Air-cathode Single-chamber Microbial Fuel Cells Research Articles

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.

Architecture Optimization of a Single-Chamber Air-Cathode MFC by Increasing the Number of Cathode Electrodes

The aim of this study was the optimization of a single-chamber microbial fuel cell (MFC) architecture, by increasing the number of cathode electrodes. An air cathode single chamber MFC with a modifiable lid and bottom was operated with 4 and 6 Gore-Tex MnO2 cathode electrodes. The anode consisted of graphite granules. It was found that the increase from 4 (total cathodic surface area of 160 cm2) to 6 (total cathodic surface area of 240 cm2) electrodes resulted in an increase of the maximum current and the maximum power output of the cell by approximately 72% and 129%, respectively. Additionally, by increasing the cathodic surface area the internal resistance (Rint) of the unit decreased by approximately 19%. The organic removal from the substrate was not affected by the addition of the new electrodes while it was high across all cases studied (chemical oxygen demand (COD) removal > 89%). The average coulombic efficiency (CE) during the 4-electrode operation was 14.3%, while the corresponding efficiency for 6-electrode operation was 18.5%.

Determination of optimum retention time in an air–cathode single-chamber microbial fuel cell batch-mode reactor by comparing different substrate types and concentrations

The disadvantages of the air–cathode single-chamber microbial fuel cell (AC-SCMFC) performance can be caused by numerous factors, and retention time (RT) is one such factor. It is difficult to conclude the ideal RT run for the specific tests under the same conditions. To determine the optimum RT for various types of microbial fuel cell (MFC), an AC-SCMFC batch-mode reactor was carried out by comparing different types and concentrations of substrates based on the main parameters of organic removal and power generation. The AC-SCMFC reactor was designed for the effective working volume of 500 mL and operated for 52 d in batch mode with factors being significantly correlated with the performance of the MFC reactor, which were two different substrates, sucrose and acetate, and three different chemical oxygen demand (COD) levels of 400; 1000, and 2500 mg/L (low, medium, and high, respectively) equipped with two graphene nanoplatelets (GNPs)-based electrodes connected to 100 Ω resistance and plugged onto a data logger. The results of this study indicated a significant pattern at the medium level, at which the optimum RT of sucrose was achieved at 24 h and that of acetate at 48 h. In comparison, the performances pattern at low and high levels of both substrates was insignificant to determine the optimum RT. For further application, the recommended RT for both substrates at any concentration is 24 h due to high overall performance, and the optimum RT established in this study could be applied to all types of MFC research, particularly in oxidizable or biodegradable organic ranges, which ensures high performance.

Water hyacinth (Eichhornia crassipes) biochar as an alternative cathode electrocatalyst in an air-cathode single chamber microbial fuel cell

In the present work, Water Hyacinth Biochar (WHB) was produced by pyrolysis at 900 °C and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDX-SEM, Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) surface area and particle size analyses. The results indicate that WHB has Oxygen Reduction Reaction (ORR) catalytic activity, with an average of 2.58 electrons per oxygen molecule transferred from WHB for ORR. The ORR catalytic activity of WHB is attributed to its physical and chemical surface properties. The maximum power density produced from an air cathode single chamber microbial fuel cell (ACSC-MFC) with WHB as the ORR catalyst versus the Pt/C catalyst were 24.7 and 12.3 mWm−2, respectively. This study demonstrates that Water Hyacinth Biochar can be used as an inexpensive catalyst for the ORR in microbial fuel cells.

Investigating effect of proton-exchange membrane on new air-cathode single-chamber microbial fuel cell configuration for bioenergy recovery from Azorubine dye degradation

One of the biggest challenges of using single-chamber microbial fuel cells (MFCs) that utilize proton-exchange membrane (PEM) air cathode for bioenergy recovery from recalcitrant organic compounds present in wastewater is mainly attributed to their high internal resistance in the anodic chamber of the single microbial fuel cell (MFC) configurations. The high internal resistance is due to the small surface area of the anode and cathode electrodes following membrane biofouling and pH splitting conditions as well as substrate and oxygen crossover through the membrane pores by diffusion. To address this issue, the fabrication of new PEM air-cathode single-chamber MFC configuration was investigated with inner channel flow open assembled with double PEM air cathodes (two oxygen reduction activity zones) coupled with spiral-anode MFC (2MA-CsS-AMFC). The effect of various proton-exchange membranes (PEMs), including Nafion 117 (N-117), Nafion 115 (N-115), and Nafion 212 (N-212) with respective thicknesses of 183, 127, and 50.08μ, was separately incorporated into carbon cloth as PEM air-cathode electrode to evaluate their influences on the performance of the 2MA-CsS-AMFC configuration operated in fed-batch mode, while Azorubine dye was selected as the recalcitrant organic compound. The fed-batch test results showed that the 2MA-CsS-AMFC configuration with PEM N-115 operated at Azorubine dye concentration of 300mgL-1 produced the highest power density of 1022.5mWm-2 and open-circuit voltage (OCV) of 1.20V coupled with enhanced dye removal (4.77mgLh-1) compared to 2MA-CsS-AMFCs with PEMs N-117 and N-212 and those in previously published data. Interestingly, PEM 115 showed remarkable reduction in biofouling and pH splitting. Apart from that, mass transfer coefficient of PEM N-117 was the most permeable to oxygen (KO = 1.72×10-4cms-1) and PEM N-212 was the most permeable membrane to Azorubine (KA= 7.52×10-8cms-1), while PEM N-115 was the least permeable to both oxygen (KO= 1.54×10-4) and Azorubine (KA= 7.70×10-10). The results demonstrated that the 2MA-CsS-AMFC could be promising configuration for bioenergy recovery from wastewater treatment under various PEMs, while application of PEM N-115 produced the best performance compared to PEMs N-212 and N-117 and those in previous studies of membrane/membrane-less air-cathode single-chamber MFCs that consumed dye wastewater.

Arsenic removal mediated by acidic pH neutralization and iron precipitation in microbial fuel cells

High concentrations of arsenic (As) in natural waters are a growing concern worldwide. In northern Chile, fluvial systems enriched in As from natural and anthropogenic sources have been found to contain microbial communities with exoelectrogenic activity. Previous work performed with Microbial Fuel Cells (MFCs) resulted in a neutralizing microbial community developed from a consortium extracted from northern Chile. Considering that the formation of iron minerals, which have been reported as good As sorbents, would be favored by pH neutralization, the use of neutralizing MFCs could result in a sustainable alternative for Fe and As removal. In this work, we quantified the removal of As and Fe from acidic waters in air-cathode single-chamber MFCs. Our results show a removal ~80% of As and Fe and, simultaneously, a pH neutralization from ~3.7 to ~7.2. Additionally, non-MFC experiments indicate that the removal of As and Fe is dependent only on the activity of the microbial community developed during MFC operation and not on the MFC electrochemical performance. In addition, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) analysis showed spatial associations between Fe and As on the surface of cathodes, suggesting the idea that iron oxyhydroxides formation would be associated with the higher oxygen concentration near the cathodes. Powder X-ray diffraction (XRD) analysis showed the dominance of iron amorphous minerals, which may be favoring the removal of As. These results indicate that acid/metal-tolerant bacteria favor pH neutralization and consequently the removal of Fe and As by processes of surface sorption and/or As-Fe co-precipitation. Furthermore, these findings expand the possible MFC applications to the simultaneous removal of Fe and As from acidic waters, enabling its use as an energetically sustainable bioremediation alternative.

Enhanced simultaneous decolorization of azo dye and electricity generation in microbial fuel cell (MFC) with redox mediator modified anode

Although the electrogenesis and decolorization performance can be effectively improved by adding redox mediator (RM) in MFC azo dye decolorization process, RMs are lost in vain when replacing substrates for batch run. To address this issue, RM modified anodes are prepared by electrodepositing riboflavin (RF) and humic acid (HA) on the surface of graphite felt, and air-cathode single-chamber MFCs with different modified anodes are built to decolour Congo red and generate electricity. Compared to the bare anode MFC, MFC with 0.5C RF, 0.5C HA, 1.25C RF and 2.5C HA modified anode exhibited excellent electrocatalysis activity and show 31%, 34%, 44% and 49% decrease in internal resistance along with 20%, 21%, 40% and 66% increase in maximum power density. MFCs with 2.5C HA and 1.25C RF modified anode result in high decolorization efficiency of Congo red to 86% and 75% in 16 h, which are higher than that of the bare controlled group. There are significant RM crystals on the modified anodes, and bacterial colonies on the anode surface after MFC running. The RM crystals on the modified anodes can accelerate electron transfer, which benefit both bioelectricity generation and decolorization.

Influence of the preparation method of MnO2-based cathodes on the performance of single-chamber MFCs using wastewater

Abstract Microbial Fuel Cells (MFCs) are a promising technology that offers new opportunities for bioenergy generation with simultaneous wastewater treatment. The search for new and inexpensive catalysts that replace precious metal-based materials for their application in air-cathode single-chamber MFCs is crucial for improving the efficiency of this technology and, thus, for its commercialization and scaling-up in the field of wastewater treatment. In this work, several types of cathodes consisting of a mixture of MnO2 as catalyst material and two different additive conductor supports, carbon nanotubes (CNTs) and acetylene black (AB), respectively, are investigated in single-chamber MFCs, in the presence and in the absence of a polymer binder, polytetrafluoroethylene (PTFE), both in terms of power performance and wastewater treatment (COD and heavy metal removal). Furthermore, the influence of two preparation methods to fix the above mixtures onto carbon cloth electrodes, spraying and mechanical pressure techniques, are compared to optimize cathode construction. Maximum values of current and power densities were observed for the cathode based on MnO2/CNT/PTFE prepared by mechanical pressure, 1.536 mA dm−3 and 511.11 mW m−3, respectively. This cathode configuration achieved the maximum chemical oxygen demand (COD) removal with a value of 77% after 240 h of MFC operation using wastewater as fuel. The analysis of the removal of heavy metals (63Cu, 66Zn, 111Cd, 121Sb, 208Pb, 55Mn and 56Fe) from wastewater in the different MFC types offered removal efficiencies within the interval 60–97% for most of the metals studied.

Iron-rich nanoparticle encapsulated, nitrogen doped porous carbon materials as efficient cathode electrocatalyst for microbial fuel cells

Developing efficient, readily available, and sustainable electrocatalysts for oxygen reduction reaction (ORR) in neutral medium is of great importance to practical applications of microbial fuel cells (MFCs). Herein, a porous nitrogen-doped carbon material with encapsulated Fe-based nanoparticles (Fe-Nx/C) has been developed and utilized as an efficient ORR catalyst in MFCs. The material was obtained through pyrolysis of a highly porous organic polymer containing iron(II) porphyrins. The characterizations of morphology, crystalline structure and elemental composition reveal that Fe-Nx/C consists of well-dispersed Fe-based nanoparticles coated by N-doped graphitic carbon layer. ORR catalytic performance of Fe-Nx/C has been evaluated through cyclic voltammetry and rotating ring-disk electrode measurements, and its application as a cathode electrocatalyst in an air-cathode single-chamber MFC has been investigated. Fe-Nx/C exhibits comparable or better performance in MFCs than 20% Pt/C, displaying higher cell voltage (601 mV vs. 591 mV), maximum power density (1227 mW m−2 vs. 1031 mW m−2) and Coulombic efficiency (50% vs. 31%). These findings indicate that Fe-Nx/C is more tolerant and durable than Pt/C in a system with bacteria metabolism and thus holds great potential for practical MFC applications.

Influence of Inoculum Pretreatment on the Performance of an Air-Cathode Single-Chamber Microbial Fuel Cell

Air-cathode single-chamber microbial fuel cells (SCMFC) using the heat pretreated seed inoculation showed shorter period of biofilm formation with the maximum current output after 25 days inoculation when compared to the non-heat pretreated seed inoculation (45 days). The results showed the high performance of the heat pretreated seed inoculation in term of a peak of voltage and current generation, except the high COD and reducing sugar removal. Better voltammogram in oxidation and reduction peaks of the heat pretreated seed anode biofilm was observed. The current densities increased with the increases of wastewater concentrations and obtained maximum of 7.37mA m-2 of 3,000mg COD L-1 for the heat pretreated seed inoculation. In addition, the current outputs and wastewater concentrations displayed a linear correlation in the concentration range of 500 to 3,000mg COD L-1 (r2=0.96).

Energy recovery of ethanolamine in wastewater using an air-cathode microbial fuel cell

Ethanolamine (ETA) is widely used as a metal corrosion inhibitor and for CO2 capture. The treatment of ETA in wastewater involves advanced oxidation or electrolysis, which requires excessive energy since it is a not readily biodegradable organic containing amine. In this study, a microbial fuel cell (MFC) for simultaneous ETA degradation and electricity generation was investigated. 80 mL of an air-cathode single-chamber MFC was designed to determine the degradation and by-products formation of ETA and the power density. The reactor was inoculated with return activated sludge taken from a local wastewater treatment plant. This system was able to remove 91% of chemical oxygen demand (COD) and 37% of ammonia when ETA was injected into the MFC. A maximum power density of 240 mW m−2 (7.65 mW m−3) and a Coulombic efficiency of 18.2% were obtained with the ETA-fed MFC. From the results, although further research is required to treat ammonium derived from ETA degradation and to improve the performance of the MFC, it was found that the MFC would be a promising technology for ETA wastewater treatment, as well as electricity production.

Microbial community analysis of a single chamber microbial fuel cell using potato wastewater.

Microbial fuel cells (MFCs) convert chemical energy to electrical energy via bio-electrochemical reactions mediated by microorganisms. This study investigated the diversity of the microbial community in an air cathode single chamber MFC that used potato-process wastewater as substrate. Terminal restriction fragment length polymorphism results indicated that the bacterial communities on the anode, cathode, control electrode, and MFC bulk fluid were similar, but differed dramatically from that of the anaerobic domestic sludge and potato wastewater inoculum. The 16S ribosomal DNA sequencing results showed that microbial species detected on the anode were predominantly within the phyla of Proteobacteria, Firmicutes, and Bacteroidetes. Fluorescent microscopy results indicated that there was a clear enhancement of biofilm formation on the anode. Results of this study could help improve understanding of the complexity of microbial communities and optimize the microbial composition for generating electricity by MFCs that use potato wastewater.

Microbial fuel cell cathode with dendrimer encapsulated Pt nanoparticles as catalyst

In this paper, we investigated the use of polyamidoamine (PAMAM) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) as a promising type of cathode catalyst for air-cathode single chamber microbial fuel cells (SCMFCs). The Pt-DENs, prepared via template synthesis method, have uniform diameter distribution with size range of 3–5 nm. The Pt-DENs then loaded on to a carbon substrate. For comparison, we also electrodeposited Pt on carbon substrate. The calculation shows that the loading amount of Pt-DENs on carbon substrate is about 0.1 mg cm −2, which is three times lower than that of the electrodeposited Pt (0.3 mg cm −2). By measuring batch experiments, the results show that Pt-DENs in air-cathode SCMFCs have a power density of 630 ± 5 mW m −2 and a current density of 5200 ± 10 mA m −2 (based on the projected anodic surface area), which is significantly better than electrodeposited Pt cathodes (power density: 275 ± 5 mW m −2 and current density: 2050 ± 10 mA m −2). Additionally, Pt-DENs-based cathodes resulted in a higher power production with 129.1% as compared to cathode with electrodeposited Pt. This finding suggests that Pt-DENs in MFC cathodes is a better catalyst and has a lower loading amount than electrodeposited Pt, and may serve as a novel and alternative catalyst to previously used noble metals in MFC applications.

Explore various co-substrates for simultaneous electricity generation and Congo red degradation in air-cathode single-chamber microbial fuel cell

Microbial fuel cell (MFC) holds a great promise to harvest electricity directly from a wide range of ready degradable organic matters and enhance degradation of some recalcitrant contaminants. Glucose, acetate sodium and ethanol were separately examined as co-substrates for simultaneous bioelectricity generation and Congo red degradation in a proton exchange membrane (PEM) air-cathode single-chamber MFC. The batch test results showed that more than 98% decolorization at the dye concentration of 300 mg/L were achieved within 36 h for all tested co-substrates during electricity generation. The decolorization rate was different with the co-substrates used. The fastest decolorization rate was achieved with glucose followed by ethanol and sodium acetate. Accumulated intermediates were observed during Congo red degradation which was demonstrated by UV-Visible spectra and high performance liquid chromatography (HPLC). Electricity generation was sustained and not significantly affected by the Congo red degradation. Glucose, acetate sodium and ethanol produced maximum power densities of 103 mW/m(2), 85.9 mW/m(2) and 63.2 mW/m(2), respectively, and the maximum voltage output decreased by only 7% to 15%. Our results demonstrated the feasibility of using various co-substrates for simultaneous decolorization of Congo red and bioelectricity generation in the MFC and showed that glucose was the preferred co-substrate.

Improved performance of air-cathode single-chamber microbial fuel cell for wastewater treatment using microfiltration membranes and multiple sludge inoculation

Abstract Substantial optimization and cost reduction are required before microbial fuel cells (MFCs) can be practically applied. We show here the performance improvement of an air-cathode single-chamber MFC by using a microfiltration membrane (MFM) on the water-facing side of the cathode and using multiple aerobic sludge (AES), anaerobic sludge (ANS), and wetland sediment (WLS) as anodic inoculums. Batch test results show that the MFC with an MFM resulted in an approximately two-fold increase in maximum power density compared to the MFC with a proton exchange membrane (PEM). The Coulombic efficiency increased from 4.17% to 5.16% in comparison with the membrane-less MFC, without a significant negative effect on power generation and internal resistance. Overall performance of the MFC was also improved by using multiple sludge inoculums in the anode. The MFC inoculated with ANS + WLS produced the greatest maximal power density of 373 mW m−2 with a substantially low internal resistance of 38 Ω. Higher power density with a decreased internal resistance was also achieved in MFC inoculated with ANS + AES and ANS + AES + WLS in comparison with those inoculated with only one sludge. The MFCs inoculated with AES + ANS achieved the highest Coulombic efficiency. Over 92% COD was removed from confectionery wastewater in all tested MFCs, regardless of the membrane or inoculum used.

Increased Power Generation in a Continuous Flow MFC with Advective Flow through the Porous Anode and Reduced Electrode Spacing

The maximum power generated in a single-chamber air-cathode microbial fuel cell (MFC) has previously been shown to increase when the spacing between the electrodes is decreased from 4 to 2 cm. However, the maximum power from a MFC with glucose (500 mg/L) decreased from 811 mW/ m2 (R(ex) = 200 omega, Coulombic efficiency of CE = 28%) to 423 mW/m2 (R(ex) = 500 omega, CE = 18%) when the electrode spacing was decreased from 2 to 1 cm (batch mode operation, power normalized by cathode projected area). This decrease in power was unexpected as the internal resistance decreased from 35 omega (2-cm spacing) to 16 omega (1-cm spacing). However, providing advective flow through the porous anode toward the cathode substantially increased power, resulting in the highest maximum power densities yet achieved in an air-cathode system using glucose or domestic wastewater as substrates. For glucose, with a 1-cm electrode spacing and flow through the anode with continuous flow operation of the MFC, the maximum power increased to 1540 mW/m2 (51 W/m3) and the CE increased to 60%. Using domestic wastewater (255 +/- 10 mg of COD/L), the maximum power density was 464 mW/m2 (15.5 W/m3; CE = 27%). Although flow through the anode could lead to plugging, especially for particulate substrates such as domestic wastewater, the system was operated using glucose for over 42 days without clogging. These results show that power output in this air-cathode single-chamber MFC can be increased by reducing the electrode spacing if the reactors are operated in continuous flow mode with advective flow through the anode toward the cathode.