1,720,984 research outputs found
Investigating a cascade of seven hydraulically connected microbial fuel cells
No full textSeven miniature microbial fuel cells (MFCs) were hydraulically linked in sequence and operated in continuous-flow (cascade). Power output and treatment efficiency were investigated using varying organic loads, flow-rates and electrical configurations. When fed synthetic wastewater low in organic load (1. mM acetate) only the first MFC operated stably over a 72-h period. Acetate feedstock at 5. mM was enough to sustain the first four MFCs, and 10. mM acetate was sufficient to maintain all MFCs at stable power densities. COD was reduced from 69 to 25. mg/L (64%, 1. mM acetate), 319-34. mg/L (90%, 5. mM acetate) and 545-264. mg/L (52%, 10. mM acetate). Fluctuating flow-rates improved performance in downstream MFCs. When connected electrically in parallel, power output was two-fold and current production 10-fold higher than when connected in series. The results suggest cascades of MFCs could be employed to complement or improve biological trickling filters. © 2012 Elsevier Ltd
Effects of flow-rate, inoculum and time on the internal resistance of microbial fuel cells
No full textTo process large volumes of wastewater, microbial fuel cells (MFCs) would require anodophilic bacteria preferably operating at high flow-rates. The effect of flow-rate on different microbial consortia was examined during anodic biofilm development, using inocula designed to enrich either aerobes/facultative species or anaerobes. All MFCs underperformed at high flow-rates in the early stages, however, the aerobic type - following anodic biofilm development - subsequently exhibited more marked improvement. Scanning electron microscopy showed some variation in biofilm formation where clumpy growth was associated with lower power. Over time both power and internal resistance increased for the low flow-rates perhaps explained by an evolving microflora that consequently changed redox potential. An overshoot was observed in power curves, which was attributed to increased internal resistance due to ionic depletion and/or microbial exhaustion. To the best of the authors' knowledge this is the first time that such phenomena are explained from the internal resistance perspective. © 2010 Elsevier Ltd. All rights reserved
A review into the use of ceramics in microbial fuel cells
Full text linkAbstractMicrobial fuel cells (MFCs) offer great promise as a technology that can produce electricity whilst at the same time treat wastewater. Although significant progress has been made in recent years, the requirement for cheaper materials has prevented the technology from wider, out-of-the-lab, implementation. Recently, researchers have started using ceramics with encouraging results, suggesting that this inexpensive material might be the solution for propelling MFC technology towards real world applications. Studies have demonstrated that ceramics can provide stability, improve power and treatment efficiencies, create a better environment for the electro-active bacteria and contribute towards resource recovery. This review discusses progress to date using ceramics as (i) the structural material, (ii) the medium for ion exchange and (iii) the electrode for MFCs
Supercapacitive paper based microbial fuel cell: High current/power production within a low cost design
Full text linkMicrobial fuel cells (MFCs) with paper separators and liquid containing elements were investigated in super- capacitive mode. MFCs (15 mL) in a supercapacitive configuration, consisted of plain wrapped carbon veil anode (negative) and conductive latex cathode (positive). The internal supercapacitor is discharged galvanostatically and is self-recharged as red-ox reactions occur on both electrodes. MFCs were discharged at different current pulses varying from 1 mA to 7 mA. The MFCs had an equivalent series resistance of 41.2 ± 3.5 Ω caused mainly by the cathode. A maximum power of 1.380 ± 0.083 mW (0.092 ± 0.006 mW mL−1) was measured. Durability tests were conducted over 24 h collecting 1000 discharge cycles (0.5 s) and self-recharges (85 s) at a current of 1 mA. Over time the anode potential dropped causing a decline in performance perhaps due to evaporation of liquid from the pyramidal structure. Resistance and apparent capacitance measured during the durability test remained approximately constant during the cycles
Comparing terracotta and earthenware for multiple functionalities in microbial fuel cells
No full textThe properties of earthenware and terracotta were investigated in terms of structural integrity and ion conductivity, in two microbial fuel cell (MFC) designs. Parameters such as wall thickness (4, 8, 18 mm), porosity and cathode hydration were analysed. During the early stages of operation (2 weeks), the more porous earthenware lost anolyte quickly and was unstable between feeding compared to terracotta. Three weeks later MFCs of all thicknesses were more stable and could sustain longer periods of power production without maintenance. In all cases, the denser terracotta produced higher open circuit voltage; however, earthenware the more porous and less iron-rich of the two, proved to be the better material for power production, to the extent that the thickest wall (18 mm) MFC produced 15 % higher power than the thinnest wall (4 mm) terracotta. After 6 weeks of operation, the influence of wall thickness was less exaggerated and power output was comparable between the 4 and 8 mm ceramic membranes. Cylindrical earthenware MFCs produced significantly higher current (75 %) and power (33 %) than terracotta MFCs. A continuous dripping mode of cathode hydration produced threefold higher power than when MFCs were submerged in water, perhaps because of a short-circuiting effect through the material. This shows a significant improvement in terms of biosystems engineering, since a previously high-maintenance half-cell, is now shown to be virtually self-sufficient.©Springer-Verlag Berlin Heidelberg 2013
Here today, gone tomorrow:biodegradable soft robots
Full text linkOne of the greatest challenges to modern technologies is what to do with them when they go irreparably wrong or come to the end of their productive lives. The convention, since the development of modern civilisation, is to discard a broken item and then procure a new one. In the 20th century enlightened environmentalists campaigned for recycling and reuse (R and R). R and R has continued to be an important part of new technology development, but there is still a huge problem of non-recyclable materials being dumped into landfill and being discarded in the environment. The challenge is even greater for robotics, a field which will impact on all aspects of our lives, where discards include motors, rigid elements and toxic power supplies and batteries. One novel solution is the biodegradable robot, an active physical machine that is composed of biodegradable materials and which degrades to nothing when released into the environment. In this paper we examine the potential and realities of biodegradable robotics, consider novel solutions to core components such as sensors, actuators and energy scavenging, and give examples of biodegradable robotics fabricated from everyday, and not so common, biodegradable electroactive materials. The realisation of truly biodegradable robots also brings entirely new deployment, exploration and bio-remediation capabilities: why track and recover a few large non-biodegradable robots when you could speculatively release millions of biodegradable robots instead? We will consider some of these exciting developments and explore the future of this new field
The overshoot phenomenon as a function of internal resistance in microbial fuel cells
Full text linkA method for assessing the performance of microbial fuel cells (MFCs) is the polarisation sweep where different external resistances are applied at set intervals (sample rates). The resulting power curves often exhibit an overshoot where both power and current decrease concomitantly. To investigate these phenomena, small-scale (1. mL volume) MFCs operated in continuous flow were subjected to polarisation sweeps under various conditions. At shorter sample rates the overshoot was more exaggerated and power generation was overestimated; sampling at 30. s produced 23% higher maximum power than at 3. min. MFCs with an immature anodic biofilm (5. days) exhibited a double overshoot effect, which disappeared after a sufficient adjustment period (5. weeks). Mature MFCs were subject to overshoot when the anode was fed weak (1. mM acetate) feedstock with low conductivity (1500 μS). MFCs developed in a pH neutral environment produced overshoot after the anode had been exposed to acidic (pH 3) conditions for 24. h. In contrast, changes to the cathode both in terms of pH and varying catholyte conductivity, although affecting power output did not result in overshoot suggesting that this is an anodic phenomenon. © 2011 Elsevier B.V
Analysis of microbial fuel cell operation in acidic conditions using the flocculating agent ferric chloride
Full text link© 2014 Society of Chemical Industry. BACKGROUND: Ferric chloride (FeCl3) is widely used as a flocculating agent during wastewater treatment but can detrimentally lower pH and increase iron concentration. Microbial fuel cells (MFCs) are a promising technology for treating waste while concomitantly producing electricity and so were tested under the extreme conditions imposed by the addition of FeCl3. MFCs were fed eight concentrations of FeCl3 over two 8-week periods and the effects on power, pH, conductivity, metal content and COD were examined. RESULTS: MFCs generated highest power (3.58Wm-3) at 1.6mmolL-1 FeCl3 (pH 3.46), however cells reversed when fed 2mmolL-1 (pH 3.29). During the second run, power almost doubled and MFCs were more resilient at higher loadings up to 2.8mmolL-1 (pH 3.02). Conductivity and pH increased following treatment while soluble phosphorus, sulphur and iron levels decreased significantly in all feedstock up to 1.6mmolL-1 FeCl3. COD reduction was observed but efficiency may have been affected by the presence of alternative electron donors such as hydrogen sulphide. CONCLUSION: These findings demonstrate the robustness and versatility of MFCs in hostile conditions. They also confirm that MFCs can complement current wastewater treatment processes, even downstream from FeCl3 dosing where conditions might be deemed unsuitable for operation
Cast and 3D printed ion exchange membranes for monolithic microbial fuel cell fabrication
Full text linkAbstractWe present novel solutions to a key challenge in microbial fuel cell (MFC) technology; greater power density through increased relative surface area of the ion exchange membrane that separates the anode and cathode electrodes. The first use of a 3D printed polymer and a cast latex membrane are compared to a conventionally used cation exchange membrane. These new techniques significantly expand the geometric versatility available to ion exchange membranes in MFCs, which may be instrumental in answering challenges in the design of MFCs including miniaturisation, cost and ease of fabrication.Under electrical load conditions selected for optimal power transfer, peak power production (mean 10 batch feeds) was 11.39 μW (CEM), 10.51 μW (latex) and 0.92 μW (Tangoplus). Change in conductivity and pH of anolyte were correlated with MFC power production. Digital and environmental scanning electron microscopy show structural changes to and biological precipitation on membrane materials following long term use in an MFC. The cost of the novel membranes was lower than the conventional CEM. The efficacy of two novel membranes for ion exchange indicates that further characterisation of these materials and their fabrication techniques, shows great potential to significantly increase the range and type of MFCs that can be produced
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