Enhanced performance of microbial fuel cells using electrochemically treated carbon felt anode

Microbial fuel cell (MFC) is a promising technology for recovering energy in wastewater through bacterial metabolism. However, it always suffers from low power density and electron transfer efficiency, restricting the application. This study fabricated the MnCo2S4-Co4S3/bamboo charcoal (MCS-CS/BC) through an easy one-step hydrothermal method, and the material was applied to carbon felt (CF) to form high-performance MFC anode. MCS-CS/BC-CF anode exhibited lower Rct (10.1 Ω) than BC-CF (17.24 Ω) and CF anode (116.1 Ω), exhibiting higher electrochemical activity. MCS-CS/BC-CF anode promoted the electron transfer rate and resulted in enhanced power density, which was 9.27 times higher (980 mW m-2) than the bare CF (105.7 mW m-2). MCS-CS/BC-CF anode showed the best biocompatibility which attracted distinctly larger biomass (146.27 mg/μL) than CF (20 mg/μL) and BC-CF anode (20.1 mg/μL). The typical exoelectrogens (Geobacter and etc.) took dramatically higher proportion on MCS-CS/BC-CF anode (59.78 %) than CF (2.99 %) and BC-CF anode (26.67 %). In addition, MCS-CS/BC stimulated the synergistic effect between exoelectrogens and fermentative bacteria, greatly favoring the extracellular electron transfer rate between bacteria and the anode and the power output. This study presented an efficient way of high-performance anode electrocatalyst fabrication for stimulating MFC power generation, giving suggestions for high-efficient energy recovery from wastewater.

Constructed wetlands (CWs) have gained a lot of attention for wastewater treatment due to robustness and natural pollutant mitigation characteristics. This widely acknowledged technology possesses enough merits to derive direct electricity in collaboration with microbial fuel cell (MFC), thus taking advantage of microbial metabolic activities in the anoxic zone of CWs. In the present study, two identical lab-scale CWs were selected, each having 56 L capacity. One of the CW integrated with MFC (CW-MFC) contains two pairs of electrodes, i.e., carbon felt and graphite plate. The first pair of CW-MFC consists of a carbon felt cathode with a graphite plate anode, and the second pair contains a graphite plate cathode with a carbon felt anode. The other CW was not integrated with MFC and operated as a traditional CW for evaluating the performance. CW-MFC and CW were operated in continuous up-flow mode with a hydraulic retention time of 3days and at different organic loading rates (OLRs) per unit surface area, such as 1.45gm-2day-1 (OLR-1), 2.43gm-2day-1 (OLR-2), and 7.25gm-2day-1 (OLR-3). The CW-MFC was able to reduce the organic matter, phosphate, and total nitrogen by 92%, 93%, and 70%, respectively, at OLR of 1.45gm-2day-1, which was found to be higher than that obtained in conventional CW. With increase in electrochemicalredox activities, the second pair of electrodes made way for 3 times higher power density of 16.33 mW m-2 as compared to the first pair of electrodes in CW-MFC (5.35 mW m-2), asserting carbon felt as a good anode material to be used in CW-MFC. The CW-MFC with carbon felt as an anode material is proposed to improve the electro-kinetic activities for scalable applications to achieve efficient domestic wastewater treatment and electricity production.

Microbial fuel cells (MFCs) represent a promising<br> technology for simultaneous bioelectricity generation and wastewater<br> treatment. Catalysts are significant portions of the cost of microbial<br> fuel cell cathodes. Many materials have been tested as aqueous<br> cathodes, but air-cathodes are needed to avoid energy demands for<br> water aeration. The sluggish oxygen reduction reaction (ORR) rate at<br> air cathode necessitates efficient electrocatalyst such as carbon<br> supported platinum catalyst (Pt/C) which is very costly. Manganese<br> oxide (MnO2) was a representative metal oxide which has been<br> studied as a promising alternative electrocatalyst for ORR and has<br> been tested in air-cathode MFCs. However the single MnO2 has poor<br> electric conductivity and low stability. In the present work, the MnO2<br> catalyst has been modified by doping Pt nanoparticle. The goal of the<br> work was to improve the performance of the MFC with minimum Pt<br> loading. MnO2 and Pt nanoparticles were prepared by hydrothermal<br> and sol gel methods, respectively. Wet impregnation method was<br> used to synthesize Pt/MnO2 catalyst. The catalysts were further used<br> as cathode catalysts in air-cathode cubic MFCs, in which anaerobic<br> sludge was inoculated as biocatalysts and palm oil mill effluent<br> (POME) was used as the substrate in the anode chamber. The asprepared<br> Pt/MnO2 was characterized comprehensively through field<br> emission scanning electron microscope (FESEM), X-Ray diffraction<br> (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic<br> voltammetry (CV) where its surface morphology, crystallinity,<br> oxidation state and electrochemical activity were examined,<br> respectively. XPS revealed Mn (IV) oxidation state and Pt (0)<br> nanoparticle metal, indicating the presence of MnO2 and Pt.<br> Morphology of Pt/MnO2 observed from FESEM shows that the<br> doping of Pt did not cause change in needle-like shape of MnO2<br> which provides large contacting surface area. The electrochemical<br> active area of the Pt/MnO2 catalysts has been increased from 276 to<br> 617 m2/g with the increase in Pt loading from 0.2 to 0.8 wt%. The<br> CV results in O2 saturated neutral Na2SO4 solution showed that<br> MnO2 and Pt/MnO2 catalysts could catalyze ORR with different<br> catalytic activities. MFC with Pt/MnO2 (0.4 wt% Pt) as air cathode<br> catalyst generates a maximum power density of 165 mW/m3, which<br> is higher than that of MFC with MnO2 catalyst (95 mW/m3). The<br> open circuit voltage (OCV) of the MFC operated with MnO2 cathode<br> gradually decreased during 14 days of operation, whereas the MFC<br> with Pt/MnO2 cathode remained almost constant throughout the<br> operation suggesting the higher stability of the Pt/MnO2 catalyst.<br> Therefore, Pt/MnO2 with 0.4 wt% Pt successfully demonstrated as an<br> efficient and low cost electrocatalyst for ORR in air cathode MFC with higher electrochemical activity, stability and hence enhanced<br> performance.

The electrodes (anode and cathode) have an important role in the efficiency of a microbial fuel cell (MFC), as they can determine the rate of charge transfer in an electrochemical process. In this study, nanoporous gold electrode, prepared from commercially available gold-made compact disk, is utilized as the anode in a two-chamber MFC. The performance of nanoporous gold electrode in the MFC is compared with that of gold film, carbon felt and acid-heat-treated carbon felt electrodes which are usually employed as the anode in the MFCs. Electrochemical surface area of nanoporous gold electrode exhibits a 7.96-fold increase rather than gold film electrode. Scanning electron microscopy analysis also indicates the homogeneous biofilm is formed on the surface of nanoporous gold electrode, while the biofilm formed at the surface of acid-heat-treated carbon felt electrode shows rough structure. Electrochemical studies show although modifications applied on carbon felt electrodes improve its performance, nanoporous gold electrode, due to its structure and better electrochemical properties, acts more efficiently as the MFC’s anode. The maximum power density produced by nanoporous gold anode is 4.71 mW m−2 at current density of 16.00 mA m−2, while this value for acid-heat-treated carbon felt anode is 3.551 mW m−2 at current density of 9.58 mA m−2.

Oxygen-reducing biocathodes previously developed for microbial fuel cells (MFCs) have required energy-intensive aeration of the catholyte. To avoid the need for aeration, the ability of biocathodes to function with passive oxygen transfer was examined here using air cathode MFCs. Two-chamber, air cathode MFCs with biocathodes produced a maximum power density of 554 ± 0 mW/m(2), which was comparable to that obtained with a Pt cathode (576 ± 16 mW/m(2)), and 38 times higher than that produced without a catalyst (14 ± 3 mW/m(2)). The maximum current density with biocathodes in this air-cathode MFC was 1.0 A/m(2), compared to 0.49 A/m(2) originally produced in a two-chamber MFC with an aqueous cathode (with cathode chamber aeration). Single-chamber, air-cathode MFCs with the same biocathodes initially produced higher voltages than those with Pt cathodes, but after several cycles the catalytic activity of the biocathodes was lost. This change in cathode performance resulted from direct exposure of the cathodes to solutions containing high concentrations of organic matter in the single-chamber configuration. Biocathode performance was not impaired in two-chamber designs where the cathode was kept separated from the anode solution. These results demonstrate that direct-air biocathodes can work very well, but only under conditions that minimize heterotrophic growth of microorganisms on the cathodes.

The overuse of resources and the frequent occurrence of environmental problems have necessitated the use of sustainable energy technologies. The microbial fuel cell (MFC) is a kind of green energy-generation technology that metabolizes the organic compounds in wastewater by the catalytic oxidation of microorganisms. This new technology provides the dual advantages of cleaning the environment and generating electricity. As MFCs can potentially convert biodegradable and recyclable wastes into clean energy, they are a promising application prospect in environmental treatment and energy utilization. However, the practical applicability of present-day MFCs is limited by their low power-generation efficiency. Anode electrodes can enrich the power generation and electron transfer of microorganisms, but require high polarization, electronic conductivity, and biological compatibility with the fuel cell. Broadly speaking, the anode electrode affects the performance and operating costs of an MFC. Commonly used carbon-based materials include graphite sheets, carbon cloths, carbon paper, and carbon felt. However, most of these materials are two-dimensional structures providing few attachment sites for microorganisms; other materials have few reactive sites, which limits their electrochemical reactive surface areas and slows the initiation of the MFC. Carbon nanomaterials have been extensively researched for their high electrical conductivity, large specific surface area, high porosity, and low cost. All of these properties are demanded in the anode materials of MFCs. This paper summarized and analyzed methods for improving the biological compatibility of electrodes, increasing the adhesion of electrically-producing microorganisms, and improving the reactive activation sites. To this end, it discussed various types of anode electrodes, electrode structure designs, and electrode material modifications. A mechanism that improved the electricity generation performance was also discussed. Finally, carbon-based electrode materials might provide theoretical guidance for preparing anode materials with high electrochemical activity.

Effects of biochar anodes in rice plant microbial fuel cells on the production of bioelectricity, biomass, and methane

BACKGROUNDThis study focuses on the treatment of brewery waste slurries (BWS) with high chemical oxygen demand (COD) using a single‐chamber microbial fuel cell (MFC) inoculated with heat‐treated anaerobic seed sludge. A co‐substrate of 5 g L−1 glycerol was added, and carbon felt (CF) was employed as the anode material, enhanced through in situ polymerization of aniline (PANI/CF). Additionally, the adsorption of ruthenium dioxide nanoparticles onto the modified CF was assessed (PANI‐RO/CF).RESULTSTests conducted at room temperature (19 °C to 22 °C) achieved an average COD reduction of 36%. The PANI‐RO/CF electrode accumulated 24% more charge, resulting in the highest coulombic efficiency of 75.1%, significantly exceeding similar studies. However, the PANI‐modified anode generated more energy, exceeding that of the bare CF by more than double, reaching 57.1 mW m−2. An optimized working volume was identified in relation to other reported works. Microbial population analysis revealed an interaction between Staphylococcus epidermidis and a rarely reported psychrophilic Bacillus species. After 30 h, lactic acid emerged as the main by‐product, with a concentration of 7.5 ± 0.6 g L−1.CONCLUSIONSThese findings highlight an optimization approach based on cell configuration and inoculum selection, as well as a significant valorization pathway that is frequently overlooked in the existing literature on brewery wastewater treatment using MFCs, particularly regarding the attractiveness of lactic acid production. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).

The present study examined optimized anodic electrode materials microbial fuel cells (MFCs) with Jashore Municipal Wastewater (JMW) as substrate in series and parallel connections. Three anodic materials, Iron plate (Fe), Carbon felt (CF), and Graphite rod (GR), were used to get green energy from waste biomass in microbial fuel cells. The output voltage, current, and power density of MFC were measured to investigate the preeminent anodic electrode material. The optimized anodic electrode material was Fe owing to high voltage generation followed by CF and GR. Results further indicated that the output voltage increased, but current density, as well as power density, decreased in series connection due to the increase of internal resistance compared to parallel at Fe-Cu combination. The maximum voltage, current density, and power density in series connection were 2238 mV, 79.98 mA/m2, and 108.850 mW⁄m2, respectively. On the other hand, in parallel connection, those values were 793 mV, 248.272 mA/m2, and 115.943 mW⁄m2, respectively. Most small electrical devices need high currents rather than high voltage imply parallel connections are preferred in this regard. Moreover, Fe-Cu combination is better to remove (87%) organic matter regarding COD removal efficiency from wastewater of MFCs.

Investigation of a two-dimensional model on microbial fuel cell with different biofilm porosities and external resistances

Microbial Fuel Cells (MFCs) are innovative environmental engineering systems that harness the metabolic activities of microbial communities to convert chemical energy in waste into electrical energy. However, MFC performance optimization remains challenging due to limited understanding of microbial metabolic mechanisms, particularly with complex substrates under realistic environmental conditions. This study investigated the effects of substrate complexity (acetate vs. starch) and varying mass transfer (stirred vs. non-stirred) on acclimatization rates, substrate degradation, and microbial community dynamics in air-cathode MFCs. Stirring was critical for acclimating to complex substrates, facilitating electrogenic biofilm formation in starch-fed MFCs, while non-stirred MFCs showed limited performance under these conditions. Non-stirred MFCs, however, outperformed stirred systems in current generation and coulombic efficiency (CE), especially with simple substrates (acetate), achieving 66% CE compared to 38% under stirred conditions, likely due to oxygen intrusion in the stirred systems. Starch-fed MFCs exhibited consistently low CE (19%) across all tested conditions due to electron diversion into volatile fatty acids (VFA). Microbial diversity was higher in acetate-fed MFCs but unaffected by stirring, while starch-fed MFCs developed smaller, more specialized communities. Kinetic analysis identified hydrolysis of complex substrates as the rate-limiting step, with rates an order of magnitude slower than acetate consumption. Combined hydrolysis-fermentation rates were unaffected by stirring, but stirring significantly impacted acetate consumption rates, likely due to oxygen-induced competition between facultative aerobes and electrogenic bacteria. These findings highlight the trade-offs between enhanced substrate availability and oxygen-driven competition in MFCs. For real-world applications, initiating reactors with dynamic stirring to accelerate acclimatization, followed by non-stirred operation, may optimize performance. Integrating MFCs with anaerobic digestion could overcome hydrolysis limitations, enhancing the degradation of complex substrates while improving energy recovery. This study introduces novel strategies to address key challenges in scaling up MFCs for wastewater treatment, bridging the gap between fundamental research and practical applications to advance environmental systems.

Power generation from furfural using the microbial fuel cell

Microbial fuel cells (MFCS) can be used in wastewater treatment and to simultaneously produce electricity (renewable energy). MFC technology has already been applied successfully in lab-scale studies to treat domestic wastewater, focussing on organic matter removal and energy production. However, domestic wastewater also contains nitrogen that needs to be treated before being discharged. The goal of this paper is to assess simultaneous domestic wastewater treatment and energy production using an air-cathode MFC, paying special attention to nitrogen compound transformations. An air-cathode MFC was designed and run treating 1.39 L d(-1) of wastewater with an organic load rate of 7.2 kg COD m(-3) d(-1) (80% removal efficiency) and producing 1.42 W m(-3). In terms of nitrogen transformations, the study demonstrates that two different processes took place in the MFC: physical-chemical and biological. Nitrogen loss was observed increasing in line with the power produced. A low level of oxygen was present in the anodic compartment, and ammonium was oxidised to nitrite and nitrate.

Here, the hybrid of inverse spinel NiCo2S4 nanoparticles coated on activated carbon (AC) has been first described as an effective nonprecious electrocatalyst for oxygen reduction reaction (ORR) used in air cathode microbial fuel cells (MFCs). MFC with NiCo2S4/AC air cathode obtains the maximum power density of 2000 ± 59 mW/m2, with a value of 125% higher than the control. The combination effect of mixed valence in NiCo2S4/AC composite is favorable for easier electron transfer to make O2 absorbed and reduced. The intensity ratio of Raman D to G band (ID/IG ) decreases from 0.85 (AC) to 0.78 (NiCo2S4/AC), indicating the formation of a partial graphite structure in NiCo2S4/AC.NiCo2S4/AC cathode shows better catalytic activity, lower internal resistance, higher kinetic activity and contains much octahedral catalytic active sites of Co3+, which favors a four electron ORR pathway. The finding shows NiCo2S4/AC will be a novel kind of promising nonprecious catalyst applied in MFC.

Engineering Shewanella carassii, a newly isolated exoelectrogen from activated sludge, to enhance methyl orange degradation and bioelectricity harvest