Upflow Microbial Fuel Cell Research Articles

Key operational parameters assessment for a chromium (VI)-reducing annular upflow microbial fuel cell

Development of upflow microbial fuel cells (MFCs) is of importance since these types of MFCs can be integrated in wastewater treatment plants for the provision of continuous treatment and energy recovery. In this study, key operational parameters were assessed for a hexavalent chromium [Cr(VI)] reducing annular upflow MFC (approximately 5 L total liquid volume). The optimized operational parameters were cathode and anode hydraulic retention times of 2 days, temperature of 34 °C, influent Cr(VI) concentration of 800 mg L−1, and anode and cathode pH of 7 and 4 respectively. This study demonstrated that a parallel configuration is advantageous since it leads to a high current and power density operation due to low internal resistance when compared to series configuration. The precipitation of Cr(III) over time was demonstrated to have a potential to reduce MFC performance and operating at high influent Cr(VI) pHs (7–10) should be avoided. The optimized peak output potential difference and maximum power density achieved under parallel configuration were 896 mV and 994 mW m−3 respectively, at a current density of 1191 mA m−3. This study provides a step into developing continuous metal reducing MFCs for use in simultaneous treatment of heavy metals in wastewater and energy recovery.

Application of halophiles in UMFC (upflow microbial fuel cell) for the treatment of saline olive oil industrial wastewater coupled with eco-energy yield.

The olive oil industry faces a major problem of treating the wastewater with high organic content and safe disposal. Olive oil industrial wastewater (OOIWW) consists of highly toxic environmental pollutants with high salinity. Saline olive oil industrial wastewater was treated using halophilic consortium in UMFC (upflow microbial fuel cell) mobilized with carbon felt as electrode. Total and soluble COD (chemical oxygen demand), total suspended solids and phenol content removal were studied at different organic loads (0.56, 0.77, 1.05, 1.26, 1.52 and 1.8 gCOD/L). UMFC with OOIWW was optimized at 1.52 gCOD/L for high organic removal and corresponding electricity production. Total COD, soluble COD, TSS and phenol removal were 91%, 89%, 78%, and complete removal of phenol was accomplished at the optimized organic load (1.52 gCOD/L). Correspondingly, the maximum bioenergy yield was 784 mV with 439 mW/m2 (power density) and 560 mA/m2 (current density), respectively. The presence of prominent halophilic exo-electrogens such as Ochrobactrum, Marinobacter, Rhodococcus and Bacillus potently treated the OOIWW and exhibited high energy yield.

Tannery wastewater treatment coupled with bioenergy production in upflow microbial fuel cell under saline condition

Tannery industry handling huge amount of leather materials release immense amount of saline organic content wastewater. The present research was focused on the treatment of tannery industrial wastewater in UMFC (upflow microbial fuel cell) under saline condition (4%). The UMFC reactor was operated at different organic load (OL) such as 0.6, 1.2, 1.8 and 2.4 gCOD/L respectively. Total chemical oxygen demand (TCOD) removal at 0.6, 1.2, 1.8 gCOD/L was 87 ± 1.2%, 91 ± 1.2% and 93 ± 1.8% respectively. Soluble chemical oxygen demand (SCOD) removal in UMFC at 0.6, 1.2, 1.8 gCOD/L was 85 ± 0.6%, 88 ± 1.2% and 91 ± 1.8% respectively. Total suspended solids (TSS) removal was 49%, 78%, 81% at 0.6, 1.2, 1.8 gCOD/L OL in UMFC. Further, raise in OL to 2.4 gCOD/L showed decrease in TCOD, SCOD (80% and 72%) and TSS (60%) removal. Maximal power production of 854 mV with corresponding PD (power density) of 462 mW/m2 and CD (current density) of 523 mA/m2 was registered at 1.8 gCOD/L OL in UMFC. Increase in OL to 2.4 gCOD/L revealed decline in energy production to 810 mV with PD (385 mW/m2) and CD (438 mA/m2) in UMFC. Maximal bioaccumulation of chromium (95%) was recorded at 1.8 gCOD/L OL. Among different OL used 1.8 gCOD/L OL was optimum for the treatment of tannery wastewater and energy production. Bacterial community analysis in anode of UMFC revealed the dominance of promising electrogenic halophilic strains such as Ochrobactrum, Marinobacter, Rhodococcus and Bacillus in all the OL. Thus, the research clearly revealed the efficacy of halophilic consortium to treat the saline tannery wastewater coupled with bioenergy production in UMFC.

Roles of Hydraulic Retention Time and Initial Substrate Concentration on Performance of Up-Flow Microbial Fuel Cells in Synthetic Landfill Leachate Treatment

Roles of Hydraulic Retention Time and Initial Substrate Concentration on Performance of Up-Flow Microbial Fuel Cells in Synthetic Landfill Leachate Treatment

Roles of Hydraulic Retention Time and Initial Substrate Concentration on Performance of Up-Flow Microbial Fuel Cells in Synthetic Landfill Leachate Treatment

Roles of Hydraulic Retention Time and Initial Substrate Concentration on Performance of Up-Flow Microbial Fuel Cells in Synthetic Landfill Leachate Treatment

Novel continuous up-flow MFC for treatment of produced water: Flow rate effect, microbial community, and flow simulation

Produced water (PW) is the main waste produced by oil and gas industry, and its treatment represents an environmental and economical challenge for governments and the industry itself. Microbial fuel cells (MFC) emerge as an ecofriendly technology able to harvest energy and remove pollutants at the same time, however high internal resistance is a key problem limiting their operating performance and practical application. In this work, a novel continuous up-flow MFC was designed and fed solely using PW under different flowrates. Effects of the different flowrates (0 mL/s, 0.2 mL/s, 0.4 mL/s, and 0.6 mL/s) in power production performance and pollutants removal were analyzed. Our results demonstrated the removal efficiency of all the pollutants improved when flowrate incremented from 0 to 0.4 mL/s (COD: 96%, TDS: 22%, sulfates: 64%, TPH: 89%), but decreased when 0.6 mL/s was applied. The best power density of 227 mW/m2 was achieved in a flowrate of 0.4 mL/s. Similar to the pollutant's removal, the power density increased together with the increment of flowrate and decreased when 0.6 mL/s was used. The reason for the performance fluctuation was the decrement of internal resistance from 80 Ω (batch mode) to 20 Ω (0.4 mL/s), and then the sudden increment to 90 Ω for 0.6 mL/s. A flow simulation revealed that until 0.4 mL/s the flow was organized and helped protons to arrive in the membrane faster, but flowrate of 0.6 mL/s created turbulence which prejudiced the transportation of protons incrementing the internal resistance. Microbial community analysis of the biofilm found that Desulfuromonas, Desulfovibrio and Geoalkalibacter were dominant bacteria in charge of pollutant removal and electricity production. This study can be helpful in guiding the use of continuous-flow MFC for PW treatment, and to accelerate the practical application of MFC technology in oil industry.

Generation of electricity from anaerobically treated leachate using up flow microbial fuel cell

Bioenergy is a renewable energy that plays a vital role in today's increasing energy demand. Microbial fuel cell (MFC) concurrently treat the wastewater and produce the energy. Upflow microbial fuel cell (UMFC) was used in this study to generate electrical energy by treating leachate. UMFC was operated at different organic loading rate (OLR) (0.27 – 1.37 gCOD/Ld) for 130 days using activated carbon fibre felt (ACFF) as electrodes. In optimum OLR of 0.64 gCOD/Ld, UMFC accomplished maximum total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD) and total suspended solids (TSS) removal of 84.6%, 88% and 79.2% respectively. The peak coulombic efficiency (CE) of 49.7% was attained at 0.27 gCOD/Ld. UMFC accomplished power density of 106.66 mW/m² along with the voltage production of 702 mV at 0.64 gCOD/Ld OLR. Bacterial community analysis revealed the dominance of proteobacteria (58.9%) followed by firmicutes (40.3%) and bacterioides (3.8%) in UMFC at 0.64 gCOD/Ld OLR. This results shows that UMFC effectively treat leachate wastewater along with the electricity generation.

The Azo Dye Degradation and Differences Between the Two Anodes on the Microbial Community in a Double-Anode Microbial Fuel Cell

The anode configuration determined the performance of power generation and contaminant removal in microbial fuel cell (MFC). In this study, double anodes were constructed along an up-flow MFC for mitigating the suppression of refractory organic azo dye Reactive Brilliant Red X-3B and increasing the power output. Results revealed that high concentration of X-3B suppressed the power generation of MFC. The maximum power density decreased from 0.413 to 0.161 W/m3, and the inner resistance rose from 448 to 698 Ω. However, double anodes weakened the suppression of X-3B to the current generation. Compared with single anode, the attenuation of MFC current decreased from 48 to 40%. Meanwhile, the X-3B removal efficiency in double-anode MFC was 19.81% higher compared with a single-anode condition when the X-3B was 1000 mg/L. The degradation pathway analysis indicated that aromatic amines formation and further oxidation were achieved sequentially in the MFC. Furthermore, microbial communities in the lower and upper anodes were analyzed, revealing that the microorganisms in the lower anode were more inclined to degrade the pollutant, whereas those in the upper anode were more inclined to generate electricity. This double-anode structure showed the potential for large concentration range of azo dye removal and the current recovery in real textile wastewater.

Power production and microbial community composition in thermophilic acetate-fed up-flow and flow-through microbial fuel cells

The microbial communities developed from a mixed-species culture in up-flow and flow-through configurations of thermophilic (55 °C) microbial fuel cells (MFCs), and their power production from acetate, were investigated. The up-flow MFC was operated for 202 days, obtaining an average power density of 0.13 W/m3, and Tepidiphilus was the dominant transcriptionally-active microorganisms. The planktonic community developed in the up-flow MFC was used to inoculate a flow-through MFC resulting in the proliferation of Ureibacillus, whose relative abundance increased from 1 to 61% after 45 days. Despite the differences between the up-flow and flow-through MFCs, including the anode electrode, hydrodynamic conditions, and the predominant microorganism, similar (p = 0.05) volumetric power (0.11–0.13 W/m3), coulombic efficiency (16–18%) and acetate consumption rates (55–69 mg/L/d) were obtained from both. This suggests that though MFC design can shape the active component of the thermophilic microbial community, the consortia are resilient and can maintain similar performance in different MFC configurations.

Domestic wastewater treatment and energy harvesting by serpentine up-flow MFCs equipped with PVDF-based activated carbon air-cathodes and a low voltage booster

Microbial fuel cells (MFCs) exhibit high capital cost and low energy output, which are major issues of the expected practical application of MFCs in wastewater treatment. Here, we have developed serpentine up-flow MFCs equipped with polyvinylidene fluoride (PVDF)-based activated carbon (AC) air-cathode (MFC-PVDF/AC) and continuously operated for more than 6 months with real domestic wastewater as a substrate. The MFC-PVDF/ACs achieved average total COD removal rates (5.11 ± 0.94 kg tCOD/m3/d) and power densities (3.96 ± 3.01 W/m3) without major water leakage, which were even higher than those of MFCs equipped with Pt-based air-cathode (MFC-Pts). The MFC-PVDF/ACs also achieved high and stable suspended solid (SS) removal efficiency (>90%) at 1.5-h HRT without any clogging event during the entire operation period. Since the PVDF-based AC air-cathode is less expensive, more durable, and easy to manufacture, expensive Pt cathodes are not necessary for MFCs treating low strength domestic wastewater. Furthermore, we have developed a low voltage booster (LVB) to increase low output voltage of MFC-PVDF/ACs (i.e., <0.4 V). Connecting a single LVB with a single MFC-PVDF/AC increased the voltage from <0.4 V to 4.35–5.2 V without the voltage reversal, which was enough to turn on three LED bulbs for >12 days. Taken together, the MFC-PVDF/AC with a LVB circuit exhibits excellent and stable performance of domestic wastewater treatment and usable power generation, suggesting that it could be used as a cost- and energy-saving primary wastewater treatment system.

Non-Platinum Group Catalysts to Improve Performance of a Membraneless Microbial Fuel Cell

Over the last couple decades, microbial fuel cells (MFCs) have become a technology of interest for renewable energy production and waste treatment/reclamation. MFCs are flexible with fuel and, for this reason, have garnered interest as biosensors, unit operations in advanced wastewater treatment, and alternative power sources. MFCs oxidize organic matter at the anode where microbes perform anaerobic respiration to convert organic matter into simpler compounds (such as carbon dioxide, methane, etc.); however, the anode electrode serves as the final electron acceptor [1, 2]. The electrons produced at the anode are used at the cathode in oxygen reduction reaction (ORR), a reaction that requires the presence of a catalyst. The system design for MFCs can vary to meet different applications [3], but one of the more popular designs is a membrane less, single chamber, air cathode microbial fuel cell [4], which has the anode submerged in an oxygen-less, nutrient solution and has an air-exposed cathode. Although promising in concept, MFCs have very low power density, making them cost inefficient. A major performance limitation in MFCs has been identified in the cathode. Overall efficiency and power density a strongly influenced by cathode design and catalyst selection for the ORR [4, 5]. Previous modeling efforts have suggested oxygen crossover to the anode, oxygen diffusion to the ORR catalyst, and the catalyst used are major factors for low power density [6-8]. In this work, improved MFC performance is demonstrated using non-platinum group catalyst material. The novel catalyst was benchmarked against a platinum group catalyst. Using the novel non-platinum catalyst results in a modest increase in open circuit potential, and a significant increase in maximum current density and power density. In addition, we have investigated the influence of non-platinum catalyst loading on the overall performance. The novel catalysts used in this work demonstrated stability over months of operation. This suggests that the non-platinum group catalyst used in this work is more efficient than platinum group catalyst, improving the cell performance while simultaneously enabling lower cost. References Jr, L.B.W., C.H. Shaw, and J.F. Castner, Bioelectrochemical fuel cells. Enzyme and Microbial Technology, 1982. 4(3): p. 6.Kim, H.J., et al., A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens. Enzyme and Microbial Technology, 2002. 30(2): p. 8.He, Z., S.D. Minteer, and L.T. Angenent, Electricity Generation from Artificial Wastewater Using an Upflow Microbial Fuel Cell. Environmental Science and Technology, 2006. 39: p. 6.Liu, H. and B.E. Logan, Electricity Generation Using an Air-Cathode Single Chamber Microbial Fuel Cell in the Presence and Absence of a Proton Exchange Membrane. Environmental Science and Technology, 2004. 38: p. 6.Rismani-Yazdi, H., et al., Cathodic limitations in microbial fuel cells: An overview. Journal of Power Sources, 2008. 180: p. 12.Ou, S., et al., Full cell simulation and the evaluation of the buffer system on air-cathode microbial fuel cell. Journal of Power Sources, 2017. 347: p. 11.Ou, S., et al., Modeling and validation of single-chamber microbial fuel cell cathode biofilm growth and response to oxidant gas composition. Journal of Power Sources, 2016. 328: p. 12.Ou, S., et al., Multi-variable mathematical models for the air-cathode microbial fuel cell system. Journal of Power Sources, 2016. 314: p. 9. Figure 1

Evaluation on the electricity generation using membrane-less fixed-bed upflow microbial fuel cell

A simple modification on commonly employed biological wastewater treatment process into microbial fuel cell (MFC) could become value added to the treatment unit for removing organic contaminant. The objective of this study was to evaluate the developed membrane-less fixed-bed upflow MFC for generating electricity from synthetic wastewater. The bioreactors were fabricated using cylinder column with 4.5 cm D × 25 cm H and gravel was loaded into the bioreactors for biofilm development. Carbon felts were used as anode and cathode at lower bed and upper bed, respectively, in the bioreactors. The effects of feeding pattern of wastewater, organic loading, biofilm on the cathode, pH at aerobic region of bioreactor, and concentration of KCl on the performance of the MFCs for power generation were evaluated. The optimum power output from the developed MFC was about 28 mW/m2 with 6.28 g/L of sodium acetate as carbon source, pH 6.5–6.6, and 9.5 h of HRT.

Electricity generation from swine wastewater in microbial fuel cell: Hydraulic reaction time effect

Microbial fuel cells (MFC) have emerged as a sustainable technology that can directly produce electricity from the oxidation of organic matter by bacteria. A two-chambered up-flow MFC with inner loop mode is evaluated for the hydraulic retention time (HRT) effect on MFC electricity generation. The MFC is constructed with a carbon cloth electrode and anion exchange membrane for electricity production. Swine wastewater containing 3300 ± 300 mg/L of total chemical oxygen demand (TCOD) was used as the substrate for the anode chamber. Potassium ferricyanide was used as the electron acceptor in the cathode chamber. The reactor was operated at 30 °C with a external resistance of 100 Ω in feed-batch mode. The TCOD removal rates at HRT 13, 14, and 20 d were 71, 73 and 83%, while the coulombic efficiencies (CE) were 7.1, 2.4 and 0.3%, respectively. The maximum power density at HRT 13 and 14 d were similar, 12 mW/m2 and 13 mW/m2, which were 26 fold greater than the HRT at 20 d (0.5 mW/m2). The effect of different HRTs on decreasing the organic content by biocatalyzing leads to less organic material for electricity generation, resulting in lower power output. The optimal COD removal efficiency, CE and power density were observed in an up-flow MFC at HRT 14 d. These results demonstrate that up-flow MFC using an inner loop with swine wastewater as the substrate could provide both effective organic removal and electricity output.

Treatment of seafood processing wastewater using upflow microbial fuel cell for power generation and identification of bacterial community in anodic biofilm

Tubular upflow microbial fuel cell (MFC) utilizing sea food processing wastewater was evaluated for wastewater treatment efficiency and power generation. At an organic loading rate (OLR) of 0.6 g d−1, the MFC accomplished total and soluble chemical oxygen demand (COD) removal of 83 and 95%, respectively. A maximum power density of 105 mW m−2 (2.21 W m−3) was achieved at an OLR of 2.57 g d−1. The predominant bacterial communities of anode biofilm were identified as RB1A (LC035455), RB1B (LC035456), RB1C (LC035457) and RB1E (LC035458). All the four strains belonged to genera Stenotrophomonas. The results of the study reaffirms that the seafood processing wastewater can be treated in an upflow MFC for simultaneous power generation and wastewater treatment.

Effect of separator electrode assembly (SEA) design and mode of operation on the performance of continuous tubular microbial fuel cells (MFCs)

Three different innovative composition of nylon-cloth (NC), J-cloth (JC) and glass fiber (GF) were examined as separators in a tubular separator electrode assembly MFCs (SEA-MFCs) with a graphite granule bed anode and a simple carbon-cloth cathode. Three experiments were designed including horizontal MFC with co-current and counter-current inflows of anolyte and catholyte as well as vertical MFC with up-flow and co-current inflows to the MFC. The arrangement of NC-JC-GF was more effective with higher maximum power density (281.30 ± 32.31 mW/m2) and lower internal resistance (562.09 Ω) compared to the other compositions. The power density was more improved as the hydraulic retention time (HRT) was decreased. The counter-current flow caused by higher species diffusion between the anode and cathode compartments compared to the co-current flow, so diminished the maximum power density significantly (270.60 ± 29.53 to 70.48 ± 5.65 mW/m2) and increased the internal resistance (614.71–1711.59 Ω). On the other hand, the horizontal operation showed better performance than the up-flow MFC.

Power generation in fed-batch and continuous up-flow microbial fuel cell from synthetic wastewater

Up-flow bioreactors have the advantages of retaining very high cell density and having high mass transfer efficiency. The recirculation rate could improve the up-flow rate in up-flow bioreactor. A two-chamber UFMFC (up-flow microbial fuel cell) is constructed with flat graphite electrodes and anion exchange membrane for electricity generation. The anode chamber is seeded with compost culture enriched on xylose and operated on synthetic wastewater with 0.5 g/L xylose, external resistance of 100 Ω, at pH 7.0 and 37 °C in fed-batch mode. The cathode chamber in the top of the UFMFC is filled with potassium ferricyanide (pH 7.0) as the electron acceptor. The effects of different recirculation rates of 1.2, 2.4, 4.8 and 7.2 RV (reactor-volumes)/h to increase the mass transfer and electricity production are determined in fed-batch mode. At a recirculation rate of 4.8 RV/h, a power density of 356 ± 24 mW/m2 with CE (coulombic efficiency) of 21.3 ± 1.0% is obtained. Decreasing HRT (hydraulic retention time) could improve the electricity production performance of UFMFC in continuous mode. The power generation is increased to 372 ± 20 mW/m2, while CE remains at 13.4 ± 0.5% with HRT of 1.7 d and optimum recirculation rate of 4.8 RV/h on continuous mode. Microbial communities were characterized with PCR (polymerase chain reaction) – DGGE (denaturing gradient gel electrophoresis). In the end of the experiment, the biofilm contained both fermenting and exoelectrogenic bacteria, while fermenting and nitrate-reducing bacteria were mainly present in the anodic solutions. Moreover, some changes occurred in the microbial communities of the anodic solutions when the MFCs were switched from fed-batch to continuous mode, while the differences were minor between different recirculation rates in fed-batch mode.

Electricity generation from retting wastewater consisting of recalcitrant compounds using continuous upflow microbial fuel cell

Recalcitrant compounds like phenol found in coconut husk retting effluent cause the deterioration of water quality when discharged from retting ponds into other water sources. Continuous upflow microbial fuel cell (MFC) was evaluated for treating retting wastewater at different loading rates to determine power generation, chemical oxygen demand (COD) consumption rate and phenol removal for a period of 270 days. A maximum power density of 254 mW/m2 was achieved during the treatment of retting wastewater (external resistance — 350Ω). COD removal of 70% was accomplished at a loading rate of 0.45 g COD/L reactor/day and phenol removal of 95% was obtained at a loading rate of 0.28 g phenol/L reactor/day. The power density exhibited an increasing pattern as the loading rate of MFC was increased from 0.45 to 2.69 g COD/L reactor/day. This study describes the treatment of retting wastewater employing continuous upflow MFC with 95% phenol removal. Therefore, MFC can be considered as an alternative for the efficient removal of phenol and current generation in retting wastewater.

Simultaneous carbon and nitrogen removal using a litre-scale upflow microbial fuel cell

A 10 L upflow microbial fuel cell (UMFC) was constructed for simultaneous carbon and nitrogen removal. During the 6-month operation, the UMFC constantly removed carbon and nitrogen, and then generated electricity with synthetic wastewater as substrate. At 5.0 mg L(-1) dissolved oxygen, 100 Ω external resistance, and pH 6.5, the maximum power density (Pmax) and nitrification rate for the UMFC was 19.5 mW m(-2) and 17.9 mg·(L d)(-1), respectively. In addition, Pmax in the UMFC with chicken manure wastewater as substrate was 16 mW m(-2), and a high chemical oxygen demand (COD) removal efficiency of 94.1% in the UMFC was achieved at 50 mM phosphate-buffered saline. Almost all ammonia in the cathode effluent was effectively degraded after biological denitrification in the UMFC cathode. The results can help to further develop pilot-scale microbial fuel cells for simultaneous carbon and nitrogen removal.

Steady state electric power generation in up-flow microbial fuel cell using the estimated time span method for bacteria growth domestic wastewater

abstract The parameters affecting steady state power generation for a lab-scale up-flow microbialfuel cell (UMFC) were studied. Single batch of domestic wastewater substrate was initiallyfed to the UMFC to determine the time span of maximum anaerobic bacterial activity bymonitoring their lag, growth and death phases. This was performed indirectly by recordingthe variations in volumetric electric power with time. The UMFC was then operated usingthe batches of substrate, fed sequentially from anaerobic basins when the previouslyestimated time span showed the maximum activity of bacteria in the basin. At themaximum bacterial activity, the UMFC could continuously generate constant volumetricpower of approximately 5.31 0.12 W m 3 . The effects of organic loading rate, flow rateand pH of the domestic wastewater on the voltage and volumetric electric current werealso investigated. The results showed that increasing the organic loading rate and flow rateat neutral pH enhanced the voltage. A higher power could be generated using the UMFC fordomestic wastewater treatment, as compared to the other works.a 2012 Elsevier Ltd. All rights reserved.

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.