Dissertations / Theses on the topic 'Microbial fuel cells'

Fundamental studies for the improvement of photo-microbial fuel cells (pMFCs) within this work comprised investigations into ceramic electrodes, toxicity of metal-organic frameworks (MOFs) and hot-pressing of air-cathode materials. A novel type of macroporous electrode was fabricated from the conductive ceramic Ti2AlC. Reticulated electrode shapes were achieved by employing the replica ceramic processing method on polyurethane foam templates. Cyclic voltammetry of these ceramics indicated that the application of potentials larger than 0.5 V with regard to a Ag/AgCl reference electrode results in the surface passivation of the electrode. Ti2AlC remained conductive and sensitive to redox processes even after electrochemical maximisation of the surface passivation, which was shown electrochemically and with four terminal sensing. Application of macroporous Ti2AlC ceramic electrodes in pMFCs with green algae and cyanobacteria resulted in higher power densities than achieved with conventional pMFC electrode materials, despite the larger surface area of the Ti2AlC ceramic. The effect of electrode surface roughness and hydrophobicity on pMFC power generation and on cell adhesion was examined using atomic force and confocal microscopy, contact angle measurements and long-term pMFC experiments. The high surface roughness and fractured structure of Ti2AlC ceramic was beneficial for cell adhesion and resulted in higher pMFC power densities than achieved with materials such as reticulated vitrified carbon foam, fluorine doped tin oxide coated glass or indium tin oxide coated plastic. Toxicity of the MOF MIL101 and its amine-modified version MIL-101(Cr)-NH2 on green algae and cyanobacteria was assessed on the basis of both growth in liquid culture and by exclusion zones of agar colonies around MOF pellets. MOF MIL101 was found harmless in concentrations up to 480 mg L-1 and MIL-101(Cr)-NH2 did not exhibit toxic effects at a concentration of 167 mg L-1. Air-cathodes were produced from a range of carbon materials and ion-exchange membranes. Hot-pressing of Zorflex Activated Carbon Cloth FM10 with the proton-selective Nafion® 115 membrane provided the best bonding quality and pMFC performance.

Photosynthetic Microbial Fuel Cell (p-MFC) research aims to develop devices containing photosynthetic micro-organisms to produce electricity. Micro-organisms within the device photosynthesise carbohydrates under illumination, and produce reductive equivalents (excess electrons) from both carbohydrate production and the subsequent carbohydrate break down. Redox mediators are utilised to shuttle electrons between the organism and the electrode. The mediator is reduced by the micro-organism and subsequently re-oxidised at the electrode. However this technology is in its early stages and extensive research is required for p-MFC devices to become economically viable. A basic p-MFC device containing a potassium ferricyanide mediator and the algae Chlorella vulgaris was assembled and tested. From these initial experiments it was realised that much more work was required to characterise cell and redox mediator activities occurring within the device. There is very little p-MFC literature dealing with cellular interaction with redox mediators, but without this knowledge the output of complete p-MFC devices can not be fully understood. This thesis presents research into the reduction of redox mediators by the micro-organisms, including rates of mediator reduction and factors affecting the rate. Both electrochemical and non-electrochemical techniques are used and results compared. Additionally, cellular effects relating to the presence of the mediator are studied; crucial to provide limits within which p-MFCs must be used. After basic characterisation, this thesis presents work into the optimisation of the basic p-MFC. Different redox mediators, photosynthetic species and anodic materials are investigated. Importantly, it is only through fundamental characterization to improve understanding that p-MFCs can be optimised.

Monitoring parameters characterizing water quality, such as temperature, pH and concentrations of heavy metals in natural waters, is often followed by transmitting the data to remote receivers using telemetry systems. Such systems are commonly powered by batteries, which can be inconvenient at times because batteries have a limited lifetime and have to be recharged or replaced periodically to ensure that sufficient energy is available to power the electronics. To avoid these inconveniences, we have designed and tested a self-renewable power source, a microbial fuel cell, which has the potential to eliminate the need for batteries to power electrochemical sensors used to monitor water quality and small telemetry systems used to transmit the data acquired by these sensors. To demonstrate the utility of the microbial fuel cell, we have combined it with low-power, high-efficiency electronic circuitry providing a stable power source for wireless data transmission. To generate enough power for the telemetry system, energy produced by the microbial fuel cell was stored in an ultracapacitor and used in short bursts when needed. Since powering commercial components of electronic circuits requires 5 Volts, and our cell was able to deliver a maximum of 2.1 V, we used a DC-DC converter to increase the potential. The DC-DC converter powered the transmitter, which gathered the data from the sensor and transmitted them to a receiver. To demonstrate the utility of the system, we initially measured temporal variations in temperature followed by the implementation of a chemical sensor to measure copper and lead concentrations in water; this data was then wirelessly transmitted to a remote receiver.

Les Piles à Combustible Microbiennes (PCMs) mettent en oeuvre le métabolisme de micro-organismes et utilisent de la matière organique pour générer de l'énergie électrique. Les applications potentielles incluent le traitement d'eau usée autonome en énergie, les bio-batteries, et le grappillage d'énergie ambiante. Les PCMs sont des équipements basse-tension et basse-puissance dont le comportement est influencé par la vitesse à laquelle l'énergie électrique est récupérée. Dans cette thèse, on étudie des méthodes pour récupérer l'énergie électrique de façon efficace. La tension à laquelle l'énergie est récupérée des PCMs influence leur fonctionnement et leurs performances électriques. La puissance délivrée est maximum pour une tension spécifique (environ 1/3 de la tension en circuit-ouvert). Les PCMs ont été testées à ce point en utilisant une charge contrôlée automatiquement qui inclut un algorithme de recherche de puissance maximale. Un tel outil a été utilisé pour évaluer la puissance maximum, la vitesse de consommation du combustible, le rendement Coulombic et le rendement de conversion de 10 PCMs à chambre unique de 1.3 L, construites de façon similaire. Bien que d'autres choix structurels et opératoires peuvent permettre d'améliorer ces performances, ces résultats ont étudié pour la première fois les performances des PCMs en condition de production d'énergie de point de puissance maximal et les PCMs ont été testées avec des conditions de récupération d'énergie réalistes. Récupérer un maximum d'énergie des PCMs est la ligne directrice de ce rapport. Cela est rendu possible par des circuits dédiés de gestion de l'énergie qui embarquent un contrôle contre-réactif pour réguler la tension des PCMs à une valeur de référence qui est égale à une fraction de leur tension en circuit ouvert. Deux scénarios typiques sont développés dans la suite. Une application critique des PCMs concerne le grappillage autonome de petites énergies, pour alimenter des équipements électroniques basse-puissance (e.g. capteurs sans fil). Dans ce cas, les contraintes basse-puissance et basse-tension imposées par les PCMs nécessitent des fonctionnalités de démarrage autonomes. L'oscillateur d'Armstrong, composé d'inductances couplées à fort rapport d'enroulement et d'un interrupteur normalement-fermé permet d'élever des tensions de façon autonome à partir de sources basse-tension continues comme les PCMs. Ce circuit a été associé à des convertisseurs d'électronique de puissance AC/DC et DC/DC pour réaliser respectivement un élévateur-de-tension et une unité de gestion de l'énergie (UGE) auto-démarrante basée sur une architecture flyback. La première est adaptée pour les puissances inférieures à 1 mW, alors que la seconde peut être dimensionnée pour des niveaux de puissance de quelques mW et permet de mettre en oeuvre une commande qui recherche le point de puissance maximal du générateur. Une seconde application d'intérêt concerne le cas où de l'énergie est récupérée depuis plusieurs PCMs. L'association série peut être utilisée pour élever la tension de sortie mais elle peut avoir des conséquences négatives en terme de performances à cause des non-uniformités entre cellules. Cet aspect peut être résolu avec des circuits d'équilibrage de tension. Trois de ces circuits ont été analysés et évalués. Le circuit " complete disconnection " déconnecte une cellule défectueuse de l'association pour s'assurer qu'elle ne diminue pas le rendement global. Le circuit " switched-capacitor " transfère de l'énergie depuis les MFCs fortes vers les faibles pour équilibrer les tensions de toutes les cellules de l'association. Le circuit " switched-MFCs " connecte les PCMs en parallèle et en série de façon alternée. Chacune des trois méthodes peut être mise en oeuvre à bas prix et à haut rendement, la plus efficace étant la " switched-capacitor " qui permet de récupérer plus de 85 % de la puissance maximum idéale d'une association très largement non uniforme

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.

Since the 1900’s it has been known that microorganisms are capable of generating electrical power through extracellular electron transfer by converting the energy found organic compounds (Potter, 1911). Microbial fuel cells (MFCs) has garnered more attention recently, and have shown promise in several applications, including wastewater treatment (Yakar et al., 2018), bioremediation (Rosenbaum & Franks, 2014), biosensors (ElMekawy et al., 2018) desalination (Zhang et al., 2018) and as an alternative renewable energy source in remote areas (Castro et al., 2014). In MFCs catalytic reactions of microorganisms oxidize an electron donor through extracellular electron transfer to the anode, under anaerobic conditions, with the cathode exposed to an electron acceptor, facilitating an electrical current (Zhuwei, Haoran & Tingyue, 2007; Lovley, 2006). For energy production in remote areas a low cost and easily accessible feed stock is required for the MFCs. Sweet sorghum is a drought tolerant feedstock with high biomass and sugar yields, good water-use efficiency, established production systems and the potential for genetic improvements. Because of these advantages sweet sorghum stalks were proposed as an attractive feedstock (Rooney et al., 2010; Matsakas & Christakopoulos, 2013). Dried sweet sorghum stalks were, therefore, tested as a raw material for power generation in a MFC, with anaerobic sludge from a biogas plant as inoculum (Sjöblom et al., 2017a). Using sorghum stalks the maximum voltage obtained was 546±10 mV, the maximum power and current density of 131±8 mW/m2 and 543±29 mA/m2 respectively and the coulombic efficiency was 2.2±0.5%. The Ohmic resistances were dominant, at an internal resistance of 182±17 Ω, calculated from polarization data. Furthermore, hydrolysis of the dried sorghum stalks did not improve the performance of the MFC but slightly increased the total energy per gram of substrate. During the MFC operation, the sugars were quickly fermented to formate, acetate, butyrate, lactate and propionate with acetate and butyrate being the key acids during electricity generation. Efficient electron transfer between the microorganisms and the electrodes is an essential aspect of bio-electrochemical systems such as microbial fuel cells. In order to design more efficient reactors and to modify microorganisms, for enhanced electricity production, understanding the mechanisms and dynamics of the electron transport chain is important. It has been found that outer membrane C-type cytochromes (OMCs) (including omcS and omcZ discussed in this study) play a key role in the electron transport chain of Geobacter sulfurreducens, a well-known, biofilm forming, electro-active microorganism  (Millo et al., 2011; Lovley, 2008). It was found that Raman microscopy is capable of providing biochemical information, i.e., the redox state of c-type cytochromes (cyt-C) without damaging the microbial biofilm, allowing for in-situ observation. Raman microscopy was used to observe the oxidation state of OMCs in a suspended culture, as well as in a biofilm of an MFC. First, the oxidation state of the OMCs of suspended cultures from three G. sulfurreducens strains (PCA, KN400 and ΔpilA) was analyzed. It was found that the oxidation state can also be used as an indicator of the metabolic state of the cells, and it was confirmed that PilA, a structural pilin protein essential for long range electron transfer, is not required for external electron transfer. Furthermore, we designed a continuous, anaerobic MFC enabling in-situ Raman measurements of G. sulfurreducens biofilms during electricity generation, while poised using a potentiostat, in order to monitor and characterize the biofilm. Two strains were used, a wild strain, PCA, and a mutant, ΔOmcS. The cytochrome redox state, observed through the Raman spectra, could be altered by applying different poise voltages to the electrodes. This change was indirectly proportional to the modulation of current transferred from the cytochromes to the electrode. This change in Raman peak area was reproducible and reversible, indicating that the system could be used, in-situ, to analyze the oxidation state of proteins responsible for the electron transfer process and the kinetics thereof.

Environmental pollution by petroleum hydrocarbons has serious environmental consequences on critical natural resources upon which all living things (including mankind) largely depend. Microbial fuel cells (MFCs) could be employed in the treatment of these environmental pollutants with concomitant bioelectricity generation. Therefore, the overarching objective of this study was to develop an MFC system for the effective and efficient treatment of petroleum hydrocarbons in both liquid and particulate systems. Biodegradation of target hydrocarbons, phenanthrene and benzene, was investigated in dual-chambered microbial fuel cells (MFCs) using different inoculum types - Shewanella oneidensis MR1 14063, Pseudomonas aeruginosa NCTC 10662, mixed cultures and their combinations thereof. All the inocula showed high potentials for phenanthrene and benzene degradation in liquid systems with a minimum degradation efficiency of 97 % and 86 % respectively with concomitant power production (up to 1.25 mWm-2). The performance of MFCs fed with a mixture of phenanthrene and benzene under various operating conditions - temperature, substrate concentration, addition of surfactants and cathodic electron acceptor type – was investigated. The interaction effects of three selected operating parameters - external resistance, salinity and redox mediator were also investigated using response surface methodology. The outcomes of this study demonstrated the robustness of MFCs with good degradation performance (range 80 - 98 %) and maximum power production up to 10 mWm-2 obtained at different treatment conditions. Interactive effects existed among the chosen independent factors with external resistance having a significant impact on MFC performance, with maximum power output of 24 mWm-2 obtained at optimised conditions - external resistance (69.80 kΩ) , redox mediator (29.30μM, Riboflavin) and salinity (1.3 % w/v NaCl). The treatment of a mixture of phenanthrene and benzene using two different tubular MFCs designed for both in situ and ex situ applications in aqueous systems was investigated over long operational periods (up to 155 days). The outcomes of this work demonstrated stable MFC performance at harsh nutrient conditions and ambient temperatures. Simultaneous removal of petroleum hydrocarbons (> 90 %) and bromate, used as catholyte, (up to 79 %) with concomitant biogenic electricity generation (i.e. peak power density up to 6.75 mWm-2) were observed. The performance of a tubular MFC system in phenanthrene-contaminated soil was investigated in the last study. The outcomes of this work has demonstrated the simultaneous removal of phenanthrene (86%) and bromate (95%) coupled with concomitant bioelectricity generation (about 4.69 mWm-2) using MFC systems within a radius of influence (ROI) up to 8 cm. The overall outcomes of this study suggest the possible application of MFC technology in the effective treatment of petroleum hydrocarbons contaminated groundwater or industrial effluents and soil systems (mostly in subsurface environments), with concomitant energy recovery. MFC technology could potentially be utilised as an independent system in lieu of other bioremediation technologies (e.g. pump and treat, electrobioremediation or permeable reactive barriers) or integrated with existing infrastructure such as monitoring wells or piezometers.

Microbial fuel cells (MFCs) are a promising form of alternative energy capable of harnessing the potential energy stores in organic waste. The oxygen reduction reaction (ORR) forms an integral role in the generation of electricity in MFCs however it is also a potential obstacle in enhancing the performance of MFCs. Platinum, a commonly used catalyst for the ORR, is expensive and rare. Significant research has been conducted into developing alternative catalysts. Metallophthalocyanines (MPc) have garnered attention for use as catalysts. Iron phthalocyanine (FePc) has been shown to have catalytic activity towards the reduction of oxygen. Coupling of the catalyst to nanostructured carbon materials, such as multi-walled carbon nanotubes, has been observed to have several advantages as nanostructures have a high surface-to-volume ratio. In this study, we have attempted to assess the suitability of FePc, both its bulk and nanostructured form, as an oxygen reduction catalyst and acid functionalized multi-walled carbon nanotubes for use as a catalyst support using electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. We showed, for the first time, the catalytic nature of nanostructured FePc towards the ORR. Applying the data obtained from the electrochemical analyses, electrodes were modified using FePc and MWCNTs and applied to an Enterobacter cloacae-based MFC. Several operational parameters of the MFC, such as temperature and ionic strength, were optimized during the course of the study. We showed that optimized FePc:MWCNT-modified electrodes compared favourably to platinum-based electrodes in terms of power densities obtained in a microbial fuel cell.

For decades microbial fuel cells (MFCs) have offered the potential to treat wastewater while concomitantly producing power, but to date scale-up has not been achieved. The goal for this thesis was initially to explore the capabilities of MFCs in the laboratory and then to test the technology in the wastewater treatment environment. The aim was to operate the demonstrator in an existing process, without altering infrastructure or adding extra energy (Le. pumping). Laboratory work yielded novel findings helping to achieve the thesis objective while also contributing to MFC knowledge. Investigations into the anodic development period revealed that inoculating while in continuous-flow primed MFCs for operation in conditions of high flow-rate. The phenomenon 'power overshoot' was described and its occurrence explained in terms of the internal resistance of the MFC. A new miniature tubular MFC was designed and up to seven units were connected in fluidic series (cascade) to mimic the trickling filter process. These efficiently removed up to 90% COD, to levels that comply with European guidelines. The influence that fluidic connection had on MFCs in terms of flow-rate and external resistance was described for the first time. To mimic hostile flocculating conditions, MFCs were fed feedstock with varying ferric chloride concentrations. Power production, COD treatment, metal reduction and increased pH were all achieved suggesting the technology could supplement and improve existing processes. Utilising experience gained in the laboratory and following visits to Wessex Water, the trickling filter was selected as test location for the demonstrator. Using a variation on the novel tubular design, under field conditions at the Saltford treatment plant, MFCs demonstrated the ability to produce power while reducing COD to levels acceptable for release into the environment. These results strongly support the hypothesis that MFCs are becoming ready to be incorporated into the wastewater treatment process.

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.

Microbial fuel cells (MFCs) hold great promise for the simultaneous treatment of wastewater and electricity production. However, the electricity recovery needs improvement if MFCs are to compete with already established technologies e.g. anaerobic digestion. The aim of this study was to investigate ways of enhancing electricity recovery from (synthetic) industrial wastewater. Initial studies investigated the use of defined cocultures as a way of improving turnover of substrate and hence electricity produced by exploiting mutualistic relationships such as syntrophy or ability of facultative microoganisms (Saccharomyces cerevisiae) to consume residual oxygen from the anode. A coculture of Shewanella oneidensis and Clostridium beijerinckii, investigated here for the first time, gave a power production of 87 mW m-2 compared to 48 mW m-2 for S. oneidensis alone or 60 mW m-2 for C. beijerinckii alone. Substrate degradation was also improved significantly from 20% (S. oneidensis alone) to 67% using the coculture. Similar improvements were observed for novel cocultures of G. sulfurreducens, S. cerevisiae and C. beijerinckii as well as cocultures of C. beijerinckii, S. oneidensis and S. cerevisiae. To improve electricity recovery from MFCs, mechanisms of electron transfer need to be understood. The contribution of direct electron transfer mechanisms to overall electron transfer was investigated for the first time by restricting S. oneidensis cells close to or away from an anode electrode. A maximum power output of 114 mW m−2 was obtained when cells were retained close to the anode. This was 3.5 times more than when the cells were separated away from the anode. This result was corroborated by another study where S. oneidensis cells were entrapped in alginate gels. To further investigate the contribution of the c-type cytochromes forming the Mtr pathway to extracellular electron transfer, Rapid DNA Prototyping Assembly was used for the first time to assemble Mtr-pathway coding genes individually or as operons. The different constructs were overexpressed in S. oneidensis and heterologously expressed in E. coli and power production compared with the wild type strains. The best power generated was from the mtrAB S. oneidensis strain (144 mW m-2) and from the mtrCAB E. coli strain (24 mW m-2). Since electricity production is linked to exoelectrons forming a biofilm on the anode, ways of enhancing biofilm formation were sought. The quorum sensing molecule N (-3-oxodecanoyl)-L-homoserine lactone of different concentrations was for the first time exogenously added to MFCs and its effect on biofilm formation and power production determined. The results were compared with control experiments without N (-3-oxodecanoyl)-L-homoserine lactone. The results indicated that power production of 184 mW m-2 , the highest obtained of all approaches taken in this investigation, could be obtained when 10 uM of the chemical was added compared to 56 mW m-2 for the control, with significant increases in biofilm density. Taken together, these results highlight the importance of using defined cocultures (e.g. for bioaugmentation of working MFCs), direct electron transfer mechanisms, overexpression of the Mtr-pathway and need to increase biofilm density on anode surfaces, for enhancing electricity recovery in microbial fuel cells.

The aim of this study was to develop a microbial fuel cell (MFC) wastewater treatment system with a reduced production of sludge; whilst generating electricity as a product. Addition of a graphite intercalated compound, Nyex, provided an opportunity to add an adsorbent system for removal of micropollutants and dyes. Electrochemical analysis, effluent analysis and biofilm analysis provided detail on power generation and wastewater treatment ability and understanding of the biofilm. An 800ml capacity two-chamber MFC was developed and operated using anaerobic wastewater sludge as the anodic inoculum, acetate based artificial waste water as an anolyte and buffered DI water as a catholyte. Separation was provided by a proton exchange membrane, Nafion 117. Nyex was incorporated into the base design using 6 different configurations. Of those, the system with 100g of Nyex loose around each electrode saw the best overall performance. Producing a maximum power density of 0.054W m-2 and current density of 0.35A m-2, an increase of 500% and 312%, respectively, compared to the base fuel cell after 60 days of operation. This is due to a reduction in internal resistance of 86%. Scanning electron microscopy of biofilm indicated species rapidly form links between electrode material to facilitate electron transfer. 16s rRNA gene analysis of used anodic biofilm in the base fuel cell identified two dominant species; P,putida and P.caeni, neither had been used as a pure MFC inoculum. When used as pure cultures and in binary combination all MFCs generated voltage, indicating the species are exoelectrogenic. P.putida produced a current density of 0.0179A m-2, a 258% increase on P.caeni alone, 99% increase on the binary inoculum and a 49% increase on the mixed sludge used for the same time period in the same cell setup. Its maximum power density was 0.0018W m-2; a 167% increase on P.caeni, a 157% increase on the binary inoculum and a 100% increase on the mixed sludge inoculum. COD removal saw a decrease of 62.2% for P.caeni, 61.6% for the binary inoculum, 50.8% for P.caeni, treating 400mL of feed and 34% for the mixed culture treating 1L of feed during the same time period with the same maturity. Based on the results of this study, using the Nyex fuel cell with loose Nyex on both sides generates a power density of 0.054W m-2 when treating 1L of artificial wastewater. Using this system to treat the 11 billion litres of wastewater generated in the UK everyday [1] would result in a total power output of 9.5MW per day. Assuming that the benefits of modifying the fuel cell configuration and modifying the biofilm are independent, their improvements on cell performance can be assumed to be cumulative. Therefore, taking the 0.054W m-2 from the mixed culture Nyex cell and accounting for the 100% power density improvement when using P.putida, the potential power density is 0.108W m-2. Which when applied to the 11 billion litres of wastewater being treated daily within the UK would produce a total power output of 19MW per day.

The increasing energy demand in the context of population explosion excites human efforts to explore more renewable power sources. Among various systems for sustainable energy producing, Microbial Fuel Cells (MFCs) are considered as a promising alternative to generate renewable energy, being an environmental biotechnology that turns the treatment of organic wastes into electricity. However, the high - and further increasing - cost of materials to build up devices, especially precious platinum catalyst at the cathode side, hinders MFCs being popular in the practical applications. This research aimed to study non-noble catalysts for oxygen reduction reaction (ORR) in order to substitute state-of-art platinum. In particular, three different synthetic strategies were explored to fabricate iron-based catalysts with low-cost and high catalytic activity towards ORR. Inorganic iron-based catalysts were obtained from a two-step deposition of i) iron from inorganic source and ii) nitrogen from ammonia gas on carbon nanotubes (CNTs). Iron was impregnated on CNTs by a reduction of iron nitrate in ethylene glycol. After that, these FeCNTs compounds were treated under ammonia gas at 700°C for 2 h. Two Fe:CNTs ratios, 0.1:10 and 1:10, were investigated resulting two catalysts, labeled as FeCNTs 0.1:10 700 and FeCNTs 1:10 700. Iron chelate-based catalysts were obtained from ethylenediamine-N,N’-bis(2- hydroxyphenylacetic acid), nitrilotriacetic acid and diethylene triamine pentaacetic acid as iron - nitrogen precursors. Iron chelates were dispersed uniformly on both carbon Vulcan and carbon nanotubes by mixing these materials in water and drying at 70°C. The catalyst activation was carried out by annealing the mixture under argon gas at 800°C for 1.5 h. The catalysts are labeled as FeEDDHA, FeNTA, FeDTPA on C/CNTs. Polyindole-based catalysts were prepared by polymerization reaction of indole on either carbon Vulcan or carbon nanotubes in the presence of iron phthalocyanine (FePc), this latter being a macrocycle complex that has been widely used as ORR catalyst. The reaction was carried out in methanol which was completely evaporated in a water bath and in a vacuum oven at 70°C, and two different FePc:(PID/CNTs) ratios were explored, 1:1 and 3:1, obtaining samples labeled as FePc-PID-CNTs 1:1 and FePc-PID-CNTs 3:1. A catalyst prepared by mechanically mixing of polyindole on CNTs and FePc, was also prepared (PIDCNTs + FePc). In both cases, no further heat treatment at high temperature was applied. Morphology of prepared catalysts was examined by means of scanning electron microscopy and transmission electron microscopy. The results showed the uniform distribution of iron catalysts on the surface of carbon substrate. Total surface area as well as total pore volume was evaluated by nitrogen physisorption experiments, demonstrating IV that the catalysts supported on CNTs had a higher surface area and pore volume than those of catalysts supported on carbon Vulcan. X-ray photoelectron spectroscopy and neutron activation analysis were used to analyze the surface and bulk content of iron, respectively and revealed active sites in coordination with nitrogen. The electrochemical activity towards ORR of these samples was assessed by cyclic voltammetry in phosphate buffer electrolyte solution at pH 7. The results indicated that these iron-based catalysts are active with oxygen. Carbon nanotubes based catalysts had a greater oxygen reduction activity than that of carbon Vulcan based catalysts due to the higher total surface and pore volume. This preliminary characterization allowed selecting the most performing catalysts: FeCNTs 1:10 700, FeEDDHA/CNTs, and FePc-PID-CNTs. The performance for electricity production of the selected electrocatalysts was verified by means of test in air-cathode single-chamber MFCs fed either with domestic wastewater or phosphate buffer solution containing acetate. Polarization and power density curves of MFC based on FeCNTs 1:10 700, FeEDDHA/CNTs, and FePc-PIDCNTs 1:1 as cathode catalysts were similar or even improved with respect to those obtained by using platinum. FePc-PID-CNTs 1:1 cathode showed power density of 796 mW/ m2 and maximum current density of 4280 mA/m2, while a standard Pt catalyst produced 705 mW/m2 and 3972 mA/m2. The stability of the catalysts was evaluated by means of durability tests during the cell functioning over 700 h. The cost of prepared iron-based catalysts was calculated in laboratory scale and they were much lower than commercial platinum catalyst, allowing for a cost reduction up to 78.8 %. In conclusion, some inexpensive and effective methods to prepare iron-based materials for ORR were developed. MFC tests indicated the prepared iron-based catalysts The increasing energy demand in the context of population explosion excites human efforts to explore more renewable power sources. Among various systems for sustainable energy producing, Microbial Fuel Cells (MFCs) are considered as a promising alternative to generate renewable energy, being an environmental biotechnology that turns the treatment of organic wastes into electricity. However, the high - and further increasing - cost of materials to build up devices, especially precious platinum catalyst at the cathode side, hinders MFCs being popular in the practical applications. This research aimed to study non-noble catalysts for oxygen reduction reaction (ORR) in order to substitute state-of-art platinum. In particular, three different synthetic strategies were explored to fabricate iron-based catalysts with low-cost and high catalytic activity towards ORR. Inorganic iron-based catalysts were obtained from a two-step deposition of i) iron from inorganic source and ii) nitrogen from ammonia gas on carbon nanotubes (CNTs). Iron was impregnated on CNTs by a reduction of iron nitrate in ethylene glycol. After that, these FeCNTs compounds were treated under ammonia gas at 700°C for 2 h. Two Fe:CNTs ratios, 0.1:10 and 1:10, were investigated resulting two catalysts, labeled as FeCNTs 0.1:10 700 and FeCNTs 1:10 700. Iron chelate-based catalysts were obtained from ethylenediamine-N,N’-bis(2- hydroxyphenylacetic acid), nitrilotriacetic acid and diethylene triamine pentaacetic acid as iron - nitrogen precursors. Iron chelates were dispersed uniformly on both carbon Vulcan and carbon nanotubes by mixing these materials in water and drying at 70°C. The catalyst activation was carried out by annealing the mixture under argon gas at 800°C for 1.5 h. The catalysts are labeled as FeEDDHA, FeNTA, FeDTPA on C/CNTs. Polyindole-based catalysts were prepared by polymerization reaction of indole on either carbon Vulcan or carbon nanotubes in the presence of iron phthalocyanine (FePc), this latter being a macrocycle complex that has been widely used as ORR catalyst. The reaction was carried out in methanol which was completely evaporated in a water bath and in a vacuum oven at 70°C, and two different FePc:(PID/CNTs) ratios were explored, 1:1 and 3:1, obtaining samples labeled as FePc-PID-CNTs 1:1 and FePc-PID-CNTs 3:1. A catalyst prepared by mechanically mixing of polyindole on CNTs and FePc, was also prepared (PIDCNTs + FePc). In both cases, no further heat treatment at high temperature was applied. Morphology of prepared catalysts was examined by means of scanning electron microscopy and transmission electron microscopy. The results showed the uniform distribution of iron catalysts on the surface of carbon substrate. Total surface area as well as total pore volume was evaluated by nitrogen physisorption experiments, demonstrating IV that the catalysts supported on CNTs had a higher surface area and pore volume than those of catalysts supported on carbon Vulcan. X-ray photoelectron spectroscopy and neutron activation analysis were used to analyze the surface and bulk content of iron, respectively and revealed active sites in coordination with nitrogen. The electrochemical activity towards ORR of these samples was assessed by cyclic voltammetry in phosphate buffer electrolyte solution at pH 7. The results indicated that these iron-based catalysts are active with oxygen. Carbon nanotubes based catalysts had a greater oxygen reduction activity than that of carbon Vulcan based catalysts due to the higher total surface and pore volume. This preliminary characterization allowed selecting the most performing catalysts: FeCNTs 1:10 700, FeEDDHA/CNTs, and FePc-PID-CNTs. The performance for electricity production of the selected electrocatalysts was verified by means of test in air-cathode single-chamber MFCs fed either with domestic wastewater or phosphate buffer solution containing acetate. Polarization and power density curves of MFC based on FeCNTs 1:10 700, FeEDDHA/CNTs, and FePc-PIDCNTs 1:1 as cathode catalysts were similar or even improved with respect to those obtained by using platinum. FePc-PID-CNTs 1:1 cathode showed power density of 796 mW/ m2 and maximum current density of 4280 mA/m2, while a standard Pt catalyst produced 705 mW/m2 and 3972 mA/m2. The stability of the catalysts was evaluated by means of durability tests during the cell functioning over 700 h. The cost of prepared iron-based catalysts was calculated in laboratory scale and they were much lower than commercial platinum catalyst, allowing for a cost reduction up to 78.8 %. In conclusion, some inexpensive and effective methods to prepare iron-based materials for ORR were developed. MFC tests indicated the prepared iron-based catalysts The increasing energy demand in the context of population explosion excites human efforts to explore more renewable power sources. Among various systems for sustainable energy producing, Microbial Fuel Cells (MFCs) are considered as a promising alternative to generate renewable energy, being an environmental biotechnology that turns the treatment of organic wastes into electricity. However, the high - and further increasing - cost of materials to build up devices, especially precious platinum catalyst at the cathode side, hinders MFCs being popular in the practical applications. This research aimed to study non-noble catalysts for oxygen reduction reaction (ORR) in order to substitute state-of-art platinum. In particular, three different synthetic strategies were explored to fabricate iron-based catalysts with low-cost and high catalytic activity towards ORR. Inorganic iron-based catalysts were obtained from a two-step deposition of i) iron from inorganic source and ii) nitrogen from ammonia gas on carbon nanotubes (CNTs). Iron was impregnated on CNTs by a reduction of iron nitrate in ethylene glycol. After that, these FeCNTs compounds were treated under ammonia gas at 700°C for 2 h. Two Fe:CNTs ratios, 0.1:10 and 1:10, were investigated resulting two catalysts, labeled as FeCNTs 0.1:10 700 and FeCNTs 1:10 700. Iron chelate-based catalysts were obtained from ethylenediamine-N,N’-bis(2- hydroxyphenylacetic acid), nitrilotriacetic acid and diethylene triamine pentaacetic acid as iron - nitrogen precursors. Iron chelates were dispersed uniformly on both carbon Vulcan and carbon nanotubes by mixing these materials in water and drying at 70°C. The catalyst activation was carried out by annealing the mixture under argon gas at 800°C for 1.5 h. The catalysts are labeled as FeEDDHA, FeNTA, FeDTPA on C/CNTs. Polyindole-based catalysts were prepared by polymerization reaction of indole on either carbon Vulcan or carbon nanotubes in the presence of iron phthalocyanine (FePc), this latter being a macrocycle complex that has been widely used as ORR catalyst. The reaction was carried out in methanol which was completely evaporated in a water bath and in a vacuum oven at 70°C, and two different FePc:(PID/CNTs) ratios were explored, 1:1 and 3:1, obtaining samples labeled as FePc-PID-CNTs 1:1 and FePc-PID-CNTs 3:1. A catalyst prepared by mechanically mixing of polyindole on CNTs and FePc, was also prepared (PIDCNTs + FePc). In both cases, no further heat treatment at high temperature was applied. Morphology of prepared catalysts was examined by means of scanning electron microscopy and transmission electron microscopy. The results showed the uniform distribution of iron catalysts on the surface of carbon substrate. Total surface area as well as total pore volume was evaluated by nitrogen physisorption experiments, demonstrating IV that the catalysts supported on CNTs had a higher surface area and pore volume than those of catalysts supported on carbon Vulcan. X-ray photoelectron spectroscopy and neutron activation analysis were used to analyze the surface and bulk content of iron, respectively and revealed active sites in coordination with nitrogen. The electrochemical activity towards ORR of these samples was assessed by cyclic voltammetry in phosphate buffer electrolyte solution at pH 7. The results indicated that these iron-based catalysts are active with oxygen. Carbon nanotubes based catalysts had a greater oxygen reduction activity than that of carbon Vulcan based catalysts due to the higher total surface and pore volume. This preliminary characterization allowed selecting the most performing catalysts: FeCNTs 1:10 700, FeEDDHA/CNTs, and FePc-PID-CNTs. The performance for electricity production of the selected electrocatalysts was verified by means of test in air-cathode single-chamber MFCs fed either with domestic wastewater or phosphate buffer solution containing acetate. Polarization and power density curves of MFC based on FeCNTs 1:10 700, FeEDDHA/CNTs, and FePc-PIDCNTs 1:1 as cathode catalysts were similar or even improved with respect to those obtained by using platinum. FePc-PID-CNTs 1:1 cathode showed power density of 796 mW/ m2 and maximum current density of 4280 mA/m2, while a standard Pt catalyst produced 705 mW/m2 and 3972 mA/m2. The stability of the catalysts was evaluated by means of durability tests during the cell functioning over 700 h. The cost of prepared iron-based catalysts was calculated in laboratory scale and they were much lower than commercial platinum catalyst, allowing for a cost reduction up to 78.8 %. In conclusion, some inexpensive and effective methods to prepare iron-based materials for ORR were developed. MFC tests indicated the prepared iron-based catalysts as good candidates for platinum substitution.

A Microbial fuel cell (MFC) is a bio-electrochemical reactor, able to convert chemical energy, contained in organic substrate, in electrical energy, thanks to the metabolic activity of microorganisms. Firstly, a fluid-dynamic modelling of different Microbial Fuel Cell configurations to study trajectories and concentration profile of the liquid containing the organic substrate during operation of the device was developed. The study of the device was joined with the study and the synthesis of carbon based aerogels to be used as new electrode materials, both for the anode and the cathode. The aim of the modelling was to understand what happen, from a fluid-dynamic point of view, inside the cell during operation. It was based on the application of equations from fluid-dynamics in order to study both the particle trajectories (using Navier-Stokes equations) and diffusion of substrate inside the reactor (using Fick’s laws). Three different MFC architecture were investigated, starting from a circular shape. To increase the area of the reactor interested by flux exchange with respect to the one in the circular configuration, a new a squared MFC, with a non-alignment of the inlet and the outlet was proposed. Starting from results obtained during the simulation for the squared reactor, to accommodate the flux distribution, a further improvement in architecture was introduced: a drop-shape MFC, with a percentage of fluid area exchanged, higher than 96%. Another possibility to improve MFC performances, is the optimization of materials used as electrodes. To be an efficient electrode, a material must satisfy some important condition: biocompatibility, good electrically conductivity, resistance to electrolytic solutions and high surface area together with high porosity to allow the formation of the biofilm. Carbon based aerogels can satisfy all these properties. Organic aerogels were synthetized following a green approach, starting from marine polysaccharides, like agar and starch and then transformed in carbon based, thanks to a thermal process. The synthesis procedure is the sol-gel technique, followed by a drying process that can extract the liquid part of the gel, leaving the solid structure, without collapse the material. Synthetized materials were analyzed both structurally and morphologically in order to understand if porosity, surface area and chemical composition were appropriate. To enhance some of these properties, a post synthesis treatment was performed: the surface of the aerogel was treated with a KOH solution in order to enlarge pores and increase the porosity of the overall material. The optimized aerogel was tested, as anode, into the square shape MFC and compared with commercial carbon material having the same function. Due to their high surface area, high porosity and good interaction with microorganisms, aerogels presented better performances of commercial materials if used as anode in MFC. Considering, instead, the addition of amino acids as nitrogen source to the previous material, it allowed the used of polysaccharide aerogel, as cathode electrode able to catalyze the oxygen reduction reaction (ORR). They were tested in MFC, compared with the most used catalyst material in literature, that is platinum. Another alternative to platinum in the catalysis of the ORR, is represented by the metal oxide aerogels. In this work, aerogels based on MnxOy were tested. The synthesis of this material is similar to the previous one, with the difference of the addition of the manganese oxide directly between initial precursors. Through the thermal process, the organic part of the material is burned, leaving an oxide structure that is active from a catalytic point of view. After the morphological, structural and chemical analysis of the sample, the catalytic activity of the material was tested, as in the previous case, using the Rotating Ring Disk Electrode (RRDE) technique, in order to investigate its catalytic properties.

The aim of my thesis work is to investigate new nanostructured materials, obtained by the electrospinning technique, in order to design 3D arrangement of the electrodes, leading thus to improve the energy efficiency of energy production devices, such as microbial fuel cells (MFCs). The carbon nanofibers reveal to be the most promising material in the field of bio electrochemistry; in fact, up to now the best performing microbial fuel cells are fabricated using carbon and carbon based material electrodes. To further enhance the performances of bio anodes and bio cathodes, a set of properties are then required to be overcome, such as a proper surface morphology and chemistry, good biofilm adhesion and electron transfer, and a good electrical conductivity. This work aims to demonstrate that the electrospun nanofibers own all the necessary properties, revealing themselves as the most innovative and promising structures for anodes and cathodes for microbial fuel cells. The nanofibers ensure all the properties listed above; in particular, during my Ph.D. I have investigated and studied the carbon based nanofibers to be applied as cathode and as anode in these kind of the devices. In this thesis, it will be demonstrated that the nanostructured electrodes improve the efficiency devices thanks both to the low impedance and to the interaction with the microorganisms. The high micrometric porosity characteristics of the realized anodic material create the ideal habitat for the microorganism’s proliferation. Moreover, different solution for the cathode material have been developed using ceramic nanofibers, such as MnxOy nanofibers and carbon nanofibers, in order to improve the performance of the devices. The layer made of these nanofibers, in fact, catalyzes the oxygen reduction reaction if the oxygen is used as terminal electron acceptor in the devices; thus these catalysts can substitute the platinum layer, which is the most used today, granting a cheaper and eco friendlier material.

Microbial fuel cell (MFC) systems capable of both treating wastewaters and recovering energy have the potential for successful scale-up as a low carbon technology. These systems utilize microorganisms residing in biofilms as biocatalytic agents in the conversion of reduced substrates to electrical energy. As such, it is important to understand how MFC anodic biofilms develop over time and also how environmental parameters such as substrate type, temperature, carbon support material, anode architecture and optimized applied potentials also affect electrogenic performance. The type of substrate was found to have a large impact on the acclimation and performance of electrogenic biofilms. Acetate produced the highest power density of 7.2 W m 3 and butyrate the lowest at 0.29 W m"3, but it was also found that biofilm acclimation to these different trophic conditions also determined the MFC response to different substrate types i.e. both acetate and butyrate substrates produced power densities of 1.07 and 1.0 W m"3 respectively in a sucrose enriched reactor. The use of MFCs for wastewater treatment in temperate regions requires the development of reactor systems that are robust to seasonal fluctuations and are energy efficient. As such, system performance was examined at three different operating temperatures (10°C, 20°C and 35°C). At each temperature a maximum steady-state voltage of 0.49 V ± 0.02V was achieved after an operational period of 47 weeks, with the time to reach steady-state voltage being dependent on acclimation temperature. The highest COD removal rates of 2.98g COD L^d * were produced in the 35°C reactor but coulombic efficiencies (CE) were found to be significantly higher at pyschrophilic temperatures. Acclimation at different operating temperatures was found to a have a significant effect on the dynamic selection of psychrophilic, psychrotolerant and mesophilic anode respiring bacteria (ARB) and also influence the development of biofilm biomass, methanogenesis and electrogenic activity. Although start-up times were inversely influenced by temperature the amount of biomass accumulation increased with higher operational temperatures and this had a direct impact on biocatalytic performance. The three dimensional structure and porosity of different carbon anode materials affected anodic performance by determining the levels of surface area available for biofilm growth and the capacity for mass transfer to occur. Novel helical electrode configurations were used to look at the effect of altering turbulent flows to increase mass transfer rates and carbon surface areas available for electrogenic growth. The spiral with the highest amount of carbon veil and the smallest gap produced the highest power production of 11.63 W m"3 . Comparative studies of a logic controlled and un-controlled external load impedance showed that control affected the biocatalyst development and hence MFC performance. The controlled MFC better optimized the electrogenic anodic biofilm for power production, indicating that improved power and substrate conversion can be achieved by ensuring sustainable current demand, applied microbial selection pressures and near-optimal impedance for power transference.

Due to the extensive use of xenobiotic azo dyes in the colour industry and their proven mutagenic and cytotoxic nature, their treatment prior to discharge is essential and is legally enforced. However, currently used wastewater treatment technologies such as activated sludge systems, anaerobic digestion, electrochemical destruction, adsorption and membrane filtration are ineffective in removing azo dyes due to reasons such as inefficient dye degradation, slow degradation kinetics, toxic metabolite formation, inhibitory costs and generation of secondary waste streams. Therefore, in this study, microbial fuel cells (MFCs) were studied as possible systems that could effectively degrade azo dyes with an additional benefit of concomitant biogenic electricity generation. The co-metabolic degradation of the model azo dye Acid Orange-7 (AO-7) using Shewanella oneidensis and mixed anaerobic cultures in MFC was carried out with particular emphasis on AO-7 degradation kinetics in the initial study. The effect of using various carbon sources including cheaper complex ones such as molasses and corn steep liquor as electron donors for azo dye degradation in MFCs was also investigated. The outcomes of this study demonstrated that fast AO-7 reductive degradation kinetics using cheap, sustainable co-substrate types can be achieved with concomitant bioelectricity generation in two-chamber MFCs. Power densities up-to 37 mWm-2 were observed in the two-chamber MFC system during AO-7 decolourisation. Co-metabolic reductive degradation of azo dye mixtures using dye acclimated mixed microbial populations under industrially relevant conditions (high temperatures and salinities) and changes in microbial community structure in the MFCs in presence of complex azo dye mixtures in two-chamber MFCs was investigated. The outcomes of this work demonstrated that efficient colour and organic content removal can be achieved under high temperatures and moderate salinities using azo dye adapted mixed microbial populations in two-chamber MFCs. Microbial community analysis of the original anaerobic consortium and the azo dye adapted microbial culture following MFC operation indicated that both cultures were dominated by bacteria belonging to the phylum Firmicutes. However, bacteria belonging to phyla Proteobacteria and Bacteroidetes also became selected following MFC operation. Peak power densities up-to 27 mWm-2 were observed in this study during decolourisation of complex azo dye mixtures. The complete degradation of the azo dye AO-7 using a sequential reductive – oxidative bioprocess in a combined MFC-aerobic bioreactor system operating at ambient temperature in continuous mode was studied. The outcomes of this study demonstrated that the azo dye AO-7 can be fully decolourised and degraded into non-toxic and simpler metabolites. Maximum power densities up-to 52 mWm-2 were observed during azo dye degradation. A modular scale-up version (with a volumetric scale-up factor of 6) of the two stage integrated bioreactor system demonstrated the capability to efficiently treat two types of real wastewater originating from colour industry without any apparent deterioration of reactor performance in terms of dye decolourisation and COD removal. The use of applied external resistance (Rext) and redox mediators as tools for enhancing azo dye degradation kinetics in dual chamber MFCs was studied. The outcomes of this work suggest that azo dye reductive degradation kinetics in MFC anodes can be influenced by varying Rext. Furthermore, AO-7 reductive degradation kinetics was improved in a concentration-dependent manner by exogenous addition of two electron shuttling compounds anthraquinone-2,6-disulfonic acid and anthraquinone-2-sulfonic acid in MFC anodes. The overall outcomes of this study implies that MFCs could be successfully applied for achieving enhanced azo dye reductive biodegradation kinetics in MFC anodes coupled with concomitant bioelectricity generation. It further demonstrated that MFC systems can be successfully integrated with existing wastewater treatment technologies such as activated sludge systems for complete degradation and toxicity removal of azo dyes and their biotransformation metabolites.

Microbial fuel cells (MiFCs) have been suggested as a means to harness energy that is otherwise unutilized during the wastewater treatment process. MiFCs have the unique ability to treat influent waste streams while simultaneously generating power which can offset energy associated with the biological treatment of wastewater. During the oxidation of organic and inorganic wastes, microorganisms known as exoelectrogens have the ability to move electrons extracellularly. MiFCs generate electricity by facilitating the microbial transfer of these electrons from soluble electron donors in feedstocks to a solid-state anode. While MiFCs are a promising renewable energy technology, current systems suffer from low power densities which hinder their practical applicability. In this study, a novel anode design using flame-deposited carbon nanostructures (CNSs) on stainless steel mesh is developed to improve the electron transfer efficiency of electrons from microorganisms to the anode and thus the power densities achievable by MiFCs. These new anodes appear to allow for increased biomass accumulation on the anode and may aid in the direct transfer of electrons to the anode in mediatorless MiFC systems. Experiments were conducted using anaerobic biomass in single-chamber MiFCs with CNS-enhanced and untreated stainless steel anodes. Fuel cells utilizing CNS-enhanced anodes generated currents up to two orders of magnitude greater than cells with untreated metal anodes, with the highest power density achieved being 510 mW m-2.
Master of Science

Manganese compounds have a high potential for treating wastewater, both for utilizing its oxidation, flocculation ability and catalyst ability in anaerobic nitrification. The promising use of manganese compounds (such as permanganate and manganese dioxide) is regarded as an effective method of treating organic compounds in wastewater from municipal and industrial wastewater. Now it is newly realized possibilities to combine manganese compounds with Microbial Fuel Cell technology. Aiming at reusing the biomass in anaerobic digested sludge for degrading organic pollutants and simultaneously recovering electric energy, Single-chamber Microbial Fuel Cell (SMFC) system was developed and investigated during the main experimental part. Considering the electricity generation rate and characteristics of cathode, MnO2 was used as the reactant on the cathode electrode; meanwhile, the substrate types in anode compartment also were investigated and then extra sodium acetate was added to investigate the power generation performance. Two parts of the research were carried out during the whole project. The chemical treatment part was mainly designed to find out the best dosage of KMnO4 in flocculation when concurrent reacted with magnesium and calcium compounds when treating reject wastewater from digester at Hammarby Sjöstadsverk. The other part was studied to see whether it is possible to improve electricity generation by degrading organic pollutants when MnO2 was used as a cathodic reactant in sediment microbial fuel cell which consisted of anaerobic digested sludge from UASB.

Wastewater treatment is an energy intensive process and sustainable processes/technologies for the treatment of wastewaters need to be considered. One such contender might be the microbial fuel cell (MFC), a subset of bioelectrochemical system (BES) which generates electricity in the process of electrogenic (generating electrons) degradation of soluble organic contaminants present in the water (or wastewater) by electrogens (electron producing bacteria) at the anode in absence of oxygen. Several issues related to the power performance (also somewhat linked to the cost) of MFCs exist causing barriers in the deployment of up-scaled MFC system and the continual research from a multitude of discipline is focusing on overcoming these issues. Implementation of an MFC system for wastewater treatment would require a large array of MFCs to meet the treatment capacity of the wastewater treatment plant. Commissioning and continual operation of such MFCs would require rapid and cost-effective start-up and improvement in their performance. Optimisation of the power performance is addressed through a systems approach in this study, where improvement in the performance is sought through the system design and control strategies applied to the MFCs. The start-up rate of MFCs has been reduced by 45% using maximum power point tracking (MPPT), which is believed to be cost-effective as exogenous energy (such as in the case of poised-potential) is not required for the rapid start-up. The control of MFC power would need to be considered when up-scaled MFC system is realised. The controller implementation benefits from linearised system models. The viability of such piecewise linearisation of the nonlinear MFC system was demonstrated and the data were shown to be reasonably represented by the 1st order process models throughout its operating range. The occurrence of voltage reversal during stack operation of MFCs is a concern in large arrays particularly, and has been shown to be avoidable by adopting the hybrid stack connectivity. Further enhancement of the performance was sought through the detailed design and fluid dynamics modeling to obtain highly mixed anolyte at low input power, using improved helical anodes which increased the MFC performance at all the tested flow rates (1, 3 and 8 mL min-1) compared to previously studied helical anodes. The up-scaling of MFCs by modularisation was demonstrated and it was shown that the use of improved helical anodes can increase the modular length of the MFC without compromising the power performance. Aggregated power produced from the multi-module MFC (containing 5 modules) was 28.05 ± 3.5 mW (19.75 ± 2.47 W m-3) with an PhD Thesis – Hitesh Chandubhai Boghani 2014 V individual MFC power of 5.61 ± 0.7 mW, when fed with 10 mM sodium acetate at 3 mL min-1 flow rate and at 22 ± 3 °C. So, this thesis presents the strategies for improvement in the performance of MFCs for their applications in wastewater treatment and such strategies may also be transferable to their other applications.

Biological wastewater treatment is typically aerobic and an energy intensive process, mainly due to the required aeration. Alternative sustainable processes are sought, such as Microbial fuel cells (MFC) where electrogenic bacteria can degrade organic matter present in the waste stream while simultaneously generating electricity. MFCs represent an emerging technology which may deliver the capability to reduce the pollution potential of low strength wastewaters (< 1500 mg COD l-1) while generating electricity which could be used to self-power the process. Waste streams high in volatile fatty acids (VFAs) with high conductivity are particularly preferred substrate streams. These may include the effluent from two stage bio-hydrogen and bio-methane systems, which in this study were treated in a four-module tubular MFC (V=1 l) to reduce the chemical oxygen demand (COD) and recover further energy from the substrate. It was shown that the power increased with increasing organic loading rate (0.036-0.572 g sCOD l-1 d-1), but COD removal efficiency decreased. The Coulombic Efficiency (CE) was found to decrease significantly at OLR ˃ 0.6 g sCOD l-1 d-1 and the energy recovery was 92.95 J l-1 (OLR=0.572 g sCOD l-1 d-1). Also, wash-down waters from a chilled food producing company were treated in the same tubular MFC, reducing the soluble COD content by 84.8%. The low power (≈ 30 W m-3) and cell potential (≈ 0.5 V) makes it necessary to investigate methods such as external capacitors, DC/DC converters or serial and parallel connection to improve the power quality. In this thesis, the use of the intrinsic capacitance was tested by switched mode, open and closed circuit (OC/CC) operation of a 2-module tubular MFC with high surface area carbon veil anode. The charge accumulated during OC and released when switched to CC was dependent on the external resistor (R = 100-3 kΩ) and duty cycle. Short period OC/CC switching further increased potential due to the pseudo-capacitance of the reactor, but only at the expense of energy efficiency, compared to continuous operation (CC) under constant load. Another approach to enhance the practical implementation of MFCs is integration with other processes such as reverse electrodialysis to increase MFC’s cell potential or e.g. desalination. In this study a MFC was integrated with supported liquid membrane technology (SLM) for the first time, for the removal of metal ions of wastewater. A three chamber reactor, with a common cathode/feed phase containing 400 mg Zn2+ l-1, enabled V the simultaneous treatment of organic- and heavy metal containing wastewaters. The MFC/SLM combination produces a synergistic effect which enhances the power performance of the MFC significantly; 0.233 mW compared to 0.094 mW in the control. It is shown that the 165±7 mV difference between the MFC/SLM system and the MFC control is partially attributable to the lower cathode pH in the integrated system experiment, the consequent lower activation overpotential and higher oxygen reduction potential. The system demonstrates that within 72 h, 93±4% of the zinc ions are removed from the feed phase. A further study, with continuously operated cathode/feed chamber (100 mg Zn2+ l-1), showed that an enhanced effect on increasing cell potential was possible and could also be maintained in continuous operation.

There is an estimated 20 million tonnes of slurry produced by 2 million dairy cows each year in the UK. The suitable treatment of dairy farm waste could address both environmental concerns and energy security. In this study, dairy farm waste was separated into liquid slurry and solid residues, and treated by Microbial Fuel Cells (MFCs) and pyrolysis to minimise the environmental impact and produce bio-energy products. The effective treatment efficiencies were achieved by using incubated slurry mixed with fresh slurry as the anodic solution in MFC reactors. Comparing MFCs with anaerobic digestion (AD) under anaerobic conditions, the highest COD removal efficiency (71 %) and total nitrogen removal efficiency (17%) were obtained in MFCs operated at 25°C and 30°C for 30 days, respectively. A higher working temperature (35°C) was found to benefit the degradation of total suspended solids (78%). The MFCs were also found to be effective for nutrient-rich solution treatment. Furthermore, the anodic solutions were pre-treated by BI-CHEM manure degrader, which could significantly benefit the bio-degradation of the TSS, COD and nitrogen removal and enhance power generation. The dairy farm solid waste was treated by pyrolysis to produce bio-oil and biochar. The highest oil yield of 51 % was obtained at 500°C. For a mixed feedstock of solid waste and bone chips (up to 15%), results suggested that co-pyrolysis could improve the biochar production yield and bio-oil quality. The optimal concentration of bone chips for oil yield was found to be 1 O~ and the optimal temperature was 500°C. The conversion technologies for dairy farm waste are discussed based on the results of the experiments in this study. The potential energy recovery of the whole treatment was 61%.

Microbial fuel cells (MFCs) are potentially advantageous as an energy-efficient approach to wastewater treatment. For single-chamber tubular MFCs, anode effluent is used as catholyte instead of tap water or buffer solutions. Therefore, exposing cathode electrode to atmosphere could be also considered as a passive aeration for further aerobic oxidation of organics and nitrification. Based on several bench-scale studies, a 200-L scale MFC system with passive aeration process has been developed for treating actual municipal wastewater after primary clarification. The integrated system was able to remove over 80% organic contaminants and solid content from primary effluent. Through parallel and serial electricity connection, the power output of ~200 mW and the conversion efficiency of ~80% for charging capacitors were achieved by using commercially available energy harvesting device (BQ 25504). The treatment system is energy-efficient for the energy saving from aeration and sludge treatment while partial energy recovery as direct electricity can be utilized on site to power small electric devices. However, the post treatments are required to polish the effluent for nutrients removal.
Ph. D.

Wastewater treatment accounts for 3-5% of the total electricity demand in developed countries. However, wastewater is estimated to have 9.3 times more energy than which is required to treat it. A sediment microbial fuel cell (SMFC) can potentially be used to treat wastewater and produce electricity by utilising the organics found in the wastewater. The challenge associated with using SMFCs is efficiency and longevity. Literature has shown that the efficiency can be increased by growing plants in a SMFC. Plants release organics and oxygen into the rhizosphere which can increase microbial growth and increase oxygen at the cathode. This research undertook to design a batch plant microbial fuel cell (PMFC) and operate it on three different municipal sludge streams namely, thickened waste activated sludge (WAS), liquid WAS and primary sludge (PS). In addition, three indigenous South African plant species, namely, C. papyrus nanus, W. thyrsiflora and P. australis were tested based on their power output potential and organic removal potential. The highest PPD (1036 ± 59 mW/m3 ) was obtained from the system using thickened WAS as substrate and planted with W. thyrsiflora. This was followed by liquid WAS as substrate planted with W. thyrsiflora (290 ± 21 mW/m3 ) and the lowest in the unplanted system using PS (119 ± 31 mW/m3 ). It was also found that COD utilisation for power generation was most efficient when using WAS. Thickened WAS produced 1330 mW/m3 per gram of COD consumed followed by liquid WAS with 508 mW/(m3 ·gCOD) and the lowest conversion in PS i.e. 124 mW/(m3 ·gCOD). Based on these factors WAS was chosen as the most suitable feed for a PMFC. Furthermore, it was found that utilising the PS in an anaerobic digestion would have over 500 times more power output making its use in a PMFC not viable. The highest organic removal efficiencies were observed when systems were planted with C. papyrus. When using WAS, C. papyrus achieved 62.2 ± 12.8%, 62.8 ± 9.6%, 58.5 ± 14.0%, 75.4 ± 8.4%, 95.3 ± 2.8% and 94.4 ± 3.5% removal efficiencies of VSS, COD, TKN, TP, FSA and OP respectively. When using PS, C. papyrus achieved 59.4 ± 9.7% 45.7 ± 10.4%, 82.0 ± 3.3%, 65.6 ± 3.2%, 97.4 ± 2.4% and 78.5 ± 2.8% removal efficiencies of VSS, COD, TKN, TP FSA and OP respectively. Therefore, it was noticed that W. thyrsiflora produced the highest power densities, but the C. papyrus produced the highest organic removal. The decision between the two plants was made based on the plant species ability to grow in sludge. It was noticed that the W. thyrsiflora died in thickened WAS. When using liquid WAS and PS, the old roots died, and new roots grew on the surface for W. thyrsiflora. Given the uncertainty of the plants ability to survive in the long term, C. papyrus was chosen as the most suitable plant species as it was able to grow in all three sludge types. Using WAS and C. papyrus, three more optimisation experiments were conducted. In the first one, it was found that using a separator between the electrodes increased the power density by 35%. The power output increased from 141 ± 16 mW/m3 to 191 ± 16 mW/m3 when a separator was used. It was noticed that the separator system had more horizontal root growth along the top surface just under the cathode of the PMFC as the separator limited vertical root growth. This may be the reason for higher power densities since more roots meant more oxygen release that can be consumed by the cathode. The second optimisation experiment focused on the use of multiple electrodes. It was found that using multiple electrodes was more efficient than single electrodes. Furthermore, it was noticed that connecting the multiple electrodes in parallel within a set-up was more efficient than connecting them in series. The peak power densities followed the order of: parallel connection 443 mW/m3 , series connection 296 ± 46 mW/m3 and 156 ± 17 mW/m3 for the control. The third optimisation experiment was focused on varying electrode distance. It was noticed that the highest peak power density was achieved when the electrode distance was halved (664 ± 122 mW/m3 ) followed by the system with 1.5 times electrode spacing which produced 453 ± 74 mW/m3 and the lowest for the standard design (290 mW/m3 ). From the three optimisation experiments, it was noticed that some variables have a larger impact on the performance of the PMFC than others. Halving the electrode distance increased the PPD 2.3 times, while doubling the electrodes increased it 2.8 times. Adding a separator only increased it by 1.4 times. This indicates that more focus should be attributed to the electrode distance and number of electrodes. In summary, this research found that, of the three plant species investigated, using C. papyrus with WAS substrate was the most practical and best performing combination for a PMFC. Furthermore, having a separator between the electrodes, having multiple electrodes connected in parallel within a set-up and decreasing the electrode distance to half all increased the power production.

The use of laboratory scale Microbial Fuel Cells (MFCs) for the combined generation of electricity and the treatment of wastewater has been well documented in literature. In addition to this the integration of MFCs into wastewater treatment reactors has also been shown to have several benefits. These include the improved treatment of wastewater, reduced solid waste and the potential to offset the energy costs of the process through the generation of electricity (Du et al., 2007). The treatment of sulphate-rich wastewater, and in particular Acid Rock Drainage (ARD), has become of increasing importance in water sparse countries like South Africa where mining is currently and has taken place. A semi-passive method of continuous ARD waste treatment is currently being investigated within the Centre for Bioprocess Engineering Research (CeBER) (van Hille et al., 2015). This research involves the use of a Linear Flow Channel Reactor (LFCR) designed for combined biological sulphide reduction and sulphide oxidation to yield a sulphur product. Sulphate Reducing Bacteria (SRB) mediate the biological sulphide reduction. Chemical and biological sulphide oxidation takes place in a Floating Sulphur Biofilm (FSB) on the surface of the reactor and is mediated by Sulphide Oxidising Bacteria (SOB). Sulphate-rich wastewater can therefore be remediated through total sulphur species removal.

This study demonstrated a technique for fabricating simple, low-cost Paper Microbial fuel cells (PMFC’s) in the model of a previous study to, for the first time, produce voltage from wastewater effluent. The PMFC’s were created by stacking and gluing the main components of an MFC together: reservoir layer; anode; cation exchange membrane (CEM); air cathode. A wax printer was used to create the hydrophobic borders of the PMFC’s on filter paper, and graphite paint was applied to the paper to create the anode. The CEM’s considered were filter paper, wax, and Nafion, with Nafion being the most efficient. Finally, the air cathode was made using carbon veil, and leads (or resistors) were placed in both anode and cathode layers for voltage measurement. Confirming previous studies’ results, the PMFC’s had a rapid startup time and sustained voltage for at least 10 minutes. The study also found that: Nafion was the best CEM; painting one side of the anode had the highest voltage; higher surface area increased voltage; increased time from sampling decreased voltage. Thus, this study proved that the small, low-cost PMFC devices described in previous studies can produce a voltage using primary effluent, and showed that the surface area of the PMFC could be optimized to increase voltage.

Sediment microbial fuel cell (SMFC) is a special type of microbial fuel cells that can be deployed in a natural water body for energy production and contaminant removal. This MS project aims to explore whether it will be viable to apply SMFCs for wastewater treatment. Experimental SMFCs were studied in several configurations and operational modes for organic removal, nitrate reduction, and energy recovery. When treating an artificial secondary effluent for nitrate removal, the SMFC could remove 44% of the nitrate, higher than that without electricity generation. The enhanced removal was attributed to the supply of electrons to nitrate reduction in the aqueous phase through oxidizing the organics in the sediment. The lack of a proper separator between the anode and the cathode led to the failure of the SMFC when treating an artificial raw wastewater. Ion exchange membranes were incorporated into the MFCs that were installed in a lab-scale open water pond (150 L in volume). Such a system achieved 100% COD removal and more than 75% removal of ammonium nitrogen. However, denitrification remained as a challenge because of a lack of anoxic zone. To reduce the cost of the cathode catalysts, a polymer-based carbon cloth was investigated and exhibited better performance than bare carbon cloth. The results of this MS project have demonstrated that SMFCs in the absence of a proper separator cannot be applied for wastewater treatment. A membrane-based MFC system integrated with open pond may function as a wastewater treatment system, though nitrogen removal efficiency must be improved.
Master of Science

Microbial fuel cell (MFC) has become one of the energy-sustainable technologies for wastewater treatment purpose in the recent years. It combines wastewater treatment and electricity generation together so as to achieve energy balance. By inoculating microorganism in the anode chamber and filling catholyte in the cathode chamber, and also with the help of a proton exchange membrane (PEM) between them, the MFC can transfer protons and produce power. Microbial desalination cells (MDC) are based on MFC’s structure and can fulfill desalination function by the addition of a middle chamber and anion exchange membrane (AEM). This study focuses on ammonium removal and electricity generation in MDC system. Mainly two types of liquid were tested, a solution of Hjorthorn Salt and filtrated supernatant. The experiments were performed at Hammarby Sjöstad research station and laboratory of Land and Water Resources department, Stockholm. It consists of a preparation stage, a MFC stage and a MDC stage. Until the end of MFC stage, biofilm in the anode chamber had been formed and matured. After that, solutions of different initial concentrations (1.5, 2.5, 5, 15 g/L) of Hjorthorn Salt and also filtrated supernatant have been tested. Ammonium removal degree can be obtained by measuring the initial concentration and cycle end concentration, while electricity generation ability can be calculated by voltage data which was continuously recorded by a multimeter. Results showed that this MDC system is suitable for ammonium removal in both of Hjorthorn Salt solutions and supernatant. The removal degrees in Hjorthorn Salt solution at desalination chamber were 53.1%, 52.7%, 60.34%, and 27.25% corresponding to initial NH4+ concentration of 340.7, 376, 376 and 2220 mg/L. The ammonium removal degrees in the supernatant were up to 53.4% and 43.7% under 21 and 71 hours operation, respectively. In power production aspect, MDC produced maximum voltage when potassium permanganate was used in the cathode chamber (217 mV). The power density in solutions of Hjorthorn Salt was relative low (46.73 - 86.61 mW/m3), but in the supernatant it showed a good performance, up to 227.7 and 190.8 mW/m3.

Computational fluid dynamics (CFD) modeling was used to predict the hydrodynamics of a column reactor. Bubble columns have applications across many engineering disciplines and improved modeling techniques help to increase the accuracy of numerical predictions. An Eulerian-Eulerian multi-fluid model was used to simulate fluidization and to capture the complex physics associated therewith. The commercial code ANSYS Fluent was used to study two-dimensional gas-liquid bubble columns. A comprehensive parameter study, including a detailed investigation of grid resolution was performed. Specific attention was paid to the bubble diameter, as it was shown to be related to cell size have significant effects on the characteristics of the flow. The parameters used to compare the two-dimensional (2D) cases to experimental results of Rampure, et. al. were then applied to a three-dimensional (3D) geometry. It was demonstrated that the increase in accuracy from 2D to 3D is negligible compared to the increase in CPU required to simulate the entire 3D domain. Additionally, the reaction chamber of a microbial fuel cell (MFC) was modeled and a preliminary parameter study investigating inlet velocity, temperature, and acetate concentration was conducted. MFCs are used in wastewater treatment and have the potential to treat water while simultaneously harvesting electricity. The spiral spacer and chemical reactions were modeled in a 3D geometry, and it was determined that inlet velocity was the most influential parameter that was simulated. There were also significant differences between the 2D and 3D geometries used to predict the MFC hydrodynamics.
Master of Science

碩士
國立宜蘭大學
機械與機電工程學系碩士班
99
Microbial fuel cells are devices that can transform organic matter into energy. It has a large potential in cleaning the environment and as a emerging energy technology. This study is based on miniature biofuel cell tanks using the bacteria E.coli (No. 51534). The tank design is divided into two parts, the application of biophysical mixers to microbial fuel cells and the effect of electrophoresis driving on power performance. Before the experiment, a study analysis of the growth curve, mediator, and methods for growing E. coli were conducted to help develop methods to impact the microbial fuel cells. In the first experiment, by adding a flow in the anode to increase the bacteria flow, a power density of 91.81mW/m3achieved. When a mixer is attatched to the microbial fuel cell, the bacteria and nutrient can be mixed with an efficiency of 99%. This can increase the power density by 28.9%, to a peak of 118.34 mW/m3. In the second experiment, results show that the electrode can receive electrons easily, but only from bacteria near the anode electrode. In addition, a maximum power density of 31.23 W/m3 can be achieved. These findings will provide useful information on promoting the electricty production of microbial fuel cells.

碩士
國立中興大學
化學工程學系所
98
Based on the Nernst equation, the mechanism of the electric response on photosynthetic microbial fuel cells (PMFC) was investigated in this study. From the experimental results, the variation of voltage can be predicted by Nernst equation under the condition of sparging with N2 or CO2. According to Nernst equation, the microbial cell growth shows little effects on the voltage of PMFC. A modified Nernst equation was proposed to describe the varieties of voltage properly. Additionally, the phenomenon of oscillation on voltage was caused by aerating gas in anode or cathode by turns. The different way on stirring was examined, and it shows the reason of oscillation was mass transfer, and there is a chance to make alternating current by Nernst equation. It is observed that the suspended algae cell will grow with little voltage change in the light condition. However when operating in the dark condition with the cell attached in the electrode, the algae cell will decline along with a large voltage response. According to these phenomena, a novel PMFC device was built. The expected change response was observed on the experimental results.

碩士
國立清華大學
工程與系統科學系
95
We have successfully demonstrated a portable microbial fuel cell that is capable of autonomously discharging CO2 bubbles and agitating aqueous anolyte to prolong its operation lifetime and facilitate the electron transport inside. This fuel cell consumes glucose and oxygen to generate electricity in a reaction catalyzed by encapsulated microorganisms. The bio-catalysts, fuels, and liquid electrolytes are sealed inside two liquid-impermeable compartments separated by a proton exchange membrane. In order to discharge generated CO2 gas, this fuel cell is equipped with a bubble guiding and venting system, which releases the pressure built inside the anode compartment and agitates the anolyte as well. In the prototype demonstration, an open-circuit potential of 0.37 V per single unit and an average power output of 32.16 μW/cm3 in the first hour is achieved. With 40 milligrams of glucose fuels, the prototype cell can continuously operate for more than 4 hours. Furthermore, a fuel-cell stack of 6 units, which has an overall potential over 1.5V, were built and successfully power a light emitting diode. As such, this fuel cell is capable of self-regulating the electricity harvesting process and producing steady voltage and current outputs for portable applications.

abstract: Microbial fuel cells(MFC) use micro-organisms called anode-respiring bacteria(ARB) to convert chemical energy into electrical energy. This process can not only treat wastewater but can also produce useful byproduct hydrogen peroxide(H2O2). Process variables like anode potential and pH play important role in the MFC operation and the focus of this dissertation are pH and potential control problems. Most of the adaptive pH control solutions use signal-based-norms as cost functions, but their strong dependency on excitation signal properties makes them sensitive to noise, disturbances, and modeling errors. System-based-norm( H-infinity) cost functions provide a viable alternative for the adaptation as they are less susceptible to the signal properties. Two variants of adaptive pH control algorithms that use approximate H-infinity frequency loop-shaping (FLS) cost metrics are proposed in this dissertation. A pH neutralization process with high retention time is studied using lab scale experiments and the experimental setup is used as a basis to develop a first-principles model. The analysis of such a model shows that only the gain of the process varies significantly with operating conditions and with buffering capacity. Consequently, the adaptation of the controller gain (single parameter) is sufficient to compensate for the variation in process gain and the focus of the proposed algorithms is the adaptation of the PI controller gain. Computer simulations and lab-scale experiments are used to study tracking, disturbance rejection and adaptation performance of these algorithms under different excitation conditions. Results show the proposed algorithm produces optimum that is less dependent on the excitation as compared to a commonly used L2 cost function based algorithm and tracks set-points reasonably well under practical conditions. The proposed direct pH control algorithm is integrated with the combined activated sludge anaerobic digestion model (CASADM) of an MFC and it is shown pH control improves its performance. Analytical grade potentiostats are commonly used in MFC potential control, but, their high cost (>$6000) and large size, make them nonviable for the field usage. This dissertation proposes an alternate low-cost($200) portable potentiostat solution. This potentiostat is tested using a ferricyanide reactor and results show it produces performance close to an analytical grade potentiostat.
Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2018