Membrane-less Microbial Fuel Cell Research Articles

Bioelectricity Generation in Batch-Fed Up-Flow Membrane-Less Microbial Fuel Cell: Effect of Surface Morphology of Carbon Materials as Aqeuous Biocathodes

The surface morphology of biocathode was one of the limiting factors for microbial fuel cell (MFC) design. Up-flow membrane-less single-chambered MFC (UFML MFC) was used to investigate the effect of surface morphology of carbon material as aqueous biocathode. Pt-loaded carbon paper, carbon felt, and carbon plate were examined and compared on the power output, surface morphology for biofilm formation, Coulombic efficiency (CE), and chemical oxygen demand (COD) reduction. The COD reduction was up to 90 % in UFML MFC with Pt-loaded carbon paper, carbon felt, and carbon plate as aqueous biocathodes. The results obtained showed that the performance in voltage output was not related to internal resistance but mainly due to the ability of cathode material in oxygen reduction process. The performance of voltage output with different materials as aqueous biocathode was mainly based on to the surface morphology as it was related to the ability of biofilm formation. Roughness of aqueous biocathode’s surface morphology could prompt the biofilm growth, while biofilm overgrowth on aqueous biocathode could decrease voltage output. Therefore, smoother surface morphology of aqueous biocathode is more suitable for long-term operation.

Micro Computed Tomography As Powerful Tool for Analyzing Post Mortem Biofilm and Carbonate on Operated Cathode in Single Chamber Microbial Fuel Cell

The cathode performances are one of the main limitations related with microbial fuel cell (MFC) that strongly limit the overall output. The low power produced is an important problem that has to be addressed for the scale up of the MFCs. Cathodic overpotential is particularly high at circumneutral pH when carbonaceous or metallic catalysts are used [1]. Overpotentials are much lower for enzymes but enzymatic biocathodes are expensive and not durable [2]. Single chamber membrane-less MFCs are preferred due to the lower cost and higher power output. In membrane-less MFCs, both electrodes (anode and cathode) are exposed directly to the electrolyte or carbon-rich solution. The presence of growing bacteria inside the chamber generates electron acceptor-rich and electron donor-rich zones, which serve as cathode and anode, respectively. In fact, bacteria consume rapidly the oxygen inside the chamber creating anaerobic conditions that are useful for electrogenic bacteria for colonizing the anode electrode and oxidize organics. The cathode used is an air-breathing cathode and it is porous and allows oxygen to penetrate through the anodic solution. A biofilm is formed also on the cathode surface consuming the oxygen and forming a natural and cheap membrane that separate the cathode from the solution and stop the oxygen leaking inside the chamber, thus ensuring anaerobic conditions. Strict anaerobes grow quickly within 1 week of operations as recently showed [3]. It has been showed previously that the biofilm formation on the cathode initially increased the cathodic reduction reaction [4]. In this work, we analyzed the cathode performances and the MFC overall performance along 6 months operations [5]. At the end of the experimentation, the cathode has been examined with X-Ray Micro Computed Tomography (microCT), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) for characterizing the organic/inorganic layer on the cathode surface facing the solution [5]. Single chamber MFC with volume of 125 mL was used and the cell was fed with raw wastewater and sodium acetate. The results obtained showed that cathode reduction reaction increased in the first 15 days but then decreased continuously over time [5]. The initial increase might be due to the formation of an initial biofilm layer that probably enhanced the cathodic reduction reaction. Over time, precipitation of compounds and fouling might take place. It has been speculated that thick biofouling decreased the performances. After 6 months, part of the cathode was dried and analyzed with SEM/EDX and the other part was analyzed as it is using microCT [5]. SEM has the great potential of very high resolution but images have to be taken after treating the sample and consequently change the morphology of the biofilm after drying it. Moreover, SEM is not able to pass through objects and consequently only the surface can be analyzed. The coupling with EDX allowed to identify sodium (Na) on the external part of the cathode and calcium (Ca) on the internal face [5]. Na and Ca were present in form of carbonate. The production of OH- due to the cathodic reaction, caused the alkalinization of solution at the interface with the cathode making the precipitation of carbonate species on the cathode is very probable. MicroCT images allowed making a complete 3D scan of the entire cathode analyzed. Interestingly, the different components (cathode, carbonate and biofilm) were clearly distinguishable (Figure 1). In fact, a compact and continuous thick layer of carbonate was clearly visible between the cathode and the biofilm (Figure 1, white color). Those results obtained using microCT clearly showed that the thick, not porous carbonate layer and not the biofilm itself might increase the proton mass transport resistance from the solution to the catalytic sites and lowering dramatically the cathode output during long terms operation. Reference [1] C. Santoro, F. Soavi, A. Serov, C. Arbizzani, P. Atanassov. Biosensors and Bioelectronics. 2016, 78, 229-235. [2] C. Santoro, S. Babanova, B. Erable, A. Schuler, P. Atanassov. Bioelectrochemistry. 2016, 108, 1-7. [3] M. Grattieri, S. Babanova, C. Santoro, E. Guerrini, S.P.M. Trasatti, P. Cristiani, M. Bestetti, P. Atanassov. Electroanalysis, 2015, 27(2), 327-335. [4] P. Cristiani, M.L. Carvalho, E. Guerrini, M. Daghio, C. Santoro, B. Li. Bioelectrochemistry, 2013, 92, 6-13. [5] M. Santini, M. Guilizzoni, M. Lorenzi, P. Atanassov, E. Marsili, S. Fest-Santini, P. Cristiani, C. Santoro. Biointerphases. 2015, 10, 031009. Figure 1. Cross Section of the cathode analyzed using microCT. Figure 1

Membrane-Less Microbial Fuel Cell Powering a Smart Phone: A Self-Stratifying Urine Column

The microbial fuel cell (MFC) is a technology in which microorganisms employ an electrode (anode) as a solid electron acceptor for anaerobic respiration. This result in direct transformation of chemical energy into electrical energy, which in turn means that organic wastewater can be used as fuel. Amongst the various organic wastes that are employed as fuel for MFCs, urine is of interest since it represents 75% of the nitrogen present in domestic wastewaters and yet only 1% of the total volume. However, here is a persistent problem for the scaling up of MFCs. The smaller the surface of electrode to volume ratio of an MFC is, the higher its power density is. Hence, to reach usable power levels, a plurality of units needs to be assembled in stack, which implies configuring both the hydraulic circuitry and the serial/parallel electrical connection patterns. Because of this plurality, the units need to have a simple design for the whole system to be cost-effective. The goal of this work is to address how to build these multiple MFCs in stack. We report a novel membrane-less stack design using manifold ceramic plates semi-submerged with anodes and cathodes sharing urine solution. The top half of each plate were semi-submerged were covered in cathodes while the anodes, on the lower half of each plate, were fully submerged. The MFCs in each box were connected in parallel and multiple modules were configured in series and placed. This allowed self-stratification of the collective environment (urine column) under the natural activity of the microbial consortia thriving in the system. For size comparisons, the module footprints were enlarged from 900 mL to 5000 mL and, importantly, this scaling-up did not negatively affect power density (» 19 W/m^3), a factor that has proven an obstacle in previous studies. However, we should note that this observation is limited for the dimensions we tested. This was achieved by maintaining a plurality of microenvironments within the collective system and resulted in a simple, robust system fuelled by urine. The developed system was then used to treat urine of single individual (» 2.5L per 24h), in order to serve as the energy source charging mobile phones. Six boxes, each comprising 20 MFCs connected in parallel, were hydraulically cascaded and connected in series. Best performances were obtained in pulse-feed batch mode. At equilibrium, the stack of six boxes was feed with 600 mL every 6h at a flow rate of 2 L/min and was producing between 110 and 125 mW. Under these conditions, a smart phone (Samsung Galaxy S, battery of 1600 mAh) was fully charged in 68 h and 80 h, when turned off or on respectively. It has to be noted that these performances were stable for a period of 8 months. We concluded that our scaling-up approach within the tested range was successful to convert chemical energy in urine to electricity and this was demonstrated by charging cell phones.

Development of anode zone using dual-anode system to reduce organic matter crossover in membraneless microbial fuel cells

To prevent the occurrence of the organic crossover in membraneless microbial fuel cells (ML-MFCs), dual-anode MFC (DA-MFC) was designed from multi-anode concept to ensure anode zone. The anode zone addressed increase the utilization of organic matter in ML-MFCs, as the result, the organic crossover was prevented and performance of MFCs were enhanced. The maximum power of the DA-MFC was 0.46mW, which is about 1.56 times higher than the ML-MFC (0.29mW). Furthermore, the DA-MFC had advantage in correlation of organic substance concentration and dissolved oxygen concentration, and even electric over-potential. In addition, in terms of cathode fouling, the DA-MFC showed clearer surface. Hence, the anode zone should be considered in the advanced ML-MFC for practically use in wastewater treatment process, and also for scale–up of MFCs.

Evaluation of energy-distribution of a hybrid microbial fuel cell–membrane bioreactor (MFC–MBR) for cost-effective wastewater treatment

A low-cost hybrid system integrating a membrane-less microbial fuel cell (MFC) with an anoxic/oxic membrane bioreactor (MBR) was studied for fouling mitigation. The appended electric field in the MBR was supplied by the MFC with continuous flow. Supernatant from an anaerobic reactor with low dissolved oxygen was used as feed to the MFC in order to enhance its performance compared with that fed with synthetic wastewater. The voltage output of MFC maintained at 0.52±0.02V with 1000Ω resister. The electric field intensity could reach to 0.114Vcm−1. Compared with the conventional MBR (CMBR), the contents rather than the components of foulants on the cake layer of fouled MFC–MBR system was significantly reduced. Although only 0.5% of the feed COD was translated into electricity and applied to MBR, the hybrid system showed great feasibility without additional consumption but extracting energy from waste water and significantly enhancing the membrane filterability.

PTFE effect on the electrocatalysis of the oxygen reduction reaction in membraneless microbial fuel cells

Influence of PTFE in the external Gas Diffusion Layer (GDL) of open-air cathodes applied to membraneless microbial fuel cells (MFCs) is investigated in this work. Electrochemical measurements on cathodes with different PTFE contents (200%, 100%, 80% and 60%) were carried out to characterize cathodic oxygen reduction reaction, to study the reaction kinetics. It is demonstrated that ORR is not under diffusion-limiting conditions in the tested systems. Based on cyclic voltammetry, an increase of the cathodic electrochemical active area took place with the decrease of PTFE content. This was not directly related to MFC productivity, but to the cathode wettability and the biocathode development. Low electrodic interface resistances (from 1 to 1.5Ω at the start, to near 0.1Ω at day 61) indicated a negligible ohmic drop. A decrease of the Tafel slopes from 120 to 80mV during productive periods of MFCs followed the biological activity in the whole MFC system. A high PTFE content in the cathode showed a detrimental effect on the MFC productivity, acting as an inhibitor of ORR electrocatalysis in the triple contact zone.The lowest PTFE content (60%) manifested mechanical instability of the cathode, together with the best performance.

Simultaneous Wastewater Treatment and Power Generation with Innovative Design of an Upflow Membrane-Less Microbial Fuel Cell

The objective of this study was to evaluate the performance of an upflow membrane-less microbial fuel cell (UFML MFC) with various types of carbon material as cathodes in power output and chemical oxygen demand (COD) reduction. The UFML MFC was designed with carbon felt as anode material, and the bioreactor was filled with 0.6-cm diameter of gravel at the anode region. Carbon flake, Pt-loaded carbon paper, and carbon felt were used as cathode electrodes. The voltage output (power density) for the carbon flake cathode and Pt-loaded carbon paper cathode was 384 ± 16 mV (44.4 ± 2.5 mW/m2) and 399 ± 9 mV (44.1 ± 3 mW/m2), respectively. The percentage of COD reduction at the anode region and effluent was above 75 and 85 %, respectively, for all cathode materials. The coulombic efficiency was 15.95, 6.09, and 15.32 % for Pt-loaded carbon paper, carbon felt, and carbon flake, respectively. The result suggests that power generation and COD reduction were influenced by the cathode material. Carbon flake can be considered as a cost-effective cathode material in UFML MFC for future application in real biological wastewater treatment process.

In Field Applications of Single Chamber Membraneless Microbial Fuel Cells (SCMFCs) for Wastewater Treatment, Metal Reduction and Nutrients Removal

In this study, prototypes of SCMFCs were applied or are in process to be applied for real world applications. Particularly, several large surface electrodes MFCs are currently operating in the 32 parallel lines wastewater treatment plant of Nosedo (Milan,Italy). Different chemical and biological conditions led to favorable environment for the development of effective bioanodes and biocathodes in MFCs immersed in the anoxic and aerobic tanks, despite low organic load in the wastewater inlet. The influence of carbon electrode surface extent was preliminary evaluated, showing the possibility of scale-up processes.Another preliminary study is currently in progress in the water of a prealpine meromictic lake (Idro Lake, Italy). The possibility of using bio-electrochemical/electrolyses system for remediating a local pollution will be deployed. The typical presence of the net separation between an aerobic and anaerobic area in the water body makes a meromictic lake affine to a massive MFC. A optimized procedure for the electro-sorption of specific oxide/hydroxide transitional metals (e.g. manganese and other metals and nutrients) on cathodes of MFC systems will be developed for the application in field, as a new innovative strategy for metal pollution remediation.Future applications will be also directed in deploying sediment MFC with anode immersed in the sediments and cathode covered by plants. Based on the preliminary results, a “garden island” will be designed for covering a wetland in order to reduce significantly also the organic load in the pool. Prototype of multi–array MFCs, with an impressive design and style of “little floating garden” will be studied and presented at the International Exposition in Milan 2015.Preliminary experimentations are now devoted to develop and validate electrochemically/chemically activated materials and hierarchically catalyzed surfaces, in collaboration with several different specialists, in order to enhance the performance of cathodes and anodes of the SCMFC tested and decrease operating costs.

Modeling of a membraneless single-chamber microbial fuel cell with molasses as an energy source

Microbial fuel cell (MFC) is a novel bio-electrochemical system that can use various organic substances as energy source. Computational models of MFC are needed for prediction and optimization of the MFC performance. A comprehensive computational modeling of a membraneless single-chamber MFC, in which bacteria consumed molasses as a substrate, is reported here. The simulated cathode had a layer of polytetrafluoroethylene, which allowed oxygen molecules to diffuse through to take part in the reduction reaction. The substrate molecules diffused through the biofilm, which deposited on the anode surface, and were oxidized by the bacteria localized within the film. The simulation program accepted inputs such as the initial amount of molasses, thickness of the biofilm layer, and dimensions of the MFC chamber. Some outputs of the program include concentration profiles of molasses and oxygen as functions of time and location, and the open-circuit voltage of the MFC as a function of time. As the cathode thickness decreased or the biofilm increased, the voltage increased. To obtain a higher voltage, increasing the biofilm thickness was more effective than decreasing the cathode thickness when the initial COD levels were >5,000 mg/L.

Enzymatic Oxygen Micro-Probe for Analysis of Microbial Fuel Cells

Microbial fuel cell (MFC) is an innovative electrochemical biotechnology capable to produce electricity directly from wet marginal biomass and various wastes. Several interests related to this area of science are progressively increasing worldwide [1, 2]. The Single Chamber Microbial Fuel Cell (SCMFC), or rather a membraneless air-cathode MFC configuration, is the most studied MFC system due to simple design and the higher performance. The membrane removal leads to positive effects such as costs reduction, decrease of the MFCs ohmic resistance and as a result enhance the MFC output. Unfortunately, the membrane removal allows the oxygen transport and diffusion into the solution (electrolyte) and it thus lower the anodic performance, which are optimized for strictly anaerobic conditions. In fact, the presence of oxygen in the SCMFC solution affects the biofilm formation and development and disturb severely the biofilm settlement on the electrode.Generally, biofilm action is not limited in a monolayer of bacteria directly in contact with the electrodes, but it needs to be considered as a 3D structure next to the surface, of hundred micrometer thickness. The biofilm is involved (completely or partially) in the electrochemical and chemical processes carring out an effective electron transfer (EET) to/from the electrodes in this three dimensional space [3]. Consequently, the determination of oxygen profiles close to the anode and cathode electrode becomes of fundamental importance. Until now, to the best of our knowledge, no exhaustive studies have been focused on the determination of oxygen profile into the electrolyte of a SCMFC and how the presence of oxygen affects the MFC output.This work aimed to measure the oxygen presence/absence in the different zones inside the SCMFC solution and particularly close to the electrodes surfaces. Accordingly, a “home made” enzymatic oxygen micro-probe based on Bilirubin Oxidase (BOx) enzyme has been designed. The main advantage of utilizing an enzyme is its selectivity towards a specific reaction and in this case BOx is able to catalyze oxygen reduction reaction to water [4]. The advantage of utilizing a micro-probe is the possibility of obtain a precise oxygen measurment inside the SCMFC solution that would permit the optimization of this technology, allowing further cell configuration development for future on-field application. The probe was prepared by immobilization of BOx on modified carbon fiber embaded in plastic body and sealed with epoxy resin (Fig. 2A). The diameter of the sensor, exposed to the electrolyte, was approximatelly 100 μm. This micro-probe was calibrated via Cyclic Voltammetry (CV) using phosphate buffer 50 mM with additional indifferent electrolyte (KCl 100 mM) in different aeration conditions using a typical three electrode electrochemical cell. The reference electrode was an Ag|AgCl electrode and a Pt wire was used as counter electrode. The calibration curve was created by plotting the current at -0.4 V vs Ag|AgCl as a function of the oxygen concentration (Figure 1).The oxygen concentration in the electrolyte during the voltammetry measurements was monitored via DO probe and used for the calibration plot.In order to precisely measure the oxygen content inside the MFCs` electrolyte for localized analysis, a computer controlled stage (Newark System Inc.) was used. The analysis setup is shown at Figure 2B. A Luggin capillary was used during the analysis in order to reduce the ohmic drop. The oxygen concentration was studied both for the anode and cathode biofilm.[1] C. Santoro, Y. Lei, Li, P. Cristiani, Biochemical Engineering J. 2012; 62:8–16[2] W. Li, G. Sheng, X. Liu, H. Yu. Bioresource Technology. 2011; 102: 244–252[3] L. Huang, J.M. Regan, X. Quan, Bioresource Technology, (2011), 102: 316-323[4] S. Brocato, C. Lau, P. Atanassov, Electrochimica Acta. 2012; 61: 44-49

Parameters characterization and optimization of activated carbon (AC) cathodes for microbial fuel cell application.

Activated carbon (AC) is employed as a cost-effective catalyst for cathodic oxygen reduction in microbial fuel cells (MFC). The fabrication protocols of AC-based cathodes are conducted at different applied pressures (175-3500 psi) and treatment temperatures (25-343°C). The effects of those parameters along with changes in the surface morphology and chemistry on the cathode performances are comprehensively examined. The cathodes are tested in a three-electrode setup and explored in single chamber membraneless MFCs (SCMFCs). The results show that the best performance of the AC-based cathode is achieved when a pressure of 1400 psi is applied followed by heat treatment of 150-200°C for 1h. The influence of the applied pressure and the temperature of the heat treatment on the electrodes and SCMFCs is demonstrated as the result of the variation in the transfer resistance, the surface morphology and surface chemistry of the AC-based cathodes tested.

New architecture for modulization of membraneless and single-chambered microbial fuel cell using a bipolar plate-electrode assembly (BEA)

A new architecture for a membraneless and single-chambered microbial fuel cell (MFC) which has a unique bipolar plate-electrode assembly (BEA) design was demonstrated. The maximum power of MFC units connected in series (denoted as a stacked MFC) was up to 22.8±0.13mW/m2 for 0.946±0.003V working voltage, which is 2.5 times higher than the averaged maximum power density of the non-stacked MFC units. The power density in the stacked MFC using BEA was comparable to the stacked MFC using electric wire. These results demonstrate that BEAs having air-exposed cathodes can potentially be used in the stacking of membraneless single-chambered MFCs. In addition, we confirmed that the current in the stacked mode flowed faster than the non-stacked mode due to voltage increase by series connection, and the poorest of the stacked units quickly faced current depletion at higher external resistance than the non-stacked mode, leading to voltage reversal. These results imply that stacked MFC units require a relatively large current capacity in order to prevent high voltage reversal at high current region. To increase total current capacity and prevent voltage reversal of stacked MFC units, we suggested series/parallel-integrated MFC module system for scaling-up. This new concept could likely allow the application of MFC technology to be extended to various wastewater treatment processes or plants.

Performance of continuous flowing membrane-less microbial fuel cell with a new application of acrylic beads separator

The performance of a membrane-less microbial fuel cell (ML-MFC) was evaluated to treat actual domestic wastewater. A novel application of inexpensive acrylic beads was examined to separate the anodic and cathodic compartments. The ML-MFC was alternatively inoculated with activated sludge and anaerobic aged sludge. Results revealed that the removal efficiencies of COD and BOD from actual wastewater were 79 and 60%, respectively, using the activated sludge as inoculum. Higher removal efficiencies up to 81 and 70% were obtained for COD and BOD removal, respectively, in ML-MFC inoculated with anaerobic sludge. Upon changing the inoculum type, a variation of current density and power generation was clearly observed. Within less than four weeks, the system generated a maximum stable current of 55.65 and 67.50 mA/m2 for ML-MFC inoculated with activated sludge and anaerobic aged sludge, respectively. Effect of inoculum type was evaluated under variable external resistance.

The Electrical Properties and Changes on the Substrates of Microbial Fuel Cells Using Excess Sludge

A single-chamber and membrane-less microbial fuel cells (MFC) was successfully started up using anaerobic sludge as inoculums without any nutrient elements for 20 d. Under 30 °C, excess sludge SS was about 21000 mg·L-1, anode area for 31.4 cm2and in 200 mM NaCl concentration agent conditions experiment MFC, while the control device (CD) directly with original sludge anaerobic digestion. The electricity generation of microbial fuel cell and the contrast of substrate changes were investigated. The results show that obtained maximum voltage is 597.3 mV, pH in MFC is slightly higher than in contrast test. Volume reduction in MFC is larger than the controls. Reducing sugar in MFC is lower than that in CDs. Proteins increase at first and then decrease, finally there is no significant difference in both of MFC and CD. Key words: Microbial Fuel Cells, Excess Sludge, Anaerobic Digestion, Reutilization

Design and Fabrication of Membrane Less Microbial Fuel Cell (ML-MFC) using Food Industries Wastewater for Power Generation

Electricity generation from the biodegradable organic substrate can be accompanied by wastewater treatment, which reduces the cost of industrial effluent treatment. In this study, effluent of local food-processing industries was treated in Membrane-Less Microbial Fuel Cell (ML-MFC) for electricity generation. Several investigations were conducted to enhance the current and voltage generation of MFC in different operating conditions, such as direct industrial effluent, adding drainage sludge concentration, aeration in cathode compartment, increasing the electrode area. In addition, COD removing capability of the ML-MFC was also studied. The study documented a maximum power density of 7.11874mW/m2 with the current density of 97.34mA/m2. COD removal was observed 47% to 74% in all experiments. DOI: http://dx.doi.org/10.3329/jce.v27i2.17803 Journal of Chemical Engineering, IEB Vol. ChE. 27, No. 2, December 2012: 55-59

Wastewater treatment and electricity generation by membrane less microbial fuel

Membrane less microbial fuel cell (ML-MFC) is one of the attractive approaches for the simultaneous electricity generation and wastewater treatment. In this present paper, electricity generation by ML-MFC has been studied in continuous mode. Several experiments such as effect of aeration in cathode compartment, sludge concentration, initial substrate concentration and the COD removing capability of the ML-MFC were investigated to maximise the performance. A maximum power density of 8.98mW/m2 was observed at the current density of 34.02 mA/m2. COD removal was detailed from 44% to 54% in all experiments.

Electrochemical Behavior of Stainless Steel Anodes in Membraneless Microbial Fuel Cells

AISI 304 stainless steel was studied as cost-effective tough anodes in membraneless single chamber microbial fuel cells (SCMFCs) fed with wastewater and sodium acetate, and compared with traditional carbon cloth (CC) anodes in terms of power generation, electrochemical properties and corrosion behavior. The performances of anodic materials were evaluated using single electrode potentiodynamic polarization curves and SEM observations. The AISI 304 SS anode showed a more complex interaction between substrate and bacteria than CC anodes under the microaerophilic or anaerobic operative conditions. A strong correlation between anode and cathode productivities was demonstrated, and significantly influenced the power generation of SCMFCs. The central role of bacteria in the processes of oxygen depletion, power generation, and stainless steel corrosion was determined, and a possible rate-determining step was proposed in agreement with recent literature. AISI 304 SS localized corrosion was found only on a part of the anode where oxygen was still present (redox potential (ORP) higher than −300 mV vs. SCE). A completely anaerobic environment prevented stainless steel corrosion, without the pit formation throughout the whole experiments (2 months). These results revealed a potential use of AISI 304 SS as a cost-effective anodic material.

A defined co‐culture of Geobacter sulfurreducens and Escherichia coli in a membrane‐less microbial fuel cell

Wastewater-fed microbial fuel cells (MFCs) are a promising technology to treat low-organic carbon wastewater and recover part of the chemical energy in wastewater as electrical power. However, the interactions between electrochemically active and fermentative microorganisms cannot be easily studied in wastewater-fed MFCs because of their complex microbial communities. Defined co-culture MFCs provide a detailed understanding of such interactions. In this study, we characterize the extracellular metabolites in laboratory-scale membrane-less MFCs inoculated with Geobacter sulfurreducens and Escherichia coli co-culture and compare them with pure culture MFCs. G. sulfurreducens MFCs are sparged to maintain anaerobic conditions, while co-culture MFCs rely on E. coli for oxygen removal. G. sulfurreducens MFCs have a power output of 128 mW m(-2) , compared to 63 mW m(-2) from the co-culture MFCs. Analysis of metabolites shows that succinate production in co-culture MFCs decreases current production by G. sulfurreducens and that the removal of succinate is responsible for the increased current density in the late co-culture MFCs. Interestingly, pH adjustment is not required for co-culture MFCs but a base addition is necessary for E. coli MFCs and cultures in vials. Our results show that defined co-culture MFCs provide clear insights into metabolic interactions among bacteria while maintaining a low operational complexity.

Use of artificial neural network for the prediction of bioelectricity production in a membrane less microbial fuel cell

Microbial fuel cells (MFCs) are the most recent bioelectrical devices which convert biodegradable organic matters to bioelectricity in presence of active biocatalyst. This system can generate electrons (e−) and protons (H+), in which electrons transfer from anode compartment to cathode chamber through an external circuit. MFC architect is one of important factor that effects on MFC performance. In this study, new membrane-less MFC was fabricated. Mixed culture of anaerobic microorganisms was collected from dairy wastewater effluents (Gella, Amol) as active biocatalysts in anode chamber. Initial open circuit voltage was less than 500mV. Maximum open circuit voltage of 750mV was achieved after 95h of operation time. Maximum obtained power density was 80.12mW/m2. Artificial neural network was applied for the prediction of bioelectricity production from glucose as electron donors. Fabricated network was presented by multilayer perceptron and had a good ability for prediction with high correlation coefficient (Raverage-ANN2=0.99).

Simultaneous carbon removal, denitrification and power generation in a membrane-less microbial fuel cell

A membrane-less microbial fuel cell (ML-MFC) was developed to investigate the simultaneous carbon removal and denitrification. The removal rates of 0.64 kg COD m(-3) of liquid cathode volume (LCV) d(-1) and 0.186 g NO3(-)-N m(-3) of LCV d(-1) were achieved, which resulted in the maximal COD and nitrate removal rates of 100% and 36.7%, respectively. The ML-MFC also achieved a maximal power output of 0.0712 W m(-3) of LCV and 0.844 A m(-3) of LCV in approximately 24h. The maximal coulombic efficiency of anode (CEAn) and cathode (CECa) was 5.1% and 475%, respectively. The anodic gas phase was consisted of 77.2±4.0% CH4, 3.9±0.5% CO2, and 3.9±1.5% N2, which indicated that the low anode coulombic efficiency was due to anodic methane production. The results of this study demonstrated the potential application of ML-MFC in simultaneous carbon and nitrogen removal and energy (electricity) production.