Cellulose – Carrageenan coated carbon felt as potential anode structure for yeast microbial fuel cell

Anode material is an important part of Microbial Fuel Cells (MFCs). Carrageenan and cellulose are strong candidates for modifying anode due to their many advantages, especially their biocompatibility. Cellulose microfibrils and microcrystalline were trapped on the surface of carbon felt (CF) using carrageenan (KC). The MFC adopted with CF/[KC/CMF] as anodes structures produced a power density of 70.98 mW?m^?2, higher than MFC that used plain CF. The presence of KC changed the CF properties from hydrophobic to hydrophilic. This can be seen from the weight of biofilms formed in CF/KC, CF/[KC/CMC], and CF/[KC/CMF] being 60, 80, and 90 mg, respectively, higher than plain CF (60 mg). Carrageenan was also successful in entrapping cellulose. Cellulose donated hydrogen ions to form oxycellulose, which has a carboxyl group, wherein can increase Direct Electron Transfer (DET) between yeast and the anode. CF/[KC/CMF] anode structure showed excellent performance and has the potential to be developed in the future.     

Enhanced sludge stabilization coupled with microbial fuel cells (MFCs)

This study presents research results on electricity production from waste activated sludge using MFCs during stabilization process. Different MFC configurations equipped with various electrodes were used. Voltage measurements were continuously done during 35 days of MFC operation. Experimental results showed that bioelectricity generation was linked to volatile solids (VS) and protein reductions as a fraction of extracellular polymeric substances (EPS). Double chamber MFC reactor equipped with graphite electrodes had better power and current densities as 312.98 mW/m² and 39.07 μA/cm² while single chamber MFC equipped with titanium electrodes revealed better power and current densities as 97.60 mW/m² and 17.63 μA/cm², respectively. Molecular results indicated that power outputs of MFCs effected by diverse microbial communities in anode biofilms. Although organic matter degradation is reported as 35%–55% VS reduction for digesters, this research provided a promising approach for sludge stabilization with enhanced degrading of organic matters up to 75% by using MFCs.     

β-FeOOH modified carbon monolith anode derived from wax gourd for microbial fuel cells

The preparation of high-performance anode materials is of significance for enhanced power generation in microbial fuel cells (MFCs). Herein, porous carbon monolith was prepared by simple freeze drying of wax gourd and subsequent pyrolysis (WGC). β-FeOOH was coated on WGC to further improve the performance of the anode (β-FeOOH/WGC). The maximum power density of the MFCs with WGC and β-FeOOH/WGC anode was 913.9 and 1355.1 mW/m² respectively, which was much higher than that of the control (558.2 mW/m²). WGC possessed three-dimensional pore structure, nitrogen and oxygen-containing functional groups, which endowed it with satisfactory bacterial loading. Improved MFC performance after β-FeOOH modification could be ascribed to two aspects: β-FeOOH enhanced the electrochemical activity and decrease the transfer resistance; β-FeOOH was conducive to exoelectrogens formation. This study demonstrated that the synthesis of β-FeOOH modified carbon monolith anode offered an efficient route to enhance the power generation of MFCs.     

Power recovery with multi-anode/cathode microbial fuel cells suitable for future large-scale applications

Multi-anode/cathode microbial fuel cells (MFCs) incorporate multiple MFCs into a single unit, which maintain high power generation at a low cost and small space occupation for the scale-up MFC systems. The power production of multi-anode/cathode MFCs was similar to the total power production of multiple single-anode/cathode MFCs. The power density of a 4-anode/cathode MFC was 1184 mW/m³, which was 3.2 times as that of a single-anode/cathode MFC (350 mW/m³). The effect of chemical oxygen demand (COD) was studied as the preliminary factor affecting the MFC performance. The power density of MFCs increased with COD concentrations. Multi-anode/cathode MFCs exhibited higher power generation efficiencies than single-anode/cathode MFCs at high CODs. The power output of the 4-anode/cathode MFCs kept increasing from 200 mW/m³ to 1200 mW/m³ as COD increased from 500 mg/L to 3000 mg/L, while the single-anode/cathode MFC showed no increase in the power output at CODs above 1000 mg/L. In addition, the internal resistance (R_in) exhibited strong dependence on COD and electrode distance. The R_in decreased at high CODs and short electrode distances. The tests indicated that the multi-anode/cathode configuration efficiently enhanced the power generation.     

Metal zeolite imidazole skeleton-based phosphate derivatives as bioanodes for enhanced microbial fuel cell energy output

Microbial fuel cells (MFCs) as green and sustainable technology for power generation still face various obstacles such as the lower power generation. In this work, a kind of phosphate-derived composites using ZIF-67 (Co–Ni-ZIF/P) as framework was prepared and employed it as anode in MFC. Results demonstrated that the Co–Ni-ZIF/P anode could reduce the electron transfer resistance and simultaneously improve the bioelectrocatalytic activity of the anode and microbial colonization. The maximum energy output of MFC with Co–Ni-ZIF/P anode reached 4.511 W m^?3, which was 2.18 times larger than that of MFC with Co–Ni-ZIF anode (2.07 W m^?3). Microbial community structure analysis proved that more electrochemically active microbial species were attracted on the proposed anodes, and their synergistic effect could facilitate the extracellular electron transfer (EET) process. In particular, Geobacter was the most typical exogenous electron-producing enriched on the Co–Ni-ZIF/P anode with a relative abundance of up to 60.83%. The present work offers a promising prospect for the application of bio-functional ZIF for the high-performance anode construction of MFCs.     

Effect of ionic strength, cation exchanger and inoculum age on the performance of Microbial Fuel Cells

Power generation in Microbial fuel cells (MFCs) is a function of various physico-chemical as well as biological parameters. In this study, we have examined the effect of ionic strength, cation exchanger and inoculum age on power generation in a mediator MFC with methylene blue as electron mediator using Enterobacter cloacae IIT-BT08. The effect of ionic strength was studied using NaCl in the anode chamber of a two chambered salt-bridge MFC at concentrations of 5 mM, 10 mM and 15 mM. Maximum power density of 12.8 mW/m² was observed when 10 mM NaCl was used. Corresponding current density was noted to be 35.5 mA/m². Effect of cation exchanger was observed by replacing salt-bridge with a proton exchange membrane of equal surface area. When the salt-bridge was replaced by a proton exchange membrane, a 3-fold increase in the power density was observed. Power density and current density of 37.8 mW/m² and 110.3 mA/m² respectively were detected. The influence of the pre-inoculum on the MFC was studied using E. cloacae IIT-BT08 grown for 12, 14, 16 and 18 h. It was observed that 16 h grown culture when inoculated in the anode chamber gave the maximum power output. Power density and current density of 68 mW/m² and 168 mA/m² respectively were obtained. We demonstrate from these results that both physico-chemical as well as biological parameters need to be optimized for improving the power generation in MFCs.     

A pilot-scale study on utilizing multi-anode/cathode microbial fuel cells (MAC MFCs) to enhance the power production in wastewater treatment

A new type of microbial fuel cell (MFC), multi-anode/cathode MFC (termed as MAC MFC) containing 12 anodes/cathodes were developed to harvest electric power treating domestic wastewater. The power density of MAC MFCs increased from 300 to 380 mW/m² at the range of the organic loading rates (0.19-0.66 kg/m³/day). MAC MFCs achieved 80% of contaminant removal at the hydraulic retention time (HRT) of 20 h but the contaminant removal deceased to 66% at the HRT of 5 h. In addition, metal-doped manganese dioxide (MnO₂) cathodes were developed to replace the costly platinum cathodes, and exhibited high power density. Cu-MnO₂ cathodes produced 465 mW/m² and Co-MnO₂ cathodes produced 500 mW/m². Due to the cathode fouling of the precipitation of calcium and sodium, a decrease in the power density (from 400 to 150 mW/m²) and an increase in internal resistance (R_in) (from 175 to 225 Ω) were observed in MAC MFCs.     

Effect of hydrogen producing mixed culture on performance of microbial fuel cells

This study examined the influence of H₂-producing mixed cultures on improving power generation using air-cathode microbial fuel cells (MFCs) inoculated with heat-treated anaerobic sludge. The MFCs installed with graphite brush anode generated higher power than the MFCs with carbon cloth anode, regardless heat treatment of anaerobic sludge. When the graphite brush anode-MFCs were inoculated selectively with H₂-producing bacteria by heat treatment, power production was not improved (about 490 mW/m²) in batch mode operation, but for slightly increased in carbon cloth anode-MFCs (from 0.16 to 2.0 mW/m²). Although H⁺/H₂ produced from H₂-producing bacteria can contribute to the performance of MFCs, suspended biomass did not affect the power density or potential, but the Coulombic efficiency (CE) increased. A batch test shows that propionate and acetate were used effectively for electricity generation, whereas butyrate made a minor contribution. H₂-producing mixed cultures do not affect the improvement in power generation and seed sludge, regardless of the pretreatment, can be used directly for the MFC performance.     

Power generation and organics removal from wastewater using activated carbon nanofiber (ACNF) microbial fuel cells (MFCs)

Carbon-based materials are the most commonly used electrode material for anodes in microbial fuel cell (MFC), but are often limited by their surface areas available for biofilm growth and subsequent electron transfer process. This study investigated the use of activated carbon nanofibers (ACNF) as the anode material to enhance bacterial biofilm growth, and improve MFC performance. Qualitative and quantitative biofilm adhesion analysis indicated that ACNF exhibited better performance over the other commonly used carbon anodes (granular activated carbon (GAC), carbon cloth (CC)). Batch-scale MFC tests showed that MFCs with ACNF and GAC as anodes achieved power densities of 3.50 ± 0.46 W/m³ and 3.09 ± 0.33 W/m³ respectively, while MFCs with CC had a lower power density of 1.10 ± 0.21 W/m³ In addition, the MFCs with ACNF achieved higher contaminant removal efficiency (85 ± 4%) than those of GAC (75 ± 5%) and CC (70 ± 2%). This study demonstrated the distinct advantages of ACNF in terms of biofilm growth and electron transport. ACNF has a potential for higher power generation of MFCs to treat wastewaters.     

Polarization and power density trends of a soil-based microbial fuel cell treated with human urine

Microbial fuel cells (MFCs) are bio-electrochemical devices that use microbial metabolic processes to convert organic substances into electricity with high efficiency. In this study, the performance of a soil-based MFC using urine as a substrate was assessed using polarization and power density curves. A single-chamber, membrane-less MFC with a carbon-felt air cathode and a carbon-felt anode fully buried in biologically active soil was constructed to examine the impact of urine treatment on the performance of the MFC. The peak power of the urine-treated MFC was 124.16 mW/m² and was obtained 24 hours after the first urine addition; a control MFC showed a value of 65.40 mW/m² in the same period. The treated MFC produced an average power of 70.75 mW/m² up to 21 days after the initial urine addition; the control MFC gave an average value of 4.508 mW/m² over the same period. The average internal resistances of the treated MFC and the control MFC obtained after the initial treatment were 269.94 and 1627.89 Ω, respectively. This study demonstrates the potential of human urine to reduce internal losses in soil MFCs and to provide stable power densities across various external resistors. These results are propitious for future advancements in soil MFCs for power generation utilizing human urine (a readily available source of nutrients) as a substrate.     

Miniature microbial fuel cells and stacks for urine utilisation

MFCs are becoming a stronger contender in the area of alternative energy sources and show great promise in utilising a wide variety of organic sources. This paper describes the utilisation of neat undiluted urine as the main feedstock for different types of individual MFCs and stacks of small-scale MFCs, for direct electricity production, with conversion efficiencies of >50%. The smallest MFC (1.4 mL total volume) produced equal amounts of power to that produced by larger MFCs (6.25 mL), resulting in increased power densities. Power densities of 4.93 mW/m² (absolute power of 1.5 mW) were recorded when 48 small-scale MFCs were connected as a stack and fed with urine. This study demonstrates the feasibility of using urine as an untreated fuel and that improved power outputs can be achieved through MFC miniaturisation and multiplication into stacks.     

Electricity generation from rice straw using a microbial fuel cell

This study demonstrated electricity generation from rice straw without pretreatment in a two-chambered microbial fuel cell (MFC) inoculated with a mixed culture of cellulose-degrading bacteria (CDB). The power density reached 145 mW/m² with an initial rice straw concentration of 1 g/L; while the coulombic efficiencies (CEs) ranged from 54.3 to 45.3%, corresponding to initial rice straw concentrations of 0.5–1 g/L. Stackable MFCs in series and parallel produced an open circuit voltage of 2.17 and 0.723 V, respectively, using hexacyanoferrate as the catholyte. The maximum power for serial connection of three stacked MFCs was 490 mW/m² (0.5 mA). In parallelly stacked MFCs, the current levels were approximately 3-fold (1.5 mA) higher than those produced from the serial connection. These results demonstrated that electricity can be produced from rice straw by exploiting CDB as the biocatalyst. Thus, this method provides a promising way to utilize rice straw for bioenergy production.     

Canteen based composite food waste as potential anodic fuel for bioelectricity generation in single chambered microbial fuel cell (MFC): Bio-electrochemical evaluation under increasing substrate loading condition

Canteen based composite food waste, which is rich in organic constituents was evaluated as anodic fuel (substrate) in single chambered microbial fuel cell (MFC; mediator less; non-catalyzed graphite electrodes; open-air cathode) to harness electrical energy via anaerobic treatment. The performance of MFC was evaluated with anaerobic consortia as anodic biocatalyst under various increasing organic loading rates (OLR1, 1.01 kg COD/m³-day; OLR2, 1.74 kg COD/m³-day; OLR3, 2.61 kg COD/m³-day). The experimental results illustrated the feasibility of bioelectricity generation from food waste along with treatment but depend on the applied organic load. The maximum power output was observed at OLR2 (295 mV; 390 mA/m²), followed by OLR3 (250 mV; 311 mA/m²) and OLR1 (188 mV; 211 mA/m²). The variation in substrate degradation has also showed a relation with organic load applied (OLR1, 44.28% (0.47 kg COD/m³-day); OLR2, 64.83% (1.13 kg COD/m³-day); OLR3, 46.28% (1.39 kg COD/m³-day)). The increase in loading from OLR1 to OLR2, the catalytic ability of biocatalyst increased from 7.5 mA (24 h) to 11.22 mA (24 h) along with the increase in power generation from 39.38 mW/m² to 107.89 mW/m². At the higher OLR (OLR3), the bioelectrocatalytic current decreased to 5.3 mA (24 h) along with decrement in power to 78.92 mW/m². The optimum organic load (OLR2) showed maximal catalytic activity and power output. Fuel cell behavior with respect to polarization, anode potential and bio-electrochemical behavior supported the higher performance of MFC at OLR2. Specific power yield was also observed to be higher at OLR2 (0.320 W/kg COD_R) indicating the combined process efficiency. Volatile fatty acids generation and pH profiles also correlated well with the observed results.     

A non-noble V2O5 nanorods as an alternative cathode catalyst for microbial fuel cell applications

This study assessed the feasibility of vanadium pentoxide (V₂O₅) as a novel cathode catalyst material in air-cathode single chamber microbial fuel cells (SCMFCs). The V₂O₅ nanorod catalyst was synthesized using a hydrothermal method. MFCs with different cathode catalyst loadings were studied. Cyclic voltammetry (CV) was used to examine the electrochemical behavior of the catalysts in the MFCs. The V₂O₅ cathode catalyst constructed with a double loading MFC exhibited the highest maximum power density of 1073 ± 18 mW m⁻² (OCP; 691±4 mV) compared with 447 ± 12 mW m⁻² (OCP; 594 ± 5 mV) and 936 ± 15 mW m⁻² (OCP; 647±5 mV) for the single loading MFC and triple loading MFC, respectively. The power density of MFC with double loaded V₂O₅ is comparable to the traditional Pt/C cathode (2067 ± 25 mW m⁻², OCP; 821 ± 4 mV), which covers up to 55% of the performance of Pt/C. This finding highlights the potential of the V₂O₅ cathode as an inexpensive catalyst material for MFCs that may have commercial applications.     

The effect of nitric acid,ethylenediamine, and diethanolamine modified polyaniline nanoparticles anode electrode in a microbial fuel cell

Anode materials are important in the power generation of microbial fuel cell. In this study, polyaniline was used as a conducting polymer anode in two chambers MFC. XPS and SEM were used for the characterization of functional groups of anode materials and the morphology. The power generation of microbial fuel cell was elevated by the modification of anode by nitric acid, ethylenediamine, and diethanolamine. The time that MFC reaches its maximum power generation was shortened by modification. Moreover the SEM photos prove that, it causes better attachment of microorganisms as biocatalysts on electrode surface. The best performance of among the MFCs with different anode electrodes, was the system working by polyaniline modified by ethylenediamine as that generated power of 136.2 mW/m² with a 21.3% Coulombic efficiency.     

Start-up investigation of the self-assembled chitosan/montmorillonite nanocomposite over the ceramic support as a low-cost membrane for microbial fuel cell application

The Chitosan/Montmorillonite (CHI/MMT) nanocomposites (1/1, 1/2, 1/4 %w/w) are self-assembled over the ceramic separator of the microbial fuel cells (MFCs). The oxygen diffusion coefficient of the ceramic membrane has diminished about a hundred times which resulted in the better growth of exoelectrogenic anodic bacteria, boosting the electrical double layer capacitance by four orders of magnitude, and decreasing the charge transfer impedances of the anode and cathode electrodes by 96.44% and 66.14%. The ohmic resistance is dropped by 73.2%, owing to the improved proton conductivity of the modified ceramic membranes. The coulombic efficiency of 86.97 ± 13.2% along with the power and current densities of 229.12 ± 18.5 mW/m² and 1422.22 ± 41.2 mA/m² are obtained during the start-up operation of the modified MFC by 1/2 (% w/w) CHI/MMT, which are more than three times higher than the values of the blank-ceramic. The wastewater treatment efficiency of the MFCs does not alter seriously.     

An insight of bioelectricity production in mediator less microbial fuel cell using mesoporous Cobalt Ferrite anode

Microbial Fuel Cells (MFCs) are an alternative sustainable approach that utilizes the bacteria present in waste water as a bio-catalyst and produce electricity. Herein, Cobalt Ferrite (CF) is fabricated hydrothermally and deposited over graphite sheet to envision a cost-effective MFC anode. The intrinsic biocompatibility, together with mesoporous structure of CF greatly enhanced the microbial colonization. A comparative time dependent study of kinetic activity of CF/Graphite in domestic waste water and artificial waste water is reported. Electrochemical characterization (CV & EIS) indicated the process of active bio film formation on anode from day 1st to day 20th and then restricted bio film till day 30th. Improved extracellular electron transfer of exoelectrogens due to the variable valence state and high redox stability of CF, facilitated the MFC to deliver an excellent power density (1856 mW m⁻²) with the maximum anodic half–cell potential of 0.65 V in waste water. High capacitance (280%) and appropriate pore size (9.3 nm) of CF formed a capacitive bridge for an effective flow of electrons generated by the electro active bacteria. Therefore, use of noble metal free, low cost anodic material Cobalt Ferrite with long-term cell stability makes it a promising and sustainable power source for commercial application.     

Microbial fuel cell (MFC) using commercially available unglazed ceramic wares: Low-cost ceramic separators suitable for scale-up

This study aimed to evaluate the influence of commercially available unglazed wall ceramic (UGWC) and unglazed floor ceramic (UGFC) separators with different thickness and porosity on the performance of dual-chamber microbial fuel cells (MFCs). These MFCs were operated under continuous condition using domestic wastewater. The UGWC-based MFC produced higher maximum power density (321 mW/m² with a thickness of 9 mm) than UGFC-based MFC (106.89 mW/m² with a thickness of 3 mm) due to lower internal resistance. Power generation using both types of separators was lower than that of obtained using the Nafion 117 membrane as control (602 mW/m²). The maximum average coulombic efficiencies (CE) of the UGWC-based MFCs (with thickness levels of 6 and 9 mm) were 58% and 68%, respectively, which was more than that of UGFC-based MFCs and also control MFC (53%). Voltammetric analysis revealed that the maximum peak current of 6 mA was obtained for UGWC-based MFC which was in the order of control MFC (5.9 mA). The UGWC separators exhibited smaller ohmic and diffusion resistances of 57, 65 and 87 Ω in MFCs at the thickness levels of 3, 6 and 9 mm, respectively, compared to the UGFC separators with that of 164.27 and 366.23 Ω in MFCs at the thickness levels of 3 and 6 mm, respectively. UGWC separators because of their low production cost, high mechanical strength and increased output power density of the MFC proved to be a suitable alternative to replace with a costly polymeric membrane such as Nafion 117.     

Three-dimensional graphitic mesoporous carbon-doped carbon felt bioanodes enables high electric current production in microbial fuel cells

Microbial fuel cells (MFCs) represent a new approach that can simultaneously enhance the treatment of waste streams and generate electricity. Although MFCs represent a promising technology for renewable energy production, they have not been successfully scaled-up mainly due to the relatively-low electricity generation and high cost associated with MFCs operation. Here, we investigated whether graphitic mesoporous carbon (GMC) decoration of carbon felt would improve the conductivity and biocompatibility of carbon felt anodes, leading to higher biomass attachment and electricity generation in MFCs fed with an organic substrate. To test this hypothesis, we applied 3 different GMC loading (i.e., 2, 5, and 10 mg/cm² of anode surface area) in MFCs compared to control MFCs (with pristine carbon felt electrodes). We observed that the internal resistances of modified anodes with GMC were 1.2–2.3-order of magnitude less than pristine carbon felt anode, leading to maximum power densities of 70.3, 33.3, and 9.8 mW/m² for 10, 5, and 2 mg/cm²-doped anode, respectively compared to only 3.8 mW/m² for the untreated carbon felt. High-throughput sequencing revealed that increasing the GMC loading rate was associated with enriching more robust anode-respiring bacteria (ARB) biofilm community. These results demonstrate that 3-D GMC-doped carbon felt anodes could be a potential alternative to other expensive metal-based electrodes for achieving high electric current densities in MFCs fed with organic substrates, such as wastewater. Most importantly, high electron transfer capability, strong chemical stability, low cost, and excellent mechanical strength of 3-D GMC-doped carbon felt open up new opportunities for scaling-up of MFCs using cheap and high-performance anodes.     

A novel microbial fuel cell stack for continuous production of clean energy

Production of sustainable and clean energy through oxidation of biodegradable materials was carried out in a novel stack of microbial fuel cells (MFCs). Saccharomyces cerevisiae as an active biocatalyst was used for power generation. The novel stack of MFCs consist of four units was fabricated and operated in continuous mode. Pure glucose as substrate was used with concentration of 30 g l⁻¹ along with 200 μmol l⁻¹ of natural red (NR) as a mediator in the anode and 400 μmol l⁻¹ of potassium permanganate as oxidizing agent in the cathode. Polarimetry technique was employed to analyze the single cell as well as stack electrical performance. Performance of the MFCs stack was evaluated with respect to amount of electricity generation. Maximum current and power generation in the stack of MFC were 6447 mA.m⁻² and 2003 mW.m⁻², respectively. Columbic efficiency of 22 percent was achieved at parallel connection. At the end of process, image of the outer surface of graphite electrode was taken by Atomic Force Microscope at magnification of 5000. The high electrical performance of MFCs was attributed to the uniform growth of microorganism on the graphite surface which was confirmed by the obtained images.