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.     

Design of a radial vanadium redox microfluidic fuel cell: A new way to break the size limitation

Microfluidic fuel cell (MFC) suffers from small single cell output power due to the inherent cell size limitation as microscale geometries are prerequisite to prevent reactant crossover between the anode and cathode. To meet the power demand of practical applications, previous works mainly focus on the creating of MFC stacks with multiple cells connected in series, parallel, or mixture of both series and parallel to increase the output power. Yet, low energy efficiency is observed because of the flow distribution nonuniformity and shunt current losses. In this work, a high performance radial vanadium redox MFC is presented to address the size limitation issue by adding a separate layer between the porous electrodes of the conventional plate‐frame MFC. Specific cell characteristics are detailed by mathematical modeling, and parametric studies are performed to evaluate the influences of the geometrical and operational parameters on the cell performance. The results show that this new radial MFC can provide a higher fuel utilization and meanwhile an improved cell performance under a fixed electrode size compared with the conventional plate‐frame MFC. Moreover, the electrode size limitation due to the reactant crossover between the anode and cathode is broken as the influences of the electrode size on the mixing region are greatly reduced. In the case with the electrode size equal to 18 mm × 18 mm , single cell output power of 0.35 mW with a fuel utilization of 53.33% is obtained under the reactant concentration of 2 mol L^?1 and flow rate of 300 μL min^?1 .     

Bioelectricity production by using goat (Capra hircus) rumen fluid from slaughterhouse waste in mediator-less microbial fuel cells

Microbial fuel cells (MFCs) grasped an outlook for bioelectricity production under global scenario. Many studies have highlighted the utilization of various wastes for electricity generation by this advantageous technology. In the present investigation, an H-type, two-chambered MFC was designed for bioelectricity production using Capra hircus rumen fluid collected from slaughterhouse, paddy straw as substrate, copper as anode, and zinc as cathode. The power output of single MFC was recorded to a maximum of 5.76 W and 8.49 W/m². Effect of acetic acid as catholyte with concentration range (0.0–2.0%) was compared with air cathode. Acetic acid was found to enhance the power output at 2% concentration. Assessment for increased power output was carried out by connecting the four MFCs in series. MFC series performed well with a maximum power output of 67.24 W at 192 h with acetate as catholyte whereas 54.76 W for air cathode. The maximum power density achieved was 42.11 W/m² for acetate in cathode and 34.39 W/m² for air cathode. The MFCs developed with rumen consortia, hay as substrate, and Cu–Zn electrodes were found to be effective in bioelectricity production.     

Recycled tire crumb rubber anodes for sustainable power production in microbial fuel cells

One of the greatest challenges facing microbial fuel cells (MFCs) in large scale applications is the high cost of electrode material. We demonstrate here that recycled tire crumb rubber coated with graphite paint can be used instead of fine carbon materials as the MFC anode. The tire particles showed satisfactory conductivity after 2-4 layers of coating. The specific surface area of the coated rubber was over an order of magnitude greater than similar sized graphite granules. Power production in single chamber tire-anode air-cathode MFCs reached a maximum power density of 421 mW m⁻², with a coulombic efficiency (CE) of 25.1%. The control graphite granule MFC achieved higher power density (528 mW m⁻²) but lower CE (15.6%). The light weight of tire particle could reduce clogging and maintenance cost but posts challenges in conductive connection. The use of recycled material as the MFC anodes brings a new perspective to MFC design and application and carries significant economic and environmental benefit potentials.     

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.     

Enhancing operating capacity of microbial fuel cells by using low-cost electrodes and multi anode-cathode connections in a membrane-less configuration

Air-cathode microbial fuel cells (MFCs) are common configurations for real scales, especially wastewater treatment due to direct access to oxygen and scaling up capability. Herein, a single-chamber MFC (SCMFC) was used. The fabrication of graphite paint/stainless steel mesh (GP/SSM) anodes in sinusoidal geometry increased the electrode surface area per unit volume of the SCMFC and made it possible to utilize the maximum reactor capacity. Under batch mode, the SCMFC produced 1597 mW/m³ using six anodes and eight air-cathodes, and the maximum COD removal was obtained 93.22% and 93.54% in the second and fourth batches, respectively. Moreover, the effect of electrode surface area on power output was investigated; the power density became 2-fold when the air-cathodes’ surface area increased eight times, and increasing the anode surface area improved the power production per unit volume. The COD removal of 82.14% with 20.46% columbic efficiency was achieved after 72 h of continuous operation.     

Modelling and simulation of two-chamber microbial fuel cell

Microbial fuel cells (MFCs) offer great promise for simultaneous treatment of wastewater and energy recovery. While past research has been based extensively on experimental studies, modelling and simulation remains scarce. A typical MFC shares many similarities with chemical fuel cells such as direct ascorbic acid fuel cells and direct methanol fuel cells. Therefore, an attempt is made to develop a MFC model similar to that for chemical fuel cells. By integrating biochemical reactions, Butler–Volmer expressions and mass/charge balances, a MFC model based on a two-chamber configuration is developed that simulates both steady and dynamic behaviour of a MFC, including voltage, power density, fuel concentration, and the influence of various parameters on power generation. Results show that the cathodic reaction is the most significant limiting factor of MFC performance. Periodic changes in the flow rate of fuel result in a boost of power output; this offers further insight into MFC behaviour. In addition to a MFC fuelled by acetate, the present method is also successfully extended to using artificial wastewater (solution of glucose and glutamic acid) as fuel. Since the proposed modelling method is easy to implement, it can serve as a framework for modelling other types of MFC and thereby will facilitate the development and scale-up of more efficient MFCs.     

Effects of unit distance and number on sediment microbial fuel cell stacks for practical power supply

Sediment microbial fuel cells (SMFCs) can covert the biomass and organic matters in sediments into electricity. SMFC stack is an essential way for the application of SMFCs. The unit distance and number will be crucial for SMFC stacks applied in practical environments. This study showed that the power density of individual SMFC increased with the unit distance when compared with SMFCs with a small distance. For hydraulically connected serial stacks, increasing unit distance from 2 to 28 cm decreased the potential loss from 50.4% to 11.3%, but the power output did not increase with either unit distance or number of units due to higher internal resistance and electrode reversal. For hydraulically connected parallel stacks, increasing unit number from one to three multiplied the power output but no further power increase was observed with four and five units, indicating an optimal unit number (OUN) in parallel stacks due to ion conduction. Similar performance was shown when using SMFC stacks to power a light‐emitting diode and an environmental sensor. The results provide important information for improving the power and cost‐effectiveness of SMFC stacks.     

Transition metal nanoparticles doped carbon paper as a cost-effective anode in a microbial fuel cell powered by pure and mixed biocatalyst cultures

The poor wettability and high cost of the carbonaceous electrodes materials prohibited the practical applications of microbial fuel cells (MFCs) on large scale. Here, a novel nanoparticles of metal sheathed with metal oxide is electrodeposited on carbon paper (CP) to introduce as high-performance anodes of microbial fuel cell (MFC). This thin layer of metal/metal oxide significantly enhance the microbial adhesion, the wettability of the anode surface and decrease the electron transfer resistance. The investigation of the modified CP anodes in an air-cathode MFCs fed by various biocatalyst cultures shows a significant improving in the MFC performance. Where, the generated power and current density was 140% and 210% higher as compared to the pristine CP. Mixed culture of exoelectrogenic microorganism in wastewater exhibited good performance and generated higher power and current density compared to yeast as pure culture. The excellent capacitance with a distinctive nanostructure morphology of the modified-CP open an avenues for practical applications of MFCs.     

Voltage reversal during microbial fuel cell stack operation

Microbial fuel cells (MFC) can be used to directly generate electricity from organic matter, but the voltage produced by a single reactor is only ∼0.5 V. Voltage can be increased by stacking cells, i.e. by linking individual reactors in series, as is commonly done with hydrogen fuel cells, to provide a higher voltage output. A two-cell air-cathode MFC stack tested here produced a working voltage of 0.9 V (external load 500 Ω) and had an open circuit voltage (OCV) of 1.3 V when operated in fed batch mode under substrate-sufficient conditions. When multiple cells are stacked together, however, charge reversal can result in the reverse polarity of one or more cells and a loss of power generation. We investigated the causes of charge reversal and the impact of prolonged reversal on power generation using a two air-cathode MFCs stack. When voltage began to decline at the end of a fed batch cycle, we observed voltage reversal with one cell producing a working voltage of 0.6 V, and the other cell having a reversed voltage of −0.58 V, producing only a minimal stack voltage of 0.02 V. The reason for the voltage reversal was shown to be fuel starvation, resulting in a loss of bacterial activity. Voltage reversal adversely affected bacteria on the anode of the affected cell, as shown by a relative decrease in cell performance following a cycle of starvation (no feeding). The control of voltage reversal will be crucial for long-term operation of MFCs in series. Rapid feeding of a cell can restore positive voltage generation, but the long-term impact of charge reversal will be inactivation of bacteria and it will require that the affected cells be short-circuited to maintain stack power production. A better understanding of the long term effects of voltage reversal on power generation by MFC stacks is needed in order to efficiently increase voltage production by using stacked MFC systems.     

Integrating engineering design improvements with exoelectrogen enrichment process to increase power output from microbial fuel cells

Microbial fuel cells (MFC) hold promise as a green technology for bioenergy production. The challenge is to improve the engineering design while exploiting the ability of microbes to generate and transfer electrons directly to electrodes. A strategy using a combination of improved anode design and an enrichment process was formulated to improve power densities. The design was based on a flow-through anode with minimal dead volume and a high electrode surface area per unit volume. The strategy focused on promoting biofilm formation via a combination of forced flow through the anode, carbon limitation, and step-wise reduction of external resistance. The enrichment process resulted in development of exoelectrogenic biofilm communities dominated by Anaeromusa spp. This is the first report identifying organisms from the Veillonellaceae family in MFCs. The power density of the resulting MFC using a ferricyanide cathode reached 300 W m⁻³ net anode volume (3220 mW m⁻²), which is about a third of what is estimated to be necessary for commercial consideration. The operational stability of the MFC using high specific surface area electrodes was demonstrated by operating the MFC for a period of over four months.     

Research progress in the application of metal organic frameworks and its complex in microbial fuel cells: Present status,opportunities, future directions and prospects

Metal organic frameworks (MOFs) could greatly improve the power generation and degradation performance of microbial fuel cells (MFCs). MOFs and their compound derivatives played key role in cathode, anode and proton exchange membrane of MFCs, which greatly promoted the power generation of MFC and the degradation efficiency of various pollutants. However, MOFs were still possessed some defects, such as complex synthesis process, difficult regulation, instability, etc. Moreover, the application of MFC was limited in low power density, system internal resistance, microbial consumption, etc. Which further limited the degradation of pollutants by MFC. The existing problems and various improvement schemes of MOFs for MFCs were further summarized, which would provide references for promoting the application of MOFs materials in MFC system. It was expected to enhance the application of MOFs materials and promote the performance of MFC.     

Filter paper membrane based microfluidic fuel cells: Toward next-generation miniaturized and low cost power supply

Micro Fuel cells or microfluidic fuel cells (μMFCs) are one of the most promising power supplies for portable electronics. However, the necessary electrode spacing is required to prevent fuel-crossover and maintain the stable operation, introducing the unavoidable ohmic resistance and retarding the miniaturization. Herein, we propose a novel μMFC device combining the cellulose paper as separator, with selective catalysts at the cathode side to eliminate the unwanted side reactions and increase the system compactness. One single reactant solution containing fuel and electrolyte is applied to keep the device stable operation. The power-generation properties are evaluated in typical alkaline conditions. A great construction simplification makes the device a substantial high-power density of 2.14 W cm^?3 and maximum current density of 15.82 A cm^?3. The μMFC stacks are arranged in series and parallel manners, which delivers a maximum power output of 23.6 mW and current of 194.6 mA. It is expected that innovative and customizable performance from commercial paper and low-cost carbonaceous catalysts can provide a forum for future advancement in chip-based electrochemical energy generation and storage devices.     

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

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

老龄垃圾渗滤液体积分数对微生物燃料电池性能的影响

研究考察不同体积分数的老龄垃圾渗滤液对微生物燃料电池(MFC)性能的影响.结果表明:在体积分数为40％时,MFC的产电效能最佳,输出电压最高可达370 mV,功率密度为939 mW/m3,且化学需氧量(COD)去除率可达43.3％;无机氮的去除与产电周期有较大关系,当体积分数为100％时,氨氮去除率可达84.1％,表明...     

Energy accumulation and improved performance in microbial fuel cells

The mechanisms for electron transfer from the microorganisms found in anaerobic sludge to the anode electrode in microbial fuel cells (MFCs) have been investigated. In doing so, both the energy accumulation and improved performance were observed as a result of the addition of exogenous Na₂SO₄. Treatment of anaerobic sludge by centrifugation and washing can provide samples devoid of sulphide/sulphate. Addition of exogenous sulphate can give matched samples of S-deplete and S-replete suspensions. When these are compared in an experimental MFC, the power output of the S-deplete is only 20% that of the S-replete system. Moreover, repeat washing of the anodic chamber to remove suspended cells (leaving only cells attached to the electrode) and addition of buffer substrate gives MFC that produce an output between 10 and 20% that of control. We conclude that anaerobic sludge MFCs are a hybrid incorporating both natural mediator and anodophillic properties. We have also shown that disconnected MFC (open circuit) continue to produce sulphide and when reconnected gives an initial burst of power output demonstrating accumulator-type activity.     

Effects of force field and design parameters on the exergy efficiency and fuel utilization of microfluidic fuel cells

Microfluidic fuel cells (MFCs) are novel systems that satisfy the critical requirements of having small dimensions and substantial power output for use in portable devices. In this study, three-dimensional mathematical models of two types of MFCs (flow-over and flow-through) are developed, by coupling multiphysics consisting of microfluidic hydrodynamics, electrochemical reaction kinetics, and species transport of fluid. Moreover, gravity, exergy, and parametric sensitivity are studied, which have tremendous impact on fuel cell performance and have been frequently overlooked in previous literature. The reliability of the numerical model is demonstrated by the excellent consistency between simulation results and experimental data. First, a parametric analysis is conducted, which includes the design parameters and gravity effect. Following this, the fuel utilization and exergy efficiency are calculated for various design parameters. Finally, a sensitivity analysis is performed to evaluate the influence of the indicators on the cell performance. It is shown that a relatively stable performance is achieved with the flow-through MFC under interference from the external environment. The reactive sites of the flow-through MFC can be utilised effectively, whereas further promotion of the flow-over MFC is limited by its inherent drawback. In addition, the sensitivity analysis reveals that cell performance depends strongly on the flow rate and fuel concentration. The results can be beneficial for the investigation of cell performance optimization.     

Upscaling of microfluidic fuel cell using planar single stacks

The commercialization of microfluidic fuel cells remains difficult because of their low‐power density. In this study, microfluidic fuel cells with a planar single‐stack structure are proposed to improve the power density. The proposed stacks connect multiple cells in series, parallel, series–parallel, and parallel–series configurations. The electrolyte flow patterns of the stacks were numerically analyzed, and cell performances were experimentally measured with a platinum electrode using formic acid as the fuel. With a minimum size, these planar cell single stacks provide better power density than a single cell. The cell stack connected in parallel and then in series, where the velocity and pressure distributions of the electrolytes were simulated as almost uniform and few inner electrical connections existed, produced the best scaling‐up efficiency of 1.93. Additionally, a common feed inlet configuration was developed to further reduce the size of the cell stack further. The results show that well‐balanced fluid flow between inlets is necessary to obtain high scalability.     

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.     

Signal trends of microbial fuel cells fed with different food-industry residues

A microbial fuel cell (MFC) is an anaerobic bioreactor where soluble metabolites liberated by hydrolysis and fermentation of macromolecules are simultaneously available for anode respiring bacteria (ARB). ARB can be influenced by chemical imbalances in the liquid phase of the bioreactor. The objective of the work was to explore the trend of electric signals generated by MFCs, in relation to anaerobic biodegradation of four different solid food-industry residual substrates. Four sets of membraneless single-chamber MFCs were operated in batch mode, with solid waste substrates characterized by a different base component: i) mixed kitchen waste (fibers), ii) whey from dairy industries (sugar), iii) fisheries residues previously processed to recover oils (proteins), iv) pulp waste from citrus juice production (acidic).All the tested MFCs were able to produce an electric output with different trends, depending on the principal component of the solid substrate. MFC potential varied as function of the COD and the feeding cycle, as well as of the substrate.The pH variability during the fermentative process significantly affected the electric output. Citrus (acidic) pulp fed MFCs started to operate only when the pH raised up 6.5. MFCs fed with mix kitchen wastes had a relatively stable electric signal; fish based waste caused spiking in the MFC signal and an averaging in the COD degradation trend. This phenomenon was attributed to a pH instability induced by proteins degradation forming ammonia.The fermentation process was strongly predominant with respect the electrochemical process in MFCs and the coulombic efficiency (CE) was low, ranging between 2 and 10%. This result call for a deeper exploration of harvesting power from solid wastes and pointed also to the possibility of using a MFC to monitor important parameters of fermentation processes in biotech production plants.