.4 W m-2, with an open-circuit potential of 550 mV. Despite a reduction in charge transfer resistance (Rct) with the treated CF anodes, the power densities remained unchanged. These results suggest that untreated CF anodes could be most promising for enhancing power output in BESs, offering a cost-effective solution for large-scale MFC applications.

Robust bimetallic metal-organic framework cathode catalyst to boost oxygen reduction reaction in microbial fuel cell

Metal-organic frameworks (MOFs) have emerged as versatile materials for widespread energy and environmental applications due to their intrinsic physical and chemical properties. To this extent, this research is focused on the synthesis of novel amine-functionalized single (Zr) and bimetallic (Zr, Ni) MOF viz. NH2-UiO-66(Zr) and NH2-UiO-66(Zr/Ni), followed by their testing as cathode catalysts to improve oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) for bioenergy recovery from organic wastes. The physical and chemical characterization techniques depicted the successful synthesis of octahedral-shaped MOF nanoparticles with similar structural integrity despite the incorporation of the secondary metal ion. However, electrochemical analyses demonstrated NH2-UiO-66(Zr/Ni) as a better catalyst, achieving a high ORR peak current, low charge transfer resistance, and high diffusion coefficient as compared to both NH2-UiO-66(Zr) and 10% Pt-C catalyzed cathodes. MFC performance evaluation further confirmed the high catalytic activity of NH2-UiO-66(Zr/Ni), allowing to recover a power density (PD) of 0.8 W/m2 at a coulombic efficiency (CE) of 75.4%, outperforming the MFC using 10 % Pt-C catalysed cathode. This study suggests that the NH2-UiO-66(Zr/Ni) can be used as an efficient ORR catalyst for application in large-scale MFCs.

Effect of Ion Selectivity on Current Production in Sewage Microbial Fuel Cell Separators.

This study compared the performance of two microbial fuel cells (MFCs) equipped with separators of anion or cation exchange membranes (AEMs or CEMs) for sewage wastewater treatment. Under chemostat feeding of sewage wastewater (hydraulic retention time of approximately 7 h and polarization via an external resistance of 1 Ω), the MFCs with AEM (MFCAEM) generated a maximum current that was 4–5 times greater than that generated by the MFC with CEM (MFCCEM). The high current in the MFCAEM was attributed to the approximately neutral pH of its cathode, in contrast to the extremely high pH of the MFCCEM cathode. Due to the elimination of the pH imbalance, the cathode resistance for the MFCAEM (13–19 Ω·m2) was lower than that for the MFCCEM (41–44 Ω·m2). The membrane resistance measured as the Cl− mobility of AEMs for the MFCAEM operated for 35, 583, and 768 days showed an increase with operation time and depth, and this increase contributed minimally to the cathode resistance of the MFCAEM. These results indicate the advantage of the AEM over the CEM for air-cathode MFCs. The membrane resistance may increase when the AEM is applied in large-scale MFCs on a meter scale for extended periods.

Economic affordable carbonized phenolic foam anode with controlled structure for microbial fuel cells

In microbial fuel cells (MFCs), the anode electrode is a core structure as the catalytic area of exoelectrogens. The anode material for large-scale MFCs needs excellent bioelectrochemical performance and low fabrication costs. Herein, carbonized phenolic foam with controllable porous structures was developed as the bio-capacitor of MFCs. The proportion of sodium dodecylbenzene sulfonate (SDBS), which improved mixing and dissolution between the resin liquid and the foaming agent, was adjusted to form open pores on the foam film and skeletons, which promoted both the capacitance and biocompatibility of the anode. Within SDBS proportion from 0 to 1.2 wt%, the anode SPF-9 (0.9 wt%) obtained the best capacitance (37 ± 0.13 F g−1), electrochemical active surface area (87 ± 0.38 cm2) and hydrophilia (contact angle 79 ± 0.2°). The MFCs with SPF-9 obtained the highest power density of 3980 ± 178 mW m−2, while those of carbon-cloth anodes were 1600 ± 28 mW m–2. The biofilm of SPF-9 also demonstrated higher activity and obtained larger abundance of exoelectrogens (68 ± 0.38%). The increased capacitance and biocompatibility mainly resulted in the good performance of SPF-9. The carbonized phenolic foam anode material was worth considering for the future application of MFCs due to its superior electrochemical performance and large-quantity fabrication capability.

Heat Treatment Effect on the Surface Properties of Carbon Cloth Electrode for Microbial Fuel Cell

In this study, we investigate the effect of heat treatment on the surface properties of carbon cloth electrodes and on the power generation efficiencies of microbial fuel cells (MFCs) configured with the heat-treated carbon cloth electrodes. Water contact angle measurements show that the hydrophobic surfaces of the carbon cloth became super-hydrophilic after heat treatment at a temperature above 500 °C, making it suitable for bacterial propagation. X-ray photoelectron spectrometry revealed that the signal of the C-O functional group of the carbon cloth electrodes increased in intensity after heat treatment. The MFCs configured with heat-treated carbon cloth electrode exhibited high power density of 16.58 mW/m2, whereas that of the untreated MFCs was only 8.86 mW m2. Compared with other chemical modifications, heat treatment does not use any environmentally unsound acidic or toxic solutions during modification and are promising for manufacturing large-scale MFC stacks.

Overview of Recent Advancements in the Microbial Fuel Cell from Fundamentals to Applications: Design, Major Elements, and Scalability

Microbial fuel cell (MFC) technology offers an alternative means for producing energy from waste products. In this review, several characteristics of MFC technology that make it revolutionary will be highlighted. First, a brief history presents how bioelectrochemical systems have advanced, ultimately describing the development of microbial fuel cells. Second, the focus is shifted to the attributes that enable MFCs to work efficiently. Next, follows the design of various MFC systems in use including their components and how they are assembled, along with an explanation of how they work. Finally, microbial fuel cell designs and types of main configurations used are presented along with the scalability of the technology for proper application. The present review shows importance of design and elements to reduce energy loss for scaling up the MFC system including the type of electrode, shape of the single reactor, electrical connection method, stack direction, and modulation. These aspects precede making economically applicable large-scale MFCs (over 1 m3 scale) a reality.

Continuous flow, large‐scale, microbial fuel cell system for the sustained treatment of swine waste

Microbial fuel cells (MFCs) have long held the promise of being a cost-effective technology for the energy-neutral treatment of wastewater. However, successful pilot-scale demonstrations for this technology are still limited to very few. Here, we present a large-scale MFC system, composed of 12 MFCs with a total volume of 110L, successfully treating swine wastewater at a small educational farm. The system was operated for over 200days in continuous mode with hydraulic residence time of 4hr. Very stable electrochemical and waste treatment performance was observed with up to 65% of chemical oxygen demand (COD) removed and a maximum treatment rate of 5.0kgCOD/m3 .day. Robust microbial enrichment was performed and adapted to metabolize and transform a diversity of compounds present. The Net Energy Recovery (NER=0.11kWhr/kg COD) is not only competitive with conventional cogeneration processes, but is in fact sufficient to sustain the operational energy requirements of the system. PRACTITIONER POINTS: This study demonstrates the design and operation of a large-scale microbial fuel cells (MFC) system for continuous treatment of swine wastewater. The system achieved a high chemical oxygen demand removal rate within a short hydraulic residence time. This study moves one-step closer to applying MFC technology for real wastewater treatment.

Impact of flow recirculation and anode dimensions on performance of a large scale microbial fuel cell

Many design and operational parameters that can impact power generation in microbial fuel cells (MFCs), such as flow over the electrodes, can only be effectively examined in larger-scale systems. A maximum power density of 0.101 ± 0.006 W m−2 (0.74 ± 0.05 W m−3) was obtained in an 85-L MFC with graphite fiber brushes (5.1 cm diameter, 61 cm long) and flat air cathode (0.62 m2 exposed area; anode-cathode spacing of 1.3 cm) in batch mode. Recirculating the anolyte diagonally through the chamber (entering the top right side of the reactor and exiting the bottom left side) further improved performance by 17% to 0.118 ± 0.006 W m−2, at a hydraulic retention time (HRT) of 22 min (3.9 L min−1), compared to static flow conditions. This power density was also higher than that obtained with parallel flow through the chamber (more evenly distributed using a manifold; 0.109 ± 0.009 W m−2). Reducing the diameter of the anode brushes from 5.1 cm to 2.5 cm did not improve the anode performance. These results demonstrate the importance of electrode spacing and hydraulic flow on large-scale MFC performance.

Mesoporous Co3O4 nanoflakes as an efficient and non-precious cathode catalyst for oxygen reduction reaction in air-cathode microbial fuel cells

Cobalt oxide is well known for its excellent oxygen reduction reaction (ORR) activity, however, its ORR activity can be further improved by synthesizing its porous architecture. Therefore, mesoporous Co3O4 nanoflakes were prepared by a two-step hydrothermal method and were employed as the cathode catalyst in a double-chamber microbial fuel cell (MFC) to explore its ORR activity for electricity generation. The electrochemical tests suggested that addition of Co3O4 nanoflakes enhanced the electrocatalytic activity of the cathode significantly. Besides, the cathode with a higher concentration of Co3O4 nanoflakes (COF-2) showed faster ORR kinetics as compared to the bare cathode. Evidently, COF-2 achieved an exchange current density of 4.18mA/cm2, which was 3.2 times higher as compared to the bare cathode. Consequently, this improved ORR activity increased the power output in MFC. COF-2 obtained a maximum power density of 347 ± 7mW/m2, which was approximately 8 times higher than the bare cathode. The enhanced ORR activity and improved electric output in the MFC can be attributed to the mesoporous nature of Co3O4 nanoflakes that exposed a higher number of ORR active sites at the cathode surface. Overall, mesoporous Co3O4 nanoflakes proved to be highly efficient and ca. 30 times cheaper than platinum, therefore, can be preferred in large-scale MFC applications over other expensive cathode catalysts.

Effects of Anode Materials on Electricity Generation and Organic Wastewater Treatment of 6 L Microbial Fuel Cells

Anode material is one of the most important factors on the application of microbial fuel cells for wastewater treatment due to its key role in forming exoelectrogenic biofilm and transferring electrons along with the high investment cost. In this study, carbon brush (CB), carbon cloth (CC) and graphite felt (GF) were investigated as alternative anode materials for 6 L single-chamber dual air-cathode microbial fuel cells (MFCs) in terms of starting-up rate and electricity production with artificial wastewater and slaughter wastewater. The cost effectiveness of anode materials was also evaluated. The results showed that anode materials had no obvious effect on the start-up of MFC. All MFCs finished their started-up on day 24. Using artificial wastewater[acetate 1 g·L-1 in 50 mmol·L-1 phosphate buffer (PBS)] as substrate, the maximum power densities for the CB, CC and GF-MFCs were (56.3±1.8) W·m-3, (46.0±1.7) W·m-3, and (40.8±1.5) W·m-3, while with slaughter wastewater MFCs could produce (19.5±0.8) W·m-3, (16.9±0.6) W·m-3, and (11.9±0.5) W·m-3, respectively. COD removals of all the MFCs were approximately 90% with both artificial wastewater and slaughter wastewater. The CB-MFCs had a cost of (3.44±0.08) mW·yuan-1 with the artificial wastewater and (0.97±0.05) mW·yuan-1 with slaughter wastewater, which were 18.6%, 12.8% higher than that of CC-MFCs and 38.7%, 80% higher than that of GF-MFCs, respectively. These results demonstrate that carbon brush is the most suitable material used in large-scale MFC.

High Performance Platinum Group Metal-Free Cathode Catalysts for Microbial Fuel Cell (MFC)

The oxygen reduction reaction (ORR) at the cathode is usually the limiting step in microbial fuel cells and improvements have to be done to increase the performances and reduce the cost. For the first time, iron-based catalysts were synthesized utilizing the polymerization-pyrolysis method and tested successfully in neutral media and in working microbial fuel cells (MFCs). The catalysts were synthesized using polymerization, salt formation, mixed with iron salt and pyrolyzed at 850°C (PABA-850) and 950°C (PABA-950) respectively. To study the kinetics, electro-activity of the catalysts was investigated using rotating ring disk electrode (RRDE). Results showed that PABA-850 had higher catalytic activity compared to that of PABA-950. Both Fe-catalysts had much better activity compared to activated carbon (AC) used as a baseline. Catalysts were then integrated into air breathing cathodes (loading 1 mg cm−2) and tested in single chamber MFC. The power peak obtained was 178 ± 3 μWcm−2 for PABA-850. Comparable power was produced from PABA-950 (173 ± 3 μWcm−2). AC power output was 131 ± 4 μWcm−2 that was roughly 40% lower compared to Fe-based catalysts. Those results demonstrated that the addition of platinum group metal free (PGM-free) catalysts increased the output of the MFCs substantially. Fe-based catalysts seem to be suitable for large-scale MFC applications.

Feasibility study of surface-modified carbon cloth electrodes using atmospheric pressure plasma jets for microbial fuel cells

Abstract This study investigated the surface and electrochemical properties of carbon cloth electrodes surface-modified by using atmospheric pressure plasma jets (APPJs) for applications involving microbial fuel cells (MFCs). APPJ treatment made the carbon cloth highly hydrophilic and did not introduce any observable cracks or flaws. MFCs configured with APPJ-treated carbon cloth electrodes exhibited electrochemical performance (maximum power density of 7.56 mW m −2 ) superior to that of MFCs configured with untreated carbon cloth electrodes (maximum power density of 2.38 mW m −2 ). This boost in performance can be attributed to the formation of abundant carboxyl and ammonium functional groups on the surface of APPJ-treated carbon cloth, which promoted the formation of anodic biofilms and the adhesion of bacteria, while facilitating the transfer of electrons from the bacteria to the electrodes. APPJ surface modification is non-toxic and environmentally friendly (no exogenous chemicals are required), which is particularly beneficial as the introduction of toxins might otherwise inhibit bacterial growth and metabolism. The APPJ surface modification process is rapid, cost-effective, and applicable to substrates covering a large area, making it ideal for the fabrication of large-scale MFCs and bioelectrochemical bioenergy devices.

Operation and Performance of Large-Scale MFCs for Treating Brewery Waste

Each year, Americans consume over 6.3 billion gallons of beer. As a result, over 50 billion gallons of brewery wastewater is created annually. Wastewater pre-treatment is an important investment for craft breweries as the biological oxygen demand (BOD) and the total suspended solids (TSS) from the waste stream leaving the brewery have to be significantly reduced before it enters the municipal system. Therefore, the treatment of brewery wastewater is an enormous and expensive part of the environmentally conscious brewing business. Brewery wastewater is characterized with high amounts of sugar, starch, and proteins, which makes it perfect candidate for Microbial Fuel Cell (MFC) application. MFCs have been proven as a promising technology for sustainable wastewater treatment and also as a way for direct recovery of electric energy [1]. In this study, two 10 liter MFCs were used to treat brewery waste collected from Stone Brewery, Escondido, CA. The MFCs had tubular design with a nanofiltration membrane separator, submerged oxygen reducing cathode and carbon cloth anode (Fig. 1). The two reactors were connected in series and operated under continuous flow. The objective of the study was to evaluate the long-term treatment capacity of the MFCs and optimize the operational parameters for maximum volumetric treatment rates and energy recovery. Three main parameters were used to evaluate the MFCs performance. These were chemical oxygen demand (COD) removal, the magnitude of the generated current density and the columbic efficiency (CE) of the COD transformation into electricity. The MFCs had an anode volume of 10L and anode surface area of 65 m2. The first MFC in the series (MFC #1) was first had an inflow of diluted buffered brewery wastewater effluent. MFC #2 was operated with the outflow of MFC #1. The MFCs was continuously running for 250 days when various flow rates of 1ml/min, 2ml/min, 3ml/min and 5ml/min were explored during the study. Over the period of 250 days and loading rates between 1ml/min to 5 ml/min, MFC #1 demonstrated an average COD removal rate of 51.6 ± 19.4%, current density of 2.77 ± 0.99 A/m3 and CE of 8 ± 7%. MFC #2 had an average COD removal of 50.9 ± 20.5%, current density of 2.0 ± 0.6 A/m3 and CE of 14 ± 11% (Fig. 2). Thus the whole system showed an average COD removal of 74.7 ± 19.2%, COD treatment rate of 0.56 ± 0.37 kg-COD/anode-m3-day, CE of 9 ± 6%, and current density of 2.4± 0.6 A/m3. This study demonstrated that MFCs could be useful devices for long-term continuous treatment of brewery wastewater. The system tested is modular, scalable and constructed from cost-effective materials. Future work will include additional large-scale pilot testing and further design and operational optimization to accomplish higher volumetric treatment rates.

Multitask Lasso Model for Investigating Multimodule Design Factors, Operational Factors, and Covariates in Tubular Microbial Fuel Cells

Microbial fuel cells (MFCs) are a promising technology for simultaneous wastewater treatment and direct electricity generation. To build an effective large-scale MFC in field operation, it is important to identify the critical design and operational factors. However, there are limited studies that focus on developing systematic models to predict MFC performance and conduct variable selection. Herein, a multitask Lasso model (MLM) was employed to characterize the relationship among the input variables (design factors, operational factors, and covariates) and the output variables (normalized energy recovery (NER) and organic removal efficiency) of a tubular MFC with five modules. The proposed MLM can not only select the important input variables to predict the MFC performance but also simultaneously and accurately predict multiple output variables. The important design and operational factors were identified on the basis of the variable selection in the MLM. It was found that cathode moisture, especially th...

Energy extraction from a large-scale microbial fuel cell system treating municipal wastewater

Development of microbial fuel cell (MFC) technology must address the challenges associated with energy extraction from large-scale MFC systems consisting of multiple modules. Herein, energy extraction is investigated with a 200-L MFC system (effective volume of 100 L for this study) treating actual municipal wastewater. A commercially available energy harvesting device (BQ 25504) is used successfully to convert 0.8–2.4 V from the MFCs to 5 V for charging ultracapacitors and running a DC motor. Four different types of serial connection containing different numbers of MFC modules are examined for energy extraction and conversion efficiency. The connection containing three rows of the MFCs has exhibited the best performance with the highest power output of ∼114 mW and the conversion efficiency of ∼80%. The weak performance of one-row MFCs negatively affects the overall performance of the connected MFCs in terms of both energy production and conversion. Those results indicate that an MFC system with balanced performance among individual modules will be critical to energy extraction. Future work will focus on application of the extracted energy to support MFC operation.

Interfacial electron transfer of Shewanella putrefaciens enhanced by nanoflaky nickel oxide array in microbial fuel cells

A uniform nanoflaky nickel oxide (NiO) array is constructed on carbon cloth via optimized conditions, and further employed as an anode in Shewanella putrefaciens (S. putrefaciens) microbial fuel cells (MFCs). Results indicate that the NiO nanoflakes/carbon cloth anode significantly improves the MFC performance in comparison to the unmodified carbon cloth, delivering about three times higher power density. This attributes to an enhanced interfacial electron transfer rate between bacteria cell and nanoflaky NiO array-modified carbon fiber and improved adhesion of bacteria cells on the modified carbon fiber for more active reaction centers. Considering the facile synthesis process, low cost and long discharging lifetime, this NiO/carbon cloth anode could be very promising to be applied for high performance, large scale MFCs.

Enhancing power generation of scale-up microbial fuel cells by optimizing the leading-out terminal of anode

Low power output and high cost are two major challenges for scaling up microbial fuel cell (MFC). The ohmic resistance of anode increasing as MFCs scale up can be one of main reasons for power density decrease. We present a simple model to simulate power loss and potential drop distribution caused by ohmic resistance of carbon mesh anodes with different dimensions and various leading-out terminals. We also conduct experiments to confirm the simulation work and the large impact of anode ohmic resistance on large-scale MFCs by varying leading-out configurations. The simulation results show that the power loss with an anode size of 1 m2 can be as high as 4.19 W at current density of 3 A m−2, and the power loss can be decreased to 0.04 W with optimized configuration of leading-out terminals and to 0.01 W by utilizing brass mesh as anode material. The experiments well confirm the simulation results with the deviations less than 11.0%. Furthermore, the experiment results also show that more than 47.1% of the power loss from small-scale to large-scale MFC comes from bad-leading-out terminal. These results demonstrate that leading-out terminal of anode is one of the key factors for scaling up MFC.

Graphene supported α-MnO2 nanotubes as a cathode catalyst for improved power generation and wastewater treatment in single-chambered microbial fuel cells

Microbial fuel cells (MFC) are a promising system to simultaneously accomplish the goal of energy production and wastewater treatment. In the MFC, the cathode plays an important role in achieving high power density and thereby improving the cell performance. In the cathode, an allotrope of carbon [activated carbon, graphite, multi-walled carbon nanotubes (MWCNTs)] is commonly used as a support material for catalysts, such as Pt. Here we show the improved performance of single-chambered MFC (sMFC) using hydrothermally synthesized α-manganese dioxide nanotubes (MnO2-NTs) as the catalyst and graphene as the support in the cathode. With a fixed MnO2-NTs loading, a maximum volumetric power density of 4.68 W m−3 was achieved from the sMFC with MnO2-NTs/graphene, which is higher than that of MnO2-NTs/MWCNTs (3.94 W m−3) and MnO2-NTs/Vulcan XC (2.2 W m−3) composite cathodes, but marginally lower than that of the benchmark Pt/C cathode (5.67 W m−3). The MnO2-NTs/graphene composite also showed a higher oxygen reduction reaction (ORR) activity than the MnO2-NTs/MWCNTs and MnO2-NTs/Vulcan XC composites implying that the former is a better catalyst than the later two. This study demonstrates the high ORR activity and high power generation ability of the cost-effective MnO2-NTs/graphene composite and makes it a potential cathode material for the replacement of expensive Pt in constructing large-scale MFC for wastewater treatment and bioelectricity production.

Effects of anolyte recirculation rates and catholytes on electricity generation in a litre-scale upflow microbial fuel cell

Microbial fuel cells (MFCs) are an attractive technology for simultaneous bioenergy recovery and organic removal; however, the lack of studies conducted with large-scale MFCs, especially those larger than 1 L, obstructs further development of this technology. In this paper, we built and operated a 4.9 L upflow microbial fuel cell (UMFC) with a liquid volume of 2.4 L. Its electricity generation and organic removal performance were examined under different operating conditions. The UMFC produced an open-circuit potential of 1.00 V with an acidified catholyte. Changing the recirculation of the anolyte did not significantly affect the power output in a short period, but a long-term test demonstrated improved electricity production at higher recirculation rates. The water produced via oxygen reduction or diffused from the anode was not sufficient for the cathode reaction; thus, an external supply of water is necessary. Lowering the pH of the catholyte benefited the cathode reaction and increased power production; however, pH is not the only factor affecting the cathode reaction and if organic matters were contained in the catholyte, for instance using the anode effluent as a catholyte, electricity generation decreased. The results and experiences gained from this study will help to further develop pilot-scale MFCs for practical applications.