abstract: Microbial Electrochemical Cell (MXC) technology harnesses the power stored in wastewater by using anode respiring bacteria (ARB) as a biofilm catalyst to convert the energy stored in waste into hydrogen or electricity. ARB, or exoelectrogens, are able to convert the chemical energy stored in wastes into electrical energy by transporting electrons extracellularly and then transferring them to an electrode. If MXC technology is to be feasible for ‘real world’ applications, it is essential that diverse ARB are discovered and their unique physiologies elucidated- ones which are capable of consuming a broad spectrum of wastes from different contaminated water sources. This dissertation examines the use of Gram-positive thermophilic (60 ◦C) ARB in MXCs since very little is known regarding the behavior of these microorganisms in this setting. Here, we begin with the draft sequence of the Thermincola ferriacetica genome and reveal the presence of 35 multiheme c-type cytochromes. In addition, we employ electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA) to gain insight into the presence of multiple pathways for extracellular electron transport (EET) and current production (j) limitations in T. ferriacetica biofilms. Next, Thermoanaerobacter pseudethanolicus, a fermentative ARB, is investigated for its ability to ferment pentose and hexose sugars prior to using its fermentation products, including acetate and lactate, for current production in an MXC. Using CA, current production is tracked over time with the generation and consumption of fermentation products. Using CV, the midpoint potential (EKA) of the T. pseudethanolicus EET pathway is revealed. Lastly, a cellulolytic microbial consortium was employed for the purpose ofassessing the feasibility of using thermophilic MXCs for the conversion of solid waste into current production. Here, a highly enriched consortium of bacteria, predominately from the Firmicutes phylum, is capable of generating current from solid cellulosic materials. / Dissertation/Thesis / Doctoral Dissertation Biological Design 2015

abstract: A Microbial fuel cell (MFC) is a bio-inspired carbon-neutral, renewable electrochemical converter to extract electricity from catabolic reaction of micro-organisms. It is a promising technology capable of directly converting the abundant biomass on the planet into electricity and potentially alleviate the emerging global warming and energy crisis. The current and power density of MFCs are low compared with conventional energy conversion techniques. Since its debut in 2002, many studies have been performed by adopting a variety of new configurations and structures to improve the power density. The reported maximum areal and volumetric power densities range from 19 mW/m2 to 1.57 W/m2 and from 6.3 W/m3 to 392 W/m3, respectively, which are still low compared with conventional energy conversion techniques. In this dissertation, the impact of scaling effect on the performance of MFCs are investigated, and it is found that by scaling down the characteristic length of MFCs, the surface area to volume ratio increases and the current and power density improves. As a result, a miniaturized MFC fabricated by Micro-Electro-Mechanical System(MEMS) technology with gold anode is presented in this dissertation, which demonstrate a high power density of 3300 W/m3. The performance of the MEMS MFC is further improved by adopting anodes with higher surface area to volume ratio, such as carbon nanotube (CNT) and graphene based anodes, and the maximum power density is further improved to a record high power density of 11220 W/m3. A novel supercapacitor by regulating the respiration of the bacteria is also presented, and a high power density of 531.2 A/m2 (1,060,000 A/m3) and 197.5 W/m2 (395,000 W/m3), respectively, are marked, which are one to two orders of magnitude higher than any previously reported microbial electrochemical techniques. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

This thesis includes both experimental and modelling studies on the treatment of drinking water. Three aspects were studied: (i) removal of fluoride (F– ) by adsorption, (ii) removal of fluoride and other contaminants by solar distillation, (iii) denitrification by a microbial fuel cell. The availability of potable water on earth is about 0.2% of the total available water. This very small quantity is polluted by anthropogenic and natural contaminants. Fluoride is a classic example of a natural contaminant, wherein the dissolution of F– bearing minerals causes the release of F– into the groundwater. Exposure to concentrations > 1 mg/L over ex-tended periods of time results in dental and skeletal fluorosis. Worldwide, about 220 million people are at risk. Nitrate is an example of anthropogenic contaminant, occurring because of addition of high quantities of fertilizers to the soil for better crop yields. The excess fertilizers penetrate the soil and mix with the groundwater, resulting in nitrate contamination. The major effect of nitrate contamination is met haemoglobin , which is caused because of the oxidation of ferrous ion in haemoglobin to ferric ion by the nitrite to form haemoglobin. The effects can be noticed by the change in colour of skin to bluish grey or brownish grey in infants. To counter the drastic effects of these anions, the World Health Organization (WHO) has prescribed permissible limits of 1.5 mg/L and 45 mg/L for F– and NO3 – , respectively. For obtaining contaminant-free water, many methods have been used. Reverse osmosis (RO) is one of the widely-used methods. Even though this process removes most of the contaminants, about 50 - 70% of the inlet water is wasted as a reject stream with higher concentrations of the contaminants. This is a very unsustainable way of using water, particularly in drought-prone areas. So, in the thesis a conceptual strategy with three different methods is developed to treat reject water. In the first part of the thesis, the removal of F– using adsorption was studied. Activated alumina (AA) and a hybrid anion exchange resin embedded with hydrous zirconium oxide nanoparticles (HAIX-Zr) (sample sent by Prof. Arup K SenGupta) were used as the adsorbents. The adsorbents were tested with synthetic water samples and reverse osmosis (RO) reject water. HAIX-Zr had a better adsorption capacity compared to AA when water containing only F– was used. The presence of high concentrations of co-ions affects the uptake of F– drastically, with a decrease of up to 34% and 79% for AA and HAIX-Zr, respectively. With AA, for a synthetic water sample with a small concentration of HCO3 – , there was a two-fold increase in the uptake of F– compared to a water sample containing only F– . There was no removal of NO3 – by AA. HAIX-Zr removes NO3 – , but to a lesser extent than F– . With AA, the pH of the inlet solution affected the adsorption capacity, because of the change in the surface charge of AA. Based on the type of water sample used, the cost of treated water varied from Re. 0.1 - 1.0/L ($ 0.0015 - 0.015/L) for AA and 0.2 - 11.5/L ($ 0.003 - 0.17/L) for HAIX-Zr. A community-level plant was set up to treat the RO reject water using AA. Due to challenges at the field level, the pilot plant had to be stopped after 80 bed volumes of water were treated. From our observations and as also reported by many authors, the adsorption of F– is affected by the presence of many ions. When modelling the adsorption of F– , it is usually taken as a single entity getting adsorbed on the adsorbent. As this is not a proper assumption, a model was developed which takes into account all the speciation reactions that take place during adsorption, and all the species like H+, OH– , Na+, Cl– , and NO3 – present in the solution along with F– . Using the model, the equilibrium constants and rate constants for the reactions were obtained. For one initial concentration of F– , a good fit was obtained to the batch adsorption data, except at short times. Due to uncertainty about the amount of impurity present in the adsorbent, at higher initial concentrations of F– , there was a significant discrepancy between predictions and data. Considering column experiments, the breakthrough curve for F– was simulated using the developed model. For the special case of negligible mass transfer resistances, the predicted break-through volume was within 3% of the observed value. In the second part of the thesis, nitrate removal was investigated using microbial fuel cell (MFC). In a MFC, power is generated by the activity of the microorganisms present in the cell. The organisms present in the anode side release electrons (e– ) by the use of substances that can be oxidized, namely, glucose, acetate, etc. On the cathode side, the organisms have the potential to take in e– and reducible substances, and release reduced products like nitrogen, hydrogen, etc. In the present case, nitrates added to the cathode side were reduced to nitrogen gas by the use of a consortium of micro-organisms taken from seawater. A similar consortium was used in the anode chamber Here, the study was focused on improving the efficiency of MFC for removal of NO3 – , by changing the buffering medium used in the cells. Commonly, phosphate buffer is used, but when using a MFC for treatment, the presence of PO43 – causes water contamination and is not suitable for drinking. There-fore, PO43 – was replaced with HCO3 – on the cathode side of the cell. This resulted in a higher removal of NO3 – and power production compared to the PO43 – buffered solution In the third part of the thesis, contaminant removal using solar distillation was investigated. For this as inclined basin still was used. Investigations were based on the evaporation rate of contaminated water, and the odour and concentrations of ions in the distillate. In order to improve the evaporation rates, different radiation absorbing materials like sand, activated charcoal, and carbon nanoparticles encapsulated in polymer sheets (PCNP) were investigated. It was observed that the evaporation rates were higher with activated carbon than the other materials. Using this technique there was about 99% removal of NO3 – , F– , SO42 – and the concentrations of ions in the distillate were well below the acceptable limits. When sand or PCNP was used as an absorbing/wicking medium, the distillate had an objectionable odour. With the use of AC, the odour could be eliminated because of the adsorption of odour-causing compounds.

Les piles à combustible microbiennes (PACM) permettent la production directe d'électricité par l'oxydation de matière organique ; à l'anode les combustibles organiques sont oxydés grâce à des microorganismes adhérés qui jouent le rôle d'électro-catalyseurs. Utiliser comme combustible la matière organique issue d'effluents ou de déchets des industries agro-alimentaires présente un double bénéfice : la réduction de l'impact environnemental et la génération d'énergie. Le travail réalisé dans le cadre de la thèse comporte trois volets : tout d'abord l'évaluation des combustibles et des sources d'inoculum en termes de capacités électro-catalytiques, ensuite la recherche de conditions opératoires favorisant la génération de courant simultanément à la biodépollution. Ces deux objectifs ont été abordés en conditions électrochimiques bien contrôlées (montages à trois électrodes, contrôle potentiostatique). Le troisième volet a porté sur la validation de ces conditions en configuration de PACM. Trois résidus issus d'industries agro-alimentaires ont été testés comme combustible : des jus de pomme fermentés, des lies du vin et des déchets de laiterie, et deux environnements comme source de micro-organismes électro-actifs : des boues anaérobies et des lixiviats de terreau de jardin. Les études en cellule électrochimique ont révélé les lixiviats de terreau comme la meilleure source de biocatalyseur et les résidus de laiterie comme le meilleur combustible. En conséquence l'amélioration du procédé a été effectuée principalement sur le couple lixiviats de terreau - résidus laitiers. Une acclimatation préliminaire de la microflore des lixiviats de terreau aux déchets de laiterie s'est révélée inutile. Des concentrations élevées des déchets de laiterie ont eu un effet négatif sur la génération de courant, bien qu'une réduction de 90% en demande chimique en oxygène (DCO) ait été atteinte. Le prétraitement de la surface de l'anode par l'adsorption du substrat a permis une augmentation du courant d'un facteur 10 par rapport à une anode non prétraitée. Les tests de températures comprises entre 10°C et 60°C suggèrent l'existence d'une large diversité de microorganismes électro-actifs. Une densité de courant de 1655 mA/m² a été atteinte à 40°C à un potentiel imposé de +0,1V/ECS sur une anode en feutre de graphite prétraitée. Différentes combinaisons « source de biocatalyseur - combustible » ont été évaluées en utilisant une PACM composée de deux compartiments séparés par une membrane échangeuse de protons et équipée d'une anode en feutre de graphite. Les meilleures performances ont été obtenues avec le lixiviat de terreau comme source de micro-organismes électro-actifs et les déchets laitiers comme combustible (92 mW/m2, 636 mA/m2). Ces résultats confirment les résultats obtenus en cellule électrochimique et se situent parmi les meilleurs dans le cadre du développement émergent des PACM pour l'exploitation de déchets bruts. / In the microbial fuel cells (MFC) electricity is produced by the oxidation of organic matter. At the anode the fuel is oxidized by the microorganisms attached to it, they act as catalyst. The use of food and agricultural industry wastes carry out to a double benefit: waste treatment and energy generation. In the present work three aspects are presented: Initially fuels and inoculum sources are evaluated in terms of their electro catalytic activity, thereafter operational parameters are studied to enhance electricity production and waste treatment. These studies are achieved in three electrodes electrochemical cells under potentiostatic control. In the last part, the materials and operational conditions selected are tested in MFC. Three wastes were tested as fuel to MFC: fermented apple juice, wine lees and dairy wastes, with two electroactive inocula: anaerobic sludge and garden compost leachate. The results in electrochemical cells indicated compost leachate and dairy wastes as the best inoculum and fuel respectively. Consequently, most of subsequent experiments were achieved with these materials. Preliminary acclimation procedure of compost leachate microbial flora to dairy wastes fuel proved not to be useful. High concentration of dairy wastes was detrimental to current generation; however the COD removal was 90%. Pre-treatment of electrode by pre-adsorbing dairy waste led to a 10-fold increase in the current density. Results from temperature test (10°C to 60°C) suggest a large diversity of electrochemically active microorganisms coming from compost. A current density of 1655 mA/m² was reached at 40°C with a pre-treated graphite felt anode under polarization at +0,1V vs. ECS. Different mixtures composed by “biocatalyst-combustible” were evaluated in a two chamber membrane microbial fuel cell, with graphite felt anode. The best performance was obtained with compost leachate as biocatalyst and dairy wastes as fuel (92 mW/m² at 636 mA/m² by polarization curve). These results confirmed those obtained in electrochemical cells and they are in the high range of performances reached with this new technology using raw materials.

Pro zpracování a nakládání s odpadními substráty lze použít řadu postupů a možností. Stále se rozšiřující spektrum metod a technologií umožňuje další využití materiálů a energie ve formě obnovitelných zdrojů. Jedním z řešení pro zpětné získávání některých odpadních materiálů je využití tzv. bílé (průmyslové) biotechnologie, která zahrnuje praktickou aplikaci metabolických aktivit celé řady různých mikroorganizmů včetně jejich specifických biologických drah k produkci látek s vysokou přidanou hodnotou. V předložené práci screeningového typu bylo pro zhodnocení odpadních surovin využito několik druhů mikroorganizmů kultivovaných za různých specifických podmínek včetně kultivace na odpadních materiálech získaných zejména ze zemědělství a potravinářství. Cílem bylo získání vybraných typů průmyslově cenných metabolitů, případně energie. Předložená studie byla zaměřena na srovnání růstu a produkčních vlastností několika kmenů karotenogenních kvasinek rodu Rhodotorula, Sporobolomyces a Cystofilobasidium, kultivovaných v médiích s obsahem glycerolu (technický a odpadní glycerol), dále v médiích obsahujících pšeničnou slámu, hydrolyzovanou slámu zpracovanou v hydrotermálním procesu při vysoké teplotě a zbytky po filtraci hydrolyzátu. Dalším testovaným odpadním substrátem byla syrovátka. Všechny testované kvasinky byly schopny využít glycerol jako jediný zdroj uhlíku. Produkce biomasy při kultivaci na technickém glycerolu se více či méně přibližovala kontrole (cca 7 - 10 gl-1), zatímco při kultivaci na odpadním glycerolu byla produkce vyšší (10.9 - 14.5 gl-1). Produkce karotenoidů a ergosterolu byla vyšší v glukózovém médiu než v médiu s obsahem glycerolu. Všechny testované kvasinky byly rovněž schopny produkovat neutrální lipidy, a to v rozmezí 11 - 15 %, s výjimkou C. capitatum, kde produkce dosahovala více než 22 % obsahu neutrálních lipidů. Pšeničná sláma a produkty z ní připravené se ukázaly být využitelnými substráty s vysokým potenciálem pro produkci biomasy i metabolitů, a to zejména u kmene S. roseus. Syrovátka, jako odpadní produkt mlékarenství, byla účinně využita jako substrát pro kokultivaci karotenogenních kvasinek a bakterií mléčného kvašení. Kokultivační proces může vyvolat nadprodukci pigmentů a ergosterolu, přičemž získaná biomasa díky obohacení o bakterie L. casei dosahovala vyšší kvality. Za účelem energetického využití mikrobiálního metabolismu formou mikrobiálních palivových článků, tzv. „Microbial Fuel Cell“ byla aplikována směsná kultura bakterií získaných z čistírny odpadních vod. Tyto mikroorganizmy hrají významnou roli při výrobě elektrické energie a současně také při čištění odpadních vod. Elektřina je generována přímo z organických látek přítomných v kultivačním médiu a lze ji použít pro provoz čistírny samotné a případně i pro další aplikace.

Efforts to remove and recover nutrients from wastewater are motivated by the United Nations Sustainable Development Goals and the National Academy of Engineering Grand Challenges of Engineering. Of the seventeen Sustainable Development Goals (SDGs), multiple SDGs relate to managing nutrients in wastewater. SDG 6, which is to “ensure availability and sustainable management of water and sanitation for all,” contains targets that aim to improve water quality by reducing pollution, halve the amount of untreated wastewater released to the environment, and increase recycling and safe reuse of wastewater (UN, 2017). SDG 2 seeks to improve food security and SDG 12 seeks to sustainably manage natural resources. Similarly, the National Academy of Engineering Grand Challenges of Engineering highlight managing the nitrogen cycle and providing access to clean water (NAE, 2019). Centralized wastewater treatment plants (WWTPs) have historically been designed to remove nutrients (such as nitrogen and phosphorus) and other contaminants prior to discharge. Modern wastewater treatment practices integrate recovery of resources including nutrients, energy, and water. The many available technologies, coupled with competing priorities, can complicate community decision-making on the choice of technology and the scale at which to implement the technology (i.e. building, community, or city), as well as determining how new upstream treatment may affect existing downstream treatment. Technologies that recover energy or manage nutrients such as anaerobic digestion, struvite precipitation, and microbial fuel cells can be implemented at a variety of scales in urban settings and may also be viable for influent types such as agricultural waste. Therefore, the overall goal of this dissertation is to contribute to the achievement of multiple sustainable development goals through the removal and recovery of nitrogen and phosphorus from a variety of influents at a variety of scales. One type of decision-making tool that assists in the choice of nutrient management technologies is a House of Quality. I developed a tool based on the House of Quality that integrated multiple priorities at three scales in a sewershed and produced rankings that generally align with current wastewater treatment practice. Accordingly, top-ranked city-scale technologies are those commonly employed (e.g. A2O, oxidation ditch) that use the dissolved organic carbon present in the wastewater to drive denitrification. Similarly, conventional treatment (e.g. flush toilet connected to a sewer) is ranked highest at the building scale because of its easy maintenance, small footprint, and inoffensive aesthetics. However, future trends such as technology development will likely affect the technologies, weightings, and scores and therefore improve the ranking of novel and emerging technologies. This trend may be amplified by the implementation of test beds, which can provide opportunities to improve the technical characteristics of developing technologies while minimizing risk for municipalities. The House of Quality planning tool was utilized in an in silico case study to analyze nutrient management technologies at three scales across the Northwest Regional Water Reclamation Facility sewershed in Hillsborough County, FL. The study demonstrated that employing treatment technologies upstream from the centralized wastewater treatment (i.e. building-scale source separation and community-scale technologies) could reduce nitrogen loading to the mainstream treatment train by over 50%. Sidestream treatment (i.e. the liquid effluent of anaerobic digestion that typically recycles back to the beginning of the mainstream treatment process) has minimal impact in nitrogen reduction, but is effective in reducing phosphorus loading to the mainstream due to high quantities of phosphorus recycling back to the head of the plant. These results can inform decision-makers about which context-specific nutrient management technologies to consider at a variety of scales, and illustrate that sidestream technologies can be the most effective in reducing phosphorus loading while building- and community-scale technologies can be most effective in reducing nitrogen loading to the centralized treatment plant. Struvite precipitation and microbial fuel cells (MFCs) can be used in combination to manage nutrients and recover energy in sidestreams of centralized WWTPs. Because the liquid effluent from engineered struvite precipitation often contains high concentrations of total nitrogen, I constructed and demonstrated a fixed-film nitrification reactor and a two-chambered MFC to further reduce total nitrogen and recover energy. The primary benefit of the MFC in the technology demonstrated here is not its ability to produce energy, but rather its ability to remove additional nitrogen through nitritation and denitritation. The sidestream nutrient removal prevents nutrients from returning to mainstream treatment, reducing operational costs. Such improvements to wastewater treatment processes can facilitate the transition to the resource recovery facility of the future by becoming a net-energy producer while also achieving the simultaneous benefits of nutrient recovery/removal and reduced costs associated with mainstream treatment. Nutrients and energy can also be recovered in agricultural settings. In this dissertation I studied an agricultural waste treatment system comprising a small-scale tubular anaerobic digester integrated with a low-cost, locally produced struvite precipitation reactor. This study investigated two digesters that treated swine waste in rural Costa Rica. I also facilitated construction of a pilot-scale struvite precipitation reactor that was built on site using local labor and local materials for approximately $920. Local products such as bittern (magnesium source) and soda ash (base) allowed for the production of struvite, a fertilizer that can replace synthetic fertilizer for rural farmers. Liquid-phase concentrations of PO43–-P and NH4+-N in agricultural wastewater increased by averages of 131% and 116%, respectively, due to release from the swine waste during anaerobic digestion. Despite this increase in liquid-phase concentrations, an average of 25% of total phosphorus and 4% of total nitrogen was removed from the influent swine manure through sedimentation in the digesters. During struvite precipitation, an average of 79% of PO43–-P and 12% of NH4+-N was removed from the waste stream and produced a solid with percentages (mass basis) of Mg, N, P of 9.9%, 2.4%, and 12.8%, respectively, indicating that struvite (MgNH4PO4) was likely formed. The treatment system offers multiple benefits to the local community: improved sanitation, removal of nutrients to prevent eutrophication, recovery of struvite as a fertilizer, and production of a final effluent stream that is suitable quality to be used in aquaculture. These are examples of how, more generally, quantifying nutrient recovery from agricultural waste and understanding recovery mechanisms can facilitate progress toward multiple sustainable development goals by improving sanitation, promoting sustainable management of wastes and natural resources, improving food security, and supporting local ecosystems. Managing nutrients from a variety of influent types at different scales can contribute to the achievement of multiple sustainable development goals. Worldwide trends of population growth and resource depletion highlight the need for models to easily allow decision-makers the ability to understand the fate of nutrients and implement infrastructure accordingly.

Microbial Fuel Cell is a novel technology that can be used for a waste water treatment in order to simultaneously remove carbonaceous matter and nitrogen while producing electrical power. Even if it is not an established technology so far, MFC could be a cost effective option for waste water treatment and the major challenge of this process will be the device scale-up. Exoelectrogenic bacteria are capable of converting the chemical energy of organic matter into electrical energy by transferring the electrons produced in the oxidation to the anode electrode. This project focused on developing a single device for nitrification, denitrification and carbon removal. Two double air-cathode single chamber MFCs are used to test the feasibility of this process that could replace the biological unit in a waste water treatment train. The cells tested in this study were manufactured with the purpose of achieving a high surface area on both the anode electrode (vitreous carbon foam) and the air-cathode electrodes (metallic mesh with diffusion layer and active layer) with different catalysts for the reduction reaction (cobalt and platinum). The bacterial biofilm growth is a fundamental step and the cells Open Circuit Potential was monitored during all the start-up period to determine the microorganism acclimation: a three days lag period was observed in both cells before the potential rise. The second cell was forced to reach higher voltage through an anode polarization and that seems to positively affect the biofilm stability at lower voltages transferring a greater amount of electrons and hence obtaining a higher current and power generation. For this reason after three weeks of inoculation the second cell reached an open circuit potential of 0.76 V which is a promising value for such a system. Electrochemical and biological tests were conduced in order to test the power production of the cell and the substrate removal from the waste water. Polarization curves were used to evaluate power generation (and the maximum production under a specific external load) and the cell voltage trend which is characterized by activation and ohmic losses: 32 mW/ and 41 mW/  are the power density normalized by cathode surface (72 ) reached by respectively first and second cell. The experimental conditions were varied from low to high temperature and from low to high inlet flow rate but the most affecting phenomenon seems to be the biofilm formation since significant voltage drops were noticed after long closed circuit operation. Higher cell voltage characterized the second cell thanks to more active cathode (platinum catalyst used) and more negative bacterial biofilm but a bigger drop in current generation over time affects the system performance and the most reliable reason is the shorter acclimation time compared to the first cell. Cyclic voltammetry tests were carried out on both electrodes to study the potential range of activity and determine an optimal operational voltage despite of mass transport or kinetic limitations. Substrate removal tests at different retention times in power generation conditions (external load 100 Ω) showed a relatively high total nitrogen consumption (maximum 72.2 %) for the first cell while lower values were achieved by the second system meaning that a longer acclimation period is beneficial for nitrifying and denitrifying bacteria to thrive on the cathode biofilm. Effluent pH level are almost similar to the initial values probably because of nitrification and denitrification protons offset.

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.

No description available.

No description available.