Simultaneous carbon and nitrogen removal using an oxic/anoxic-biocathode microbial fuel cells coupled system

A coupled microbial fuel cell (MFC) system comprising of an oxic-biocathode MFC (O-MFC) and an anoxic-biocathode MFC (A-MFC) was implemented for simultaneous removal of carbon and nitrogen from a synthetic wastewater. The chemical oxygen demand (COD) of the influent was mainly reduced at the anodes of the two MFCs; ammonium was oxidized to nitrate in the O-MFC’s cathode, and nitrate was electrochemically denitrified in the A-MFC’s cathode. The coupled MFC system reached power densities of 14 W/m³ net cathodic compartment (NCC) and 7.2 W/m³ NCC for the O-MFC and the A-MFC, respectively. In addition, the MFC system obtained a maximum COD, NH₄⁺-N and TN removal rate of 98.8%, 97.4% and 97.3%, respectively, at an A-MFC external resistance of 5 Ω, a recirculation ratio (recirculated flow to total influent flow) of 2:1, and an influent flow ratio (O-MFC anode flow to A-MFC anode flow) of 1:1.     

Bioelectricity generation enhancement in a dual chamber microbial fuel cell under cathodic enzyme catalyzed dye decolorization

Enzymatic decolorization of reactive blue 221 (RB221) using laccase was investigated in a dual-chamber microbial fuel cell (MFC). Suspended laccase was used in the cathode chamber in the absence of any mediators in order to decolorize RB221 and also improve oxygen reduction reaction in the cathode. Molasses was utilized as low cost and high strength energy source in the anode chamber. The capability of MFC for simultaneous molasses and dye removal was investigated. A decolorization efficiency of 87% was achieved in the cathode chamber and 84% COD removal for molasses was observed in the anode chamber. Laccase could catalyze the removal of RB221 and had positive effect on MFC performance as well. Maximum power density increased about 30% when enzymatic decolorization was performed in the cathode chamber.     

Simultaneous carbon and nitrogen removal from piggery wastewater using loop configuration microbial fuel cell

Simultaneous carbon and nitrogen removal using loop configuration microbial fuel cell (MFC) with relatively large size of 5 L was investigated in this study. Four MFC reactors were constructed with a loop configuration to eliminate the pH gradient, and the reactor performance was examined with different separators and cathode materials. The performance of the reactors in terms of electricity generation and contaminant removal rate was examined. Results showed that a maximum power density of 1415.6 mW/m³ (The empty bed volume of anode chamber) was obtained at a current density of 3258.5 mA/m³ with cation exchange membrane as separator and graphite felt (Pt coated) as cathode using the piggery wastewater as feed, and the organic removal rate obtained was approximately 0.523 kg COD/m³/d (total anode chamber) with nitrogen removal rate of 0.194 kg N/m³/d (total cathode chamber).     

A membrane-free baffled microbial fuel cell for cathodic reduction of Cu(II) with electricity generation

A membrane-free baffled microbial fuel cell (MFC) was developed to treat synthetic Cu(II) sulfate containing wastewater in cathode chamber and synthetic glucose-containing wastewater fed to anode chamber. Maximum power density of 314 mW/m³ with columbic efficiency of 5.3% was obtained using initial Cu²⁺ concentration of 6400 mg/L. Higher current density favored the cathodic reduction of Cu²⁺, and removal of Cu²⁺ by 70% was observed within 144 h using initial concentration of 500 mg/L. Powder X-ray diffraction (XRD) analysis indicated that the Cu²⁺ was reduced to Cu₂O or Cu₂O plus Cu which deposited on the cathode, and the deficient cathodic reducibility resulted in the formation of Cu₄(OH)₆SO₄ at high initial Cu²⁺ concentration (500-6400 mg/L). This study suggested a novel low-cost approach to remove and recover Cu(II) from Cu²⁺-containing wastewater using MFC-type reactor.     

Enhanced wastewater treatment efficiency through microbially catalyzed oxidation and reduction: synergistic effect of biocathode microenvironment

Microbially catalyzed treatment of wastewater was evaluated in both the anode and cathode chambers in dual chambered microbial fuel cell (MFC) under varying biocathode microenvironment. MFC operation with aerobic biocathode showed significant increment in both TDS (cathode, 90.2±1%; anode, 39.7±0.5%) and substrate (cathode, 98.07±0.06%; anode, 96.2±0.3%) removal compared to anaerobic biocathode and abiotic cathode operations (COD, 80.25±0.3%; TDS, 30.5±1.2%). Microbially catalyzed reduction of protons and electrons at cathode will be higher during aerobic biocathode operation which leads to gradual substrate removal resulting in stable bio-potential for longer periods facilitating salts removal. Bio-electro catalytic behavior showed higher exchange current density during aerobic biocathode operation resulting in induced electrochemical oxidation which supports the enhanced treatment. Anaerobic biocathode operation depicted relatively less TDS removal (anode, 16.35%; cathode, 16.04%) in both the chambers in spite of good substrate degradation (anode, 84%; cathode, 87.39%). Both the chambers during anaerobic biocathode operation competed as electron donors resulting in negligible bio-potential development.     

Treatment of Process Water Containing Heavy Metals with a Two‐Stage Electrolysis Procedure in a Membrane Electrolysis Cell

The capability of a two‐stage electrochemical treatment for the regeneration of acidic heavy‐metal containing process water was examined. The process water came from sediment bioleaching and was characterized by a wide spectrum of dissolved metals, a high sulfate content, and a pH of about 3. In the modular laboratory model cell used, the anode chamber and the cathode chamber were separated by a central chamber fitted with an ion exchanger membrane on either side. The experiments were carried out applying a platinum anode and a graphite cathode at a current density of 0.1 A/cm². The circulation flow of the process water in the batch process amounted to 35 L/h, the electrolysis duration was 5.5 h at maximum and the total electrolysis current was about 1 A. In the first stage, the acidic process water containing metals passed through the cathode chamber. In the second stage, the cathodically pretreated process water was electrolyzed anodically. In the cathode chamber the main load of dissolved Cu, Zn, Cr and Pb was eliminated. The sulfuric acid surplus of 3–4 g/L decreased to about 1 g/L, the pH rose from initially 3.0 to 4–5, but the desired pH of 9–10 was not achieved. Precipitation in the proximity to the cathode evidently takes place at a higher pH than farther away. The dominant process in the anode chamber was the precipitation of amorphous MnO₂ owing to the oxidation of dissolved Mn(II). The further depletion of the remaining heavy metals in the cathodically pretreated process water by subsequent anodic treatment was nearly exhaustive, more than 99 % of Cd, Cr, Cu, Mn, Ni, Pb, and Zn were removed from the leachate. The high depletion of heavy metals might be due to both the sorption on MnO₂ precipitates and/or basic ferrous sulfate formed anodically, and the migration of metal ions through the cation exchanger membrane via the middle chamber into the cathode chamber. In the anode chamber, the sulfuric acid content increased to 6–7 g/L and the pH sank to 1.7. All heavy metals contained, with the exception of Zn, were removed to levels below the German limits for discharging industrial wastewaters into the receiving water. Moreover, the metal‐depleted and acid‐enriched process waters could be returned to the leaching process, hence reducing the output of wastewater. The results indicated that heavy metals could be removed from acidic process waters by two‐stage electrochemical treatment to a large extent. However, to improve the efficiency of metal removal and to establish the electrochemical treatment in practice, further work is necessary to optimize the operation of the process with respect to current density, energy consumption, discharging of metal precipitates deposited in the electrode chambers and preventing membrane clogging.     

Bioelectricity generation using two chamber microbial fuel cell treating wastewater from food processing

Electricity generation from microbial fuel cells which treat food processing wastewater was investigated in this study. Anaerobic anode and aerobic cathode chambers were separated by a proton exchange membrane in a two-compartment MFC reactor. Buffer solutions and food industry wastewater were used as electrolytes in the anode and cathode chambers, respectively. The produced voltage and current intensity were measured using a digital multimeter. Effluents from the anode compartment were tested for COD, BOD₅, NH₃, P, TSS, VSS, SO₄ and alkalinity. The maximum current density and power production were measured 527 mA/m² and 230 mW/m² in the anode area, respectively, at operation organic loading (OLR) of 0.364 g COD/l.d. At OLR of 0.182 g COD/l.d, maximum voltage and columbic efficiency production were recorded 0.475 V and 21%, respectively. Maximum removal efficiency of COD, BOD₅, NH₃, P, TSS, VSS, SO₄ and alkalinity were 86, 79, 73, 18, 68, 62, 30 and 58%, respectively. The results indicated that catalysts and mediator-less microbial fuel cells (CAML-MFC) can be considered as a better choice for simple and complete energy conversion from the wastewater of such industries and also this could be considered as a new method to offset wastewater treatment plant operating costs.     

Oxygen availability effect on the performance of air‐breathing cathode microbial fuel cell

The effect of the oxygen availability over the performance of an air‐breathing microbial fuel cell (MFC) was studied by limiting the oxygen supply to the cathode. It was found that anodic reaction was the limiting stage in the performance of the MFC while oxygen was fully available at cathode. As the cathode was depleted of oxygen, the current density becomes limited by oxygen transport to the electrode surface. The exerted current density was maintained when oxygen mole fraction was higher than 10% due to the very good performance of the cathodic catalysts. However, the current density drastically falls when working at lower concentrations because of mass transfer limitations. In this sense it must be highlighted that the maximum exerted power, when oxygen mole fraction was higher than 10%, was almost three times higher than that obtained when oxygen mole fraction was 5%. Regarding to the wastewater treatment, a significant decrease in the COD removal was obtained when the MFC performance was reduced due to the limited availability of oxygen, which indicates the significant role of the electrogenic microorganisms in the COD removal in MFC. In addition, the low availability of oxygen at the cathode leads to a lower presence of oxygen at the anode, resulting in an increase in the coulombic efficiency. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:900–907, 2015     

In-situ Cr(VI) reduction with electrogenerated hydrogen peroxide driven by iron-reducing bacteria

Cr(VI) was reduced in-situ at a carbon felt cathode in an air-cathode dual-chamber microbial fuel cell (MFC). The reduction of Cr(VI) was proven to be strongly associated with the electrogenerated H₂O₂ at the cathode driven by iron-reducing bacteria. At pH 2.0, only 42.5% of Cr(VI) was reduced after 12 h in the nitrogen-bubbling-cathode MFC, while complete reduction of Cr(VI) was achieved in 4 h in the air-bubbling-cathode MFC in which the reduction of oxygen to H₂O₂ was confirmed. Conditions that affected the efficiency of the reduction of Cr(VI) were evaluated experimentally, including the cathodic electrolyte pH, the type of iron-reducing species, and the addition of redox mediators. The results showed that the efficient reduction of Cr(VI) could be achieved with an air-bubbling-cathode MFC.     

Electricity generation using chocolate industry wastewater and its treatment in activated sludge based microbial fuel cell and analysis of developed microbial community in the anode chamber

Feasibility of using chocolate industry wastewater as a substrate for electricity generation using activated sludge as a source of microorganisms was investigated in two-chambered microbial fuel cell. The maximum current generated with membrane and salt bridge MFCs was 3.02 and 2.3 A/m², respectively, at 100 Ω external resistance, whereas the maximum current generated in glucose powered MFC was 3.1 A/m². The use of chocolate industry wastewater in cathode chamber was promising with 4.1 mA current output. Significant reduction in COD, BOD, total solids and total dissolved solids of wastewater by 75%, 65%, 68%, 50%, respectively, indicated effective wastewater treatment in batch experiments. The 16S rDNA analysis of anode biofilm and suspended cells revealed predominance of β-Proteobacteria clones with 50.6% followed by unclassified bacteria (9.9%), α-Proteobacteria (9.1%), other Proteobacteria (9%), Planctomycetes (5.8%), Firmicutes (4.9%), Nitrospora (3.3%), Spirochaetes (3.3%), Bacteroides (2.4%) and γ-Proteobacteria (0.8%). Diverse bacterial groups represented as members of the anode chamber community.     

A novel configuration of microbial fuel cell stack bridged internally through an extra cation exchange membrane

This paper reports a novel configuration of stacked microbial fuel cells (MFCs) bridged internally through an extra cation exchange membrane (CEM). The MFC stack (MFC_stack), assembled from two single MFCs (MFC_single), resulted in double voltage output and half optimal external resistance. COD removal rate was increased from 32.4% to 54.5%. The performance improvement could be attributed to the smaller internal resistance and enhanced cations transfer. A result from a half cell study further confirmed the important role of the extra CEM. This study also demonstrated MFCs where the anode and cathode were sandwiched between two CEMs possessed significantly high power outputs     

Air-cathode structure optimization in separator-coupled microbial fuel cells

Microbial fuel cells (MFC) with 30% wet-proofed air cathodes have previously been optimized to have 4 diffusion layers (DLs) in order to limit oxygen transfer into the anode chamber and optimize performance. Newer MFC designs that allow close electrode spacing have a separator that can also reduce oxygen transfer into the anode chamber, and there are many types of carbon wet-proofed materials available. Additional analysis of conditions that optimize performance is therefore needed for separator-coupled MFCs in terms of the number of DLs and the percent of wet proofing used for the cathode. The number of DLs on a 50% wet-proofed carbon cloth cathode significantly affected MFC performance, with the maximum power density decreasing from 1427 to 855 mW/m² for 1–4 DLs. A commonly used cathode (30% wet-proofed, 4 DLs) produced a maximum power density (988 mW/m²) that was 31% less than that produced by the 50% wet-proofed cathode (1 DL). It was shown that the cathode performance with different materials and numbers of DLs was directly related to conditions that increased oxygen transfer. The coulombic efficiency (CE) was more affected by the current density than the oxygen transfer coefficient for the cathode. MFCs with the 50% wet-proofed cathode (2 DLs) had a CE of >84% (6.8 A/m²), which was substantially larger than that previously obtained using carbon cloth air-cathodes lacking separators. These results demonstrate that MFCs constructed with separators should have the minimum number of DLs that prevent water leakage and maximize oxygen transfer to the cathode.     

Long-term operation of double chambered microbial fuel cell for bio-electro denitrification

The main aim of this study is to investigate the performance of organic oxidation and denitrification of the system under long-term operation. The MFC reactor was operated in continuous mode for 180 days. Nitrate was successfully demonstrated as terminal electron acceptor, where nitrate was reduced at the cathode using electron provided by acetate oxidation at the anode. The removal efficiencies of chemical oxygen demand (COD) and nitrate were higher in the closed circuit system than in open circuit system. Both COD and nitrate reduction improved with the increase of organic loading and subsequently contributed to higher power output. The maximum nitrate removal efficiency was 88 ± 4 % (influent of 141 ± 14 mg/L). The internal resistant was 50 Ω, which was found to be low for a double chambered MFC. The maximum power density was 669 mW/m³ with current density of 3487 mA/m³.     

Comparison of membrane- and cloth-cathode assembly for scalable microbial fuel cells: Construction,performance and cost

The aim of this study is to compare the performance of different membrane cathode assembly (MCA) and cloth-cathode assembly (CCA) in air-chamber microbial fuel cells (MFCs) and provide an optimum cathode configuration for MFC scaling up. Two MCAs were prepared by hot-pressing carbon cloth containing cathodic catalyst to anion exchange membrane (AEM) and cation exchange membrane (CEM), respectively. A CCA was built by coating GORE-TEX^® cloth with a mixture of nickel-based conductive paint and cathodic catalyst. Under the fed-batch mode using brewery wastewater, the MFCs were compared with respect to power production, coulombic efficiency, COD removal, internal resistance and material cost. The experimental results show that CCA is a more favorable alternative than MCAs due to its easier preparation, higher maximum power density and COD removal, and lower internal resistance and cost. The optimum cathode assembly of CCA is cost-effective and mechanically robust enough to meet the important requirements for MFC scalability.     

Analysis of ammonia loss mechanisms in microbial fuel cells treating animal wastewater

Ammonia losses during swine wastewater treatment were examined using single- and two-chambered microbial fuel cells (MFCs). Ammonia removal was 60% over 5 days for a single-chamber MFC with the cathode exposed to air (air-cathode), versus 69% over 13 days from the anode chamber in a two-chamber MFC with a ferricyanide catholyte. In both types of systems, ammonia losses were accelerated with electricity generation. For the air-cathode system, our results suggest that nitrogen losses during electricity generation were increased due to ammonia volatilization with conversion of ammonium ion to the more volatile ammonia species as a result of an elevated pH near the cathode (where protons are consumed). This loss mechanism was supported by abiotic tests (applied voltage of 1.1 V). In a two-chamber MFC, nitrogen losses were primarily due to ammonium ion diffusion through the membrane connecting the anode and cathode chambers. This loss was higher with electricity generation as the rate of ammonium transport was increased by charge transfer across the membrane. Ammonia was not found to be used as a substrate for electricity generation, as intermittent ammonia injections did not produce power. The ammonia-oxidizing bacterium Nitrosomonas europaea was found on the cathode electrode of the single-chamber system, supporting evidence of biological nitrification, but anaerobic ammonia-oxidizing bacteria were not detected by molecular analyses. It is concluded that ammonia losses from the anode chamber were driven primarily by physical-chemical factors that are increased with electricity generation, although some losses may occur through biological nitrification and denitrification.     

Performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration

During field application, the microbial fuel cell (MFC) will be exposed to variations in operating parameters. Hence, the performance of MFC, exposed to variation in temperature, pH, external resistance and influent chemical oxygen demand (COD), was investigated in the terms of coulombic efficiency (CE) and COD removal efficiency, while treating a synthetic wastewater. The performance was analyzed under two temperature ranges such as 20-35 degrees C and 8-22 degrees C. Operation under higher temperature range favored higher COD removal efficiency of 90% and lower current (0.7 mA) and CE (1.5%). At lower temperature range, although the COD removal efficiency of MFC decreased (59%), it gave higher current (1.4 mA) and CE (5%). The highest current was generated at pH of 6.5 in the anodic chamber with CE of 4%. Higher pH difference between anodic and cathodic electrolyte favored higher current and voltage. Within the range of COD tested (100-600 mg/l), linear correlation was observed between the current and substrate removed.     

Enhancement of electricity production in a mediatorless air–cathode microbial fuel cell using <Emphasis Type="Italic">Klebsiella</Emphasis> sp. IR21

A novel dissimilatory iron-reducing bacteria, Klebsiella sp. IR21, was isolated from the anode biofilm of an MFC reactor. Klebsiella sp. IR21 reduced 27.8 % of ferric iron to ferrous iron demonstrating that Klebsiella sp. IR21 has electron transfer ability. Additionally, Klebsiella sp. IR21 generated electricity forming a biofilm on the anode surface. When a pure culture of Klebsiella sp. IR21 was supplied into a single chamber, air–cathode MFC fed with a mixture of glucose and acetate (500 mg L^?1 COD), 40–60 mV of voltage (17–26 mA m^?2 of current density) was produced. Klebsiella sp. IR21 was also utilized as a biocatalyst to improve the electrical performance of a conventional MFC reactor. A single chamber, air–cathode MFC was fed with reject wastewater (10,000 mg L^?1 COD) from a H₂ fermentation reactor. The average voltage, current density, and power density were 142.9 ± 25.74 mV, 60.5 ± 11.61 mA m^?2, and 8.9 ± 3.65 mW m^?2, respectively, in the MFC without inoculation of Klebsiella sp. IR21. However, these electrical performances of the MFC were significantly increased to 204.7 ± 40.24 mV, 87.5 ± 17.20 mA m^?2, and 18.6 ± 7.23 mW m^?2, respectively, with inoculation of Klebsiella sp. IR21. The results indicate that Klebsiella sp. IR21 can be utilized as a biocatalyst for enhancement of electrical performance in MFC systems.     

Understanding the role of Fe(III)/Fe(II) couple in mediating reductive transformation of 2-nitrophenol in microbial fuel cells

The Fe(III)/Fe(II) couple can play a significant role in the abiotic reduction of 2-nitrophenol (2-NP) at the cathode chamber of a microbial fuel cell (MFC). Experimental results demonstrate that Fe(II) addition to the cathode chamber contributes to a significant increase in the reaction rate of 2-NP removal and the power performance of MFC. Observed pseudo first-order rate constants and power densities are heavily dependent on the identity of the Fe(II)-complexing ligands. The Fe(II) complex coordinated with citrate results in the highest rate constant up to 0.12 h⁻¹ as compared to other organically complexed iron species including Fe(II)-EDTA, Fe(II)-acetate and Fe(II)-oxalate, and iron species uncomplexed with any organic ligands. In addition, the presence of Fe(II)-citrate species leads to a maximum volumetric power density of 1.0 W m⁻³, which is the highest value among those obtained with other iron species for the similar MFC system.     

Biochemical evaluation of bioelectricity production process from anaerobic wastewater treatment in a single chambered microbial fuel cell (MFC) employing glass wool membrane

Biochemical functioning of single chambered microbial fuel cell (MFC) using glass wool as proton exchange membrane (PEM) operated with selectively enriched acidogenic mixed culture was evaluated in terms of bioelectricity production and wastewater treatment. Performance of MFC was studied at two different organic/substrate loading rates (OLR) (2.64 and 3.54 kg COD/m(3)) and operating pH 6 and 7 using non-coated plain graphite electrodes (mediatorless anode; air cathode). Applied OLR in association with operating pH showed marked influence on the power output and substrate degradation efficiency. Higher current density was observed at acidophilic conditions [pH 6; 98.13 mA/m(2) (2.64 kg COD/m(3)-day; 100 Omega) and 111.29 mA/m(2) (3.54 kg COD/m(3)-day; 100 Omega)] rather than neutral conditions [pH 7; 100.52 mA/m(2) (2.64 kg COD/m(3)-day; 100 Omega) and 98.13 mA/m(2) (3.54 kg COD/m(3)-day; 100 Omega)]. On the contrary, effective substrate degradation was observed at neutral pH. MFC performance was evaluated employing polarization curve, impedance analysis, cell potential, Coulombic efficiency and bioprocess monitoring. Sustainable power yield was calculated at stable cell potential.     

A multi-electrode continuous flow microbial fuel cell with separator electrode assembly design

Scaling up microbial fuel cells (MFCs) requires the development of compact reactors with multiple electrodes. A scalable single chamber MFC (130 mL), with multiple graphite fiber brush anodes and a single air-cathode cathode chamber (27 m²/m³), was designed with a separator electrode assembly (SEA) to minimize electrode spacing. The maximum voltage produced in fed-batch operation was 0.65 V (1,000 Ω) with a textile separator, compared to only 0.18 V with a glass fiber separator due to short-circuiting by anode bristles through this separator with the cathode. The maximum power density was 975 mW/m², with an overall chemical oxygen demand (COD) removal of >90% and a maximum coulombic efficiency (CE) of 53% (50 Ω resistor). When the reactor was switched to continuous flow operation at a hydraulic retention time (HRT) of 8 h, the cell voltage was 0.21 ± 0.04 V, with a very high CE = 85%. Voltage was reduced to 0.13 ± 0.03 V at a longer HRT = 16 h due to a lower average COD concentration, and the CE (80%) decreased slightly with increased oxygen intrusion into the reactor per amount of COD removed. Total internal resistance was 33 Ω, with a solution resistance of 2 Ω. These results show that the SEA type MFC can produce stable power and a high CE, making it useful for future continuous flow treatment using actual wastewaters.