Developing Energy Harvest Efficient Strategies with Microbial Fuel Cells

Nowadays, thinking of energetic efficiency is to determine how to decrease consumption and to reuse resources. This is a major concern when addressing hydric resources. The consumption of drinking water is seeing an unaffordable growth and, although most of it is replenished to the environment, the water quality is affected by pollutants and impurities. As such, using wastewater, a by-product of our routine and way of life, as resource is an asset. Even more when thinking about the heightened energy costs of a wastewater treatment station. The hypotheses of this work show how to achieve this goal by using microbial fuel cells. The organic composition of this water increases its energy production potential, where the bacterial metabolism can be used to, simultaneously, produce energy and help to clean the water. This document is divided in 5 chapters. The strategic positioning of the theme happens in chapter 1. Chapter 2 explains how the main elements of microbial fuel cell technology can work and determine its operation. In chapter 3, the power management systems used with microbial fuel cells are presented and discussed, with the identification of optimization strategies. The second-to-last chapter corresponds to the experimental results discussion and validation, while focusing improved energy production efficiencies. The outputs of this chapter pilot the future work analysis on chapter 5, together with the main conclusions and research trends. The validity and usefulness of this work is cleared with an application example.Pensar em economia energética é, hoje, considerar soluções para a redução de consumo e reutilização de recursos. Esta preocupação é importante ao examinar a utilização dos recursos hídricos. O consumo de água potável está a crescer insustentavelmente e, apesar de grande parte desse consumo ser restituído ao meio ambiente, a qualidade da água é afetada por poluentes ou impurezas. A utilização de água residual, um produto da nossa rotina e qualidade de vida, como um recurso é, por isso, uma mais valia. É ainda mais evidente ao considerar os elevados consumos energéticos de uma estação de tratamento de água residual. As hipóteses abordadas neste trabalho mostram como é possível atingir este objetivo usando células microbianas de combustível. A composição orgânica desta água faz com que o seu potencial energético possa ser explorado, usando o metabolismo bacteriano para produzir energia e, simultaneamente, auxiliar na limpeza da água. Este documento está dividido em 5 capítulos. O posicionamento do tema ocorre no capítulo 1. O capítulo 2 observa os principais elementos da tecnologia das células microbianas de combustível, permitindo compreender o seu funcionamento e conhecer que variáveis afetam o seu funcionamento. No capítulo 3 são apresentadas as tipologias de abordagem à gestão energética para esta pilha bacteriológica, discutindo-se as vantagens e otimizações de cada sistema. O penúltimo capítulo corresponde à exploração de resultados experimentais e à validação de hipóteses, orientadas para a maior eficiência energética. Surgem assim recomendações que servirão para guiar os trabalhos futuros, discutidos no capítulo final. Este, o capítulo 5, conta ainda com a apresentação das principais conclusões e das tendências de pesquisa. O trabalho termina com um exemplo de aplicação que solidifica a validade e utilidade da aplicação desta tecnologia

Electricity production by the application of a low voltage DC-DC boost converter to a continuously operating flat-plate microbial fuel cell

An ultra-low voltage customized DC-DC booster circuit was developed using a LTC3108 converter, and used continuously on a flat-plate microbial fuel cell (FPM) system. The boost converter successfully stepped up the microbial fuel cell (MFC) voltage from ~0.5 V to 3.3 and 5.0 V of outputs. The designed circuit and system displayed the dynamic variations of the source FPM as well as the output voltage through the designed three connection points within the booster circuit. The source MFC voltage was interrelated with the booster circuit and its performance, and it adapted to the set points of the booster dynamically. The maximum output power density of the MFC with the DC-DC booster circuit was 8.16 W/m3 compared to the maximum source FPM input power of 14.27 W/m3 at 100 Ω, showing a conversion efficiency of 26–57%, but with a 10-fold higher output than that of the source voltage. The combined LTC3108 with FPM supplied power for electronic devices using synthetic and real domestic wastewater. This report presents a promising strategy for utilizing the electrical energy produced from MFCs, and expands the applicability of bioelectrochemical systems with an improved energy efficiency of the present wastewater treatment system

Small scale/large scale MFC stacks for improved power generation and implementation in robotic applications

Microbial Fuel Cells (MFCs) are biological electrical generators or batteries that have shown to be able to energise electronic devices solely from the breakdown of organic matter found in wastewater. The generated power from a single unit is currently insufficient to run standard electronics hence alternative strategies are needed for stepping-up their performance to functional levels. This line of work deals with MFC miniaturisation; their proliferation into large stacks; power improvement by using new electrode components and finally a novel method of energy harvesting that will enhance the operation of a self-sustainable robotic platform. A new-design small-MFC design was developed using 3D printing technology that outperformed a pre-existing MFC of the same volume (6.25 mL) highlighting the importance of reactor configuration and material selection. Furthermore, improvements were made by the use of a cathode electrode that facilitates a higher rate of oxygen reduction reaction (ORR) due to the high surface area carbon nanoparticles coated on the outer layer. Consequently, a 24-MFC stack was built to simulate a small-scale wastewater treatment system. The MFC units were connected in various arrangements, both fluidically as a series of cascades and electrically in-parallel or in-series, for identifying the best possible configuration for organic content reduction and power output. Results suggest that in-parallel connections allow for higher waste removal and the addition of extra units in a cascade is a possible way to ensure that the organic content of the feedstock is always reduced to below the set or permitted levels for environmental discharge. Finally, a new method of fault-proof energy harvesting in stacks was devised and developed to produce a unique energy autonomous energy harvester without any voltage boosting and efficiencies above 90%. This thesis concludes with the transferability of the above findings to a robotic test platform which demonstrates energy autonomous behaviour and highlights the synergy between the bacterial engine and the mechatronics

CMOS indoor light energy harvesting system for wireless sensing applications

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e de ComputadoresThis research thesis presents a micro-power light energy harvesting system for indoor environments. Light energy is collected by amorphous silicon photovoltaic (a-Si:H PV) cells, processed by a switched-capacitor (SC) voltage doubler circuit with maximum power point tracking (MPPT), and finally stored in a large capacitor. The MPPT Fractional Open Circuit Voltage (VOC) technique is implemented by an asynchronous state machine (ASM) that creates and, dynamically, adjusts the clock frequency of the step-up SC circuit, matching the input impedance of the SC circuit to the maximum power point (MPP) condition of the PV cells. The ASM has a separate local power supply to make it robust against load variations. In order to reduce the area occupied by the SC circuit, while maintaining an acceptable efficiency value, the SC circuit uses MOSFET capacitors with a charge reusing scheme for the bottom plate parasitic capacitors. The circuit occupies an area of 0.31 mm2 in a 130 nm CMOS technology. The system was designed in order to work under realistic indoor light intensities. Experimental results show that the proposed system, using PV cells with an area of 14 cm2, is capable of starting-up from a 0 V condition, with an irradiance of only 0.32 W/m2. After starting-up, the system requires an irradiance of only 0.18 W/m2 (18 mW/cm2) to remain in operation. The ASM circuit can operate correctly using a local power supply voltage of 453 mV, dissipating only 0.085 mW. These values are, to the best of the authors’ knowledge, the lowest reported in the literature. The maximum efficiency of the SC converter is 70.3% for an input power of 48 mW, which is comparable with reported values from circuits operating at similar power levels.Portuguese Foundation for Science and Technology (FCT/MCTES), under project PEst-OE/EEI/UI0066/2011, and to the CTS multiannual funding, through the PIDDAC Program funds. I am also very grateful for the grant SFRH/PROTEC/67683/2010, financially supported by the IPL – Instituto Politécnico de Lisboa

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

Energy Harvesting and Modeling of Photosynthetic Power Cell

The need for energy is inevitable for mankind. Climate change, depletion of natural resources, pollution and other factors have created the necessity to look for energy from renewable sources. Furthermore, there are challenges aplenty in the field of renewable energy as renewable energy sources are unpredictable, non-dependable and limited such as wind, solar photo voltaic and tidal power. Apart from these there are few unconventional renewable energy sources that have not been explored thoroughly or exploited. The photosynthetic power cell is one among them. The photosynthetic power cell (PSC) harvests the energy produced at the lowest level of the food cycle which is “photosynthesis” in plants. The photosynthetic power cell extracts the energy produced during photosynthesis and respiration in form of electrical energy. The developed device differs from other published works in terms of improved performance, fabrication technique and material of structure. The two main types of sources used in the photosynthetic power cell are aerobic unicellular organisms (e.g. algae and cyanobacteria) and sub-cellular thylakoid photosystems / chloroplasts isolated from plant cells (e.g. spinach plant’s sub-cellular thylakoid photosystems isolated from the plant cells). The photosynthetic power cell produces energy under both dark and light conditions. The developed PSC is a polymer based structure instead of silicon, integrating the conventional MEMS processes with polymers. The principle of the operation of the device is based on ‘photosynthesis’. Photosynthesis and respiration both involve electron transfer chains. The electrons are extracted with the help of electrodes and a redox agent, and a power electronic converter is designed to harvest the energy. The developed device is capable of producing an open circuit voltage of 0.9 volts and about 200 μW of peak power. The μPSC has an active area of 4.84 cm2 which approximately translates to a power density of 400 mW/m2. This makes it as one of the best performing μPSC. The other top performing μPSC devices report power densities between 100 to 250 mW/m2. In order to harvest energy from μPSC, power electronic converters are a necessity. Three different power electronic topologies are investigated to find the feasibility of energy harvesting using μPSC. Also, the cell should be operated at the maximum power point in order to get the best results. Common maximum power point tracking (MPPT) techniques as well as a novel MPPT technique is devised and tested for the energy harvesting application using μPSC. In this thesis work, the device’s working principle, fabrication of the device and testing of the developed prototype along with the design and development of the power electronic converters with MPPT algorithm for energy harvesting application with μPSC are presented. A short introduction, basic photosynthesis process, background and history of μPSC are discussed in first chapter. The cell design, construction, working and fabrication of the cell are discussed in the second chapter. The third chapter deals with the experimental set up, characterization and testing of the cell. In the fourth chapter, modeling, analysis, simulation of PSC is executed. Analysis, identification and simulation of suitable power electronic converters with MPPT are investigated in the fifth chapter. Conclusions, future work form the epilogue

Combination of bioelectrochemical systems and electrochemical capacitors: Principles, analysis and opportunities

© 2019 The Authors Bioelectrochemical systems combine electrodes and reactions driven by microorganisms for many different applications. The conversion of organic material in wastewater into electricity occurs in microbial fuel cells (MFCs). The power densities produced by MFCs are still too low for application. One way of increasing their performance is to combine them with electrochemical capacitors, widely used for charge storage purposes. Capacitive MFCs, i.e. the combination of capacitors and MFCs, allow for energy harvesting and storage and have shown to result in improved power densities, which facilitates the up scaling and application of the technology. This manuscript summarizes the state-of-the-art of combining capacitors with MFCs, starting with the theory and working principle of electrochemical capacitors. We address how different electrochemical measurements can be used to determine (bio)electrochemical capacitance and show how the measurement data can be interpreted. In addition, we present examples of the combination of electrochemical capacitors, both internal and external, that have been used to enhance MFC performance. Finally, we discuss the most promising applications and the main existing challenges for capacitive MFCs

Energy Management of Microbial Fuel Cells for High Efficiency Wastewater Treatment and Electricity Generation

In order to develop communities in a sustainable manner it is necessary to think about how to provide basic and affordable services including sanitation and electricity. Wastewater has energy embedded in the form biodegradable organic matter, but most of the conventional systems use external energy to treat the wastewater instead of harvest its energy. Microbial fuel cells (MFCs) are unique systems that are capable of converting chemical energy of biodegradable substrates embedded in the waste materials into renewable electricity. Even though the technology showed great progress, the direct electrical energy output from MFC reactors is still very low and the electrical interface with microbial activities is not well understood.In this work, I investigated the development and deployment of energy management systems to improve energy harvesting of microbial fuel cells during wastewater treatment. The specific studies presented in this dissertation consist of the first AC power generation from microbial fuel cells, the development of harvesting strategies to maximize microbial fuel cell performance in different conditions, and the understanding of microbial community and activities under different harvesting conditions. To enable the application of MFC technology for treating actual wastewaters and providing net electricity output, I also investigated the integration of AC-powered electrocoagulation with granular biochar to treat hydraulic fracturing water, and I used the electricity generated by MFCs to directly power electrocoagulation for oily wastewater treatment, achieving energy positive wastewater treatment for distributed applications. System scale up and integration will be next steps for technology development

A Novel Non-Enzymatic Glucose Biofuel Cell with Mobile Glucose Sensing

Herein, we report a novel non-enzymatic glucose biofuel cell with mobile glucose sensing. We characterized the power generation and biosensing capabilities in presence of glucose analyte. This system was developed using a non-enzymatic glucose biofuel cell consisting of colloidal platinum coated gold microwire (Au-co-Pt) employed as an anode and the cathode which was constructed using a Gas diffusion electrode (GDE) with a platinum catalyst. The non-enzymatic glucose biofuel cell produced a maximum open circuit voltage of 0.54 V and delivered and a maximum short circuit current density of 1.6 mA/cm2 with a peak power density of 0.226 mW/cm2 at a concentration of 1 M glucose. The non-enzymatic glucose biofuel cell produced an open circuit voltage of 0.38 V and delivered and a short circuit current density of 0.225 mA/cm2 with a peak power density of 0.022 mW/cm 2 at a concentration of 5 mM glucose. These findings showed that glucose biofuel cells can be further investigated in the development of a self-powered glucose biosensor. When used as self-powered glucose sensor, the system showed a good sensitivity of 0.616 μA mM−1 and linear dependence with a correlation coefficient of 0.995 in the glucose concentration range of 2 mM to 50 mM. The system was further characterized by testing the performance of the system at various temperature, pH and amidst various interfering and competing chemical species such as uric acid, ascorbic acid, fructose, maltose and galactose. A charge pump circuit consisting of a blinking LED was connected to the biofuel cell to amplify the input voltage to power small electronic devices. The blinking frequency of the LED corresponds to the glucose concentration. An android mobile phone camera application was used to measure this LED blinking frequency which was in turn converted into the glucose concentration readings using image processing in MATLAB. The user was notified via text message and an email