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.     

Effect of sediment microbial fuel cell stacks on 9 V/12 V DC power supply

Sediment microbial fuel cell (SMFC) is a bio-electrochemical device that uses anaerobic bacteria to produce renewable energy. The voltage generated by SMFC is very low, so directly it cannot be applied to modern electronic devices. But, it is feasible to raise the output voltage of SMFC by connecting them in series-parallel combinations. In the present work, four SMFC modules are developed in the laboratory and by connecting in four different ways the output voltage as well as the output current are raised to the utility levels. The primary cause to avoid the practical application of series and parallel connected SMFC is voltage reversal problem. To do away with this problem, in this work each group of SMFCs is first used to charge a super-capacitor (4 F, 5.5 V) and then it has been used to power the dc boost converter. Moreover, in this research work, the effects of charging and discharging times of super capacitors for each module are also investigated. In the final stage, a dc boost converter is presented to step-up the voltage of stacked SMFCs which provides a regulated output voltage (9 V/12 V) at the load. The results obtained, show that module-4 connected boost converter provides higher output current for a longer duration as compared to other super capacitor connected modules. This technique of energy harvesting from SMFCs can be used as a power source (either of 9 V or 12 V) in practical electronic devices.     

Energy harvesting from sediment microbial fuel cell to supply uninterruptible regulated power for small devices

Sediment microbial fuel cell (SMFC) is a bio‐electrochemical device that generates direct current by microbes present in the soil. The main drawback of SMFC is the low voltage and fluctuations. Therefore, a suitable scheme is required to obtain sufficient voltage with insignificant fluctuation. This paper proposes an energy harvester power management system (PMS) to get rid of low voltage and fluctuation problem of SMFC. The proposed PMS is composed of a dc‐dc boost converter, switches, and super capacitors. The boost converter (using LTC3108 IC) successfully steps up the voltage up to 2.658 V and provides it to the load for 1.5 minutes. Four SMFCs connected with four individual super capacitors and a single boost converter has been used to implement this scheme. In this strategy, the charging and discharging time of the SMFCs are controlled in such a way that the continuous power will be supplied to the load with the optimum number of SMFCs. This scheme is tested on an experimental setup. It is found that the energy harvester PMS supplies a continuous voltage of 2.658 V with the efficiency of 85.46%, which is sufficient to power for small devices such as remote environment sensors, temperature sensors, LED lighting, and submersible ultrasonic receiver.     

Supercapacitors accumulating energy harvesting from stacked sediment microbial fuel cells and boosting input power for power management systems

Supercapacitors, are commonly connected to the sediment microbial fuel cell (SMFC) and then serves as the input source for the power management system (PMS). To compare and analyze functions of supercapacitors in SMFC energy harvesting, PMSs (PMS I and PMS II) are powered by SMFC stack or charged supercapacitors as the input source. Tests indicate that the charged supercapacitor results in a higher input power and a larger output power. In addition, the overall efficiency of PMSs is rarely affected by the capacitance, but the initial voltage of the supercapacitor. By charging supercapacitors connected in parallel and then discharging them in series, the overall power efficiency of PMS II is increased from 44.33% to 69.52%. In conclusion, supercapacitors firstly storing SMFC energy is beneficial to provide sufficient energy, resulting in an improved PMS performance. Further, these results can be useful and informative to PMS design for efficiently harvesting and utilize MFC energy.     

Anodic biofilm in single-chamber microbial fuel cells cultivated under different temperatures

The microorganisms in anodic biofilms of a microbial fuel cell (MFC) oxidize substrates to generate electrons, protons, and metabolic products. This study started up two single-chamber MFCs at different temperatures (25 °C for MFC A and 15 °C for MFC B); after successful startup, the cell temperatures were swapped. The MFC A had peak voltage at 540 mV at 25 °C, which was decreased rapidly as fed substrate was consumed. At 15 °C, the MFC A yielded a nearly constant voltage of 500 mV over complete feed cycle. Conversely, the MFC B produced higher maximum power than MFC A, and can deliver nearly constant voltage over the entire feed cycle at either 15 or 25 °C. Electrochemical analysis revealed that the MFC B had lower internal resistance than MFC A, with the former having much lower anodic resistance than the latter. Microbial analysis showed that the MFC started up at low temperatures had anodic biofilm enriched with psychrophilic bacteria Simplicispira psychrophila LMG 5408(T)[AF078755] and Geobacter psychrophilus P35(T)[AY653549]. This study suggests the strategy to promote the development of anodic biofilms at low temperatures that are capable of yielding electricity at constant voltage.     

Cobalt/nitrogen-Co-doped nanoscale hierarchically porous composites derived from octahedral metal-organic framework for efficient oxygen reduction in microbial fuel cells

Microbial fuel cell, a promising energy conversion technology, plays a crucial role in the field of renewable and sustainable energy. In an air-cathode microbial fuel cell, the oxygen reduction reaction catalytic activity of cathode catalyst is a critical factor that determines the performance of microbial fuel cell. This work reports a facile route for the synthesis of Co/N incorporated carbonaceous electrocatalyst using a Zr-based metal-organic framework UiO66-NH₂ as a template. This electrocatalyst exhibits outstanding activity and stability toward four-electron mechanism. In the microbial fuel cell application, Co/UiO66-900 shows superb electrochemical performance with a stable output voltage of 395 mV and maximum power density of 299.62 mW/m², which is 95.8% of the power density achieved in microbial fuel cell catalyzed by Pt/C catalyst (312.59 mW/m²). Co/UiO66-900 possesses high-performance catalytic activity because of its 3D-structured micropores, nitrogen-coordinated cobalt species and the synergistic effects between carbon and metal ion center. These unique properties can facilitate the oxygen reduction reaction by exposing abundant efficient active sites and accelerating mass transfer at oxygen reduction reaction interfaces. This work suggests that Co/UiO66-900 catalyst with superb electrocatalytic ORR activity is a promising alternative which can replace the expensive Pt/C in air-cathode MFC.     

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.     

Study on power generation and Congo red decolorization of 3D conductive PPy-CNT hydrogel in bioelectrochemical system

In this paper, a polypyrrole-carbon nanotube hydrogel (PPy-CNT) with 3D macroporous structure was prepared by secondary growth method. This self-supporting material with good conductivity and biocompatibility can be directly used as anode in a microbial fuel cell (MFC). The prepared material had a uniform structure with rich 3D porosity and showed good water retention performance. The effect of the mass ratio of PPy and CNT in the hydrogel were also investigated to evaluate the electrical performance of MFC. The MFC with 10:1 PPy-CNT hydrogel anode could reached the maximum power density of 3660.25 mW/m3 and the minimal electrochemical reaction impedance of anode was 5.06 Ω. The effects of Congo red concentration, external resistance and suspended activated sludge on decolorazation and electricity generation were also investigated in the MFC with the best performance hydrogel. When the Congo red concentration was 50 mg/L and the external resistance was 200 Ω, the dye decolorization rate and chemical oxygen demand (COD) removal rate could reach 94.35% and 42.31% at 48h while the output voltage of MFC was 480 mV. When activated sludge was present, the decolorization rate and COD removal rate could be increased to 99.55% and 48.08% at 48 h. The above results showed that the porous hydrogel anode had broad application prospects in synchronous wastewater treatment and electricity production of MFC.     

Electricity harvest from nitrate/sulfide-containing wastewaters using microbial fuel cell with autotrophic denitrifier, Pseudomonas sp. C27

Toxicity prevents the bioenergy content of certain industrial effluents from being recovered. In operation of microbial fuel cell (MFC), microorganisms can be inhibited with high levels of sulfide. This study applied a pure culture, an autotrophic denitrifier, Pseudomonas sp. C27, to start up a two-chambered MFC using sulfide as the sole electron donor. The MFC can successfully convert sulfide to elementary sulfur with electricity generation at a maximum power density of 40 mW m⁻². The addition of acetate interfered biofilm activity to convert sulfide to electricity. Nitrate was revealed as the more powerful electron acceptor than anode in the MFC. The present device introduces a route for treating sulfide laden wastewaters with electricity harvest.     

Influence of growth curve phase on electricity performance of microbial fuel cell by Escherichia coli

The microbial fuel cell of Escherichia coli can convert microorganism biochemistry energy into electrical energy. To realize the influence of the growth curve phase with respect to different culture times on electricity performance, three kinds of E. coli (BCRC No. 10322, 10675, 51534) are selected, and it is both required and important to improve the performance of the microbial fuel cell (MFC). Results show that the BCRC No. 51534 of E. coli would be a better choice because a larger open-circuit voltage of 0.88 V and a limiting current of 10.1 mA possessed by it would result in an excellent power density of 547 mW/m². In addition, the selection of culture timing set as at the middle of the logarithmic phase and phase transition from logarithmic to stationary is suggested because the growth curve is suitable for electricity generation of the MFC. These observations would be useful for the improvement of the MFC.     

Enhanced bioelectrochemical performance by NiCoAl-LDH/MXene hybrid as cathode catalyst for microbial fuel cell

In this work, NiCoAl-layered double hydroxide (LDH)/MXene was successfully prepared through straightforward hydrothermal method. NiCoAl-LDH was tightly and uniformly coated on MXene, forming a kind of porous structure. NiCoAl-LDH/MXene exhibited the (002) (012) (105) (100) crystal planes of hydrotalcite reflection. NiCoAl-LDH/MXene also showed superior catalytic oxygen reduction reaction (ORR) in response current according to electrochemical test (cyclic voltammetry (CV) etc.). The maximum power density and output voltage of NiCoAl-LDH/MXene as cathode in microbial fuel cell (MFC) was 362.404 mW/m² and 450 mV, respectively, which was 1.54 times of MXene-MFC (234.256 mW/m²) and 1.71 times of NiCoAl-LDH-MFC (211.56 mW/m²). The results indicated that NiCoAl-LDH/MXene was a kind of potential cathode catalyst for MFC and was full of future application.     

Double-chamber microbial fuel cells started up under room and low temperatures

This study examined the performances of two double-chamber microbial fuel cells (MFCs) at 25 °C and 15 °C. After successful startup, the cell temperature of MFC A was decreased from 25 to 15 °C, yielding a sudden breakdown of the entire system. Conversely, the MFC B, started up at 15 °C, delivering higher power density at 25 °C than MFC A at the same temperature. The electrochemical analysis revealed that the MFC B had lower anodic resistance than MFC A. Additionally, a negative temperature dependence of the polarization resistances of the anodic biofilm was noted, a novel phenomenon only reported in this double-chambered study. Microbial analysis showed that the psychrophilic bacteria were enriched in anodic biofilms of MFC B, which likely contributed to the robust cell performance of the present double-chambered MFCs.     

Influence of biomass addition on electricity harvesting from solid phase microbial fuel cells

In this study, two types of biomass (Acorus calamus leaves and wheat straw) were added to a matrix of sediment and soil inside the anode of solid phase microbial fuel cells (SMFCs) in order to increase their output power. SMFC containing 3% leaves in their sediment had a maximum power density of 195 mW m⁻² in contrast to 4.6 mW m⁻² of that SMFC without leaves. Similarly, SMFC containing 1% wheat straw in their soil environment had a maximum power density of 167 mW m⁻². It suggests that the addition of biomass in appropriate proportions increases contact opportunities between the matrix, the anode and the added biomass, increases organic matter content, and enhances cellulase activity, thus serving as an important method for enhancing output power in SMFCs.     

Dynamic modeling of a continuous two-chamber microbial fuel cell with pure culture of Shewanella

Microbial fuel cell is a bioreactor which converts the chemical energy stored in chemical bonds of the organic compounds to electrical energy through the catalytic reactions. In this work, the previous model which was proposed by our group [M. Esfandyari, M.A. Fanaei, R. Gheshlaghi, M.A. Mahdavi, Chemical Engineering Research and Design, 117 (2017) 34–42] for a batch two-chamber microbial fuel cell (MFC) is extended to the continuous operation. In the selected continuous MFC, lactate is used as the substrate, Shewanella as the microbial agent, and oxygen of air as the final electron acceptor in the cathode chamber. An experimental setup is applied for the collection of data needed for the verification of the proposed model. A Good agreement was observed between the predicted and the experimental data of the current and voltage produced by MFC as well as the substrate and carbon dioxide concentration in the liquid bulk of anode chamber of MFC. The proposed model has simple structure and can be used for the optimization, and design of control system of microbial fuel cell.     

Effect of dissolved oxygen concentration on nitrogen removal and electricity generation in self pH-buffer microbial fuel cell

A double-chamber self pH-buffer microbial fuel cell (MFC) was used to investigate the effect of dissolved oxygen (DO) concentration on cathodic nitrification coupled with anodic denitrification MFC. It was found that nitrogen and COD removal, electricity generation were positively correlated with DO concentration in the cathode chamber. When total inorganic nitrogen of influent was 202.51 ± 7.82 mg/L at DO 6.8 mg/L, the maximum voltage output was 282 mV and the maximum power density was 149.76 mW/m². After 82 h operation, the highest removal rate of total inorganic nitrogen was 91.71 ± 0.38%. Electrochemical impedance spectroscopy (EIS) test showed that the internal resistance of the reactor with different DO concentration was related to the diffusion internal resistance. The data of bacterial analysis in the cathode chamber revealed that there were not only ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), but also a large number of exoelectrogens. Compared with the traditional biological denitrification and related MFC denitrification research, this method does not need pH-buffer solution and external circulation device through the anion exchange membrane (AEM). It can generate electricity and remove nitrogen simultaneously, and the oxygen utilization rate in the cathode can also be enhanced.     

Stable and high energy generation by a strain of Bacillus subtilis in a microbial fuel cell

In this study, the Gram-positive aerobic bacterium Bacillus subtilis has for the first time been employed in a microbial fuel cell (MFC). A glucose-fed MFC with M9 minimal medium in the anode chamber was operated for 3 months, establishing a highly active MFC using filtered M9 medium as the catholyte, carbon cloth as the anode and a 20% platinum electrode as the cathode. The bioelectrical responses of the MFC were characterized by the circuit potential, measured at an average value of 370 mV. A potential of 115 mV appeared to characterize the maximum power produced from a polarization test was 1.05 mW cm⁻² at a resistance of 0.56 kΩ. In situ cyclic voltammograms with and without biofilm anodes were performed in the growth phase and showed that redox metabolites were produced, which varied with physiological status. Voltammograms obtained from a comparative study of broth, supernatant and resuspended bacterial cells revealed that the electrochemical activity in the anode chamber arose from the redox compounds in the supernatant. The results show that the microorganism B. subtilis is electrochemically active and that the electron transfer mechanism is mainly due to the excreted redox compounds (mediator) in the broth solution and not to the membrane-bound proteins.     

Using rhodium as a cathode catalyst for enhancing performance of microbial fuel cell

Rhodium with activated carbon as carbon base layer (Rh/AC) was exploited as an oxygen reduction reaction (ORR) catalyst to explore its applicability in microbial fuel cell (MFC). Four MFCs were fabricated using the Rh/AC catalyst, adopting varying Rh loadings of 0.5, 1.0 and 2.0 mg cm⁻² and without Rh on carbon felt cathode in order to understand the optimum loading of this catalyst to enhance the performance of MFC. The participation of Rh/AC in ORR was confirmed by cyclic voltammetry and electron impedance spectroscopy analysis, which supported the enhanced charge transfer capacity of the cathode modified with the prepared catalysts. Volumetric power density of MFC was found to be improved by 2.6 times when Rh/AC was used as cathode catalyst (9.36 W m⁻³) at a loading of 2.0 mg cm⁻² in comparison to the control MFC (3.65 W m⁻³) without Rh on the cathode. It was thus inferred that the increase in the Rh loading up to 2 mg cm⁻² can improve the performance of MFC significantly.     

Factors that influence the performance of two-chamber microbial fuel cell

The two-chamber microbial fuel cell (MFC) was operated in batch mode, using acclimated hydrogen-producing mixed bacteria as the anodic inoculum, artificial sucrose wastewater as the substrate (sucrose concentration 10.0 g/L). The performance of the MFC was analyzed at different anodic pH microenvironments, such as the initial pH of the anolyte of 8.57, 7.3, 7.0 and 6.0, respectively, while anodic pH-controlled of 7.3 and 7.0. It showed that the best performance was obtained when the MFC was carried out at anodic pH-controlled of 7.3. Taking the interaction of factors into consideration, we adopted response surface methodology (RSM) to investigate the effects of sucrose concentration, operating temperature and ferrous sulfate concentration on the performance of MFC. The optimum condition for maximum output voltage of the two-chamber MFC (external resistance 1000 Ω) was thus obtained.     

Bioelectricity production on xylose with a compost enrichment culture

An exoelectrogenic culture was enriched on 1.0 g/L xylose from a compost sample in two-chamber microbial fuel cells (MFCs). Electricity production was optimized by changing mixing type, external resistance, xylose concentration and pH. Furthermore, the changes in microbial communities after each optimization step were monitored with PCR-DGGE. Electricity production was highly dependent on operational conditions that affected power densities (PD), Coulombic efficiencies (CE), substrate degradation, utilization of soluble metabolites for electricity production and stability of MFC performance. The optimum operational conditions for electricity production were without mixing, 100 Ω external resistance, 0.5 g/L xylose and pH 7. With optimized operational conditions PD of 590 mW/m² and CE of 82% were obtained. Microbial community composition, consisting mainly of Geobacter sulfurreducens, Escherichia coli, Sphaerochaeta sp. TQ1 and Bacteroides species, was mainly affected by MFC configuration, i.e. electrical connections, which likely affected the anode potential.     

Single-step inkjet-printed paper-origami arrayed air-breathing microfluidic microbial fuel cell and its validation

Microfluidic paper based microbial fuel cells (μP-MFCs) have gained considerable popularity due to their compact, quick and low-cost fluid manipulation paradigm. Compared to conventional technologies, paper as a substrate with advanced nanomaterial electrode material has many distinct advantages from point-of-care monitoring to energy harvesting. As a result, these have been used and are more popular in a variety of fields, such as health diagnostics, environmental and food quality management. By this encouragement, herein a portable microbial fuel cell as an origami array has been demonstrated using custom carbon electrodes with a modified the transition metal oxide MnO₂ nanomaterial. This customized electrode design was first printed using a tabletop PCB inkjet printer where the anode was further modified with synthesized MnO₂ nanoparticles. The entire cell was formed by folding the paper along predefined edges where the fuel, Shewanella putrefaciens, was streamed continuously via inherent capillary cation. Various studies, such as morphological, surface catalyst coating, amount loading and volumetric culture optimization experiments, have also been accomplished to find the most appropriate optimum parameter to enhance power conversion efficiency. The developed origami arrayed microbial fuel generated an open-circuit potential (OCP) for two parallel connected MFCs of 0.534 V and a maximum power density of 15.9 μW/cm² with a maximum current density of 130 μA/cm². In the end, the harvested power was used by powering the digital watch circuit through the ultra-low DC-DC booster board. Such an MFC origami array, with simple electrode manufacturing and modification process, has a great potential and bright future in Internet of Things (IoT) applications by making multiple stacks where the data can be monitored.