Waste and wastewater clean-up using microbial fuel cells

A sustainable energy portfolio should include a range of carbon-neutral and renewable energy technologies. Amongst the renewable energy technologies, MFCs can offer a solution for both sustainable energy and clean water demands. In order to take the MFC technology to commercial level, more effort has to be spent to improve the performance and treatment efficiency. The goal for this thesis was to improve anode performance and waste utilisation. To achieve this goal, the approach taken was system scale-up through multiples of relatively small sized MFC units. Two main aspects of the MFC anode, design and biofilm affecting parameters, were investigated in order to better understand and enhance the anode performance. Through a number of experiments, better performing material for each MFC component was chosen. For example, by replacing the previous electrode material with modified anode and cathode, a 2.2 and 4.9 fold increase in power output was achieved respectively. Investigations into biofilm affecting parameters such as temperature, external load and feedstock, yielded novel findings helping to understand the dynamic characteristics of MFC anode biofilms. For the final part of this thesis, these findings were used to implement the MFC technology for practical applications such as treating wastes and resource recovery as well as producing electrical energy. Two troublesome wastes, urine and uric scale showed great potential for being power sources of MFC electricity generation. Furthermore it was demonstrated that MFCs can contribute to recovery of resources such as nitrogen and phosphorus in the form of struvite. A commercial electronic appliance was run continuously, powered by a stack of 8 MFCs fed with neat human urine, which successfully demonstrated a great potential of the MFC technology for both electricity generation and waste treatment

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

Novel Analytical Microbial Fuel Cell Design for Rapid in Situ Optimisation of Dilution Rate and Substrate Supply Rate, by Flow, Volume Control and Anode Placement

© 2018 MDPI AG. All rights reserved. A new analytical design of continuously-fed microbial fuel cell was built in triplicate in order to investigate relations and effects of various operating parameters such as flow rate and substrate supply rate, in terms of power output and chemical oxygen demand (COD) removal efficiency. This novel design enables the microbial fuel cell (MFC) systems to be easily adjusted in situ by changing anode distance to the membrane or anodic volume without the necessity of building many trial-and-error prototypes for each condition. A maximum power output of 20.7 ± 1.9 µW was obtained with an optimal reactor configuration; 2 mM acetate concentration in the feedstock coupled with a flow rate of 77 mL h−1, an anodic volume of 10 mL and an anode electrode surface area of 70 cm2 (2.9 cm2 projected area), using a 1 cm anode distance from the membrane. COD removal almost showed the reverse pattern with power generation, which suggests trade-off correlation between these two parameters, in this particular example. This novel design may be most conveniently employed for generating empirical data for testing and creating new MFC designs with appropriate practical and theoretical modelling

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

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

Multidimensional benefits of improved sanitation: Evaluating 'PEE POWER®' in Kisoro, Uganda

With 2.3 billion people around the world lacking adequate sanitation services, attention has turned to alternative service provision models. This study suggests an approach for meeting the sanitation challenge, especially as expressed in Sustainable Development Goal 6.2, using a toilet technology system, such as Pee Power® that generates electricity using diverted urine as a fuel. A field trial was carried out in a girls' school in Kisoro, Uganda, where the generated electricity was used to light the existing toilet block. The trial was evaluated in terms of social acceptability and user experience using a multidimensional assessment protocol. The results of our assessment show that users felt safer when visiting the toilets at night. Lights provided from the technology also helped with the perceived cleanliness of the toilets. The technology was well accepted, with 97% of the respondents saying that they liked the idea of the Pee Power® technology and 94% preferring it over other facilities on site. This shows how the technology helps meet SDG target 6.2, with its particular focus on vulnerable populations

A systematic review of machine-learning solutions in anaerobic digestion

The use of machine learning (ML) in anaerobic digestion (AD) is growing in popularity and improves the interpretation of complex system parameters for better operation and optimisation. This systematic literature review aims to explore how ML is currently employed in AD, with particular attention to the challenges of implementation and the benefits of integrating ML techniques. While both lab and industry-scale datasets have been used for model training, challenges arise from varied system designs and the different monitoring equipment used. Traditional machine-learning techniques, predominantly artificial neural networks (ANN), are the most commonly used but face difficulties in scalability and interpretability. Specifically, models trained on lab-scale data often struggle to generalize to full-scale, real-world operations due to the complexity and variability in bacterial communities and system operations. In practical scenarios, machine learning can be employed in real-time operations for predictive modelling, ensuring system stability is maintained, resulting in improved efficiency of both biogas production and waste treatment processes. Through reviewing the ML techniques employed in wider applied domains, potential future research opportunities in addressing these challenges have been identified

Impact of disinfectant on the electrical outputs of urine-fed ceramic and membrane-less microbial fuel cell cascades

The application of microbial fuel cells in sanitation has demonstrated feasibility in supplying electricity and providing safety in underserved communities, especially at toilet blocks. Two different designs of urine fed MFC cascades, ceramic MFCs (c-MFC) and self-stratifying MFCs (s-MFC), have been employed in large-scale feasibility studies. As part of a pre-commercialisation approach, this study verified the resilience of each design when a commercial disinfectant was introduced into the system. Five different conditions, varying in concentrations (24.2 mM–604.5 mM) and the total volume (50–500 mL) of sodium hypochlorite disinfectant introduced, were tested. Upon adding the disinfectant, both types of MFC-cascades exhibited rapid power drops with response times lower than 5 min in all tested conditions, followed by relatively swift recovery times of up to 250 min. The volume of disinfectant introduced had a greater impact on power output than its concentration or dose. Comparing the two designs, the c-MFC demonstrated a much larger voltage drop, up to 0 mV, and shorter recovery time compared to the s-MFC under most test conditions, mainly attributed to the presence (c-MFC) or absence (s-MFC) of a membrane. Overall, both types of MFCs exhibited strong resilience to sodium hypochlorite additions, thereby highlighting the commercial potential of the technology towards safe off-grid sanitation

Neural networks predicting microbial fuel cells output for soft robotics applications

The development of biodegradable soft robotics requires an appropriate eco-friendly source of energy. The use of Microbial Fuel Cells (MFCs) is suggested as they can be designed completely from soft materials with little or no negative effects to the environment. Nonetheless, their responsiveness and functionality is not strictly defined as in other conventional technologies, i.e. lithium batteries. Consequently, the use of artificial intelligence methods in their control techniques is highly recommended. The use of neural networks, namely a nonlinear autoregressive network with exogenous inputs was employed to predict the electrical output of an MFC, given its previous outputs and feeding volumes. Thus, predicting MFC outputs as a time series, enables accurate determination of feeding intervals and quantities required for sustenance that can be incorporated in the behavioural repertoire of a soft robot