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Scaling-up of a novel, simplified MFC stack based on a self-stratifying urine column.

Walter XA, Gajda I, Forbes S, Winfield J, Greenman J, Ieropoulos I - Biotechnol Biofuels (2016)

Bottom Line: This scaling-up increased power but did not negatively affect power density (≈12 W/m(3)), a factor that has proven to be an obstacle in previous studies.The scaling-up approach, with limited power-density losses, was achieved by maintaining a plurality of microenvironments within the module, and resulted in a simple and robust system fuelled by urine.This scaling-up approach, within the tested range, was successful in converting chemical energy in urine into electricity.

View Article: PubMed Central - PubMed

Affiliation: Bristol BioEnergy Centre (B-BiC), Bristol Robotics Laboratory, T-Block, Frenchay Campus, University of the West of England, Bristol, BS16 1QY UK.

ABSTRACT

Background: The microbial fuel cell (MFC) is a technology in which microorganisms employ an electrode (anode) as a solid electron acceptor for anaerobic respiration. This results in direct transformation of chemical energy into electrical energy, which in essence, renders organic wastewater into fuel. Amongst the various types of organic waste, urine is particularly interesting since it is the source of 75 % of the nitrogen present in domestic wastewater despite only accounting for 1 % of the total volume. However, there is a persistent problem for efficient MFC scale-up, since the higher the surface area of electrode to volume ratio, the higher the volumetric power density. Hence, to reach usable power levels for practical applications, a plurality of MFC units could be connected together to produce higher voltage and current outputs; this can be done by combinations of series/parallel connections implemented both horizontally and vertically as a stack. This plurality implies that the units have a simple design for the whole system to be cost-effective. The goal of this work was to address the built configuration of these multiple MFCs into stacks used for treating human urine.

Results: We report a novel, membraneless stack design using ceramic plates, with fully submerged anodes and partially submerged cathodes in the same urine solution. The cathodes covered the top of each ceramic plate whilst the anodes, were on the lower half of each plate, and this would constitute a module. The MFC elements within each module (anode, ceramic, and cathode) were connected in parallel, and the different modules connected in series. This allowed for the self-stratification of the collective environment (urine column) under the natural activity of the microbial consortia thriving in the system. Two different module sizes were investigated, where one module (or box) had a footprint of 900 mL and a larger module (or box) had a footprint of 5000 mL. This scaling-up increased power but did not negatively affect power density (≈12 W/m(3)), a factor that has proven to be an obstacle in previous studies.

Conclusion: The scaling-up approach, with limited power-density losses, was achieved by maintaining a plurality of microenvironments within the module, and resulted in a simple and robust system fuelled by urine. This scaling-up approach, within the tested range, was successful in converting chemical energy in urine into electricity.

No MeSH data available.


Related in: MedlinePlus

a Electrical outputs of the serial connections of increasing numbers of units in a single cascade. Resistances were set from the result of the first polarisation sweep. b Polarisation sweep of the cascade comprising four units connected in series. c Polarisation sweep of individual stack within the cascade. The dotted squares indicate the last points, prior to a non-planned refuelling, that are considered as the maximum power points. Each resistor, ranging from 30 k to 11 Ω, was connected for a period of 10 min
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Fig8: a Electrical outputs of the serial connections of increasing numbers of units in a single cascade. Resistances were set from the result of the first polarisation sweep. b Polarisation sweep of the cascade comprising four units connected in series. c Polarisation sweep of individual stack within the cascade. The dotted squares indicate the last points, prior to a non-planned refuelling, that are considered as the maximum power points. Each resistor, ranging from 30 k to 11 Ω, was connected for a period of 10 min

Mentions: The scale-up in the current study focused on increasing the overall footprint, while at the same time maintaining microenvironments, so that the distances between electrodes were maintained, regardless of overall footprint. This resulted in less-pronounced mass-transfer losses compared to systems where each component has simply been enlarged in relation to the total volume. In addition, the close proximity of the electrodes submerged in the same fluid ensured there were fewer ‘dead spaces’ compared to previous reports of scale-up. Moreover, compared to previous set-ups with a relatively close design (benthic MFC), the power density of M5-11 stack was higher with 21.1 mW produced (Fig. 8b) for a total footprint volume of 5 dm3 instead of 36 mW for 30 dm3 [8]. When normalising to the total footprint surface (0.0459 m2), the power density of the M5–11 stack was 460 mW/m2, which is in the high range of existing systems employing more complex architectures [41] and even 1 order of magnitude higher than the most cost-effective single chamber system with similar volume (1.1 L; [28]). This is nevertheless not an accurate comparison, since these different set-ups employed fuels other than urine. Comparison with other MFCs employing urine as fuel indicates that the design developed here generated higher power densities: ~12.6 instead of ~10 [34], or 2.6 W/m3 [42]. This was all performed using inexpensive sustainable materials such as ceramics and a natural waste product—urine-as fuel.Fig. 8


Scaling-up of a novel, simplified MFC stack based on a self-stratifying urine column.

Walter XA, Gajda I, Forbes S, Winfield J, Greenman J, Ieropoulos I - Biotechnol Biofuels (2016)

a Electrical outputs of the serial connections of increasing numbers of units in a single cascade. Resistances were set from the result of the first polarisation sweep. b Polarisation sweep of the cascade comprising four units connected in series. c Polarisation sweep of individual stack within the cascade. The dotted squares indicate the last points, prior to a non-planned refuelling, that are considered as the maximum power points. Each resistor, ranging from 30 k to 11 Ω, was connected for a period of 10 min
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4862055&req=5

Fig8: a Electrical outputs of the serial connections of increasing numbers of units in a single cascade. Resistances were set from the result of the first polarisation sweep. b Polarisation sweep of the cascade comprising four units connected in series. c Polarisation sweep of individual stack within the cascade. The dotted squares indicate the last points, prior to a non-planned refuelling, that are considered as the maximum power points. Each resistor, ranging from 30 k to 11 Ω, was connected for a period of 10 min
Mentions: The scale-up in the current study focused on increasing the overall footprint, while at the same time maintaining microenvironments, so that the distances between electrodes were maintained, regardless of overall footprint. This resulted in less-pronounced mass-transfer losses compared to systems where each component has simply been enlarged in relation to the total volume. In addition, the close proximity of the electrodes submerged in the same fluid ensured there were fewer ‘dead spaces’ compared to previous reports of scale-up. Moreover, compared to previous set-ups with a relatively close design (benthic MFC), the power density of M5-11 stack was higher with 21.1 mW produced (Fig. 8b) for a total footprint volume of 5 dm3 instead of 36 mW for 30 dm3 [8]. When normalising to the total footprint surface (0.0459 m2), the power density of the M5–11 stack was 460 mW/m2, which is in the high range of existing systems employing more complex architectures [41] and even 1 order of magnitude higher than the most cost-effective single chamber system with similar volume (1.1 L; [28]). This is nevertheless not an accurate comparison, since these different set-ups employed fuels other than urine. Comparison with other MFCs employing urine as fuel indicates that the design developed here generated higher power densities: ~12.6 instead of ~10 [34], or 2.6 W/m3 [42]. This was all performed using inexpensive sustainable materials such as ceramics and a natural waste product—urine-as fuel.Fig. 8

Bottom Line: This scaling-up increased power but did not negatively affect power density (≈12 W/m(3)), a factor that has proven to be an obstacle in previous studies.The scaling-up approach, with limited power-density losses, was achieved by maintaining a plurality of microenvironments within the module, and resulted in a simple and robust system fuelled by urine.This scaling-up approach, within the tested range, was successful in converting chemical energy in urine into electricity.

View Article: PubMed Central - PubMed

Affiliation: Bristol BioEnergy Centre (B-BiC), Bristol Robotics Laboratory, T-Block, Frenchay Campus, University of the West of England, Bristol, BS16 1QY UK.

ABSTRACT

Background: The microbial fuel cell (MFC) is a technology in which microorganisms employ an electrode (anode) as a solid electron acceptor for anaerobic respiration. This results in direct transformation of chemical energy into electrical energy, which in essence, renders organic wastewater into fuel. Amongst the various types of organic waste, urine is particularly interesting since it is the source of 75 % of the nitrogen present in domestic wastewater despite only accounting for 1 % of the total volume. However, there is a persistent problem for efficient MFC scale-up, since the higher the surface area of electrode to volume ratio, the higher the volumetric power density. Hence, to reach usable power levels for practical applications, a plurality of MFC units could be connected together to produce higher voltage and current outputs; this can be done by combinations of series/parallel connections implemented both horizontally and vertically as a stack. This plurality implies that the units have a simple design for the whole system to be cost-effective. The goal of this work was to address the built configuration of these multiple MFCs into stacks used for treating human urine.

Results: We report a novel, membraneless stack design using ceramic plates, with fully submerged anodes and partially submerged cathodes in the same urine solution. The cathodes covered the top of each ceramic plate whilst the anodes, were on the lower half of each plate, and this would constitute a module. The MFC elements within each module (anode, ceramic, and cathode) were connected in parallel, and the different modules connected in series. This allowed for the self-stratification of the collective environment (urine column) under the natural activity of the microbial consortia thriving in the system. Two different module sizes were investigated, where one module (or box) had a footprint of 900 mL and a larger module (or box) had a footprint of 5000 mL. This scaling-up increased power but did not negatively affect power density (≈12 W/m(3)), a factor that has proven to be an obstacle in previous studies.

Conclusion: The scaling-up approach, with limited power-density losses, was achieved by maintaining a plurality of microenvironments within the module, and resulted in a simple and robust system fuelled by urine. This scaling-up approach, within the tested range, was successful in converting chemical energy in urine into electricity.

No MeSH data available.


Related in: MedlinePlus