Allometric scaling of microbial fuel cells and stacks: The lifeform case for scale-up

© 2017 Elsevier B.V. This case study reports for the first time on the comparison between allometric scaling of lifeforms and scale-up of microbial fuel cell entities; enlarging individual units in volume, footprint and electrode surface area but also multiplying a static size/footprint and electrode surface area to scale-up by stacking. A study published in 2010 by DeLong etal. showed for the first time that Kleiber's law does not apply uniformly to all lifeforms, and that in fact growth rate for prokaryotes is superlinear, for protists is linear and for metazoa is sublinear. The current study, which is utilising data from previous experiments, is showing for the first time that for individual MFC units, which are enlarged, growth rate/power is sublinear, whereas for stacks this is superlinear

Complete microbial fuel cell fabrication using additive layer manufacturing

Improving the efficiency of microbial fuel cell (MFC) technology by enhancing the system performance and reducing the production cost is essential for commercialisation. In this study, building an additive manufacturing (AM)-built MFC comprising all 3D printed components such as anode, cathode and chassis was attempted for the first time. 3D printed base structures were made of low-cost, biodegradable polylactic acid (PLA) filaments. For both anode and cathode, two surface modification methods using either graphite or nickel powder were tested. The best performing anode material, carbon-coated non-conductive PLA filament, was comparable to the control modified carbon veil with a peak power of 376.7 µW (7.5 W m−3) in week 3. However, PLA-based AM cathodes underperformed regardless of the coating method, which limited the overall performance. The membrane-less design produced more stable and higher power output levels (520−570 µW, 7.4−8.1 W m−3) compared to the ceramic membrane control MFCs. As the final design, four AM-made membrane-less MFCs connected in series successfully powered a digital weather station, which shows the current status of low-cost 3D printed MFC development

Scalability and stacking of self-stratifying microbial fuel cells treating urine

The 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

Scalability of self-stratifying microbial fuel cell: Towards height miniaturisation

© 2019 The Authors 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

A new method for urine electrofiltration and long term power enhancement using surface modified anodes with activated carbon in ceramic microbial fuel cells

This work is presenting for the first time the use of inexpensive and efficient anode material for boosting power production, as well as improving electrofiltration of human urine in tubular microbial fuel cells (MFCs). The MFCs were constructed using unglazed ceramic clay functioning as the membrane and chassis. The study is looking into effective anodic surface modification by applying activated carbon micro-nanostructure onto carbon fibres that allows electrode packing without excessive enlargement of the electrode. The surface treatment of the carbon veil matrix resulted in 3.7 mW (52.9 W m−3 and 1626 mW m−2) of power generated and almost a 10-fold increase in the anodic current due to the doping as well as long-term stability in one year of continuous operation. The higher power output resulted in the synthesis of clear catholyte, thereby i) avoiding cathode fouling and contributing to the active splitting of both pH and ions and ii) transforming urine into a purified catholyte - 30% salt reduction - by electroosmotic drag, whilst generating - rather than consuming – electricity, and in a way demonstrating electrofiltration. For the purpose of future technology implementation , the importance of simultaneous increase in power generation, long-term stability over 1 year and efficient urine cleaning by using low-cost materials, is very promising and helps the technology enter the wider market

Microbial fuel cells in the house: A study on real household wastewater samples for treatment and power

In line with the global movement towards sustainable buildings and dwellings, this work investigated the potential for integrating microbial fuel cell technology into future architecture. Various types of domestic greywater and wastewater from five different sources (bathroom, kitchen sink, dishwasher, laundry washing machine and urinal) were tested as feedstock in otherwise identical MFCs. In terms of power output, urine outperformed other feedstock types by producing a maximum power of 3.91 ± 0.27 mW (97.8 ± 6.8 W m−3). The urine-fed MFCs showed a COD removal rate of 38.9 ± 1.1% and coulombic efficiency of 15.1 ± 3.4%. When urine was diluted with either bathwater or tap water, which represents a realistic scenario where flushing toilets are installed, results showed that MFC power output decreased with increasing dilutions. Interestingly, when commercial bleach was added in full concentration, although the level of instantaneous power dropped, performance recovered to the previous levels within 48 h after this was replaced with fresh urine. This suggests that the MFC systems are fairly robust and can be resistant to short-term domestic chemical exposure. These novel findings provide a stepping-stone to more sustainable future buildings and cities with fully integrated MFC technology

Living architecture: Toward energy generating buildings powered by microbial fuel cells

In this study, possibilities of integrating microbial fuel cell (MFC) technology and buildings were investigated. Three kinds of conventional house bricks from two different locations were tested as MFC reactors and their electrochemical characteristics were analysed. European standard off-the-shelf house bricks generated a maximum power of 1.2 mW (13.5 mW m−2) when fed with human urine. Ugandan house air bricks produced a maximum power of 2.7 mW (32.8 mW m−2), again with human urine. Different cathode types made by surface modifications using two kinds of carbon compounds and two PTFE based binders were tested in both wet and dry cathode conditions. The effects of both anode and cathode sizes, electrode connection, electrode configuration, and feedstock on brick MFC power generation were also studied. Water absorption test results showed higher porosity for the Ugandan air bricks than European engineering bricks, which contributed to its higher performance. This study suggests that the idea of converting existing and future buildings to micro-power stations and micro-treatment plants with the help of integrated MFCs and other renewable technologies is achievable, which will be a step closer to a truly sustainable life

On hybrid circuits exploiting thermistive properties of slime mould

Slime mould Physarum polycephalum is a single cell visible by the unaided eye. Let the slime mould span two electrodes with a single protoplasmic tube: if the tube is heated to approximately ≈40 °C, the electrical resistance of the protoplasmic tube increases from ≈3 Mω to ≈10,000 Mω. The organisms resistance is not proportional nor correlated to the temperature of its environment. Slime mould can therefore not be considered as a thermistor but rather as a thermic switch. We employ the P. polycephalum thermic switch to prototype hybrid electrical analog summator, NAND gates, and cascade the gates into Flip-Flop latch. Computing operations performed on this bio-hybrid computing circuitry feature high repeatability, reproducibility and comparably low propagation delays

Developing 3D-printable cathode electrode for monolithically printed microbial fuel cells (MFCs)

© 2020 by the authors. Microbial Fuel Cells (MFCs) employ microbial electroactive species to convert chemical energy stored in organic matter, into electricity. The properties of MFCs have made the technology attractive for bioenergy production. However, a challenge to the mass production of MFCs is the time-consuming assembly process, which could perhaps be overcome using additive manufacturing (AM) processes. AM or 3D-printing has played an increasingly important role in advancing MFC technology, by substituting essential structural components with 3D-printed parts. This was precisely the line of work in the EVOBLISS project, which investigated materials that can be extruded from the EVOBOT platform for a monolithically printed MFC. The development of such inexpensive, eco-friendly, printable electrode material is described below. The electrode in examination (PTFE-FREE-AC), is a cathode made of alginate and activated carbon, and was tested against an off-the-shelf sintered carbon (AC-BLOCK) and a widely used activated carbon electrode (PTFE-AC). The results showed that the MFCs using PTFE-FREE-AC cathodes performed better compared to the PTFE-AC or AC-BLOCK, producing maximum power levels of 286 μW, 98 μW and 85 μW, respectively. In conclusion, this experiment demonstrated the development of an air-dried, extrudable (3D-printed) electrode material successfully incorporated in an MFC system and acting as a cathode electrode