Cathodic Electron Acceptor Research Articles

Simultaneous nitrification and denitrification in a novel membrane bioelectrochemical reactor with low membrane fouling tendency.

Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor for electrochemical denitrification, yet there is little knowledge about how to apply them into current wastewater treatment process to achieve efficient nitrogen removal. In this study, two dual-chamber MFCs were integrated with an aerobic membrane bioreactor to construct a novel membrane bioelectrochemical reactor (MBER) for simultaneous nitrification and denitrification under specific aeration. The effects of chemical oxygen demand (COD) loading rate, COD/N ratio, hydraulic retention time (HRT), and external resistance on the system performance were investigated. High effluent quality was obtained in the MBER in terms of COD and ammonium. During the operation, denitrification simultaneously occurred with nitrification at the bio-cathode of the MBER, achieving a maximal nitrogen removal efficiency of 84.3%. A maximum power density of 1.8W/m3 and a current density of 8.5A/m3 were achieved with a coulombic efficiency of 12.1%. Furthermore, compared to the control system, the MBER exhibited lower membrane fouling tendency due to mixed liquor volatile suspended solids (MLVSSs) and extracellular polymeric substance (EPS) reductions, EPSp/EPSc ratio decrease, and particle size increase of the sludge. These results suggest that the MBER holds potential for efficient nitrogen removal, electricity production, and membrane fouling mitigation.

Performance of sodium bromate as cathodic electron acceptor in microbial fuel cell

The potential of using sodium bromate as a cathodic electron acceptor in a microbial fuel cell (MFC) was determined in this study. The effects of sodium bromate concentration and initial catholyte pH on the electricity production of the MFC were investigated. The MFC performance improved with increasing sodium bromate concentration and decreasing catholyte pH. The maximum voltage output (0.538V), power density (1.4908Wm−3), optimal open circuit potential (1.635V), coulombic efficiency (11.1%), exchange current density (0.538Am−3) and charge transfer resistance (4274.1Ω) were obtained at pH 3.0 and 100mM sodium bromate. This work is the first to confirm that sodium bromate could be used as an electron acceptor in MFCs.

Effect of cathode electron acceptors on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell.

The current investigation reports the effect of cathode electron acceptors on simultaneous sulfide and nitrate removal in two-chamber microbial fuel cells (MFCs). Potassium permanganate and potassium ferricyanide were common cathode electron acceptors and evaluated for substrate removal and electricity generation. The abiotic MFCs produced electricity through spontaneous electrochemical oxidation of sulfide. In comparison with abiotic MFC, the biotic MFC showed better ability for simultaneous nitrate and sulfide removal along with electricity generation. Keeping external resistance of 1,000 Ω, both MFCs showed good capacities for substrate removal where nitrogen and sulfate were the main end products. The steady voltage with potassium permanganate electrodes was nearly twice that of with potassium ferricyanide. Cyclic voltammetry curves confirmed that the potassium permanganate had higher catalytic activity than potassium ferricyanide. The potassium permanganate may be a suitable choice as cathode electron acceptor for enhanced electricity generation during simultaneous treatment of sulfide and nitrate in MFCs.

Current status, key challenges and its solutions in the design and development of graphene based ORR catalysts for the microbial fuel cell applications.

Microbial fuel cells (MFC) are considered as the futuristic energy device that generates electricity from the catalytic degradation of biodegradable organic wastes using microbes, which exist in waste water. In MFCs, oxygen serves as a cathodic electron acceptor and oxygen reduction kinetics played a significant role in the determination of overall efficiency. A wide range of strategies have been developed for the preparation and substantial modification of oxygen reduction reaction (ORR) catalysts to improve the maximum volumetric power density of MFCs, in which the efforts on graphene based ORR catalysts are highly imperative. Although numerous research endeavors have been achieved in relation with the graphene based ORR catalysts applicable for MFCs, still their collective summary has not been developed, which hinders the acquirement of adequate knowledge on tuning the specific properties of said catalysts. The intension of this review is to outline the significant role of ORR catalysts, factors influencing the ORR activity, strategies behind the modifications of ORR catalysts and update the research efforts devoted on graphene based ORR catalysts. This review can be considered as a pertinent guide to understand the design and developmental strategies of competent graphene based ORR catalysts, which are not only applicable for MFCs but also for number of electrochemical applications.

Development of bioelectrocatalytic activity stimulates mixed-culture reduction of glycerol in a bioelectrochemical system.

In a microbial bioelectrochemical system (BES), organic substrate such as glycerol can be reductively converted to 1,3-propanediol (1,3-PDO) by a mixed population biofilm growing on the cathode. Here, we show that 1,3-PDO yields positively correlated to the electrons supplied, increasing from 0.27 ± 0.13 to 0.57 ± 0.09 mol PDO mol−1 glycerol when the cathodic current switched from 1 A m−2 to 10 A m−2. Electrochemical measurements with linear sweep voltammetry (LSV) demonstrated that the biofilm was bioelectrocatalytically active and that the cathodic current was greatly enhanced only in the presence of both biofilm and glycerol, with an onset potential of −0.46 V. This indicates that glycerol or its degradation products effectively served as cathodic electron acceptor. During long-term operation (> 150 days), however, the yield decreased gradually to 0.13 ± 0.02 mol PDO mol−1 glycerol, and the current–product correlation disappeared. The onset potentials for cathodic current decreased to −0.58 V in the LSV tests at this stage, irrespective of the presence or absence of glycerol, with electrons from the cathode almost exclusively used for hydrogen evolution (accounted for 99.9% and 89.5% of the electrons transferred at glycerol and glycerol-free conditions respectively). Community analysis evidenced a decreasing relative abundance of Citrobacter in the biofilm, indicating a community succession leading to cathode independent processes relative to the glycerol. It is thus shown here that in processes where substrate conversion can occur independently of the electrode, electroactive microorganisms can be outcompeted and effectively disconnected from the substrate.

Enhancing waste activated sludge digestion and power production using hypochlorite as catholyte in clayware microbial fuel cell

Waste activated sludge was digested in anodic compartment of dual chambered clayware microbial fuel cell (MFC). Performance of MFC was evaluated using oxygen (MFC-1) and hypochlorite (MFC-2) as cathodic electron acceptors. Power production of 8.7W/m3 was achieved using hypochlorite as catholyte, which was two times higher than using oxygen (4.2W/m3). Total chemical oxygen demand of sludge was reduced by 65.4% and 84.7% in MFC-1 and MFC-2, respectively. Total and volatile suspended solids reductions were higher in MFC-2 (75.8% and 80.2%, respectively) as compared to MFC-1 (66.7% and 76.4%, respectively). Use of hypochlorite demonstrated 3.8 times higher Coulombic efficiency (13.8%) than oxygen. Voltammetric and impedance analysis revealed increase in reduction peak (from 8 to 24mA) and decreased polarization resistance (from 42.6 to 26.5Ω). Hypochlorite proved to be better cathodic electron acceptor, supporting rapid sludge digestion within 8days of retention time and improved power production in MFC.

Biomass-electrochemical integrated system for distillery wastewater treatment with electricity generation using anaerobic mixed consortium in microbial fuel cells

The electricity generation and industrial wastewater treatment using microbial fuel cells (MFCs) with primary treated distillery wastewater as substrate and permanganate as cathodic electron acceptor was studied. Initially, low voltage (0.625 V) and current (2.9 mA) were obtained at a substrate loading of 2,680 mg COD l−1 and further increased (1.165 V and 5.40 mA) at 4,360 mg COD l−1 with the provided larger anode surface area and the cathode electron acceptor. As a wastewater treatment, 85% COD was removed at a 2,680 mg COD l−1, whereas at 4,360 mg COD l−1 57% of COD removal was observed. During electrochemical oxidation, 24.3% and 36% of melanoidins decolourisation with 41.8% and 31% of coulombic efficiency were also achieved at 2,680 mg COD l−1 and 4360 mg COD l−1 due to the biocatalytic activity of mixed bacterial consortium. This study shows the capability of MFC system to treat the high-organic load as well as generation of energy using biocatalytic oxidation.

Self-Driven Bioelectrochemical Mineralization of Azobenzene by Coupling Cathodic Reduction with Anodic Intermediate Oxidation

Bioelectrochemical systems have been intensively studied as a promising technology for wastewater treatment and environment remediation. Coupling of the anodic and cathodic electrochemical reactions allows an enhanced degradation of recalcitrant organics, but external power supply is usually needed to overcome the thermodynamic barrier. In this work, we report a self-driven degradation of azobenzene in a microbial fuel cell (MFC), where the cathodic reduction of azobenzene was effectively coupled with the anodic oxidation of its reduction degradation intermediate (i.e., aniline). The anodic degradation rate of aniline, as the sole carbon source, was significantly higher than that under open-circuit conditions, suggesting a considerable bioelectrochemical oxidation of aniline. Output voltages up to 8mV were obtained in the MFC. However, a shift of cathodic electron acceptor from oxygen to azobenzene resulted in a decreased aniline degradation rate and output voltage. The present work may provide valuable implications for development of sustainable bioelectrochemical technologies for environmental remediation.

Electricity generation from tetrathionate in microbial fuel cells by acidophiles

Inorganic sulfur compounds, such as tetrathionate, are often present in mining process and waste waters. The biodegradation of tetrathionate was studied under acidic conditions in aerobic batch cultivations and in anaerobic anodes of two-chamber flow-through microbial fuel cells (MFCs). All four cultures originating from biohydrometallurgical process waters from multimetal ore heap bioleaching oxidized tetrathionate aerobically at pH below 3 with sulfate as the main soluble metabolite. In addition, all cultures generated electricity from tetrathionate in MFCs at pH below 2.5 with ferric iron as the terminal cathodic electron acceptor. The maximum current and power densities during MFC operation and in the performance analysis were 79.6mAm−2 and 13.9mWm−2 and 433mAm−2 and 17.6mWm−2, respectively. However, the low coulombic efficiency (below 5%) indicates that most of the electrons were directed to other processes, such as aerobic oxidation of tetrathionate and unmeasured intermediates. The microbial community analysis revealed that the dominant species both in the anolyte and on the anode electrode surface of the MFCs were Acidithiobacillus spp. and Ferroplasma spp. This study provides a proof of concept that tetrathionate serves as electron donor for biological electricity production in the pH range of 1.2–2.5.

Simultaneous electricity generation and pollutant removal in microbial fuel cell with denitrifying biocathode over nitrite

The influences of hydraulic retention time, temperature and free buffer on the performance of short-cut denitrifying microbial fuel cell were investigated after it was successfully started up using nitrite as the cathodic electron acceptor. The results revealed that a power density of 8.3±0.5Wm−3NC was obtained after 15days operation. The desirable hydraulic retention time was found in this study to be 8h, with a COD removal rate of 2.117±0.006kgm−3NCd−1 and a total nitrogen removal rate of 0.041±0.002kgm−3NCd−1, respectively. It demonstrated that temperature had different effects on the electricity generation and pollutant removal performance of microbial fuel cell. The suitable temperature for power generation and pollutant removal was found to be 20°C and 25°C, respectively. Free buffer led to 50% decrease of both total nitrogen removal rate and power density of microbial fuel cell compared to that with phosphate buffer solution addition. The optimal total nitrogen removal rate obtained in the case with sodium azide addition (0.075±0.008kgm−3NCd−1) increased by 50% as compared to that without sodium azide addition. It suggested that abolishing oxygen or inhibiting nitrite oxidizing bacteria would favor nitrogen removal.

Comparison of oxygen and hypochlorite as cathodic electron acceptor in microbial fuel cells

Effect of oxygen and sodium hypochlorite (NaOCl) as cathodic electron acceptors on performance of a clayware microbial fuel cell (MFC) was evaluated in this study. Maximum power density of 6.57 W/m(3) was obtained with NaOCl as catholyte, which is about 9 times higher than oxygen being used as an electron acceptor. Voltammetry and Tafel analysis further supported the faster reduction kinetics lead to increase in power output and reduction in internal resistance of MFC operated with NaOCl as an electron acceptor. Using NaOCl as catholyte, higher exchange current density of 10.91 and 11.52 mA/m(2) and lower charge transfer resistance of 0.58 and 0.56 kΩ m(2) was observed for anode and cathode, respectively. Higher organic matter removal of about 90% with 25% Coulombic efficiency was achieved using NaOCl as catholyte. Higher internal resistance, lower cathode potential and slow reduction kinetics deteriorated performance of MFC using oxygen as cathodic electron acceptor.

Effects of temperature and ferrous sulfate concentrations on the performance of microbial fuel cell

The two-chambered microbial fuel cell (MFC) was operated in a batch mode, using enriched hydrogen-producing mixed bacteria as the anodic inoculum, artificial sucrose wastewater as the substrate (sucrose concentration 10.0 g/L) and potassium ferricyanide as cathodic electron acceptor. The performance of the MFC was analyzed under five different temperatures of 40, 35, 25, 20, and 15 °C, respectively. The microbial fuel cells (MFCs) which were operated at high operating temperatures (35 and 40 °C) had greater power generation than the other MFCs at start-up. However, only the MFC operated at 35 °C exhibiting stable and high power output over a long period. As for the effect of ferrous sulfate concentration on performance of the MFC, ferrous sulfate had efficiently accelerated influence on power generation during the initial operation period (0–9 d), but had inhibitive influence on power generation after 9 days of operation when the concentration increment of 50–400 mg/L in anolyte. The maximum increase was observed at the concentration increment of 50 mg/L in anolyte.

Effects of cathodic electron acceptors and potassium ferricyanide concentrations on the performance of microbial fuel cell

The effects of different cathodic electron acceptors and potassium ferricyanide concentrations on performance of a two-chambered microbial fuel cell (MFC) were studied. The MFC was operated in a batch mode, using enriched hydrogen-producing mixed bacteria as the anodic inoculum and artificial sucrose wastewater as the substrate. To find out the excellent electron acceptor for the two-chambered MFC, three MFCs using potassium ferricyanide catholyte sparged with air (M1), aerated catholyte (M2) and potassium ferricyanide catholyte (M3) were operated separately to elucidate the difference in power generation under similar anodic operating conditions (sucrose concentration 10.0 g/L). The results show that the power generation in M3 was slightly higher than that in M1, while both were much higher than that in M2. The effect of potassium ferricyanide concentrations in catholyte (pH 7.0, 100 mM phosphate buffer solution) on electricity generation characteristics was studied under constant anodic operational conditions. The maximum resultant MFC output power density (181.48 mW/m3) was produced using a potassium ferricyanide concentration of 0.1 M in the catholyte.

Enhanced electricity generation from whey wastewater using combinational cathodic electron acceptor in a two-chamber microbial fuel cell

While energy consumption is increasing worldwide due to population growth, the fossil fuels are unstable and exhaustible resources for establishing sustainable life. Using biodegradable compounds present in the wastewater produced in industrial process as a renewable source is an enchanting approach followed by scientists for maintaining a sustainable energy production to vanquish this problem for ulterior generations. In this research, bioelectricity generation with whey degradation was investigated in a two-chamber microbial fuel cell with humic acid as anodic electron mediator and a cathode compartment including combinational electron acceptor. Escherichia coli was able to use the carbohydrate originated from whey to generate bioelectricity. The open-circuit potential in absence of mediator was 751.5 mV at room temperature. The voltage was stable for more than 24 h. Humic acid was used as a suitable mediator. In addition, some mixed chemicals were employed as catholyte. Based on polarization curve, the power and current values in the presence of a mixed solution of potassium iodide (KI), ferric chloride [FeCl3 (Ш)] and manganese chloride tetrahydride (MnCl2·4H2O) with doubling of oxidant (oxygen) concentration using agitation with magnet stirrer in cathode compartment without any buffer solution were boosted to 562.9 μW and 1906.1 μA, respectively, and demonstrated the best result for power generation.

Light Fuel Cell (LFC): A Novel Device for Interpretation of Microorganisms-Involved Mineral Photochemical Process

Geophotocatalysis of natural semiconducting minerals plays key roles in driving redox reactions on the earth's surface. Whether it is related to microbial metabolism remains unknown. This study proposed a novel device, light fuel cell (LFC) to investigate a new aspect of microbe-mineral interactive pathway involved by both microorganisms and semiconducting minerals. When using O2 as the cathodic electron acceptor, the volumetric power density of a LFC with a microbial anode and a visible light-irradiated rutile-cathode was 12.1 W/m3, 1.6 times higher than that obtained in the dark (7.5 W/m3). Electrochemical impedance spectroscopy (EIS) data indicated that the cathodic polarization resistance of the LFC in light was 196 Ω, while that operated in the dark was 2820 Ω. These results manifested the bio-photo-electrochemically interactive pathway between the microorganisms and semiconducting minerals, in which the semiconductor photocatalysis significantly improved the electron transfer efficiency. A thorough investigation was then performed on a LFC to evaluate the parameters such as catholyte pH, electron acceptor concentration, equipment configuration, electrode preparation method and the type of semiconducting minerals that affected its performance. The results reported in this study showed that further improvements of LFCs with the special purpose of minimizing ohmic resistances, maximizing solar to chemical energy conversion efficiency and enhancing the rates of photocatalytic reaction, will finally lead to potential applications of LFCs in wastewater treatment.

Simultaneous reduction of vanadium (V) and chromium (VI) with enhanced energy recovery based on microbial fuel cell technology

Vanadium (V) and chromium (VI) are the main metals found in vanadium containing wastewater with large amount and great toxicity. In present study, reduction of V(V) and Cr(VI) together with electricity generation is successfully achieved in double chamber microbial fuel cells (MFCs) by employing vanadium containing wastewater as the cathodic electron acceptor. The V(V) and Cr(VI) reduction efficiencies for 240h operation approach up to 67.9±3.1% and 75.4±1.9%, respectively, with a maximum power density of 970.2±20.6mWm−2. The power output is enhanced, compared with the results from MFCs with V(V) as the sole electron acceptor, while the decrease of the cathode efficiency caused by deposits from Cr(VI) reduction process can also be mitigated. After reduction, chromium is mainly deposited on the cathode surface in the form of Cr(III), while most of vanadium can be precipitated from the exhausted catholyte by adjusting pH, thus treating vanadium containing wastewater successfully with energy harvest based on MFC technology. The operating principles of MFCs with two different electron acceptors are also reported for the first time.

Biocathodic Nitrous Oxide Removal in Bioelectrochemical Systems

Anthropogenic nitrous oxide (N(2)O) emissions represent up to 40% of the global N(2)O emission and are constantly increasing. Mitigation of these emissions is warranted since N(2)O is a strong greenhouse gas and important ozone-depleting compound. Until now, only physicochemical technologies have been applied to mitigate point sources of N(2)O, and no biological treatment technology has been developed so far. In this study, a bioelectrochemical system (BES) with an autotrophic denitrifying biocathode was considered for the removal of N(2)O. The high N(2)O removal rates obtained ranged between 0.76 and 1.83 kg N m(-3) net cathodic compartment (NCC) d(-1) and were proportional to the current production, resulting in cathodic coulombic efficiencies near 100%. Furthermore, our experiments suggested the active involvement of microorganisms as the catalyst for the reduction of N(2)O to N(2), and the optimal cathode potential ranged from -200 to 0 mV vs standard hydrogen electrode (SHE) in order to obtain high conversion rates. Successful operation of the system for more than 115 days with N(2)O as the sole cathodic electron acceptor strongly indicated that N(2)O respiration yielded enough energy to maintain the biological process. To our knowledge, this study provides for the first time proof of concept of biocathodic N(2)O removal at long-term without the need for high temperatures and expensive catalysts.

Electrochemical analysis of Clostridium propionicum and its acrylic acid production in microbial fuel cells

AbstractCurrently, acrylic acid is produced at a low yield by the resting cells of Clostridium propionicum with the supplement of extra electron acceptors. As an alternative way, acrylic acid production coupled with electricity generation was achieved by C. propionicum‐based microbial fuel cells (MFCs). Electricity was generated in the salt‐bridge MFCs with cysteine and resazurin in the anode chamber as mediators, and K3Fe(CN)6 as the cathode electron acceptor. Power generation was 21.78 mW/m2 with an internal resistance of 9809 Ω. Cyclic voltammograms indicated the main mechanism of power production was the electron transfer facilitated by mediators in the system. In the salt‐bridge MFC system, 0.694 mM acrylic acid was produced together with electricity generation.

Effect of the cathode/anode ratio and the choice of cathode catalyst on the performance of microbial fuel cell transducers for the determination of microbial activity

Microbial activity can be measured using sensors based on microbial fuel cell technology. In these sensors, microorganisms in contact with the anode generate a current proportional to their metabolic activity. Proper operation of such a device requires that activity at the anode is not impaired by the ability of the cathode to transfer current to the cathodic electron acceptor. Therefore, we have determined the minimum cathode to anode ratio required for unhindered performance of the microbial fuel cell. Our results indicate that for the same level of biological activity, the optimal cathode/anode ratios depend on the type of cathode being used. Thus, while carbon paper/ferricyanide cathodes require ratios of 4, platinum cathodes need much higher ratios of about 27. Cyclic voltammetry measurements indicate that platinum cathodes have a much slower dynamic behaviour than cathodes based on carbon paper/ferricyanide. While these results indicate that carbon paper/ferricyanide cathodes provide the most current for the same cathode area, extended experiments carried over a period of several days indicate a progressive degradation of fuel cell performance in cells using iron catalysts. Overall, our conclusion is that soluble iron-based catalysts provide much higher power output than solid phase platinum catalysts, but at the expense of a reduced life span which limits their use for applications requiring extended operation.

Performance of a batch two‐chambered microbial fuel cell operated at different anode potentials

AbstractBACKGROUND: For a microbial fuel cell (MFC), the anode potential is an important electrochemical parameter for the growth, electron distribution and electrical activity of exoelectrogenic bacteria.RESULTS: The performance of a batch‐flow two‐chambered MFC was investigated operated at anode potentials of − 400, − 200, 0, + 200 and + 400 mV versus Ag/AgCl reference electrode. Glucose was used as substrate and ferricyanide as cathodic electron acceptor. At potentials from − 400 to + 200 mV, increasing maximum current outputs were obtained, ranging from 6.0 to 8.6 mA. However, the maximum current output decreased to 6.9 mA when the anode potential was further increased to + 400 mV. More positive potentials resulted in higher Coulombic efficiencies (CEs), with values increased from 64% (−400 mV) to 88% (+400 mV). Electrons deposited as H2 and CH4 resulted in lower CEs at more negative potentials (−400, − 200 and 0 mV). When + 400 mV was applied to the anode, the growth yield dropped from 0.25 ± 0.05 to 0.11 mol biomass mol−1 COD (chemical oxygen demand) with inhibition of electrical activity.CONCLUSIONS: The most positive anode potential reduced growth yield and inhibited bacterial growth, but electrical activity increased for potentials ranged from − 400 to + 200 mV. When the potential was increased to + 400 mV, growth yield was limited, affecting MFC performance. Copyright © 2011 Society of Chemical Industry