Performance improvement of air-cathode single-chamber microbial fuel cell using a mesoporous carbon modified anode

A novel mesoporous carbon (MC) modified carbon paper has been constructed using layer-by-layer self-assembly method and is used as anode in an air-cathode single-chamber microbial fuel cell (MFC) for performance improvement. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we have demonstrated that the MC modified electrode exhibits a more favorable and stable electrochemical behavior, such as increased active surface area and enhanced electron-transfer rate, than that of the bare carbon paper. The MFC equipped with MC modified carbon paper anode achieves considerably better performance than the one equipped with bare carbon paper anode: the maximum power density is 81% higher and the startup time is 68% shorter. CV and EIS analysis confirm that the MC layer coated on the carbon paper promotes the electrochemical activity of the anodic biofilm and decreases the charge transfer resistance from 300 to 99 Ω. In addition, the anode and cathode polarization curves reveal negligible difference in cathode potentials but significant difference in anode potentials, indicating that the MC modified anode other than the cathode was responsible for the performance improvement of MFC. In this paper, we have demonstrated the utilization of MC modified carbon paper to enhance the performance of MFC.     

Improved performance of air-cathode microbial fuel cell through additional Tween 80

The ability of electron transfer from microbe cell to anode electrode plays a key role in microbial fuel cell (MFC). This study explores a new approach to improve the MFC performance and electron transfer rate through addition of Tween 80. Results demonstrate that, for an air-cathode MFC operating on 1 g L⁻¹ glucose, when the addition of Tween 80 increases from 0 to 80 mg L⁻¹, the maximum power density increases from 21.5 to 187 W m⁻³ (0.6-5.2 W m⁻²), the corresponding current density increases from 1.8 to 17 A m⁻², and the resistance of MFC decreases from 27.0 to 5.7 Ω. Electrochemical impedance spectroscopy (EIS) analysis suggests that the improvement of overall performance of the MFC can be attributed to the addition of Tween 80. The high power density achieved here may be due to the increase of permeability of cell membranes by addition of Tween 80, which reduces the electron transfer resistance through the cell membrane and increases the electron transfer rate and number, consequently enhances the current and power output. A promising way of utilizing surfactant to improve energy generation of MFC is demonstrated.     

Effects of periodically alternating temperatures on performance of single-chamber microbial fuel cells

Practical applications of microbial fuel cells (MFCs) for wastewater treatment are usually operated over a wide range of temperature, especially day–night temperature difference. Here, MFCs at alternating temperatures were compared with those at constant temperatures. MFCs at 6/18 °C reached a steady-state voltage of 0.41 ± 0.05 V at 6 °C and 0.36 ± 0.04 V at 18 °C, which were lower than that of MFCs at 18/30 °C (0.42 ± 0.01 V at 18 °C and 0.47 ± 0.02 V at 30 °C). MFCs at 18/30 °C produced the highest power density of 2169 ± 82 mW m⁻² at 30 °C, even higher than that of MFCs at constant temperature 30 °C. Moreover, MFCs at 6/18 °C and 18/30 °C obtained a comparable coulombic efficiencies (94.6 ± 5.2%, 83.2 ± 4.1%, respectively) compared with MFCs at constant temperatures (86.3 ± 7.3% at 18 °C and 84.1 ± 5.5% at 30 °C). These results demonstrate that MFCs could be successfully adapted for use under day–night temperature difference conditions.     

Scale-up of membrane-free single-chamber microbial fuel cells

Scale-up of microbial fuel cells (MFCs) will require a better understanding of the effects of reactor architecture and operation mode on volumetric power densities. We compared the performance of a smaller MFC (SMFC, 28 mL) with a larger MFC (LMFC, 520 mL) in fed-batch mode. The SMFC produced 14 W m⁻³, consistent with previous reports for this reactor with an electrode spacing of 4 cm. The LMFC produced 16 W m⁻³, resulting from the lower average electrode spacing (2.6 cm) and the higher anode surface area per volume (150 m² m⁻³ vs. 25 m² m⁻³ for the SMFC). The effect of the larger anode surface area on power was shown to be relatively insignificant by adding graphite granules or using graphite fiber brushes in the LMFC anode chamber. Although the granules and graphite brushes increased the surface area by factors of 6 and 56, respectively, the maximum power density in the LMFC was only increased by 8% and 4%. In contrast, increasing the ionic strength of the LMFC from 100 to 300 mM using NaCl increased the power density by 25% to 20 W m⁻³. When the LMFC was operated in continuous flow mode, a maximum power density of 22 W m⁻³ was generated at a hydraulic retention time of 11.3 h. Although a thick biofilm was developed on the cathode surface in this reactor, the cathode potentials were not significantly affected at current densities <1.0 mA cm⁻². These results demonstrate that power output can be maintained during reactor scale-up; increasing the anode surface area and biofilm formation on the cathode do not greatly affect reactor performance, and that electrode spacing is a key design factor in maximizing power generation.     

Increased microbial fuel cell performance using quaternized poly ether ether ketone anionic membrane electrolyte for electricity generation

A high-performance hydroxide exchange membrane was prepared by the chloromethylation and quaternization of Poly ether ether ketone (PEEK) for microbial fuel cell applications. The study reports on the synthesis of a novel quaternized poly ether ether ketone (QPEEK) membrane and subsequent utilization of the ionomer as an anion exchange membrane (AEM). The structural characterization of chloromethylation and quaternization of PEEK was confirmed by FT-IR and ₁H¹ NMR spectroscopy and the morphologies were viewed by scanning electron microscopy. The effects of oxygen crossover and specific substrate crossover on cathode potential were also studied in detail. The investigation of QPEEK with the commercially available AEM (AMI-7001) revealed that the QPEEK shows excellent static properties, i.e. ion-exchange capacity, water uptake, thickness, etc.; and kinetic properties, i.e. diffusion permeability and better durability over 250 days. Power density obtained from an MFC containing the QPEEK-AEM produced higher value (60 W/m³) than the commercial AMI-7001 AEM (52 W/m³). This study shows that QPEEK could be used as an efficient and a cost effective AEM for an MFC.     

Tubular ceramic performance as separator for microbial fuel cell: A review

The depletion of unsustainable conventional energy sources and global warming issues create world demand for green energy sources. The microbial fuel cell (MFC) technology with the capability to convert environmental waste to energy can be improved with cheap ceramic material. The ceramic is structurally porous, thus allow a direct exchange of cation. The ceramic material also enhances stability thermally and chemically, non-ion selective characteristic, high mechanical strength, and easily washable. Commercially produced ceramic structures have been proven to reduce Chemical Oxygen Demand up to 92% and allow high power output. It is also comparatively durable in the long-term operation of MFC, compared to the commercially available membrane. The novelty of using tubular design is the efficient use of space, which leads to the possibility of scaling up. As a conclusion, a combination of both ceramic material and tubular design could be an excellent alternative separator for MFC.     

Simultaneous degradation of P-nitroaniline and electricity generation by using a microfiltration membrane dual-chamber microbial fuel cell

Microfiltration membrane, a potential alternative for traditional proton exchange membrane (PEM) due to its strong ability of proton transfer, cost-effectiveness, sustainability and high anti-pollution capability in microbial fuel cell (MFC). In this study, a novel MFC using bilayer microfiltration membrane as separator, inoculated sludge as biocatalyst and P-nitroaniline (PNA) as electron donor was successfully constructed to evaluate its performance. Furthermore, we also investigated the effects of initial PNA concentration, co-substrate (acetate) and cultivated microorganisms on MFC performance. Results showed that the maximum power density of 4.43, 3.05, 2.62 and 2.18 mW m^?2 was acquired with 50, 100, 150 and 300 mg L^?1 of PNA as substrate, respectively. However, with the addition of 500 mg L^?1 of acetate into reaction system contained 100 mg L^?1 of PNA, the higher power production of 6.24 mW m^?2 was obtained, which was 2.05 times higher than that using 100 mg L^?1 of PNA as the sole substrate. Meanwhile, the MFC working on cultivated microorganisms displayed a maximal power density of 7.32 mW m^?2 and a maximum PNA degradation efficiency of 54.75%. And after an electricity production cycle, the number of microbes in the anode chamber significantly increased. This study provides a promising technology for bioelectricity generation by biodegrading biorefractory pollutants in wastewater.     

Enhanced electrochemical performance in microbial fuel cell with carbon nanotube/NiCoAl-layered double hydroxide nanosheets as air-cathode

The ternary component NiCoAl-layered double hydroxide (NiCoAl-LDH) and carbon nanotube (CNT) nano-composite (CNT/NiCoAl-LDH) were successfully prepared by a simple hydrothermal method. The NiCoAl-LDH nanosheets were effectively and uniformly grown on CNTs, forming a cross-linked conductive network structure, and stainless steel (SS) mesh was used as the base to load CNT/NiCoAl-LDH for microbial fuel cell (MFC) cathode. X-ray diffraction (XRD) results presented that the CNT/NiCoAl-LDH hybrid exhibited the (003), (006), (012), (015), (018), (110) and (113) crystal planes of hydrotalcite reflection. The surface functional groups C-O, C=O, C-H, C-N and M-O of the hybrid were confirmed. The cross-linked network structure of the hybrid was observed and the content and proportion of each element of the hybrid were found. CNT/NiCoAl-LDH showed excellent catalytic oxygen reduction reaction (ORR) ability by cyclic voltammetry (CV) and linear voltammetry (LSV) due to its abundant electrochemical active sites and excellent conductivity. The maximum output voltage of CNT/NiCoAl-LDH catalyst as MFC cathode was 450 mV, the maximum power density was 433.5 ± 14.8 mW/m², and the maximum voltage stabilization time was 7–8 d. The results indicated that the CNT/NiCoAl-LDH hybrid was full potential as a high-performance, low-cost MFC cathode catalyst in future.     

Electricity generation using membrane-less microbial fuel cell powered by sludge supplemented with lignocellulosic waste

A membrane-less microbial fuel cell (ML-MFC) is an electrochemical device that incorporates microorganisms into the design in order to produce electricity through biologically catalyzed oxidation of soluble, electron-donating substrates. In this study, three lignocellulosic raw materials were added into the ML-MFC whereby the sludge acted as the pseudomembrane. All three materials were used as the substrates in ML-MFC for the production of electricity that was measured using a digital multimeter. Results showed that the ML-MFC that contained sludge supplemented with banana peel produced the highest electricity, followed by corn bran and palm oil mill effluent (POME) at 237.1 mV (23.75 mW/m²), 176.8 mV (12.65 mW/m²), and 138 mV (22.03 mW/m²) after 138 h, 192 h, and 108 h of incubation period, respectively. For the control test (sludge only), about 162.7 mV was recorded at shorter incubation period (84 h). This showed that long-term operation of the ML-MFC using these complex lignocellulosic compounds as a direct substrate for electricity generation is feasible, though their degradation is slow.     

Performance of plug flow microbial fuel cell (PF-MFC) and complete mixing microbial fuel cell (CM-MFC) for wastewater treatment and power generation

Two flow patterns (plug flow (PF) and complete mixing (CM)) of microbial fuel cells (MFCs) with multiple anodes–cathodes were compared in continuous flow mode for wastewater treatment and power generation. The results indicated that PF-MFCs had higher power generation and columbic efficiency (CE) than CM-MFCs, and the power generation varied along with the flow pathway in the PF-MFCs. The gradient of substrate concentrations along the PF-MFCs was the driving force for the power generation. In contrast, the CM-MFCs had higher wastewater removal efficiency than PF-MFCs, but had lower power conversion efficiency and power generation. This work demonstrated that MFC configuration is a key factor for enhancing power generation and wastewater treatment.     

Investigating the effect of membrane layers on the cathode potential of air-cathode microbial fuel cells

This study investigates the effect of cation exchange membrane (CEM) diffusion layers on cathode potential behavior in microbial fuel cells based on a cobalt electrodeposited anode that works in actual industrial wastewater. The structural properties of the modified anode materials were evaluated using scanning electron microscopy (SEM), which showed a strong and clear biofilm layer on the anode surface. Additionally, the structural properties of the utilized cathode materials were evaluated using energy dispersive X-ray (EDX) spectrometry and field emission scanning electron microscopy (FE-SEM) techniques, which confirmed the transfer of cobalt ions through the CEM to the cathode surface. Finally, the performance of the modified anode material with various CEMs as diffusion layers was investigated in air-cathode microbial fuel cells. The results indicate that the metal electrodeposition strategy, which utilizes multiple CEM layers, enhanced the power and current generation by 498.2 and 455%, respectively. Moreover, the Columbic efficiency (CE) increased by 77%, 154.5%, and 232% for the MFC with one, two and three CEM layers, respectively.     

Process engineering for stable power recovery from dairy wastewater using microbial fuel cell

Microbial fuel cells (MFCs) are one of the sustainable technologies that can effectively treat wastewater with concomitant generation of electricity. The present study investigated the treatment of real dairy wastewater (RDW) using Shewanella algae (MTCC-10608) within a single chamber microbial fuel cell (SCMFC). The study was conducted in both batch and fed-batch modes with initial chemical oxygen demand (COD) of 4000 mg/L and 2000 mg/L, respectively, in 0.2 L working volume of RDW for 15 days. However, the fed-batch strategy involved subsequent feeding of dairy wastewater with 6000 mg/L and 8000 mg/L COD on the 5th and 10th day, respectively. This two-step feeding strategy resulted in a maximum open-circuit voltage of 666 mV at 286 h of incubation with a COD removal efficiency of 92.21% and a columbic efficiency of 27.45%. The kinetic studies predicted the saturation constant of 55.83 mg COD/L and current density of 143.3 mA/m², which are similar to the findings from the experiments and polarization curve obtained. The maximum current density and power density from experiments were found to be 141 mA/m² and 50 mW/m² respectively. Thus, this study successfully indicates the utilization of dairy wastewater as a potential substrate for the sustainable power generation using Shewanella algae as a biocatalyst in the microbial fuel cell.     

A graphite-granule membrane-less tubular air-cathode microbial fuel cell for power generation under continuously operational conditions

An air-cathode microbial fuel cell (MFC) is an efficient and sustainable MFC configuration for recovering electrical energy from organic substances. In this paper, we developed a graphite-granule anode, tubular air-cathode MFC (GTMFC) capable of continuous electricity generation from glucose-based substrates. This GTMFC produced a maximum volumetric power of 50.2 W m⁻³ at current density of 216 A m⁻³ (R_EX = 22 Ω). Electrochemistry impedance spectroscopy (EIS) measurements demonstrated an overall internal resistance of 27 Ω, consisting of ohmic resistance of R_ohm = 13.8 Ω (51.1%), a charge-transfer resistance of R_c = 6.1 Ω (22.6%) and a diffusion resistance of R_d = 7.2 Ω (26.3%). Power generation with respect to initial chemical oxygen demand (COD) concentration was described well by an exponential saturation model. Recirculation was to found to have a significant effect on electrochemical performance at low COD concentrations, while such effect was absent at high COD concentrations. This study suggests a feasible and simple method to reduce internal resistance and improve power generation of sustainable air-cathode MFCs.     

Enhanced Coulombic efficiency and power density of air-cathode microbial fuel cells with an improved cell configuration

Single chamber air-cathode microbial fuel cells (MFCs) that lack a proton exchange membrane (PEM) hold a great promise for many practical applications due to their low operational cost, simple configuration and relative high power density. One of the great challenges for PEM-less MFC is that the Coulombic efficiency is much lower than those containing PEM. In this study, single-chamber PEM-less MFCs were adapted by applying a J-Cloth layer on the water-facing side of air cathode. Due to the significant reduction of oxygen diffusion by the J-Cloth, the MFCs with two-layers of J-Cloth demonstrated an over 100% increase in Coulombic efficiency in comparison with those without J-Cloth (71% versus 35%) at the same current density of 0.6 mA cm⁻². A new cell configuration, cloth electrode assembly (CEA), therefore, was designed by sandwiching the cloth between the anode and the cathode. Such an MFC configuration greatly reduced the internal resistance, resulting in a power density of 627 W m⁻³ when operated in fed-batch mode and 1010 W m⁻³ in continuous-flow mode, which is the highest reported power density for MFCs and more than 15 times higher than those reported for air-cathode MFCs using similar electrode materials. This study indicates that the Coulombic efficiency and power density of air-cathode MFCs can be improved significantly using an inexpensive cloth layer, which greatly increases the feasibility for the practical applications of MFCs.     

Effect of ammonium and COD concentrations on the performance of fixed-bed air-cathode microbial fuel cells treating reject water

In this study, a bio-electrochemical reactor comprising of anaerobic and aerobic chambers with filled granular activated carbon as biocarrier and third electrode was developed to investigate the effect of ammonium and COD concentrations on the power generation and COD removal. Two important operating parameters including initial COD concentrations (50–2000 mg/L) and initial ammonium concentrations (40–1000 mg/L) were optimized to attain the best response of electricity generation and COD removal using response surface methodology (RSM) through an experiments design software. A total of thirteen runs of experiments were employed for statistical analysis of data and developing empirical model, which has ability to predict optimum condition. Based on the results, the maximum COD removal efficiency was 96.8%, when the produced current at the maximum level was 1.149 mA. It was found that main variables as solely or combination effects significantly affect the efficiency of MFCs.     

Power generation from furfural using the microbial fuel cell

Furfural is a typical inhibitor in the ethanol fermentation process using lignocellulosic hydrolysates as raw materials. In the literature, no report has shown that furfural can be utilized as the fuel to produce electricity in the microbial fuel cell (MFC), a device that uses microbes to convert organic compounds to generate electricity. In this study, we demonstrated that electricity was successfully generated using furfural as the sole fuel in both the ferricyanide-cathode MFC and the air-cathode MFC. In the ferricyanide-cathode MFC, the maximum power densities reached 45.4, 81.4, and 103 W m⁻³, respectively, when 1000 mg L⁻¹ glucose, a mixture of 200 mg L⁻¹ glucose and 5 mM furfural, and 6.68 mM furfural were used as the fuels in the anode solution. The corresponding Coulombic efficiencies (CE) were 4.0, 7.1, and 10.2% for the three treatments, respectively. For pure furfural as the fuel, the removal efficiency of furfural reached up to 95% within 12 h. In the air-cathode MFC using 6.68 mM furfural as the fuel, the maximum values of power density and CE were 361 mW m⁻² (18 W m⁻³) and 30.3%, respectively, and the COD removal was about 68% at the end of the experiment (about 30 h). Increase in furfural concentrations from 6.68 to 20 mM resulted in increase in the maximum power densities from 361 to 368 mW m⁻², and decrease in CEs from 30.3 to 20.6%. These results indicated that some toxic and biorefractory organics such as furfural might still be suitable resources for electricity generation using the MFC technology.     

Improved performance of microbial fuel cell using combination biocathode of graphite fiber brush and graphite granules

The efficiency and sustainability of microbial fuel cell (MFC) are heavily dependent on the cathode performance. We show here that the use of graphite fiber brush (GBF) together with graphite granules (GGs) as a basal material for biocathode (MFC reactor type R1) significantly improve the performance of a MFC compared with MFCs using GGs (MFC reactor type R2) or GFB (MFC reactor type R3) individually. Compared with R3, the use of the combination biocathode (R1) can shorten the start-up time by 53.75%, improve coulombic efficiencies (CEs) by 21.0 ± 2.7% at external resistance (R_EX) of 500 Ω, and increase maximum power densities by 38.2 ± 12.6%. Though the start-up time and open circuit voltage (OCV) of the reactor R2 are similar to R1, the CE (R_EX = 500 Ω) and maximum power density of R2 are 21.4 ± 1.7% and 38.2 ± 15.6% lower than that of R1. Fluorescence in situ hybridization (FISH) analyses indicate the bacteria on cathodes of R1 and R2 are richer than that of R3. Molecular taxonomic analyses reveal that the biofilm formed on the biocathode surface is dominated by strains belonging to Nitrobacter, Achromobacter, Acinetobacter, and Bacteroidetes. Combination of GFB and GGs as biocathode material in MFC is more efficient and can achieve sustainable electricity recovery from organic substances, which substantially increases the viability and sustainability of MFCs.     

Simultaneous processes of electricity generation and ceftriaxone sodium degradation in an air-cathode single chamber microbial fuel cell

A single chamber microbial fuel cell (MFC) with an air-cathode is successfully demonstrated using glucose-ceftriaxone sodium mixtures or ceftriaxone sodium as fuel. Results show that the ceftriaxone sodium can be biodegraded and produce electricity simultaneously. Interestingly, these ceftriaxone sodium-glucose mixtures play an active role in production of electricity. The maximum power density is increased in comparison to 1000 mg L⁻¹ glucose (19 W m⁻³) by 495% for 50 mg L⁻¹ ceftriaxone sodium + 1000 mg L⁻¹ glucose (113 W m⁻³), while the maximum power density is 11 W m⁻³ using 50 mg L⁻¹ ceftriaxone sodium as the sole fuel. Moreover, ceftriaxone sodium biodegradation rate reaches 91% within 24 h using the MFC in comparison with 51% using the traditional anaerobic reactor. These results indicate that some toxic and bio-refractory organics such as antibiotic wastewater might be suitable resources for electricity generation using the MFC technology.     

Assessment of two ionic exchange membranes in a bioelectrochemical system for wastewater treatment and hydrogen production

Bioelectrochemical systems are devices where organic matter (e.g. wastewater) is oxidized through exoelectrogenic bacteria; this process is a new alternative to energy crisis and to mitigate climate change. If the products of such oxidation are electrons they are called microbial fuel cell (MFC), otherwise if the product is hydrogen these devices are called microbial electrolysis cells (MEC) Mostly, MEC's studies have reported double chamber designs, where the anode and cathode are separated by an ion exchange membrane. Nafion is a proton exchange membrane widely used to study bioelectrochemical devices; however, to our knowledge there are no reports of bipolar membranes (BPM) in these systems. In this study, a double-chambered MEC was constructed to evaluate the performance of the system using Nafion^® 117, and FUMASEP^®FBM bipolar membrane, separately. Biofilm formation was monitored by cyclic voltammetry and open circuit potential (OCP); maximum power for MFC-Nafion and MFC-BPM were 105.1 and 3.6 mW/m², respectively. Hydrogen yield and COD removal were significantly different for both MEC systems. Whereas COD removal for MEC-BPM was 44.8%; MEC-Nafion exhibited a COD removal of 87.4%. Solely the latter system produced hydrogen, with a yield of 7.6%.     

The use of double-sided cloth without diffusion layers as air-cathode in microbial fuel cells

The cost of electrode materials is one of the most important factors limiting the scale of microbial fuel cells (MFCs). In this study, a novel double-sided cloth (DC) without diffusion layer is using as air-cathode, which decreases the cost and simplifies electrode production process. Using Pt as catalyst, the maximum power density of MFC using DC cathode is 0.70 ± 0.02 W m⁻², which is similar to that obtained using carbon cloth (CC) cathodes (0.66 ± 0.01 W m⁻²). After running in stable status, the Coulombic efficiencies (CEs) (18 ± 1%) and COD removal rates (75 ± 3%) are almost the same as those of CC cathode with diffusion layers. Using carbon powder as catalyst on the DC cathode, the maximum powder density is 0.41 ± 0.01 W m⁻², with a COD removal rate of 66 ± 2% and a CE of 13.9 ± 0.5%. The total cost of cathode based on power output decreases as follows: CC with Pt (CC-Pt, 2652$ W⁻¹), DC with Pt (DC-Pt, 1007$ W⁻¹) and DC with carbon powder (DC-C, 22$ W⁻¹), showing that DC is an inexpensive and promising cathode material for future applications.