Performance of pilot scale plug flow microbial fuel cell for sustainable wastewater treatment and energy recovery

Wastewater is increasingly considered a resource rather than a problem. This study investigates the rapidly developing Microbial Fuel Cell technology and its potential to be used in an industrial scale and environment in the context of the whisky industry and to be used as an alternative or complementary sustainable wastewater treatment process. This study describes the development of a 122 litre multi-electrode open air cathode Microbial Fuel Cell. Throughout this study the reactor’s performance is assessed on two levels; energy recovery and effluent quality. During initial studies the principle of the MFC’s ability to treat whisky distillation by-products was established. The reactor was operated directly on diluted spent wash in ambient Scottish temperatures. During successful start-up, no correlation was found to temperature. During long-term operation, a positive correlation was found between temperature and the positive energy balance achieved by the MFC while tCOD removal efficiency was maintained at approximately 83 %. The reactor was further optimised in regards to electrical connections, thus its electrical performance which was also validated through a bench scale study. The successful initial experiments led to the integration of an operationally optimised pilot study in a local whisky distillery. The pilot set-up was successfully operated complementary to an anaerobic digester for over one year in the industrial environment achieving energy savings and a sustainable tCOD removal efficiency of over 80 %. Latterly, a simplified electrochemical model was examined to describe the performance of the MFC to be further developed. This study concludes that the nature of industrial wastewater treatment is a complex subject and equally so is the multi-disciplinary MFC technology. The MFC developed for this study and the industrial experience gained contributes towards a more sustainable, energy saving and efficient treatment technology with the potential to be used complementary to existing technologies

Establishing and Understanding the Electron Balance in Microbial Fuel Cells

Microbial fuel cells (MFCs) have been intensively studied in the past decade as a promising alternative wastewater treatment technology. However, the critical mass balances such as carbon (or electrons) balances have not well addressed before. Clear understanding of a carbon balance in the anode of an MFC will help to identify electron distribution among different electron acceptors, and the limiting factors that divert electrons from electricity generation. In this study, the effect of substrate loading rate, sulfate, temperature, substrate type and nitrate concentration on MFC\u27s performance were investigated. At different operation condition, the biomass, current, biogas, dissolved oxygen, sulfate and nitrate concentrations were monitored to make an electron balance. The results suggested that COD removal rate, current, biomass and biogas can increase with the increase of organic loading rate. The sulfate concentration has a negative effect on biogas production, but, it has a positive effect on the current, COD removal rate which is different from previous study. The substrate type (fermentative or un-fermentative) can increase the electricity production

Self sustainable cathodes for microbial fuel cells

The ultimate goal of this thesis was to investigate and produce an MFC with self-sustainable cathode so it could be implemented in real world applications. Using methods previously employed [polarisation curve experiments, power output measurements, chemical assays for determining COD in wastewater and other elements present in anolyte or catholyte, biomass assessments] and with a focus on the cathode, experiments were conducted to compare and contrast different designs, materials and nutrient input to microbial fuel cells with appropriate experimental control systems.Results from these experiments show that: Firstly, the choice of polymeric PEM membrane showed that the most effective materials in terms of power performance were cation exchange membranes. In terms of cost effectiveness the most promising was CM-I, which was the preferred separator for later experiments.Secondly, a completely biotic MFC with the algal cathode was shown to produce higher power output (7.00 mW/m2) than the abiotic control (1.52 mW/m2). At the scale of the experimental system, the reservoir of algal culture produced sufficient dissolved oxygen to serve the MFCs in light or dark conditions. To demonstrate usable power, 16 algal cathode-designed MFCs were used to power a dc pump as a practical application.It has been presented that the more power the MFC generates, the more algal biomass will be harvested in the connected photoreactor. The biomass grown was demonstrated to be a suitable carbon-energy resource for the same MFC units in a closed loop scenario, whereby the only energy into the system was light.In the open to air cathode configuration various modifications to the carbon electrode materials including Microporous Layer (MPL) and Activated Carbon (AC) showed catholyte synthesis directly on the surface of the electrode and elemental extraction such as Na, K, Mg, from wastewater in a power dependent manner. Cathode flooding has been identified as an important and beneficial factor for the first time in MFCs, and has been demonstrated as a carbon capture system through wet scrubbing of carbon dioxide from the atmosphere. The captures carbon dioxide was mineralised into carbonate and bicarbonate of soda (trona). The novel inverted, tubular MFC configuration integrates design and operational simplicity showing significantly improved performance rendering the MFC system feasible for electricity recovery from waste. The improved power (2.58 mW) from an individual MFC was increased by 5-fold compared to the control unit, and 2-fold to similar sized tubular systems reported in the literature; moreover it was able to continuously power a LED light, charge a mobile phone and run a windmill motor, which was not possible before

Power Management Circuits for Energy Harvesting Applications

Energy harvesting is the process of converting ambient available energy into usable electrical energy. Multiple types of sources are can be used to harness environmental energy: solar cells, kinetic transducers, thermal energy, and electromagnetic waves. This dissertation proposal focuses on the design of high efficiency, ultra-low power, power management units for DC energy harvesting sources. New architectures and design techniques are introduced to achieve high efficiency and performance while achieving maximum power extraction from the sources. The first part of the dissertation focuses on the application of inductive switching regulators and their use in energy harvesting applications. The second implements capacitive switching regulators to minimize the use of external components and present a minimal footprint solution for energy harvesting power management. Analysis and theoretical background for all switching regulators and linear regulators are described in detail. Both solutions demonstrate how low power, high efficiency design allows for a self-sustaining, operational device which can tackle the two main concerns for energy harvesting: maximum power extraction and voltage regulation. Furthermore, a practical demonstration with an Internet of Things type node is tested and positive results shown by a fully powered device from harvested energy. All systems were designed, implemented and tested to demonstrate proof-of-concept prototypes

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

Steering biogas performance by implementation of bioelectrochemical cell (BEC) technology

A new concept for integrating conventional anaerobic digester (AD) with bioelectrochemical cell (BEC) technology was investigated in the current study. The BEC technology can convert energy stored in organic matter directly into bioelectricity. Coupling AD with BEC could be a profitable approach that could lead to overcoming limiting factors in AD, such as hydrogen partial pressure and accumulation of volatile fatty acids, inhibiting the methanogenesis

The performance of varying PTFE coated fabric cloth on electricity production using synthetic wastewater with aid of activated carbon air-cathode

M.Tech. (Chemical Engineering)Abstract: Microbial fuel cell is the energy harvesting technology being studied; this technology concerns various substrates, microbes and wastewater into electrical energy by the catalytic reaction of micro-organisms. The thesis of the project research seeks to establish a comparison in the performance of biochemical properties for microbial fuel cells using synthetic wastewater and activated carbon. The cathode electrode used was a stainless steel pressed with activated carbon and was sectioned to a surface area of 36cm2 same with the proton exchange membrane and the carbon cloths were also sectioned at 36cm2. The experimental set-up consisted of a double chamber membrane which consisted of the anode and air-cathode chamber. The anode and air-cathode chamber were immersed in the open water bath regulated at a temperature of 35oC. On the start-up, the anode chamber was filled with 280ml of synthetic wastewater which was mixed and prepared in the lab to reach the ideal COD levels which meet the raw domestic wastewater COD levels and the air-cathode was filled with 8L of tap water. The anode chamber after every experiment was changed and fitted with a new and different carbon cloth coating, whereby the cathode chamber had to be changed with an addition of the pulverized activated carbon. The 50% PTFE coated carbon cloth is more efficient in generating power than the other which were compared to in the experiment; however the performance of individual carbon cloths varies significantly with the type or percentage of coating added and this directly affects the overall performance of the MFC, and this was highly aided with the addition of the activated carbon. An air-cathode with activated carbon with different particle sizes which was embedded on a stainless steel mesh. Microbial fuel cell (MFC) containing synthetic wastewater was constructed and compared to different types of carbon coated polytetrafluroethylene (PTFEs). The synthetic wastewater contained in MFCs was investigated and together with the aid of activated carbon which was pulverized to different sizes for oxygen removal. The synthetic wastewater MFC had a power output of 86.80mW/m2, compared to 17.47mW/m2 for the domestic wastewater. The limiting current density is 0.0347mA/m2 for the activated carbon in synthetic wastewater compared to 0.0046mA/m2 for domestic wastewater without an..