1,720,979 research outputs found
Scalability of self-stratifying microbial fuel cell:Towards height miniaturisation
Full text link The scalability of bioelectrochemical systems is a key parameter for their practical implementation in the real-world. Up until now, only urine-fed self-stratifying microbial fuel cells (SSM-MFCs) have been shown to be scalable in width and length with limited power density losses. For practical reasons, the present work focuses on the scalability of SSM-MFCs in the one dimension that has not yet been investigated, namely height. Three different height conditions were considered (1 cm, 2 cm and 3 cm tall electrodes). The normalised power density of the 2 cm and 3 cm conditions were similar either during the durability test under a hydraulic retention time of ≈39 h (i.e. 15.74 ± 0.99 μW.cm −3 ) and during the polarisation experiments (i.e. 27.79 ± 0.92 μW.cm −3 ). Conversely, the 1 cm condition had lower power densities of 11.23 ± 0.07 μW.cm −3 and 17.73 ± 3.94 μW.cm −3 both during the durability test and the polarisation experiment, respectively. These results confirm that SSM-MFCs can be scaled in all 3 dimensions with minimal power density losses, with a minimum height threshold for the electrode comprised between 1 cm and 2 cm. </p
Scalability and stacking of self-stratifying microbial fuel cells treating urine
Full text linkThe scalability of Microbial fuel cells (MFCs) is key to the development of stacks. A recent study has shown that self-stratifying membraneless MFCs (S-MFCs) could be scaled down to 2 cm without performance deterioration. However, the scaling-up limit of S-MFC is yet unknown. Here the study evaluates the scale-up height of S-MFCs treating urine, from 2 cm, 4 cm to 12 cm high electrodes. The electrochemical properties of the S-MFCs were investigated after steady-states were established, following a 70-days longevity study. The electrochemical properties of the 2 cm and 4 cm conditions were similar (5.45 ± 0.32 mW per cascade). Conversely, the 12 cm conditions had much lower power output (1.48 ± 0.15 mW). The biofilm on the 12 cm cathodes only developed on the upper 5–6 cm of the immersed part of the electrode suggesting that the cathodic reactions were the limiting factor. This hypothesis was confirmed by the cathode polarisations showing that the 12 cm S-MFC had low current density (1.64 ± 9.53 µA cm−2, at 0 mV) compared to the other two conditions taht had similar current densities (192.73 ± 20.35 µA cm−2, at 0 mV). These results indicate that S-MFC treating urine can only be scaled-up to an electrode height of around 5–6 cm before the performance is negatively affected.</p
Field Trial of Self-Stratifying Membrane-Less Microbial Fuel Cells Stacks in an Autonomous and Self-Powered Urinal
No full textThe main competitive advantage of the microbial fuel cell (MFC) technology is to generate electricity from organic waste, which is otherwise considered expensive to treat; as such, interest in this field has intensified over the two last decades. Efforts have mainly focussed on improving the materials employed, the design configuration and the energy-harvesting peripherals. Many improvement solutions have been proposed within the last decade, more and more pilot-scale systems feeding on various kinds of feedstock have been tested (e.g. domestic wastewater, brewery waste, marine sediments, urine). A previous field trial at Glastonbury Music Festival has already demonstrated the feasibility of directly using urine from festival goers to light-up a urinal, thereby setting a benchmark in urine fuelled-MFCs for self-sustainable applications [1]. Furthermore, the concept of self-stratifying membraneless MFC (SSM-MFC) has also been reported. This approach allows scaling-up units’ sizes without significant power density losses, within the tested range (from 900 mL to 5000mL), a factor that has proven an obstacle in previous studies. This design had only been tested under controlled laboratory conditions and never trialled under real usage conditions [2, 3].In the current study the results of an autonomous system, which was tested at the Glastonbury Music Festival 2016 are presented. To perform this trial, large MFC modules were built, tested and integrated in a setup that comprised a urinal, a stack of 12 SSM-MFCs modules, and an energy management control system harvesting the generated energy to power the lighting of the urinal. The urinal was large enough to accommodate 12 users at any given time and consisted of troughs directing urine to a buffer tank. This tank, equipped with an over flow redirecting excess urine, was connected to a passive feeding mechanism that was supplying urine to a MFC stack of 12 modules every time a volume of 9 L was reached. The stack was set with 6 independent cascades, each having 2 MFC modules electrically connected in parallel. Each module of the cascade comprised 38 MFCs submerged in the same electrolyte and electrically connected in parallel. All six cascades were electrically connected in series. The energy was then harvested and stored in a battery bank. At night (≈9h30 duty-cycles), the control board was redirecting the energy towards 6 LED strips (2.862W) lighting the urinal.Results from laboratory conditions have shown that the power density of a single module was ~2.75 W.m-3, whereas under real conditions the power density ranged from ~1.70 to ~2.36 W.m-3 (total volumetric footprint). The energy harvested from the undiluted urine was sufficient to power the PEE POWER® lights for 9h30 every day. Under laboratory conditions, at 44h hydraulic retention time (HRT) the COD was reduced from 5.586 mg COD.L-1 to 0.625 mg COD.L-1 (88%); the nitrogen was also reduced by 29%. In the field, with a HRT of 11h40, the COD decreased by 48% and the total nitrogen content by 13%. When plotting data from the laboratory tests together with the ones of the field trial, the fitted Michaelis-Menten curve (r2=0.960) indicates that with a HRT of ≈64h, the COD could be reduced to the European Union standard for discharge (0.125 mg COD.L-1). Compared to the 2015 field trial benchmark [1], the present system demonstrates a 37 % higher COD removal with a 50% shorter HRT, and produced ≈30% more energy in a third of the total volumetric footprint. Overall, these results correspond to an over 7-fold technological improvement.[1] Ieropoulos IA, Stinchcombe A, Gajda I, Forbes S, Merino-Jimenez I, Pasternak G, Sanchez-Herranz D and Greenman J. Pee power urinal - microbial fuel cell technology field trials in the context of sanitation. Environ. Sci.-Wat. Res. Technol. 2016;2:336-343[2] Walter XA, Gajda I, Forbes S, Winfield J, Greenman J and Ieropoulos I. Scaling-up of a novel, simplified MFC stack based on a self-stratifying urine column. Biotechnology for Biofuel 2016;9:93[3] Walter XA, Stinchcombe A, Greenman J and Ieropoulos I. Urine transduction to usable energy: a modular MFC approach for smartphone and remote system charging. Applied Energy 2017;192:575-58
Urine transduction to usable energy: A modular MFC approach for smartphone and remote system charging
Full text linkAbstractThis study reports for the first time the full charging of a state-of-the-art mobile smartphone, using Microbial Fuel Cells fed with urine. This was possible by employing a new design of MFC that allowed scaling-up without power density losses. Although it was demonstrated in the past that a basic mobile phone could be charged by MFCs, the present study goes beyond this to show how, simply using urine, an MFC system successfully charges a modern-day smartphone. Several energy-harvesting systems have been tested and results have demonstrated that the charging circuitry of commercially available phones may consume up to 38% of energy on top of the battery capacity. The study concludes by developing a mobile phone charger based on urine, which results in 3h of phone operation (outgoing call) for every 6h of charge time, with as little as 600mL (per charge) of real neat urine
From single MFC to cascade configuration: The relationship between size, hydraulic retention time and power density
Full text linkAbstractAchieving useful electrical power production with the MFC technology requires a plurality of units. Therefore, the main objective of much of the MFC research is to increase the power density of each unit. Collectives of MFCs will inherently include units grouped in cascades, whereby the outflow of one is the inflow to the next unit; such an approach allows for better fuel utilisation. However, such a configuration is subject to some important considerations, including: the size of the MFCs; the number of units i.e. the length of the cascade; hydraulic retention time; fuel quality; and optimisation of anode surface and microbial colonisation. In the present study, optimisation of the aforementioned aspects has been investigated in order to establish the most appropriate cascade design. Results demonstrate that an increased flow rate of treated urine achieved equal power density with the same setup when fed with fresh urine at a lower flow rate. The independent investigations of these parameters have led to the design of a cascade that maintains uniformity with regard to the aforementioned parameters, by incorporating units of decreasing size, thus allowing locally shorter hydraulic retention times and therefore leading to increased power density levels
Self-stratifying microbial fuel cell: The importance of the cathode electrode immersion height
Full text linkPower generation of bioelectrochemical systems (BESs) is a very important electrochemical parameter to consider particularly when the output has to be harvested for practical ap- plications. This work studies the effect of cathode immersion on the performance of a self- stratified membraneless microbial fuel cell (SSM-MFC) fuelled with human urine. Four different electrolyte immersion heights, i.e. 1 4, 2 4, 3 4 and fully submerged were consid- ered. The SSM-MFC performance improved with increased immersion up to 3 4. The output dropped drastically when the cathode was fully submerged with the conditions becoming fully anaerobic. SSM-MFC with 3 4 submerged cathode had a maximum power output of 3.0 mW followed by 2.4 mW, 2.0 mW, and 0.2 mW for the 2 4, 1 4 and fully submerged conditions. Durability tests were run on the best performing SSM-MFC with 3 4 cathode immersed and showed an additional increase in the electrochemical output by 17% from 3.0 mW to 3.5 mW. The analysis performed on the anode and cathode separately demonstrated the stability in the cathode behaviour and in parallel an improvement in the anodic performance during one month of investigation
Microbial fuel cells directly powering a microcomputer
No full textMany studies have demonstrated that microbial fuel cells (MFC) can be energy-positive systems and power various low power applications. However, to be employed as a low-level power source, MFC systems rely on energy management circuitry, used to increase voltage levels and act as energy buffers, thus delivering stable power outputs. But stability comes at a cost, one that needs to be kept minimal for the technology to be deployed into society. The present study reports, for the first time, the use of a MFC system that directly and continuously powered a small application without any electronic intermediary. A cascade comprising four membrane-less MFCs modules and producing an average of 62 mA at 2550 mV (158 mW) was used to directly power a microcomputer and its screen (Gameboy Color, Nintendo®). The polarisation experiment showed that the cascade produced 164 mA, at the minimum voltage required to run the microcomputer (ca. 1.850 V). As the microcomputer only needed ≈70 mA, the cascade ran at a higher voltage (2.550 V), thus, maintaining the individual modules at a high potential (>0.55 V). Running the system at these high potentials helped avoid cell reversal, thus delivering a stable level of energy without the support of any electronics
In Situ Development of Efficient Electrogenic Bacterial Community in Urine Fed Microbial Fuel Cell Cascades
No full textMicrobial fuel cell technology harnesses the potential of some naturally occurring bacteria for electricity generation. To initiate the operation of microbial fuel cells, inoculation with different types of bacterial community, including those found in activated sludge, are employed. There are however, health hazards associated with the use of digested activated sludge and this of course depends on where the sample has been sourced from. Organisms such as Mycobacterium tuberculosis, Pseudomonas aeruginosa and enteric viruses have been reported in activated sludge, which can have practical difficulties when working with such samples. Therefore, the development of an efficient electroactive bacterial community, capable of producing optimum power output without the need for sludge inoculation, would eliminate any potential risks. In the current study, we developed an efficient electroactive bacterial community within a ceramic based MFC system, using only fresh urine as the inoculum. Efficient biofilm development was achieved by stepwise adjustment of the external resistance, following 48 hours of open circuit operation. This resulted in a uniform bacterial community with power output levels >50% higher than those inoculated (as per standard practice) with activated sludge. The results showed that power generation begins within 2 days of experimental set-up, compared to at least 5 days in sludge inoculated systems, thus significantly reducing start up time. Incidentally, the development of the bacterial community occurs irrespective of the freshness or age of the urine feed. Given the difficulty in moving suitable activated sludge across countries/borders and that practical application of MFCs technology is more likely to occur in remote rural locations, it is possible that suitable activated sludge might not be available for inoculation locally. Therefore, deployment of MFC systems capable of producing optimum power without the need for sludge-inoculation would be beneficial to their widespread global application. This is the first report of an in situ development of an electroactive bacterial community in urine-fed MFC systems that outperform those initially inoculated with activated sludge
Binder materials for the cathodes applied to self-stratifying membraneless microbial fuel cell
Full text link© 2018 The Authors The recently developed self-stratifying membraneless microbial fuel cell (SSM-MFC) has been shown as a promising concept for urine treatment. The first prototypes employed cathodes made of activated carbon (AC) and polytetrafluoroethylene (PTFE) mixture. Here, we explored the possibility to substitute PTFE with either polyvinyl-alcohol (PVA) or PlastiDip (CPD; i.e. synthetic rubber) as binder for AC-based cathode in SSM-MFC. Sintered activated carbon (SAC) was also tested due to its ease of manufacturing and the fact that no stainless steel collector is needed. Results indicate that the SSM-MFC having PTFE cathodes were the most powerful measuring 1617 μW (11 W·m−3 or 101 mW·m−2). SSM-MFC with PVA and CPD as binders were producing on average the same level of power (1226 ± 90 μW), which was 24% less than the SSM-MFC having PTFE-based cathodes. When balancing the power by the cost and environmental impact, results clearly show that PVA was the best alternative. Power wise, the SAC cathodes were shown being the less performing (≈1070 μW). Nonetheless, the lower power of SAC was balanced by its inexpensiveness. Overall results indicate that (i) PTFE is yet the best binder to employ, and (ii) SAC and PVA-based cathodes are promising alternatives that would benefit from further improvements
Scaling up self-stratifying supercapacitive microbial fuel cell
Full text linkSelf-stratifying microbial fuel cells with three different electrodes sizes and volumes were operated in supercapacitive mode. As the electrodes size increased, the equivalent series resistance decreased, and the overall power was enhanced (small: ESR = 7.2 Ω and Pmax = 13 mW; large: ESR = 4.2 Ω and Pmax = 22 mW). Power density referred to cathode geometric surface area and displacement volume of the electrolyte in the reactors. With regards to the electrode wet surface area, the large size electrodes (L-MFC) displayed the lowest power density (460 μW cm−2) whilst the small and medium size electrodes (S-MFC, M-MFC) showed higher densities (668 μW cm−2 and 633 μW cm−2, respectively). With regard to the volumetric power densities the S-MFC, the M-MFC and the L-MFC had similar values (264 μW mL−1, 265 μW mL−1 and 249 μW cm−1, respectively). Power density normalised in terms of carbon weight utilised for fabricating MFC cathodes-electrodes showed high output for smaller electrode size MFC (5811 μW g−1-C- and 3270 μW g−1-C- for the S-MFC and L-MFC, respectively) due to the fact that electrodes were optimised for MFC operations and not supercapacitive discharges. Apparent capacitance was high at lower current pulses suggesting high faradaic contribution. The electrostatic contribution detected at high current pulses was quite low. The results obtained give rise to important possibilities of performance improvements by optimising the device design and the electrode fabrication
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