Pesticide detection by a miniature microbial fuel cell under controlled operational disturbances

The Microbial Fuel Cell (MFC) technology holds enormous potential for inexpensive real-time and onsite testing of water sources. With the intent of defining optimal operational conditions, we investigated the effect of environmental factors (changes in temperature, pH and ionic strength), on the performance of a single chamber miniature MFC sensor. The pH of the influent had the greatest effect on the MFC performance, with a 0.531 ± 0.064 µA cm-2 current variation per unit change of pH. Within the range tested, temperature and ionic strength had only a minor impact (0.010 ± 0.001 µA °C-1 cm-2 and of 0.027 ± 0.003 µA mS-1 cm cm-2 respectively). Under controlled operational conditions, for the first time, we demonstrated the ability of this biosensor to detect one of the most commonly applied pesticides worldwide, atrazine. The sensitivity to atrazine was 1.39 ± 0.26 ppm-1 cm-2, with a detection range of 0.05 – 0.3 ppm. Guidelines for systematic studies of MFC-biosensors for practical applications through a factorial design approach are also provided. Consequently, our work not only enforces the promise of miniature MFC-biosensors for organic pollutants detection in waters, but it also provides important directions towards future investigations for infield applications

Electricity generation from untreated fresh digestate with a cost-effective array of floating microbial fuel cells

Over one billion tons of food waste is generated every year worldwide. This waste represents a substantial part of municipal solid waste and is usually incinerated. The effective integration of the anaerobic digester process with the microbial fuel cell technology is an ecofriendly and promising solution for the treatment of food waste, which leads to clean energy generation and by-products of industrial interest. In this context, we here report the development of a floating air-cathode microbial fuel cell device and demonstrate electricity generation from fresh digestate, directly collected from an anaerobic digester effluent with no pre-treatment, used as the electrolyte, fuel and source of electroactive bacteria. The floating fuel cells are characterised by a simple yet innovative design. No metal catalyst is used at the cathode, and the use of a membrane is not required thanks to a natural vertical stratification of microorganisms in the digestate that prevents oxygen diffusion to the anode. Both the wettability and the surface area of the anode are enhanced with a two-step pre-treatment, which enhances the electrochemical performance of the electrode, leading to an oxidation peak twice greater than the non-treated electrode. The individual microbial fuel cell unit generated a power peak of 0.043 ± 0.001 mW, which increased linearly by connecting several units electrically in parallel in a stack and reached the value of 0.43 mW (corresponding to 51 ± 2 mW m −3) with ten units. Considering the simplicity and affordability of the design proposed, which facilitates upscaling, this work paves the way for a promising and environmentally friendly alternative to food waste incineration. </p

Continuous power generation from glucose with two different miniature flow-through enzymatic biofuel cells

AbstractEnzymatic biofuel cells (EBFCs) can generate energy from metabolites present in physiological fluids. They represent an attractive alternative to lithium batteries to power implantable devices, as they work at body temperature, are light and easy-to-miniaturise. To be implantable in blood vessels, EBFCs should not only be made of non-toxic and biocompatible compounds but should also be able to operate in continuous flow-through mode. The EBFC devices reported so far, however, implement carbon-based materials of questionable toxicity and stability, such as carbon nanotubes, and rely on the use of external redox mediators for the electrical connection between the enzyme and the electrode. With this study, we demonstrate for the first time continuous power generation by flow through miniature enzymatic biofuel cells fed with an aerated solution of glucose and no redox mediators. Non-toxic highly porous gold was used as the electrode material and the immobilisation of the enzymes onto the electrodes surface was performed via cost-effective and easy-to-reproduce methodologies. The results presented here are a significant step towards the development of revolutionary implantable medical devices that extract the power they require from metabolites in the body

Towards effective energy harvesting from stacks of soil microbial fuel cells

The 2050 net-zero carbon target can only be achieved with renewable energy solutions that can drastically reduce carbon emissions. Soil microbial fuel cells (SMFCs) have significant potential as a low-cost and carbon-neutral energy conversion technology. Finding the most practical and energy efficient strategy to operate SMFCs is crucial for transitioning this technology from the lab to field implementations. In this study, an innovative self-sustaining and model-based energy harvesting strategy was developed and tested for the first time on SMFC stacks. The model, based on a first-order equivalent electrical circuit (EEC), enables real-time and continuous maximum power point tracking, without the need for offline analysis of electrochemical parameters. Power extraction from the SMFCs to fully charge a 3.6 V NiMH battery, was carried out for 24 h: the longest test duration reported so far on biological fuel cells for such energy harvesting strategy. A novel second-order EEC was also proposed to better describe the electrical dynamics of the SMFC. Our results provide important advances on both accurate model-based electrochemical parameter identification techniques and maximum power point tracking algorithms, for optimal energy extraction from SMFCs. Consequently, this study paves the way for successful implementations of SMFCs towards viable green energy solutions.</p

Voltage Evolution and Electrochemical Behaviour of Soil Microbial Fuel Cells Operated in Different Quality Soils

The desire for a net-zero carbon future is a key driver for innovation in renewable energy. Amongst several emerging solutions, soil microbial fuel cells (SMFCs) pose an interesting addition as a low-cost, carbon–neutral technology. A full understanding on the electro-generative processes in SMFCs has, however, yet to be achieved, hindering the technology’s translation into practical applications. In this study, an in-depth investigation into the evolution of the output voltage generated by membrane-less, flat-plate SMFCs that accounts for the contribution of both the anode and cathode potential is provided for the first time, along with a study of the influence that organic matter content and porosity in soil has on voltage dynamics. Four stages in voltage evolution over time were observed, which depended on soil properties. The content of organic matter had the greatest effect, leading to an output voltage nearly-three times higher, when it increased from 10 % to 50 %. In this case, the anode potential reached a value of −450 mV, which prompted an exponential increase in the cathode potential and led to a power density of 68 mWm−2. The experimental findings were used to develop a novel computational model that, by predicting the electrochemical behaviour of the SMFC in different soils, becomes a powerful guide for operating strategies that can markedly enhance electricity generation. Consequently, this study sets the foundation for effective system optimisation and real applications.<br/

Towards Miniature Microbial Fuel Cells for Water Quality Monitoring

To ensure adequate sanitation of water supplies a rapid, cheap and simple method to test water systems is required. The microbial fuel cell (MFC) technology has potential for the effective testing of water sources in real time. A single chamber (68 μL) miniature MFC biosensor for detection of the biological oxygen demand (BOD) of water systems and to detect toxicants is presented. The device showed a response to a change in BOD within 19 minutes. The effect of operational conditions (pH, temperature, flow rate) on current generation was shown to have a maximum sensitivity of 0.944 μA cm-2 per unit change of the operational parameter. The power output of the device was enhanced by a factor of 28 by doubling the length of the anodic chamber and doping the cathode with a sustainable biochar based catalyst. The promise for detection of ‘emerging’ contaminants and toxicants in developing countries is discussed

Water quality monitoring in developing countries; can microbial fuel cells be the answer?

The provision of safe water and adequate sanitation in developing countries is a must. A range of chemical and biological methods are currently used to ensure the safety of water for consumption. These methods however suffer from high costs, complexity of use and inability to function onsite and in real time. The microbial fuel cell (MFC) technology has great potential for the rapid and simple testing of the quality of water sources. MFCs have the advantages of high simplicity and possibility for onsite and real time monitoring. Depending on the choice of manufacturing materials, this technology can also be highly cost effective. This review covers the state-of-the-art research on MFC sensors for water quality monitoring, and explores enabling factors for their use in developing countries

Glucose oxidase directly immobilized onto highly porous gold electrodes for sensing and fuel cell applications

AbstractThe successful implementation of redox-enzyme electrodes in biosensors and enzymatic biofuel cells has been the subject of extensive research.For high sensitivity and high energy-conversion efficiency, the effective electron transfer at the protein-electrode interface has a key role. This is difficult to achieve in the case of glucose oxidase, due to the fact that for this enzyme the redox centre is buried inside the structure, far from any feasible electrode binding sites.This study reports, a simple and rapid methodology for the direct immobilisation of glucose oxidase into highly porous gold electrodes. When the resulting electrode was tested as glucose sensor, a Michaelis-Menten kinetic trend was observed, with a detection limit of 25μM. The bioelectrode sensitivity, calculated against the superficial surface area of the bioelectrode, was of 22.7±0.1μAmM−1cm−2.This glucose oxidase electrode was also tested as an anode in a glucose/O2 enzymatic biofuel cell, leading to a peak power density of 6μWcm−2 at a potential of 0.2V