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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

Voltage monitoring of two independent MFCs submerged in the same liquid. Each MFC was loaded with a 600-Ω resistor. aStar indicates when only one of the two MFCs was put in open circuit. The blue dotted line is the voltage monitoring when the two MFCs were electrically connected in series (double star, 1200 Ω resistor). b The arrows indicate when the resistive loads were swapped between 600 and 400 Ω. Data show the independent electrical behaviours of both MFCs
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Fig2: Voltage monitoring of two independent MFCs submerged in the same liquid. Each MFC was loaded with a 600-Ω resistor. aStar indicates when only one of the two MFCs was put in open circuit. The blue dotted line is the voltage monitoring when the two MFCs were electrically connected in series (double star, 1200 Ω resistor). b The arrows indicate when the resistive loads were swapped between 600 and 400 Ω. Data show the independent electrical behaviours of both MFCs

Mentions: The two MFCs, of the tubular MFC, were initially connected electrically in parallel and results showed that up to 500 µW of power was generated (data not shown), despite the anodes and cathodes sharing the same electrolyte and only being 2 mm apart from each other. The question that arose from this was in relation to the ‘boundary’ that would constitute an individual microbial fuel cell. Thus, the electrical connection of the test-MFC was such that each MFC (Fig. 1a), was electrically independent. The voltage of each MFC was then monitored under separate, variable resistive loads. Results demonstrated that the two MFCs displayed independent behaviours when different loads were applied to them (Fig. 2). It is worth noting that the optimum urine fluid level i.e. ¾ submerged cathode was empirically found after testing different configurations: ¼ submerged cathode (¾ exposed to air) gave lower but stable performance and a completely submerged cathode initially gave a higher output, but collapsed after only 2 h (eventually decreasing to zero).Fig. 2


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)

Voltage monitoring of two independent MFCs submerged in the same liquid. Each MFC was loaded with a 600-Ω resistor. aStar indicates when only one of the two MFCs was put in open circuit. The blue dotted line is the voltage monitoring when the two MFCs were electrically connected in series (double star, 1200 Ω resistor). b The arrows indicate when the resistive loads were swapped between 600 and 400 Ω. Data show the independent electrical behaviours of both MFCs
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig2: Voltage monitoring of two independent MFCs submerged in the same liquid. Each MFC was loaded with a 600-Ω resistor. aStar indicates when only one of the two MFCs was put in open circuit. The blue dotted line is the voltage monitoring when the two MFCs were electrically connected in series (double star, 1200 Ω resistor). b The arrows indicate when the resistive loads were swapped between 600 and 400 Ω. Data show the independent electrical behaviours of both MFCs
Mentions: The two MFCs, of the tubular MFC, were initially connected electrically in parallel and results showed that up to 500 µW of power was generated (data not shown), despite the anodes and cathodes sharing the same electrolyte and only being 2 mm apart from each other. The question that arose from this was in relation to the ‘boundary’ that would constitute an individual microbial fuel cell. Thus, the electrical connection of the test-MFC was such that each MFC (Fig. 1a), was electrically independent. The voltage of each MFC was then monitored under separate, variable resistive loads. Results demonstrated that the two MFCs displayed independent behaviours when different loads were applied to them (Fig. 2). It is worth noting that the optimum urine fluid level i.e. ¾ submerged cathode was empirically found after testing different configurations: ¼ submerged cathode (¾ exposed to air) gave lower but stable performance and a completely submerged cathode initially gave a higher output, but collapsed after only 2 h (eventually decreasing to zero).Fig. 2

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