Development of a solar-powered microbial fuel cell

Aims: To understand factors that impact solar‐powered electricity generation by Rhodobacter sphaeroides in a single‐chamber microbial fuel cell (MFC). Methods and Results: The MFC used submerged platinum‐coated carbon paper anodes and cathodes of the same material, in contact with atmospheric oxygen. Power was measured by monitoring voltage drop across an external resistance. Biohydrogen production and in situ hydrogen oxidation were identified as the main mechanisms for electron transfer to the MFC circuit. The nitrogen source affected MFC performance, with glutamate and nitrate‐enhancing power production over ammonium. Conclusions: Power generation depended on the nature of the nitrogen source and on the availability of light. With light, the maximum point power density was 790 mW m^?2 (2·9 W m^?3). In the dark, power output was less than 0·5 mW m^?2 (0·008 W m^?3). Also, sustainable electrochemical activity was possible in cultures that did not receive a nitrogen source. Significance and Impact of the Study: We show conditions at which solar energy can serve as an alternative energy source for MFC operation. Power densities obtained with these one‐chamber solar‐driven MFC were comparable with densities reported in nonphotosynthetic MFC and sustainable for longer times than with previous work on two‐chamber systems using photosynthetic bacteria.     

Renewable sustainable biocatalyzed electricity production in a photosynthetic algal microbial fuel cell (PAMFC)

Electricity production via solar energy capturing by living higher plants and microalgae in combination with microbial fuel cells are attractive because these systems promise to generate useful energy in a renewable, sustainable, and efficient manner. This study describes the proof of principle of a photosynthetic algal microbial fuel cell (PAMFC) based on naturally selected algae and electrochemically active microorganisms in an open system and without addition of instable or toxic mediators. The developed solar-powered PAMFC produced continuously over 100 days renewable biocatalyzed electricity. The sustainable performance of the PAMFC resulted in a maximum current density of 539 mA/m² projected anode surface area and a maximum power production of 110 mW/m² surface area photobioreactor. The energy recovery of the PAMFC can be increased by optimization of the photobioreactor, by reducing the competition from non-electrochemically active microorganisms, by increasing the electrode surface and establishment of a further-enriched biofilm. Since the objective is to produce net renewable energy with algae, future research should also focus on the development of low energy input PAMFCs. This is because current algae production systems have energy inputs similar to the energy present in the outcoming valuable products.     

A microbial fuel cell capable of converting glucose to electricity at high rate and efficiency

A microbial fuel cell containing a mixed bacterial culture utilizing glucose as carbon source was enriched to investigate power output in relation to glucose dosage. Electron recovery in terms of electricity up to 89% occurred for glucose feeding rates in the range 0.5–3 g l^–1 d^–1, at powers up to 3.6 W m^–2 of electrode surface, a five fold higher power output than reported thus far. This research indicates that microbial electricity generation offers perspectives for optimization.     

Microdischarge‐Based Direct Current Triboelectric Nanogenerator via Accumulation of Triboelectric Charge in Atmospheric Condition

Direct conversion of mechanical energy into direct current (DC) by triboelectric nanogenerators (TENGs) is one of the desired features in terms of energy conversion efficiency. Although promising applications have been reported using the triboelectric effect, effective DC generating TENGs must be developed for practical purposes. Here, it is reported that continuous DC generation within a TENG itself, without any circuitry, can be achieved by triggering air breakdown via triboelectrification. It is demonstrated that DC generation occurs in combination with i) charge accumulation to generate air breakdown, ii) incident discharge (microdischarge), and iii) conveyance of charges to make the device sustainable. 10.5 mA m^?2 of output current and 10.6 W m^?2 of output power at 33 MΩ load resistance are achieved. Compared to the best DC generating TENGs ever reported, the TENG in this present study generates about 20 times larger root‐mean square current density.     

A single chamber stackable microbial fuel cell with air cathode

A single chamber stackable microbial fuel cell (SCS-MFC) comprising four MFC units was developed. When operated separately, each unit generated a volumetric power density (P_max,V) of 26.2 W/m³ at 5.8 mA or 475 mV. The total columbic efficiency was 40% for each unit. Parallel connection of four units produced the same level of power output (P_max,V of 22.8 W/m³ at 27 mA), which was approximately four times higher than a single unit alone. Series connection of four units, however, only generated a maximum power output of 14.7 W/m³ at 730 mV, which was less than the expected value. This energy loss appeared to be caused by lateral current flow between two units, particularly in the middle of the system. The cathode was found to be the major limiting factor in our system. Compared to the stacked operation of multiple separate MFCs, our single chamber reactor does not require a delicate water distribution system and thus is more easily implemented in pre-existing wastewater treatment facilities with serpentine flow paths, such as fixed-bed reactors, with minimal infrastructure changes.     

Investigating microbial fuel cell bioanode performance under different cathode conditions

A compact, three‐in‐one, flow‐through, porous, electrode design with minimal electrode spacing and minimal dead volume was implemented to develop a microbial fuel cell (MFC) with improved anode performance. A biofilm‐dominated anode consortium enriched under a multimode, continuous‐flow regime was used. The increase in the power density of the MFC was investigated by changing the cathode (type, as well as catholyte strength) to determine whether anode was limiting. The power density obtained with an air‐breathing cathode was 56 W/m³ of net anode volume (590 mW/m²) and 203 W/m³ (2160 mW/m²) with a 50‐mM ferricyanide‐based cathode. Increasing the ferricyanide concentration and ionic strength further increased the power density, reaching 304 W/m³ (3220 mW/m², with 200 mM ferricyanide and 200 mM buffer concentration). The increasing trend in the power density indicated that the anode was not limiting and that higher power densities could be obtained using cathodes capable of higher rates of oxidation. The internal solution resistance for the MFC was 5–6 Ω, which supported the improved performance of the anode design. A new parameter defined as the ratio of projected surface area to total anode volume is suggested as a design parameter to relate volumetric and area‐based power densities and to enable comparison of various MFC configurations. Published 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Energy from algae using microbial fuel cells

Bioelectricity production from a phytoplankton, Chlorella vulgaris, and a macrophyte, Ulva lactuca was examined in single chamber microbial fuel cells (MFCs). MFCs were fed with the two algae (as powders), obtaining differences in energy recovery, degradation efficiency, and power densities. C. vulgaris produced more energy generation per substrate mass (2.5 kWh/kg), but U. lactuca was degraded more completely over a batch cycle (73 ± 1% COD). Maximum power densities obtained using either single cycle or multiple cycle methods were 0.98 W/m² (277 W/m³) using C. vulgaris, and 0.76 W/m² (215 W/m³) using U. lactuca. Polarization curves obtained using a common method of linear sweep voltammetry (LSV) overestimated maximum power densities at a scan rate of 1 mV/s. At 0.1 mV/s, however, the LSV polarization data was in better agreement with single‐ and multiple‐cycle polarization curves. The fingerprints of microbial communities developed in reactors had only 11% similarity to inocula and clustered according to the type of bioprocess used. These results demonstrate that algae can in principle, be used as a renewable source of electricity production in MFCs. Biotechnol. Bioeng. 2009;103: 1068–1076. © 2009 Wiley Periodicals, Inc.     

Electricity generation at high ionic strength in microbial fuel cell by a newly isolated Shewanella marisflavi EP1

Increasing the ionic strength of the electrolyte in a microbial fuel cell (MFC) can remarkably increase power output due to the reduction of internal resistance. However, only a few bacterial strains are capable of producing electricity at a very high ionic strength. In this report, we demonstrate a newly isolated strain EP1, belonging to Shewanella marisflavi based on polyphasic analysis, which could reduce Fe(III) and generate power at a high ionic strength of up to 1,488 mM (8% NaCl) using lactate as the electron donor. Using this bacterium, a measured maximum power density of 3.6 mW/m² was achieved at an ionic strength of 291 mM. The maximum power density was increased by 167% to 9.6 mW/m² when ionic strength was increased to 1,146 mM. However, further increasing the ionic strength to 1,488 mM resulted in a decrease in power density to 5.2 mW/m². Quantification of the internal resistance distribution revealed that electrolyte resistance was greatly reduced from 1,178 to 50 Ω when ionic strength increased from 291 to 1,488 mM. These results indicate that isolation of specific bacterial strains can effectively improve power generation in some MFC applications.     

Life Cycle Water Use of Ford Focus Gasoline and Ford Focus Electric Vehicles

Literature data for vehicle life cycle water consumption are limited and contradictory; there are no published estimates of vehicle life cycle water withdrawal. To place future discussions of sustainable mobility on a firmer technical basis, we report the results of a cradle‐to‐grave assessment of water withdrawal and water consumption for the gasoline internal combustion engine vehicle (ICEV) and battery electric vehicle (BEV) variants of the 2012 Ford Focus. U.S. average life cycle water withdrawal and consumption of 531 and 131 cubic meters (m³), respectively, for a lifetime driving distance of 160,000 miles are estimated for the Focus ICEV using E10 gasoline. Employing our upper bound of water use in oil refinery operations and corn and ethanol production increases the life cycle withdrawal and consumption to 1,570 and 761 m³, respectively. The U.S. average life cycle water withdrawal for the Focus BEV is 3,770 m³ (7 times that for the ICEV, reflecting the large volume of cooling water required during electricity generation), whereas the water consumption is 170 m³ (comparable to that for the ICEV). Vehicle use is the most significant phase of the life cycle with fuel production, accounting for 49% of water withdrawal and 82% of water consumption for the ICEV. For the BEV, fuel (electricity) production accounts for 92% of life cycle water withdrawal and 85% of consumption. The results highlight the importance of renewable and sustainable fuels and increased vehicle energy efficiency in providing sustainable mobility.     

Granular activated carbon single-chamber microbial fuel cells (GAC-SCMFCs): A design suitable for large-scale wastewater treatment processes

As an emerging biotechnology capable of removing contaminants and producing electricity, microbial fuel cells (MFCs) hold a promising future in wastewater treatment. However, several main problems, including the high internal resistance (R_in), low power output, expensive material, and complicated configuration have severely hindered the large-scale application of MFCs. The study targeted these challenges by developing a novel MFC system, granular activated carbon single-chamber MFC, termed as GAC-SCMFC. The batch tests showed that GAC was a good substitute for carbon cloth and GAC-SCMFCs generated high and stable power outputs compared with the traditional two-chamber MFCs (2CMFCs). Critical operational parameters (i.e. wastewater substrate concentrations, GAC amount, electrode distance) affecting the performance of GAC-SCMFCs were examined at different levels. The results showed that the R_in gradually decreased from 60 Ω to 45 Ω and the power output increased from 0.2 W/m³ to 1.2 W/m³ when the substrate concentrations increased from 100 mg/L to 850 mg/L. However, at high concentrations of 1000–1500 mg/L, the power output leveled off. The R_in of MFCs decreased 50% when the electrode distance was reduced from 7.5 cm to 1 cm. The highest power was achieved at the electrode distance of 2 cm. The power generation increased with more GAC being added in MFCs due to the higher amount of biomass attached. Finally, the multi-anode GAC-SCMFCs were developed to effectively collect the electrons generated in the GAC bed. The results showed that the current was split among the multiple anodes, and the cathode was the limiting factor in the power production of GAC-SCMFCs.     

Increased sustainable electricity generation in up-flow air-cathode microbial fuel cells

Sustainable electricity was generated from glucose in up-flow air-cathode microbial fuel cells (MFCs) with carbon cloth cathode and carbon granular anode. Plastic sieves rather than membrane were used to separate the anode and cathode. Based on 1g/l glucose as substrate, a maximum volumetric power density of 25+/-4 W/m(3) (89 A/m(3)) was obtained for the MFC with a sieve area of 30 cm(2) and 49+/-3 W/m(3) (215 A/m(3)) for the MFC with a sieve area of 60 cm(2). The increased power density with larger sieve area was mainly due to the decrease of internal resistance according to the electrochemistry impedance spectroscopy analysis. Increasing the sieve area from 30 cm(2) to 60 cm(2) resulted in a decrease of overall internal resistance from 41 ohm to 27.5 ohm and a decrease of ohmic resistance from 24.3 ohm to 14 ohm. While increasing operational recirculation ratio (RR) decreased internal resistance and increased power output at low substrate concentration, the effect of RR on cell performance was negligible at higher substrate concentration.     

Biofuel Cells Select for Microbial Consortia That Self-Mediate Electron Transfer

Microbial fuel cells hold great promise as a sustainable biotechnological solution to future energy needs. Current efforts to improve the efficiency of such fuel cells are limited by the lack of knowledge about the microbial ecology of these systems. The purposes of this study were (i) to elucidate whether a bacterial community, either suspended or attached to an electrode, can evolve in a microbial fuel cell to bring about higher power output, and (ii) to identify species responsible for the electricity generation. Enrichment by repeated transfer of a bacterial consortium harvested from the anode compartment of a biofuel cell in which glucose was used increased the output from an initial level of 0.6 W m⁻² of electrode surface to a maximal level of 4.31 W m⁻² (664 mV, 30.9 mA) when plain graphite electrodes were used. This result was obtained with an average loading rate of 1 g of glucose liter⁻¹ day⁻¹ and corresponded to 81% efficiency for electron transfer from glucose to electricity. Cyclic voltammetry indicated that the enhanced microbial consortium had either membrane-bound or excreted redox components that were not initially detected in the community. Dominant species of the enhanced culture were identified by denaturing gradient gel electrophoresis and culturing. The community consisted mainly of facultative anaerobic bacteria, such as Alcaligenes faecalis and Enterococcus gallinarum, which are capable of hydrogen production. Pseudomonas aeruginosa and other Pseudomonas species were also isolated. For several isolates, electrochemical activity was mainly due to excreted redox mediators, and one of these mediators, pyocyanin produced by P. aeruginosa, could be characterized. Overall, the enrichment procedure, irrespective of whether only attached or suspended bacteria were examined, selected for organisms capable of mediating the electron transfer either by direct bacterial transfer or by excretion of redox components.     

Estimation of mechanical power and energy cost in elite wheelchair racing by analytical procedures and numerical simulations

Abstract

The aim was to compare the mechanical power and energy cost of an elite wheelchair sprinter in the key-moments of the stroke cycle. The wheelchair-athlete system was 3D scanned and then computational fluid dynamics was used to estimate the drag force. Mechanical power and energy cost were derived from a set of formulae. The effective area in the catch, release and recovery phases were 0.41 m², 0.33 m² and 0.24 m², respectively. Drag increased with speed and varied across the key-moments. The catch required the highest total power (range: 62.76–423.46 W), followed-up by the release (61.50–407.85 W) and the recovery (60.09–363.89 W).     

Proton exchange membrane and electrode surface areas as factors that affect power generation in microbial fuel cells

Power generation in microbial fuel cells (MFCs) is a function of the surface areas of the proton exchange membrane (PEM) and the cathode relative to that of the anode. To demonstrate this, the sizes of the anode and cathode were varied in two-chambered MFCs having PEMs with three different surface areas (A _PEM=3.5, 6.2, or 30.6 cm²). For a fixed anode and cathode surface area (A _An=A _Cat=22.5 cm²), the power density normalized to the anode surface area increased with the PEM size in the order 45 mW/m² (A _PEM=3.5 cm²), 68 mW/m² (A _PEM=6.2 cm²), and 190 mW/m² (A _PEM=30.6 cm²). PEM surface area was shown to limit power output when the surface area of the PEM was smaller than that of the electrodes due to an increase in internal resistance. When the relative cross sections of the PEM, anode, and cathode were scaled according to 2A _Cat=A_PEM=2A _An, the maximum power densities of the three different MFCs, based on the surface area of the PEM (A _PEM=3.5, 6.2, or 30.6 cm²), were the same (168±4.53 mW/m²). Increasing the ionic strength and using ferricyanide at the cathode also increased power output.     

Wood Composite as an Energy Efficient Building Material: Guided Sunlight Transmittance and Effective Thermal Insulation

Among many other requirements, energy efficient building materials require effective daylight harvesting and thermal insulation to reduce electricity usage and weatherization cost. The most commonly used daylight harvesting material, glass, has limited light management capability and poor thermal insulation. For the first time, transparent wood is introduced as a building material with the following advantages compared with glass: (1) high optical transparency over the visible wavelength range (>85%); (2) broadband optical haze (>95%), which can create a uniform and consistent daylight distribution over the day without glare effect; (3) unique light guiding effect with a large forward to back scattering ratio of 9 for a 0.5 cm thick transparent wood; (4) excellent thermal insulation with a thermal conductivity around 0.32 W m^?1 K^?1 along the wood growth direction and 0.15 W m^?1 K^?1 in the cross plane, much lower than that of glass (≈1 W m^?1 K^?1); (5) high impact energy absorption that eliminates the safety issues often presented by glass; and (6) simple, scalable fabrication with reliable performance. The demonstrated transparent wood composite exhibits great promise as a future building material, especially as a replacement of glass toward energy efficient building with sustainable materials.     

A Triboelectric Generator Based on Checker‐Like Interdigital Electrodes with a Sandwiched PET Thin Film for Harvesting Sliding Energy in All Directions

A triboelectric generator based on checker‐like interdigital electrodes (TEGC) with a sandwiched polyethylene terephthalate (PET) thin film that can convert translation kinetic energy in all directions to electricity is reported. The design of the sandwiched PET thin film can effectively avoid direct wear between metal electrodes and sliding panel. The mechanism of the TEGC is described in detail. The performance of the TEGC in different sliding directions is studied, indicating a maximum output power density of 1.9 W m^‐2 and open‐circuit voltage of 210 V achieved in the X or Y sliding direction. The TEGC is used to charge a 110 μF commercial capacitor to 5 V in 35 s and light up two light‐emitting diodes (LEDs) connected with the capacitor simultaneously. The TEGC based mouse pad and sliding panel are fabricated to harvest mouse operation energy to light up LEDs connected in antiparallel when the computer mouse operates a game. The TEGC has advantages of being flexible, light weight, durable, cost effective, and portable by folding or rolling into a small part. This work presents a significant progress toward the structure design of triboelectric generator for its practical applications.     

Electricity production by an overflow-type wetted-wall microbial fuel cell

An overflow-type wetted-wall MFC (WWMFC) was developed to generate a stable voltage from acetate-based substrates. The maximum power density of 18.21 W/m³ was obtained. The power generation showed a saturation-type relationship as a function of initial COD, with a maximum power density (P_max) of 18.82 W/m³ and a saturation constant (K_s) of 227.4 mg/l. Forced air flowing through the cathode chamber had a negligible effect on power generation. Influent flow rate could greatly affect the power generation. The maximum power density was increased by 72.8% when the influent flow rate increased from 5 to 30 ml/min. In addition, increasing ionic strength did not affect the power density and internal resistance. Oxygen could be restrained to diffuse into the anode chamber effectively in the overflow-type WWMFC. And the overflow-type WWMFC could be scaled up conveniently in practical application.     

Photosynthetic performance of a cyanobacterium in a vertical flat-plate photobioreactor for outdoor microalgal production and fixation of CO2

A vertical flat-plate photobioreactor was developed for the outdoor culture of microalgae using sunlight as the light source. The ability for biomass production and CO₂ fixation was evaluated by using a cyanobacterium, Synechocystis aquatilis SI-2. The average areal productivity was 31 g biomass m^–2 d^–1, which corresponded to a CO₂ fixation rate of 51 g CO₂ m^–2 d^–1, sustainable in the northern region of Japan during the winter time (January and February). The relationships between the efficiency of solar energy utilization of the reactor and its effect factors (cell concentration and irradiation) were investigated.     

Granular activated carbon single-chamber microbial fuel cells (GAC-SCMFCs): A design suitable for large-scale wastewater treatment processes

As an emerging biotechnology capable of removing contaminants and producing electricity, microbial fuel cells (MFCs) hold a promising future in wastewater treatment. However, several main problems, including the high internal resistance (R_in), low power output, expensive material, and complicated configuration have severely hindered the large-scale application of MFCs. The study targeted these challenges by developing a novel MFC system, granular activated carbon single-chamber MFC, termed as GAC-SCMFC. The batch tests showed that GAC was a good substitute for carbon cloth and GAC-SCMFCs generated high and stable power outputs compared with the traditional two-chamber MFCs (2CMFCs). Critical operational parameters (i.e. wastewater substrate concentrations, GAC amount, electrode distance) affecting the performance of GAC-SCMFCs were examined at different levels. The results showed that the R_in gradually decreased from 60 Ω to 45 Ω and the power output increased from 0.2 W/m³ to 1.2 W/m³ when the substrate concentrations increased from 100 mg/L to 850 mg/L. However, at high concentrations of 1000–1500 mg/L, the power output leveled off. The R_in of MFCs decreased 50% when the electrode distance was reduced from 7.5 cm to 1 cm. The highest power was achieved at the electrode distance of 2 cm. The power generation increased with more GAC being added in MFCs due to the higher amount of biomass attached. Finally, the multi-anode GAC-SCMFCs were developed to effectively collect the electrons generated in the GAC bed. The results showed that the current was split among the multiple anodes, and the cathode was the limiting factor in the power production of GAC-SCMFCs.     

Composition and distribution of internal resistance in three types of microbial fuel cells

High internal resistance is a key problem limiting the power output of the microbial fuel cell (MFC). Therefore, more knowledge about the internal resistance is essential to enhance the performance of the MFC. However, different methods are used to determine the internal resistance, which makes the comparison difficult. In this study, three different types of MFCs were constructed to study the composition and distribution of internal resistance. The internal resistance (R _i) is partitioned into anodic resistance (R _a), cathodic resistance (R _c), and ohmic resistance () according to their origin and the design of the MFCs. These three resistances were then evaluated by the “current interrupt” method and the “steady discharging” method based on the proposed equivalent circuits for MFCs. In MFC-A, MFC-B, and MFC-C, the R _i values were 3.17, 0.35, and 0.076 Ω m², the values were 2.65, 0.085, and 0.008 Ω m², the R _a values were 0.055, 0.115, and 0.034 Ω m², and the R _c values were 0.466, 0.15, and 0.033 Ω m², respectively. For MFC-B and MFC-C, the remarkable decrease in R _i compared with the two-chamber MFC was mainly ascribed to the decline in and R _c. In MFC-C, the membrane electrodes’ assembly lowered the ohmic resistance and facilitated the mass transport through the anode and cathode electrodes, resulting in the lowest R _i among the three types.