Ammonia inhibition and microbial adaptation in continuous single-chamber microbial fuel cells

Here, we report that a continuous single-chamber microbial fuel cell (MFC) is applicable to wastewaters containing a high nitrogen concentration using a process of adaptation. Continuous experiments are conducted to investigate the inhibitory effect of total ammonia nitrogen (TAN) on the MFC using influents with various concentrations of TAN ranged from 84 to 10,000 mg N L⁻¹. As the TAN concentration increases up to 3500 mg N L⁻¹, the maximum power density remains at 6.1 W m⁻³. However, as the concentration further increases, TAN significantly inhibits the maximum power density, which is reduced at saturation to 1.4 W m⁻³ at 10,000 mg N L⁻¹. We confirm that the adapted electrical performance of a continuous MFC can generate approximately 44% higher power density than the conductivity control. A comparative study reveals that the power densities obtained from a continuous MFC can sustain 7-fold higher TAN concentration than that of previous batch MFCs. TAN removal efficiencies are limited to less than 10%, whereas acetate removal efficiencies remain as high as 93-99%. The increased threshold TAN of the continuous MFC suggests that microbial acclimation in a continuous MFC can allow the electrochemical functioning of the anode-attached bacteria to resist ammonia inhibition.     

Exoelectrogens in microbial fuel cells toward bioelectricity generation: a review

Exoelectrogens are catalytic microorganisms competent to shuttle electrons exogenously to the electrode surface without utilizing artificial mediators. Diverse microorganisms acting as exoelectrogens in the fluctuating ambience of microbial fuel cells (MFCs) propose unalike metabolic pathways and incompatible, specific proteins or genes for their inevitable performance toward bioelectricity generation. A pivotal mechanism known as quorum sensing allows bacterial population to communicate and regulates the expression of biofilm‐related genes. Moreover, it has been found that setting the anode potential affects the metabolism of the exoelectrogens and hence the output of MFCs. Microscopic, spectrometry investigations and gene deletion studies have confirmed the expression of certain genes for outer‐membrane multiheme cytochromes and conductive pili, and their potential roles in the exoelectrogenic activity. Further, cyclic voltammetry has suggested the role of multifarious redox‐active compounds secreted by the exoelectrogens in direct electron transport mechanisms. Besides, it also explores the various mechanisms of exoelectrogens with genetic and molecular approaches, such as biofilm formation, microbial metabolism, bioelectrogenesis, and electron transfer mechanisms from inside the exoelectrogens to the electrodes and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of furan derivatives and phenolic compounds on electricity generation in microbial fuel cells

Lignocellulosic biomass is an attractive fuel source for MFCs due to its renewable nature and ready availability. Furan derivatives and phenolic compounds could be potentially formed during the pre-treatment process of lignocellulosic biomass. In this study, voltage generation from these compounds and the effects of these compounds on voltage generation from glucose in air-cathode microbial fuel cells (MFCs) were examined. Except for 5-hydroxymethyl furfural (5-HMF), all the other compounds tested were unable to be utilized directly for electricity production in MFCs in the absence of other electron donors. One furan derivate, 5-HMF and two phenolic compounds, trans-cinnamic acid and 3,5-dimethoxy-4-hydroxy-cinnamic acid did not affect electricity generation from glucose at a concentration up to 10 mM. Four phenolic compounds, including syringaldeyhde, vanillin, trans-4-hydroxy-3-methoxy, and 4-hydroxy cinnamic acids inhibited electricity generation at concentrations above 5 mM. Other compounds, including 2-furaldehyde, benzyl alcohol and acetophenone, inhibited the electricity generation even at concentrations less than 0.2 mM. This study suggests that effective electricity generation from the hydrolysates of lignocellulosic biomass in MFCs may require the employment of the hydrolysis methods with low furan derivatives and phenolic compounds production, or the removal of some strong inhibitors prior to the MFC operation, or the improvement of bacterial tolerance against these compounds through the enrichment of new bacterial cultures or genetic modification of the bacterial strains.     

Power recovery with multi-anode/cathode microbial fuel cells suitable for future large-scale applications

Multi-anode/cathode microbial fuel cells (MFCs) incorporate multiple MFCs into a single unit, which maintain high power generation at a low cost and small space occupation for the scale-up MFC systems. The power production of multi-anode/cathode MFCs was similar to the total power production of multiple single-anode/cathode MFCs. The power density of a 4-anode/cathode MFC was 1184 mW/m³, which was 3.2 times as that of a single-anode/cathode MFC (350 mW/m³). The effect of chemical oxygen demand (COD) was studied as the preliminary factor affecting the MFC performance. The power density of MFCs increased with COD concentrations. Multi-anode/cathode MFCs exhibited higher power generation efficiencies than single-anode/cathode MFCs at high CODs. The power output of the 4-anode/cathode MFCs kept increasing from 200 mW/m³ to 1200 mW/m³ as COD increased from 500 mg/L to 3000 mg/L, while the single-anode/cathode MFC showed no increase in the power output at CODs above 1000 mg/L. In addition, the internal resistance (R_in) exhibited strong dependence on COD and electrode distance. The R_in decreased at high CODs and short electrode distances. The tests indicated that the multi-anode/cathode configuration efficiently enhanced the power generation.     

Power generation using an activated carbon fiber felt cathode in an upflow microbial fuel cell

An activated carbon fiber felt (ACFF) cathode lacking metal catalysts is used in an upflow microbial fuel cell (UMFC). The maximum power density with the ACFF cathode is 315 mW m⁻², compared to lower values with cathodes made of plain carbon paper (67 mW m⁻²), carbon felt (77 mW m⁻²), or platinum-coated carbon paper (124 mW m⁻², 0.2 mg-Pt cm⁻²). The addition of platinum to the ACFF cathode (0.2 mg-Pt cm⁻²) increases the maximum power density to 391 mW m⁻². Power production is further increased to 784 mW m⁻² by increasing the cathode surface area and shaping it into a tubular form. With ACFF cutting into granules, the maximum power is 481 mW m⁻² (0.5 cm granules), and 667 mW m⁻² (1.0 cm granules). These results show that ACFF cathodes lacking metal catalysts can be used to substantially increase power production in UMFC compared to traditional materials lacking a precious metal catalyst.     

Generation of electricity by the degradation of electro-Fenton pretreated latex wastewater using double chamber microbial fuel cell

A double chamber microbial fuel cell (MFC) reactor with anode and cathode chamber separated by a Nafion proton exchange membrane was developed and performance was evaluated for treatment of electro Fenton pretreated latex processing and production wastewater containing chemical oxygen demand of 2660 and 780 mg L⁻¹, respectively. After 12 days, MFC treatment, the COD reduced to 133 mg/L (96%) and 86 mg/L (88.5%) for latex processing and production wastewater respectively. The MFC treatment system generated electrical energy of 1.57 and 1.04 Wh L⁻¹ for latex processing and production wastewaters respectively that was utilized to drive the electro-Fenton reactor. These results indicated that effective wastewater treatment, energy production, and discharge standards could be obtained in the system.     

微生物燃料电池阴极电子受体与结构的研究进展

从工程应用的角度分析了微生物燃料电池的结构变化趋势;从电化学角度介绍了几种两室微生物燃料电池中阴极室采用不同电子受体对提高电池输出功率的影响和单室空气阴极微生物燃料电池的研究现状及应用前景;分析了电池组在电池放大过程中可能存在的串挠和电压反转等问题,为微生物燃料电池的工程应用提供了理论参考。     

Electricity generation from sediment microbial fuel cells with algae-assisted cathodes

One major limiting factor for sediment microbial fuel cells (SMFC) is the low oxygen reduction rate in the cathode. The use of the photosynthetic process of the algae is an effective strategy to increase the oxygen availability to the cathode. In this study, SMFCs were constructed by introducing the algae (Chlorella vulgaris) to the cathode, in order to generate oxygen in situ. Cyclic voltammetry and dissolved oxygen analysis confirmed that C. vulgaris in the cathode can increase the dissolved oxygen concentration and the oxygen reduction rate. We showed that power generation of SMFC with algae-assisted cathode was 21 mW m⁻² and was further increased to 38 mW m⁻² with additional carbon nanotube coating in the cathode, which was 2.4 fold higher than that of the SMFC with bare cathode. This relatively simple method increases the oxygen reduction rate at a low cost and can be applied to improve the performance of SMFCs.     

Generation of electricity in microbial fuel cells at sub-ambient temperatures

Direct generation of electricity from a mixture of carbon sources was examined using single chamber mediator-less air cathode microbial fuel cells (MFCs) at sub-ambient temperatures. Electricity was directly generated from a carbon source mixture of d-glucose, d-galactose, d-xylose, d-glucuronic acid and sodium acetate at 30 °C and <20 °C (down to 4 °C). Anodic biofilms enriched at different temperatures using carbon source mixtures were examined using epi-fluorescent, scanning electron microscopy, and cyclic voltammetry for electrochemical evaluation. The maximum power density obtained at different temperatures ranged from 486 ± 68 mW m⁻² to 602 ± 38 mW m⁻² at current density range of 0.31 mA cm⁻² to 0.41 mA cm⁻² (14 °C and 30 °C, respectively). Coulombic efficiency increased with decreasing temperature, and ranged from 24 ± 3 to 38 ± 1% (20 °C and 4 °C, respectively). Chemical oxygen demand (COD) removal was over 68% for all carbon sources tested. Our results demonstrate adaptation, by gradual increase of cold-stress, to electricity production in MFCs at sub-ambient temperatures.     

Carbon nanotube modified air-cathodes for electricity production in microbial fuel cells

The use of air-cathodes in microbial fuel cells (MFCs) has been considered sustainable for large scale applications, but the performance of most current designs is limited by the low efficiency of the three-phase oxygen reduction on the cathode surface. In this study we developed carbon nanotube (CNT) modified air-cathodes to create a 3-D electrode network for increasing surface area, supporting more efficient catalytic reaction, and reducing the kinetic resistance. Compared with traditional carbon cloth cathodes, all nanotube modified cathodes showed higher performance in electrochemical response and power generation in MFCs. Reactors using carbon nanotube mat cathodes showed the maximum power density of 329 mW m⁻²; more than twice that of the peak power obtained with carbon cloth cathodes (151 mW m⁻²). The addition of Pt catalysts significantly increased the current densities of all cathodes, with the maximum power density obtained using the Pt/carbon nanotube mat cathode at 1118 mW m⁻². The stable maximum power density obtained from other nanotube coated cathodes varied from 174 mW m⁻² to 522 mW m⁻². Scanning electron micrographs showed the presence of conductive carbon nanotube networks on the CNT modified cathodes that provide more efficient oxygen reduction.     

Study of electrochemical process conditions for the electricity production in microbial fuel cell

The aim of this study was to focus on the optimization of various process parameters such as time (days), pH, and electrode type on electricity production by a microbial fuel cell (MFC). The efficiency of MFC was examined based on the current (A) and potential (V) measurements. In MFC, the anode section was filled with 500 mL of rumen fluid, slaughter house waste, and 2 g of hay as substrate. The cathode section was filled with distilled water, which acted as the air cathode. The results obtained confirmed that copper anode explores the maximum efficiency compared to stainless steel and aluminum. The biofilm attached to the electrode is electrochemically active as per the redox potential shown in cyclic voltammogram results.     

Effects of magnetic fields on electricity generation in a photosynthetic ceramic microbial fuel cell

The aim of this study was to improve the efficiency of traditional proton exchange membranes by replacement using ceramic membranes with microalgae cathodes under various magnetic fields (MFs) of 100–300 mT in a ceramic microbial fuel cell (CMFC). The experimental results showed that the power generation can be enhanced by 61% when implementing a 200 mT MF. The application of a higher MF intensity, up to 200 mT, increased the electric charge generation yet decreased it with a higher MF value. Additionally, the MF had the ability to improve the power density of the CMFC, and a maximum power density of 35.9 mW m^?2 and maximum current density of 158.7 mA m^?2 were achieved with the 200 mT MF. Moreover, biocathode maintains a stable pH value that obtained more microalgae biomass by 200 mT MF stimulation. Further work will be focused on optimizing the appropriate MF intensity along with the capacity of carbon dioxide (CO₂) absorption by microalgae in CMFC.     

Plant microbial fuel cell applied in wetlands: Spatial,temporal and potential electricity generation of Spartina anglica salt marshes and Phragmites australis peat soils

The plant microbial fuel cell (PMFC) has to be applied in wetlands to be able to generate electricity on a large scale. The objective of this PMFC application research is to clarify the differences in electricity generation between a Spartina anglica salt marsh and Phragmites australis peat soil based on experimental data and theoretical calculated potential. PMFC in salt marsh generated more than 10 times more power than the same PMFC in peat soil (18 vs 1.3 mW m⁻² plant growth area). The salt marsh reached a record power output for PMFC technology per cubic meter anode: 2.9 W m⁻³. Most power is generated in the top layer of the salt marsh due to the presence of the plants and the tidal advection. The potential current generation for the salt marsh is 0.21–0.48 A m⁻² and for peat soil 0.15–0.86 A m⁻². PMFC technology is potentially able to generate a power density up to 0.52 W m⁻², which is more than what is generated for biomass combustion or anaerobic digestion using the same plant growth area.     

Electricity generation using membrane-less microbial fuel cell powered by sludge supplemented with lignocellulosic waste

A membrane-less microbial fuel cell (ML-MFC) is an electrochemical device that incorporates microorganisms into the design in order to produce electricity through biologically catalyzed oxidation of soluble, electron-donating substrates. In this study, three lignocellulosic raw materials were added into the ML-MFC whereby the sludge acted as the pseudomembrane. All three materials were used as the substrates in ML-MFC for the production of electricity that was measured using a digital multimeter. Results showed that the ML-MFC that contained sludge supplemented with banana peel produced the highest electricity, followed by corn bran and palm oil mill effluent (POME) at 237.1 mV (23.75 mW/m²), 176.8 mV (12.65 mW/m²), and 138 mV (22.03 mW/m²) after 138 h, 192 h, and 108 h of incubation period, respectively. For the control test (sludge only), about 162.7 mV was recorded at shorter incubation period (84 h). This showed that long-term operation of the ML-MFC using these complex lignocellulosic compounds as a direct substrate for electricity generation is feasible, though their degradation is slow.     

Small boreholes embedded in the sediment layers make big difference in performance of sediment microbial fuel cells: Bioelectricity generation and microbial community

The practical applications of sediment microbial fuel cells (SMFCs) are limited by their low power densities. In this work, a novel SMFC configuration with a cylindrical borehole embedded in the sediment layer is proposed with expectations of reducing internal resistance, enhancing mass transfer, and accordingly increasing power density. Two types of boreholes with same diameter of 10 cm, but different depths of 3 cm and 6 cm are constructed in SMFCs (SMFC-3 and SMFC-6). Results demonstrate that SMFC-3 produces the highest maximum power density (65.6 mW/m²), which is 25.5% and 65.6% higher than that in SMFC-6 (52.3 mW/m²) and the control SMFC (SMFC-C, 39.4 mW/m²), respectively. The improved power performance in SMFC-3 is mainly due to the greatly reduced internal resistance. Compared to SMFC-6, the higher power density in SMFC-3 is also due to the relatively low overlying water pH values, providing suitable pH condition for cathodic reactions. Microbial community analyses demonstrate that Alphaproteobacteria and Gammaproteobacteria are major contributors to the bioelectricity, and that electroactive species enriched on the top and bottom sides of anodes are significantly different. Generally, embedding a small borehole into the sediment layer is an easy-to-implement and cost-effective strategy for improving the power performance of SMFCs.     

Energy harvest with mangrove benthic microbial fuel cells

Benthic microbial fuel cells (BMFCs) are continuous electricity generators using electroactive microorganisms and organic matter from aquatic environment, respectively, as catalysts and substrate. In this paper, first a low‐cost PVC‐made structure is constructed to harvest electricity from mangrove environment located in French Guiana. An in situ BMFC has given power density of 30 mW/m² of the anodic surface area. This performance has been confirmed by experience in laboratory where inter‐electrode distance and electrode surface area appeared to be power increasing factors. However, the output power of one BMFC is not used to supply real devices such as autonomous sensors. Second, to meet this expectation, in parallel and in series associations were considered. These associations were made in order to increase the output voltage and consequently the power, to reach levels that can supply small sensors (about 3 V). Finally, to improve the performance of the series association and to avoid the voltage reversal phenomenon, a voltage balancing circuit was simulated and added to the series connections. With balancing method, the cell voltage of BMFCs can be equalized, and the performances can be improved. This allows an optimal energy harvesting and a better global efficiency of the set. Copyright © 2014 John Wiley & Sons, Ltd.     

Polypyrrole/carbon black composite as a novel oxygen reduction catalyst for microbial fuel cells

A polypyrrole/carbon black (Ppy/C) composite has been employed as an electrocatalyst for the oxygen reduction reaction (ORR) in an air-cathode microbial fuel cell (MFC). The electrocatalytic activity of the Ppy/C is evaluated toward the oxygen reduction using cyclic voltammogram and linear sweep voltammogram methods. In comparison with that at the carbon black electrode, the peak potential of the ORR at the Pp/C electrode shifts by approximate 260 mV towards positive potential, demonstrating the electrocatalytic activity of Ppy toward ORR. Additionally, the results of the MFC experiments show that the Ppy/C is well suitable to fully substitute the traditional cathode materials in MFCs. The maximum power density of 401.8 mW m⁻² obtained from the MFC with a Ppy/C cathode is higher than that of 90.9 mW m⁻² with a carbon black cathode and 336.6 mW m⁻² with a non-pyrolysed FePc cathode. Although the power output with a Ppy/C cathode is lower than that with a commercial Pt cathode, the power per cost of a Ppy/C cathode is 15 times greater than that of a Pt cathode. Thus, the Ppy/C can be a good alternative to Pt in MFCs due to the economic advantage.     

Increasing power generation of microbial fuel cells with a nano-CeO2 modified anode

Nano-CeO₂ was used to modify the carbon felt anode in microbial fuel cell (MFC). The MFC with the modified anode obtained the higher closed circuit voltage resulting from the lower anode potential, the higher maximum power density (2.94 W m^?2), and the lower internal resistance (77.1 Ω). Cyclic voltammetry (CV) results implied that the bioelectrochemical activity of exoelectrogens was promoted by nano-CeO₂. Electrochemical impedance spectroscopy (EIS) results revealed that the anodic charge transfer resistance of the MFC decreased with modified anode. This study demonstrates that the nano-CeO₂ can be an effective anodic catalyst for enhancing the power generation of MFC.     

Power generation using polyaniline/multi‐walled carbon nanotubes as an alternative cathode catalyst in microbial fuel cells

Optimization of the cathode catalyst is critical to the study of microbial fuel cells (MFCs). By using the open circuit voltage and power density as evaluation standards, this study focused on the use of polyaniline (PANI)/multi‐walled carbon nanotube (MWNT) composites as cathode catalysts for the replacement of platinum (Pt) in an air‐cathode MFC, which was fed with synthetic wastewater. Scanning electron microscopy and linear scan voltammogram methods were used to evaluate the morphology and electrocatalytic activity of cathodes. A maximum power density of 476 mW/m² was obtained with a 75% wt PANI/MWNT composite cathode, which was higher than the maximum power density of 367 mW/m² obtained with a pure MWNT cathode but lower than the maximum power density of 541 mW/m² obtained with a Pt/C cathode. Thus, the use of PANI/MWNT composites may be a suitable alternative to a Pt/C catalyst in MFCs. PANI/MWNT composites were initially used as cathodic catalysts to replace Pt/C catalysts, which enhanced the power generation of MFCs and substantially reduced their cost. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluating the performance of microbial fuel cells powering electronic devices

A microbial fuel cell (MFC) is capable of powering an electronic device if we store the energy in an external storage device, such as a capacitor, and dispense that energy intermittently in bursts of high-power when needed. Therefore its performance needs to be evaluated using an energy-storing device such as a capacitor which can be charged and discharged rather than other evaluation techniques, such as continuous energy dissipation through a resistor. In this study, we develop a method of testing microbial fuel cell performance based on storing energy in a capacitor. When a capacitor is connected to a MFC it acts like a variable resistor and stores energy from the MFC at a variable rate. In practice the application of this method to testing microbial fuel cells is very challenging and time consuming; therefore we have custom-designed a microbial fuel cell tester (MFCT). The MFCT evaluates the performance of a MFC as a power source. It uses a capacitor as an energy storing device and waits until a desired amount of energy is stored then discharges the capacitor. The entire process is controlled using an analog-to-digital converter (ADC) board controlled by a custom-written computer program. The utility of our method and the MFCT is demonstrated using a laboratory microbial fuel cell (LMFC) and a sediment microbial fuel cell (SMFC). We determine (1) how frequently a MFC can charge a capacitor, (2) which electrode is current-limiting, (3) what capacitor value will allow the maximum harvested energy from a MFC, which is called the “optimum charging capacitor value,” and (4) what capacitor charging potential will harvest the maximum energy from a MFC, which is called the “optimum charging potential.” Using a LMFC we find that (1) the time needed to charge a 3-F capacitor from 0 to 500 mV is 108 min, (2) the optimum charging capacitor value is 3 F, and (3) the optimum charging potential is 300 mV. Using a SMFC we find that (1) the time needed to charge a 3-F capacitor from 0 to 500 mV is 5 min, (2) the optimum charging capacitor value is 3 F, and (3) the optimum charging potential is 500 mV. Our results demonstrate that the developed method and the MFCT can be used to evaluate and optimize energy harvesting when a MFC is used with a capacitor to power wireless sensors monitoring the environment.