Connecting several microbial fuel cell (MFC) units in series or parallel can increase voltage and current; the effect on the microbial electricity generation was as yet unknown. Six individual ...continuous MFC units in a stacked configuration produced a maximum hourly averaged power output of 258 W m-3 using a hexacyanoferrate cathode. The connection of the 6 MFC units in series and parallel enabled an increase of the voltages (2.02 V at 228 W m-3) and the currents (255 mA at 248 W m-3), while retaining high power outputs. During the connection in series, the individual MFC voltages diverged due to microbial limitations at increasing currents. With time, the initial microbial community decreased in diversity and Gram-positive species became dominant. The shift of the microbial community accompanied a tripling of the short time power output of the individual MFCs from 73 W m-3 to 275 W m-3, a decrease of the mass transfer limitations and a lowering of the MFC internal resistance from 6.5 ± 1.0 to 3.9 ± 0.5 Ω. This study demonstrates a clear relation between the electrochemical performance and the microbial composition of MFCs and further substantiates the potential to generate useful energy by means of MFCs.
The anode potential in microbial fuel cells controls both the theoretical energy gain for the microorganisms as the output of electrical energy. We operated three reactors fed with acetate ...continuously at a poised anode potential of 0 (R ₀), -200 (R -₂₀₀) and -400 (R -₄₀₀) mV versus Ag/AgCl and investigated the resulting bacterial activity. The anode potential had no influence on the start-up time of the three reactors. During a 31-day period, R -₂₀₀ produced 15% more charge compared to R ₀ and R -₄₀₀. In addition, R -₂₀₀ had the highest maximal power density (up to 199 W m-³ total anode compartment during polarization) but the three reactors evolved to the same power density at the end of the experimental period. During polarization, only the current of R -₄₀₀ levelled off at an anode potential of -300 mV versus Ag/AgCl. The maximum respiration rate of the bacteria during batch tests was also considerably lower for R -₄₀₀. The specific biomass activity however, was the highest for R -₄₀₀ (6.93 g chemical oxygen demand g-¹ biomass-volatile suspended solids (VSS) d-¹ on day 14). This lowered during the course of the experiment due to an increase of the biomass concentration to an average level of 578 ± 106 mg biomass-VSS L-¹ graphite granules for the three reactors. This research indicated that an optimal anode potential of -200 mV versus Ag/AgCl exists, regulating the activity and growth of bacteria to sustain an enhanced current and power generation.
A tubular, single-chambered, continuous microbial fuel cell (MFC) that generates high power outputs using a granular graphite matrix as the anode and a ferricyanide solution as the cathode is ...described. The maximal power outputs obtained were 90 and 66 W m-3 net anodic compartment (NAC) (48 and 38 W m-3 total anodic compartment (TAC)) for feed streams based on acetate and glucose, respectively, and 59 and 48 W m-3 NAC for digester effluent and domestic wastewater, respectively. For acetate and glucose, the total Coulombic conversion efficiencies were 75 ± 5% and 59 ± 4%, respectively, at loading rates of 1.1 kg chemical oxygen demand m-3 NAC volume day-1. When wastewater was used, of the organic matter effectively removed (i.e., 22% at a loading of 2 kg organic matter m-3 NAC day-1), up to 96% was converted to electricity on a Coulombic basis. The lower overall efficiency of the wastewater-treating reactors is related to the presence of nonreadily biodegradable organics and the interference of alternative electron acceptors such as sulfate present in the wastewater. To further improve MFCs, focus has to be placed on the enhanced conversion of nonrapidly biodegradable material and the better directing of the anode flow toward the electrode instead of to alternative electron acceptors. Also the use of sustainable, open-air cathodes is a critical issue for practical implementation.
In a bioelectrochemical system (BES) operated with a bioanode, the anode performance plays an important part in the overall performance. Fundamental aspects of bioanodes have been intensively ...investigated, enabling us to better understand the growth, kinetics functioning and interactions of anodophilic microorganisms. Recently, various technological advances have improved the properties and operation of anodes and have increased bioanode performance by up to tenfold. To further boost the performance of bioanodes by several orders of magnitude, practical microbiological approaches deserve more investigation. This article reviews the factors affecting bioanode performance, the recent advances and the prospective strategies for improving it. Future application perspectives of bioanodes are also proposed.
The electricity generation, electrochemical and microbial characteristics of five microbial fuel cells (MFCs) with different three-dimensional electrodes (graphite and carbon felt, 2
mm and 5
mm ...graphite granules and graphite wool) was examined in relation to the applied loading rate and the external resistance. The graphite felt electrode yielded the highest maximum power output amounting up to 386
W
m
−3 total anode compartment (TAC). However, based on the continuous current generation, limited differences between the materials were registered. Doubling the loading rate to 3.3
g
COD
L
−1
TAC
d
−1 resulted only in an increased current generation when the external resistance was low (10.5–25
Ω) or during polarization. Conversely, lowering the external resistance resulted in a steady increase of both the kinetic capacities of the biocatalyst and the continuous current generation from 77 (50
Ω) up to 253 (10.5
Ω)
A
m
−3
TAC. Operating a MFC at an external resistance close to its internal resistance, allows to increase the current generation from enhanced loading rates while maximizing the power generation.
Microbial fuel cell (MFC) research is a rapidly evolving field that lacks established terminology and methods for the analysis of system performance. This makes it difficult for researchers to ...compare devices on an equivalent basis. The construction and analysis of MFCs requires knowledge of different scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. Describing MFC systems therefore involves an understanding of these different scientific and engineering principles. In this paper, we provide a review of the different materials and methods used to construct MFCs, techniques used to analyze system performance, and recommendations on what information to include in MFC studies and the most useful ways to present results.
Microbial fuel cells (MFCs) that remove carbon as well as nitrogen compounds out of wastewater are of special interest for practice. We developed a MFC 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 net cathodic compartment (NCC) d-1 (0.080 kg NO3 --N m-3 total cathodic compartment d-1 (TCC)) at a current 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 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 reduction of soluble Pd(II) by cells of Shewanella oneidensis MR-1 and of an autoaggregating mutant (COAG) resulted in precipitation of palladium Pd(0) nanoparticles on the cell wall and ...inside the periplasmic space (bioPd). As a result of biosorption and subsequent bioreduction of Pd(II) with H2, formate, lactate, pyruvate or ethanol as electron donors, recoveries higher than 90% of Pd associated with biomass could be obtained. The bioPd(0) nanoparticles thus obtained had the ability to reductively dehalogenate polychlorinated biphenyl (PCB) congeners in aqueous and sediment matrices. Bioreduction was observed in assays with concentrations up to 1000 mg Pd(II) l(-1) with depletion of soluble Pd(II) of 77.4% and higher. More than 90% decrease of PCB 21 (2,3,4-chloro biphenyl) coupled to formation of its dechlorination products PCB 5 (2,3-chloro biphenyl) and PCB 1 (2-chloro biphenyl) was obtained at a concentration of 1 mg l(-1) within 5 h at 28 degrees C. Bioreductive precipitation of bioPd by S. oneidensis cells mixed with sediment samples contaminated with a mixture of PCB congeners, resulted in dechlorination of both highly and lightly chlorinated PCB congeners adsorbed to the contaminated sediment matrix within 48 h at 28 degrees C. Fifty milligrams per litre of bioPd resulted in a catalytic activity that was comparable to 500 mg l(-1) commercial Pd(0) powder. The high reactivity of 50 mg l(-1) bioPd in the soil suspension was reflected in the reduction of the sum of seven most toxic PCBs to 27% of their initial concentration.
Bio-electrochemical systems (BESs) enable microbial catalysis of electrochemical reactions. Plain electrical power production combined with wastewater treatment by microbial fuel cells (MFCs) has ...been the primary application purpose for BESs. However, large-scale power production and a high chemical oxygen demand conversion rates must be achieved at a benchmark cost to make MFCs economical competitive in this context. Recently, a number of valuable oxidation or reduction reactions demonstrating the versatility of BESs have been described. Indeed, BESs can produce hydrogen, bring about denitrification, or reductive dehalogenation. Moreover, BESs also appear to be promising in the field of online biosensors. To effectively apply BESs in practice, both biological and electrochemical losses need to be further minimized. At present, the costs of reactor materials have to be decreased, and the volumetric biocatalyst activity in the systems has to be increased substantially. Furthermore, both the ohmic cell resistance and the pH gradients need to be minimized. In this review, these losses and constraints are discussed from an electrochemical viewpoint. Finally, an overview of potential applications and innovative research lines is given for BESs.
Using the anode effluent to compensate the alkalinization in a bio-cathode has recently been proposed as a way to operate a microbial fuel cell (MFC) in a continuous and pH neutral way. In this ...research, we 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-L-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 bio-cathode activity still needs to be improved significantly with a factor 10-50 in order achieve desirable current densities of 1,000 A m⁻³ MFC.
