Showing papers on "Microbial electrolysis cell published in 2009"

Direct Biological Conversion of Electrical Current into Methane by Electromethanogenesis

Abstract: New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. Here we demonstrate that methane can directly be produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis. At a set potential of less than −0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At −1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane pro...

Selecting Anode-Respiring Bacteria Based on Anode Potential: Phylogenetic, Electrochemical, and Microscopic Characterization

Abstract: Anode-respiring bacteria (ARB) are able to transfer electrons contained in organic substrates to a solid electrode. The selection of ARB should depend on the anode potential, which determines the amount of energy available for bacterial growth and maintenance. In our study, we investigated how anode potential affected the microbial diversity of the biofilm community. We used a microbial electrolysis cell (MEC) containing four graphite electrodes, each at a different anode potential (Eanode = −0.15, −0.09, +0.02, and +0.37 V vs SHE). We used wastewater-activated sludge as inoculum, acetate as substrate, and continuous-flow operation. The two electrodes at the lowest potentials showed a faster biofilm growth and produced the highest current densities, reaching up to 10.3 A/m2 at the saturation of an amperometric curve; the electrode at the highest potential produced a maximum of 0.6 A/m2. At low anode potentials, clone libraries showed a strong selection (92−99% of total clones) of an ARB that is 97% simila...

High Surface Area Stainless Steel Brushes as Cathodes in Microbial Electrolysis Cells

Abstract: Microbial electrolysis cells (MECs) are an efficient technology for generating hydrogen gas from organic matter, but alternatives to precious metals are needed for cathode catalysts. We show here that high surface area stainless steel brush cathodes produce hydrogen at rates and efficiencies similar to those achieved with platinum-catalyzed carbon cloth cathodes in single-chamber MECs. Using a stainless steel brush cathode with a specific surface area of 810 m2/m3, hydrogen was produced at a rate of 1.7 +/- 0.1 m3-H2/m3-d (current density of 188 +/- 10 A/m3) at an applied voltage of 0.6 V. The energy efficiency relative to the electrical energy input was 221 +/- 8%, and the overall energy efficiency was 78 +/- 5% based on both electrical energy and substrate utilization. These values compare well to previous results obtained using platinum on flat carbon cathodes in a similar system. Reducing the cathode surface area by 75% decreased performance from 91 +/- 3 A/m3 to 78 +/- 4 A/m3. A brush cathode with graphite instead of stainless steel and a specific surface area of 4600 m2/m3 generated substantially less current (1.7 +/- 0.0 A/m3), and a flat stainless steel cathode (25 m2/m3) produced 64 +/- 1 A/m3, demonstrating that both the stainless steel and the large surface area contributed to high current densities. Linear sweep voltammetry showed that the stainless steel brush cathodes both reduced the overpotential needed for hydrogen evolution and exhibited a decrease in overpotential over time as a result of activation. These results demonstrate for the first time that hydrogen production can be achieved at rates comparable to those with precious metal catalysts in MECs without the need for expensive cathodes.

Fate of H2 in an upflow single-chamber microbial electrolysis cell using a metal-catalyst-free cathode.

Abstract: With the goal of maximizing the H2-harvesting efficiency, we designed an upflow single-chamber microbial electrolysis cell (MEC) by placing the cathode on the top of the MEC and carried out a program to track the fate of H2 and electron equivalents in batch experiments. When the initial acetate concentration was 10 mM in batch-evaluation experiments lasting 32 h, the cathodic conversion efficiency (CCE) from coulombs (i.e., electron equivalents in current from the anode to the cathode) to H2 was 98 ± 2%, the Coulombic efficiency (CE) was 60 ± 1%, the H2 yield was 59 ± 2%, and methane production was negligible. However, longer batch reaction time (∼ 7 days) associated with higher initial acetate concentrations (30 or 80 mM) led to significant H2 loss due to CH4 accumulation: up to 14 ± 1% and 16 ± 2% of the biogas at 30 and 80 mM of acetate, respectively. Quantitative PCR proved that no acetoclastic methanogens were present, but that hydrogenotrophic methanogens (i.e., Methanobacteriales) were present on b...

Hydrogen Production by Geobacter Species and a Mixed Consortium in a Microbial Electrolysis Cell

Abstract: A hydrogen utilizing exoelectrogenic bacterium (Geobacter sulfurreducens) was compared to both a nonhydrogen oxidizer (Geobacter metallireducens) and a mixed consortium in order to compare the hydrogen production rates and hydrogen recoveries of pure and mixed cultures in microbial electrolysis cells (MECs). At an applied voltage of 0.7 V, both G. sulfurreducens and the mixed culture generated similar current densities (ca. 160 A/m3), resulting in hydrogen production rates of ca. 1.9 m3 H2/m3/day, whereas G. metallireducens exhibited lower current densities and production rates of 110 ± 7 A/m3 and 1.3 ± 0.1 m3 H2/m3/day, respectively. Before methane was detected in the mixed-culture MEC, the mixed consortium achieved the highest overall energy recovery (relative to both electricity and substrate energy inputs) of 82% ± 8% compared to G. sulfurreducens (77% ± 2%) and G. metallireducens (78% ± 5%), due to the higher coulombic efficiency of the mixed consortium. At an applied voltage of 0.4 V, methane production increased in the mixed-culture MEC and, as a result, the hydrogen recovery decreased and the overall energy recovery dropped to 38% ± 16% compared to 80% ± 5% for G. sulfurreducens and 76% ± 0% for G. metallireducens. Internal hydrogen recycling was confirmed since the mixed culture generated a stable current density of 31 ± 0 A/m3 when fed hydrogen gas, whereas G. sulfurreducens exhibited a steady decrease in current production. Community analysis suggested that G. sulfurreducens was predominant in the mixed-culture MEC (72% of clones) despite its relative absence in the mixed-culture inoculum obtained from a microbial fuel cell reactor (2% of clones). These results demonstrate that Geobacter species are capable of obtaining similar hydrogen production rates and energy recoveries as mixed cultures in an MEC and that high coulombic efficiencies in mixed culture MECs can be attributed in part to the recycling of hydrogen into current.

A solar-powered microbial electrolysis cell with a platinum catalyst-free cathode to produce hydrogen.

Abstract: This paper reports successful hydrogen evolution using a dye-sensitized solar cell (DSSC)-powered microbial electrolysis cell (MEC) without a Pt catalyst on the cathode, indicating a solution for the inherent drawbacks of conventional MECs, such as the need for an external bias and catalyst. DSSCs fabricated by assembling a ruthenium dye-loaded TiO(2) film and platinized FTO glass with an I(-)/I(3)(-) redox couple were demonstrated as an alternative bias (V(oc) = 0.65 V). Pt-loaded (0.3 mg Pt/cm(2)) electrodes with a Pt/C nanopowder showed relatively faster hydrogen production than the Pt-free electrodes, particularly at lower voltages. However, once the applied photovoltage exceeded a certain level (0.7 V), platinum did not have any additional effect on hydrogen evolution in the solar-powered MECs: hydrogen conversion efficiency was almost comparable for either the plain (71.3-77.0%) or Pt-loaded carbon felt (79.3-82.0%) at >0.7 V. In particular, the carbon nanopowder-coated electrode without Pt showed significantly enhanced performance compared to the plain electrode, which indicates efficient electrohydrogenesis, even without Pt by enhancing the surface area. As the applied photovoltage was increased, anodic methanogenesis decreased gradually, resulting in increasing hydrogen yield.

Enhanced nitrogen removal in bio-electrochemical systems by pH control.

Abstract: Microbial fuel cells can be designed to remove nitrogenous compounds out of wastewater, but their performance is at present limited to 0.33 kg NO3 −-Nm−3 net cathode compartment (NCC) d−1. By maintaining the pH in the cathode at 7.2, nitrogen removal was increased from 0.22 to 0.50 kg NO3 −-Nm−3 NCC d−1. Bio-electrochemical active microorganisms seem to struggle with the deterioration of their own environment due to slow proton fluxes. Therefore, the results suggest that an appropriate pH adjustment strategy is necessary to allow a sustained and enhanced biological activity in bio-electrochemical systems.

Hydrogen Production from Glycerol in a Membraneless Microbial Electrolysis Cell

Abstract: Hydrogen production from glycerol was studied in a microbial electrolysis cell (MEC) with a 250 mL anodic chamber and a gas-phase cathode. A membraneless MEC design was employed, where a graphite f...

Electrodes as electron donors for microbial reduction processes

Abstract: In bio-electrochemical systems (BESs), at least one of the anodic or cathodic reactions is biologically catalyzed. If a BES is producing electrical energy, the term microbial fuel cell (MFC) is used whereas a microbial electrolysis cell (MEC) indicates that a BES is consuming electrical energy to drive the electrochemical reactions. Up till now, most BESs consisted of a biocatalyzed anode combined with an abiotic cathode. Recently, there has been an increasing interest in replacing abiotic cathodes for biocathodes in which microorganisms enhance the reduction catalysis. Microbial fuel cells that remove carbon as well as nitrogen compounds out of wastewater are of special interest for practice. A MFC was developed in which microorganisms in the cathode performed a complete denitrification by using electrons supplied by microorganisms oxidizing acetate in the anode. The MFC with a cation exchange membrane was designed as a tubular reactor with an internal cathode and was able to remove up to 0.146 kg NO3--N m-3 nett cathodic compartment (NCC) d-1 (0.080 kg NO3--N m-3 total cathodic compartment d-1 (TCC)) at a current density of 58 A m-3 NCC (32 A m-3 TCC) and a cell voltage of 0.075 V. The highest power output in the denitrification system was 8 W m-3 NCC (4 W m-3 TCC) with a cell voltage of 0.214 V and a current density of 35 A m-3 NCC. The denitrification rate and the power production was limited by the cathodic microorganisms, which only denitrified significantly at a cathodic electrode potential below 0 V versus standard hydrogen electrode (SHE). This is, to our knowledge, the first study in which a MFC has both a biological anode and cathode performing simultaneous removal of an organic substrate, power production, and complete denitrification without relying on H2-formation or external added power. Microbial fuel cells (MFCs) designed to remove nitrogen compounds out of wastewater are limited in performance up to 0.33 kg NO3--N m-3 nett cathode compartment (NCC) d-1 at present. The aim was to increase the denitrification rate in the biocathode of a bio-electrochemical system. By maintaining the pH in the cathode at 7.2, the nitrogen removal was increased from 0.22 to 0.50 kg NO3--N m-3 NCC d-1. The improved MFC performance was observed through an increase in cathode potential with increasing denitrification rates with a fixed external resistor, indicating a decrease of the concentration overpotentials. Bio-electrochemical active microorganisms struggle with the deterioration of their own environment due to slow proton fluxes. Therefore, the results suggest that an appropriate pH adjustment strategy is necessary to allow a sustained and enhanced biological activity in bio-electrochemical systems. The reduction of oxygen at the cathode is one of the major bottlenecks of microbial fuel cells. While research so far has mainly focused on chemical catalysis of this oxygen reduction, here a continuously wetted cathode was presented with micro-organisms that act as biocatalysts for oxygen reduction. The anode of an acetate oxidizing tubular microbial fuel cell was combined with an open air biocathode for electricity production. The maximum power production was 83 11 W m-3 MFC (0.183 L MFC) for batch fed systems (20 - 40 % coulombic yield) and 65 5 W m-3 MFC for a continuous system with an acetate loading rate of 1.5 kg COD m-3 MFC d-1 (90 3 % coulombic yield). Electrochemical precipitation of manganese oxides on the cathodic graphite felt decreased the start-up period with approximately 30 % versus a non-treated graphite felt. After the start-up period, the cell performance was similar for the pretreated and the non-treated cathodic electrode. Several reactor designs were tested and it was found that enlargement of the 0.183 L MFC reactor by a factor 2.9 to 3.8 reduced the volumetric power output by 60 - 67 %. Biocathodes alleviate the need to use noble or non-noble catalysts for the reduction of oxygen, which increases substantially the viability and sustainability of MFCs. Two types of rapidly biodegradable vegetable products (the liquid fraction of clover and the glycerol containing sidestream from biodiesel production) were selected for anodic oxidation in microbial fuel cells equipped with an open air biocathode. As benchmark references, five abundant amino-acids in plant sap (L-glutamine, L-glutamic acid, L-asparagine, L-aspartic acid and L-alanine) were tested separately. Their performance was in the same order of magnitude of clover sap oxidation (145 - 225 A m-3 MFC; 39 - 95 W m-3 MFC). Glycerol oxidation resulted in competitive current and power outputs (111 A m-3 MFC; 23 W m-3 MFC). Using the anode effluent to compensate the alkalinization in a biocathode has recently been proposed as a way to operate a microbial fuel cell in a continuous and pH neutral way. In this research it was successfully demonstrated that the operation of a MFC without any pH adjustments is possible by completing the liquid loop over cathode and anode. During the complete loop operation, a stable current production of 23.2 ± 2.5 A m-3 MFC was obtained, even in the presence of 3.2 - 5.2 mg O2 L-1 in the anode. The use of current collectors and subdivided electrical circuitries for relative large 2.5 litre-scale MFCs resulted in ohmic cell resistances in the order of 1.4 - 1.7 mΩ m3 MFC, which were comparable to values of ten times smaller MFCs. Nevertheless, the biocathode activity still needs to be improved significantly with a factor 10-50 in order achieve desirable current densities of 1000 A m-3 MFC. Biocatalyzed electrolysis is a bio-electrochemical technology for the generation of hydrogen gas and other reduced products out of organic electron donors. Examples of electron donors are acetate and wastewater. An external power supply can support the process and therefore circumvent thermodynamical constraints that normally render the generation of compounds such as hydrogen unlikely. We have investigated the possibility of biocatalyzed electrolysis for the generation of methane. The cathodically produced hydrogen could be converted into methane at a ratio of 0.41 mol methane mol-1 acetate, at temperatures of 22 ± 2 °C. The anodic oxidation of acetate was not hampered by ammonium concentrations up to 5 g N L-1. Operation of microbial electrolysis cells without an ion exchange membrane could help to lower the construction costs while lowering the ohmic cell resistance and improving MEC conversion rates by minimizing the pH gradient between anode and cathode. In this research it was demonstrated that membraneless MECs with plain graphite can be operated for methane production without pH adjustment and that the ohmic cell resistance could be lowered with approximately 50 % by removing the cation exchange membrane. As a result, the current production increased from 66 ± 2 to 156 ± 1 A m-3 MEC by removing the membrane with an applied voltage of -0.8 V. Methane was the main energetic product despite continuous operation under carbonate limited and slightly acidified conditions (pH 6.1 - 6.2). These results suggest that continuous production of hydrogen in membraneless MECs will be challenging because methane production might not be avoided easily. The electrical energy invested was not always completely recovered under the form of an energy-rich biogas: however, our results indicate that membraneless MECs might be a viable polishing step for the treatment of the effluent of anaerobic digesters as methane was produced under low organic loading conditions and at room temperature. Losses of a BES need to be characterized to minimize the global voltage loss to values that allow current densities in the order of 1400 A m-3 BES (10 kg COD m-3 BES d-1). For MFCs, 400 W m-3 MFC should be taken as an objective, while 10 m3 H2 m-3 MEC at an applied voltage of 0.3 - 0.4 V should be the goal for MECs. Improving the reactor configuration and operation, and decreasing the costs of material use are the main abiotic challenges. In case of wastewater treatment, the benchmark cost of 0.3 € m-3 wastewater, should be taken into account. Engineering electron transfer functionality within the microbial community and biofilm structure optimization appear to be the most challenging microbial parameters. Scaling BESs up will be difficult and, although useful strategies have already been brought forward, technological innovation is still needed to obtain economically feasible large scale BESs as the postulated performance has not been achieved yet on a litre scale. Although COD oxidation rates are already in a competitive order of magnitude of 2 kg COD m-3 d-1, it is doubtful whether the power production of MFCs or hydrogen production of MECs alone will render BESs economically feasible. Therefore, further research should not only focus on optimization of cost effective materials and optimizing microbial functionality, but also on creating extra added value for bio-electrochemical systems. There might be several opportunities for small scale and more specialized applications. Cost calculations and life cycle assessments will be necessary to convince policy makers and industries of the environmental and economical assets of versatile and controllable BESs.

An Analysis of Anaerobic Dual-Anode Chambered Microbial Fuel Cell (MFC) Performance

Abstract: Microbial Fuel Cell (MFC) technology utilizes bacterial growth in carbon-containing solutions to generate electricity or hydrogen For the direct production of electricity, an MFC operates aerobically at the cathode and anaerobically at the anodes The same basic design can be used with minor changes to produce hydrogen at the cathode by applying an additional overpotential and omitting oxygen from the cathode In this configuration, the device is called an MEC (Microbial Electrolysis Cell) However, the term “MFC” is frequently used to describe both devices The primary objectives of this study were to determine optimal operating conditions and to minimize the internal resistance in the MFC in order to improve the reactor performance for power generation or hydrogen production using the organism Shewanella oneidesis MR-1 In this study, MFC performance was evaluated under various operating conditions with a modified MFC system architecture called a “Dual-Anode Chambered MFC” which incorporates two anode chambers flanking a single cathode chamber This design leads to improvements in reactor performance and reduced internal resistance by minimizing electrode separation and providing parallel electrical connectivity, which increases the maximum current the MFC can supply for a given time (mA) These improvements lead to increased maximum specific power output (W/m3), volumetric hydrogen production rate (m3-H2/m3-substrate/day), and hydrogen yield on substrate (mol-H2/mol-substrate) An analysis of reactor performance using the new MFC reactor system included as system variables the size of the electrode surface area, substrate (lactate) concentration (5mM, 10mM, 20mM), substrate flow rate (1ml/min, 3ml/min, 5ml/min), and internal resistance (Ohms) for electricity production The maximum volumetric power density of 236 W/m3 (standard deviation: 225, error: 13) and hydrogen yield of 0438 mol-H2/mol-substrate were obtained under optimized conditions; these conditions were then used to compare the reactor performance to that of a single-anode chambered MFC Results indicated that the dual-anode MFC produced power per unit anode volume of 236 W/m3, about 12 times the power of a single-anode MFC (202 W/m3) This was due to the reduction of internal resistance within the dual-anode MFCs The internal resistance was reduced by 45 %, from 106 Ohms (single-anode) to 583 Ohms (dual-anode)

Microbial electrolysis cell modelling and simulation using MATLAB

Abstract: Hydrogen is considered as an attractive energy source in the 21st century and as a fuel to replace conventional fossil fuels. Apart from being a potential source of unlimited clean power, it is also widely used in the chemical process industries and is likely to become a dominant fuel in the transportation sector. Microbial conversion of biomass is a newly developed and unique process, which involves the fermentation of organic substrates such as carbohydrates present in organic wastewater by a consortium of bacteria to produce hydrogen. The study outlined in this paper provides a review of the microbial conversion process and describes the mathematical modelling of the microbial electrolysis cell behaviour in MATLAB.

Isolation and Analysis of Novel Electrochemically Active Bacteria for Enhanced Power Generation in Microbial Fuel Cells

Abstract: : Using a U-tube MFC approach developed earlier as a part of this project, we isolated a pure culture classified Enterobactcr cloacae based on 16S rDNA sequencing and physiological and biochemical characterization This strain was remarkable because it was able to produce electricity in a microbial fuel cell from the degradation of cellulose This is the first time that a bacterium has been shown to be able to accomplish both of these tasks We examined the communities that developed in MFCs based on electrode surface material and the effects of light on the community We have also shown that Rhodopseudomonas palustris strain DX-l, a strain previously isolated as a part of this project, was capable of being used in a microbial electrolysis cell for the biologically-driven electrochemical production of hydrogen gas