Οι πολυφαινόλες είναι μια κατηγορία οργανικών χημικών ουσιών, που χαρακτηρίζονται από την παρουσία ενός ή περισσότερων υδροξυλίων, συνδεδεμένων με έναν ή περισσότερους αρωματικούς ή ετεροκυκλικούς δακτυλίους φαινόλης. Το ταννικό οξύ (ΤΑ), μια ειδική εμπορική μορφή της τανίνης, χρησιμοποιείται ευρέως στη βιομηχανία και αποτελεί μία από τις κυριότερες ουσίες των βιομηχανικών λυμάτων που διοχετεύονται στα υδάτινα οικοσυστήματα και στο έδαφος. Παρόλο το γεγονός ότι οι πολυφαινόλες δρουν αντιοξειδωτικά στα κύτταρα, η ισορροπία μεταξύ της αντιοξειδωτικής και της οξειδωτικής δράσης τους είναι υπό διερεύνηση. Η παρούσα μελέτη διερευνά τις αντιοξειδωτικές και οξειδωτικές επιπτώσεις του ταννικού οξέος σε αιμοκύτταρα του μυδιού Mytilus galloprovincialis, παρουσία τοξικών συγκεντρώσεων καδμίου. Συγκεκριμένα, αιμοκύτταρα που εκτέθηκαν σε διαφορετικές συγκεντρώσεις ΤΑ (1, 10, 20, 40 και 60 μΜ) για 1 h, έδειξαν σημαντική μείωση της βιωσιμότητάς τους, μόνο σε συγκεντρώσεις ΤΑ μεγαλύτερες από 40 μΜ. Παράλληλα, αιμοκύτταρα που εκτέθηκαν σε μικρομοριακές συγκεντρώσεις του μετάλλου (50 και 100 μΜ) έδειξαν σημαντική μείωση της βιωσιμότητάς τους. Προκειμένου να προσδιορίσουμε την αντιοξειδωτική ή οξειδωτική ικανότητα του ΤΑ, αιμοκύτταρα που είχαν προηγουμένως προ-επωαστεί σε διαφορετικές συγκεντρώσεις ΤΑ για 15 min, εκτέθηκαν σε μικρομοριακές συγκεντρώσεις του μετάλλου. Σύμφωνα με τα αποτελέσματά μας, κύτταρα που είχαν προ-επωαστεί σε συγκεντρώσεις ΤΑ 1- 40 μΜ, έδειξαν σημαντική αναστολή των οξειδωτικών επιπτώσεων του μετάλλου (παραγωγή σουπεροξειδικών ανιόντων/∙O2 −, οξειδίων του αζώτου/ ΝΟ, και προϊόντων λιπιδικής υπεροξείδωσης/ επίπεδα μηλονικής διαλδεϋδης), όσο και της ικανότητάς του να μειώνει τη βιωσιμότητα των κυττάρων, συγκριτικά με τις τιμές που μετρήθηκαν σε κύτταρα που εκτέθηκαν μόνο στο μέταλλο. Αντίθετα, σε κύτταρα που προ-επωάστηκαν σε ΤΑ 60 μΜ, πριν την έκθεσή τους στο μέταλλο, το ΤΑ εμφανίστηκε να δρα συνεργατικά με το μέταλλο. Τα αποτελέσματα της παρούσας μελέτης οδηγούν στο συμπέρασμα ότι το ΤΑ σε μικρομοριακές συγκεντρώσεις 1-40 μΜ μπορεί να δράσει ως ένας ισχυρός αντιοξειδωτικός παράγοντας, ενώ σε υψηλότερες συγκεντρώσεις μπορεί να προκαλέσει οξειδωτικές επιπτώσεις, ανάλογες με αυτές που προκύπτουν από ισχυρούς οξειδωτικούς παράγοντες, όπως τα κάδμιο. / Polyphenols are well-known organic substances, mainly characterized by the presence of one or more hydroxyl groups on one or more aromatic or heterocyclic phenol rings. Tannic acid (TA), a specific commercial form of tannin is a natural polyphenol, widely used in food, pharmaceutical, leather and chemical industry. It is one of the main organic compounds of industrial effluents discharged into aquatic ecosystems and soil, causing environmental pollution. Despite the fact that a lot of studies reported that polyphenols could act as antioxidants in different cells, the balance between their antioxidant and pro-oxidant properties remains still unclear. According to the later, the present study investigates the antioxidant and pro-oxidant potency of TA in haemocytes of mussel Mytilus galloprovincialis in the presence or the absence of micromolar concentrations of cadmium (Cd). Specifically, haemocytes exposed to different concentrations of TA (1, 10, 20, 40 and 60 μΜ) for 1 h, showed a significant reduction of their viability, only in concentrations higher than 40 μΜ. Furthermore, cells exposed to micromolar concentrations of Cd (50 and 100 μΜ), showed significantly increased levels of cell death, compared to those observed in control cells. In order to investigate the antioxidant or pro-oxidant ability of TA, haemocytes pre-treated for 15 min with different concentrations of TA were exposed to micromolar concentrations of the metal. According to the results, cells pre-treated with TA 1-40 μΜ, showed a significant attenuation of Cd induced effects, such as the production of superoxide (∙O2 −) and nitric oxides (NO), MDA content as well as cell death, compared to those occurred in the presence of the metal alone. On the contrary, in cells pre-treated with TA 60 μΜ before their exposure to the metal, TA seemed to act synergistically with the metal. The results of the present study could lead to the suggestion that TA in concentrations ranged within 1 and 40 μΜ could act as a major antioxidant factor, whereas in higher concentrations TA could cause oxidant effects, similar with those caused by well-known pro-oxidants, such as cadmium.

Quantifying charcoal particles preserved in sedimentary environments is an established method for estimating levels of fire activity in the past, both on human and geological timescales. It has been proposed that the morphology of these particles is also a valuable source of information, for example allowing inferences about the nature of the vegetation burned. This thesis aims to broaden the theoretical basis for these methods, and to integrate morphometric study of sedimentary charcoal with its quantification. Three key questions are addressed: firstly, whether the elongation of mesocharcoal particles is a useful indicator of fuel type; secondly, whether different sedimentary archives tend to preserve different charcoal morphologies; and finally, the critical question of how morphology affects charcoal quantification. The results corroborate the idea that grasses and trees produce mesocharcoal with distinctly different aspect ratios. However, the application of this as an indicator of vegetation change is complicated by the inclusion of species which are neither grasses nor trees, and by considerations of the effects of transportation. Charcoal morphotypes in diverse sedimentary environments are shown to be influenced by vegetation types, transportation history, and nature of the fire that produced them. Previous research has treated charcoal quantification and charcoal morphology as separate issues. Here it is shown that understanding morphology is essential for the accurate quantification of charcoal, since it affects the relationship between volumes and the two-dimensional areas from which measurements are taken. Understanding this relationship could allow such measurements to be used not just as relative measures of past fire activity, but to enable the accurate quantification of the charcoal sequestered in soils and sediments. This has important implications for our ability to understand the effects of fire on carbon cycling, and the role that fire plays in the Earth system.

This study investigated the fate of lignocellulosic biomass (wheat-feed and perennial rye grass) in different anaerobic digestion systems, evaluating the role of substrate specificity on the pattern of degradation. The two-stage (biohydrogen-biomethane) anaerobic system was found to be more effective in the degradation of lignocellulose, when compared to the conventional single-stage system. The perennial rye grass substrate possessed about 21% higher holocellulose concentration when compared to the wheat-feed; its exploitation in the acidogenic digestion was however poor, resulting in a 2.9% lower biogas yield in a equivalent two-stage system. The study therefore developed a treatment technique involving the use of cellulase and ferulic acid esterase enzyme combinations for the treatment of perennial rye grass. The enzyme cocktail at 0.202 ml enzyme/g VS added resulted in efficient bioconversion of the complex polymers to soluble carbohydrates, evident in the yield increase of soluble COD, to 321.0±10.9 mg/gVS, a 393.2% yield increase, when compared to the no enzyme added control. The yield of bio-hydrogen after enzymatic addition was 48ml/gVS, 335% higher when compared to the alkaline treatment; and more than seven fold higher than the yield obtained from the fermentation with no pre-treatment. The acetate to butyrate ratio varied from 4:1, when no pre-treatment was used, to 2:1when alkaline pre-treatment was used, then to 1:1 after the enzymatic treatment. The downstream effect of the prior hydrolysis on the subsequent processes to acidogenic fermentation like biomethane and PHA production and lignin recovery were also investigated. The hydrogenic/acidogenic fermentation resulted in methane yield improvement of 45.7%. The study shows that the more effective a hydrolysis procedure is in the depolymerisation of complex polymers, the greater the accumulation of PHA in the PHA biosynthesis operations. The enhanced hydrogenic /acidogenic fermentation having effectively degraded the holocellulose component of the perennial rye grass substrate ensured that relatively high quality lignin was obtained in an Organosolv lignin-extraction procedure. FT-IR profile show less contamination of polysaccharides and proteins in the lignin extracted from the enzymatically enhanced acidogenic fermentation. An evaluation of the economic viability of the investigated secondary processes showed that direct integrations of those processes to the biohydrogen process may not be as economically advantageous, when compared to a 2nd -stage biomethanation system.

The purpose of this thesis was to carry out the experimental study of direct ammonia fuel cells. The use of hydrogen in fuel cells poses a lot of problems. There is a lot of safety, technical and economic issues to be overcome to make its use as a fuel widespread. Ammonia is being considered as a very promising source of hydrogen for fuel cells. However, until now its use in fuel cells has received very little attention. Ammonia presents many advantages over hydrogen and other potential sources of hydrogen such as an easy storage and a world-wide distribution network. Ammonia is a suitable hydrogen carrier and can be easily cracked at high temperatures such as those used in solid oxide fuel cells. The present study was conducting using ammonia as fuel and argon as carrier gas in different solid oxide fuel cell systems: an annular design, a planar design and a micro laminated reactor. The electrolyte materials were calcia stabilized zirconia and yttria stabilized zirconia. As far as the electrodes are concerned, silver, platinum and nickel cermet were used as anode/materials and silver was employed as cathode material. The cell yoltage was measured as function of reactor configuration, space time, ammonia flow rate and ammonia concentration. The results demonstrate the high potential of ammonia over hydrogen when nickel is used as anode material. Solid proton conducting fuel cells operating on ammonia fuel were also studied. The electrolyte materials were fabricated from neodymium and gadolinium doped barium and strontium cerates. The dopant fraction ranged from 1 to 20 wt%. Silver was employed as cathode and anode material and was spray deposited. The application of proton conducting electrolytes results in higher current densities for a given voltage than the using typical oxide ion conductors such as 8mol % yttria stabilized zirconia. The potential of the proton conducting materials for application in ammonia synthesis at atmospheric pressure was also studied. They demonstrated promising results and could prove to be an alternative to the common ammonia synthesis processes.

Biofuels have been identified as one of several GHG emission strategies to reduce the use of fossil fuels in the transport sector. Fast pyrolysis of biomass is one approach to producing second generation biofuels. The bio-oil product of fast pyrolysis can be upgraded into essential gasoline and diesel range products with conventional refinery technologies. Thus, it is important to assess their techno- economic and environmental performance at an early stage prior to commercialisation. This research was conducted with the goal of evaluating and comparing the techno-economic and environmental viability of the production of biofuels from fast pyrolysis of biomass and upgrading of bio-oil via two refinery technologies, viz. hydroprocessing and zeolite cracking. In order to achieve this aim, process models of fast pyrolysis of biomass and bio-oil upgrading via hydroprocessing and zeolite cracking were developed. The fast pyrolysis model was based on multi-step kinetic models. In addition, lumped kinetic models of the hydrodeoxygenation reactions of bio-oil were implemented. The models were verified against experimental measurements with good prediction and formed the foundation for the development of a 72 t/day fast pyrolysis plant model in Aspen Plus®. Several strategies were proposed for the two pathways to enhance energy efficiency and profitability. All in all, the results revealed that the hydroprocessing route is 16% more efficient than the zeolite cracking pathway. Moreover, the hydroprocessing route resulted in a minimum fuel selling price of 15% lower than that from the zeolite cracking pathway. Sensitivity analysis revealed that the techno-economic and environmental performance of the both pathways depends on several process, economic and environmental parameters. In particular, biofuel yield, operating cost and income tax were identified as the most sensitive techno-economic parameters, while changes in nitrogen feed gas to the pyrolysis reactor and fuel yield had the most environmental impact. It was concluded that hydroprocessing is a more suitable upgrading pathway than zeolite cracking in terms of economic viability, energy efficiency, and GHG emissions per energy content of fuel produced.

Utilisation of biomass resources and CO2 abatement systems in currently exploited fossil resource based energy systems are the key strategies in resolving energy sustainability issue and combating against global climate change. These strategies are affected by high energy penalty and high investment. Therefore, it is imperative to assess the viability of these energy systems and further identify niche problem areas associated with energy efficiency and economic performance improvement. The current research work has two parts. The first part presents techno-economic investigation of thermochemical conversion of biomass into the production of fuels (Fischer-Tropsch liquid or methanol) and electricity. The work encompasses centralised bio-oil integrated gasification plant, assuming that the bio-oil is supplied from distributed pyrolysis plant. Bio-oil is a high energy density liquid derived from biomass fast pyrolysis process, providing advantages in transport and storage. Various bio-oil based integrated gasification system configurations were studied. The configurations were varied based on oxygen supply units, once-through and full conversion configurations and a range of capacities from small to large scale. The second part of this thesis considers integration of various CO2 abatement strategies in coal integrated gasification systems. The CO2 abatement strategies under consideration include CO2 capture and storage, CO2 capture and reuse as well as CO2 reuse from flue gas. These facilities are integrated into cogeneration or polygeneration systems. The cogeneration concept refers to the production of combined heat and power while polygeneration concept is an integrated system converting one or more feedstocks into three or more products. Polygeneration is advocated in this work attributed to its high efficiency and lower emission. Furthermore, it can generate a balanced set of products consisting of fuels, electricity and chemicals. It is regarded as a promising way of addressing the future rapidly growing energy demands. A holistic approach using systematic analytical frameworks comprising simulation modelling, process integration and economic analysis has been developed and adopted consistently throughout the study for the techno-economic performance evaluation of decarbonised fossil and bio-oil based systems. Important design methodology, sensitivity analysis of process parameters and process system modifications are proposed. These are to enhance the efficiency as well as lower the economic and environmental impacts of polygeneration systems. A shortcut methodology has also been developed as a decision-making tool for effective selection from a portfolio of CO2 abatement options and integrated systems. Critical and comprehensive analyses of all the systems under considerations are presented. These embrace the impact of carbon tax, product price evaluation and recommendations for sustainability of low carbon energy systems.

This thesis considers the control of combustion oscillations, motivated by the susceptibility of lean premixed combustion to such oscillations, and the long and expensive development and commissioning times that this is giving rise to. The controller used is both closed-loop, employing an actuator to modify some system parameter in response to a measured signal, and adaptive, meaning that it is able to maintain control over a wide range of operating conditions. The controller is applied to combustion systems with annular geometries, where instabilities can occur both longitudinally and azimuthally, and which require multiple sensors and multiple actuators for control. One of the requirements of Lyapunov-based adaptive control which is particularly troublesome for combustion systems is then addressed: that the sign of the high-frequency gain of the open-loop system is known. We address it by using an adaptive controller which employs a Nussbaum gain, and successfully apply it experimentally to combustion oscillations in a Rijke tube. Another type of fluid-acoustic resonance is then considered: the compressible flow past a shallow cavity. We start by finding a linear model of the cavity flow's dynamics, or its 'transfer function', which we identify from direct numerical simulations. We compare this measured transfer function to that given by a conceptual model which is based on the Rossiter mechanism, and which models each component of the flow physics separately. We then look at using closed-loop control to eliminate these cavity oscillations. We start by designing a robust H₂ controller based on a balanced reduced order model of the system, the model being provided by the Eigensystem Realization Algorithm (ERA). The robust controller provides closed-loop stability over a much wider Mach number range than seen in previous studies. Finally, we look at the suitability of the adaptive controller, earlier developed for combustion oscillations, for the cavity. Based on some general properties of the cavity flow, and by using collocated control, the oscillations are eliminated at all Mach numbers tested in the range 0.4 ≤ M ≤ 0.8.

In the effort to introduce fuel cell technology in the field of decentralized and mobile power generators, a hydrocarbon reformer to syngas seems to be the way for the market uptake. In this thesis, a potential technology is developed and investigated, in order to convert commercial liquid fuel (diesel, kerosene and biodiesel) to syngas. The fundamental concept is to oxidise the fuel in a oxygen depleted environment, obtaining hydrogen and carbon monoxide as main products of the reaction. In order to extend the flammability limit of hydrocarbon/air mixtures, the rich combustion experiments have been carried out in a two-layer porous medium combustor, which stabilises a flame at the matrix interface and recirculates the enthalpy of the hot products in order to enhance the reaction rates at ultra-rich equivalence ratio. This thesis demonstrates the feasibility of the concept, by exploring characteristic parameters for a compact, reliable and cost effective device. Specifically, a range of equivalence ratios, thermal loads and porous materials have been examined. n-heptane was successfully reformed up to an equivalence ratio of 3, reaching a conversion efficiency (based on the lower heating value of H2 and CO over the fuel input) up to 75% for a packed bed of alumina beads. Thermal loads from P=2 to 12 kW at phi=2.0 demonstrated that heat losses can be reduced to 10%.Similarly, diesel, kerosene and bio-diesel were reformed to syngas in a Zirconia foam burner with conversion efficiency over 60%. The effect of different burners, thermal loads and equivalence ratios have also been assessed for these commercial fuels, leading to equivalent conclusions. A preliminary attempt to reduce the content of CO and hydrocarbons in the reformate has been also performed using commercial steam reforming and water-gas shift reaction catalysts, obtaining encouraging results. Finally, soot emission has been assessed, demonstrating particle formation for all the fuels above phi=2.0, with biodiesel showingthe lowest soot formation tendency among all the fuels tested.

In order to satisfy the global requirement for transport fuel sustainably, renewable liquid biofuels must be developed. Currently, two biofuels dominate the market; bioethanol for spark ignition and biodiesel for compression ignition engines. However, both fuels exhibit technical issues such as low energy density, poor low temperature performance and poor stability. In addition, bioethanol and biodiesel sourced from first generation feedstocks use arable land in competition with food production, and can only meet a fraction of the current demand. To address these issues it is vital that biofuels be developed from truly sustainable sources, such as lignocellulosic waste resources, and possess improved physical properties. To improve and control the physical properties of a fuel for specific application, one must be able to tailor the products formed in its production process. All studies within this thesis, therefore, have the aim of assessing the fuels produced for their variability in physical property, or the aim of directing the process considered to specific fuel molecules. In Chapter 2, spent coffee grounds from a range of geographical locations, bean types and brewing processes were assessed as a potential feedstock for biodiesel production. While the lipid yield was comparable to that of conventional biodiesel sources, the fatty acid profile remained constant irrespective of the coffee source. Despite this lack of variation, the fuel properties varied widely, presumably due to a range of alternative biomolecules present in the lipid. Though coffee biodiesel was produced from a waste product, the fuel properties were found to be akin to palm oil biodiesel, with a high viscosity and pour point. The blend level would therefore be restricted. In Chapter 3 the coffee lipid, as well as a range of microbial oils potentially derived from renewable sources were transformed into a novel aviation and road transport fuel through cross-metathesis with ethene. Hoveyda-Grubbs 2nd generation catalyst was found to be the most suitable, achieving 41% terminal bond selectivity under optimum conditions. Metathesis yielded three fractions: an alkene hydrocarbon fraction suitable for aviation, a shorter chain triglyceride fraction that upon transesterification produced a short chain biodiesel fuel, and a multifunctional volatile alkene fraction that could potentially have application in the polymer industry. Though there was variation for the road transport fuel fraction due to the presence of long chain saturates, the compounds fell within the US standard for biodiesel. The aviation fraction lowered the viscosity, increased the energy density, and remained soluble with Jet A-1 down to the required freezing point. Oleaginous organisms generally only produce a maximum of 40% lipid, leaving a large portion of fermentable biomass. In Chapter 4, a variety of ethyl and butyl esters of organic acids – potentially obtainable from fermentation – were assessed for their suitability as fuels in comparison to bioethanol. One product, butyl butyrate, was deemed suitable as a Jet A-1 replacement while four products, diethyl succinate, dibutyl succinate, dibutyl fumarate and dibutyl malonate, were considered as potential blending agents for diesel. Diethyl succinate, being the most economically viable of the four, was chosen for an on-engine test using a 20 vol% blend of DES (DES 20) on a chassis dynamometer under pseudo-steady state conditions. DES20 was found to cause an increase in fuel demand and NOx emissions, and a decrease in exhaust temperature, wheel force, and CO emissions. While fermentation is generally directed to one product, producing unimolecular fuels, they do not convert the entirety of the biomass available. An alternative chemical transformation is pyrolysis. In Chapter 5, zeolite-catalysed fast pyrolysis of a model compound representative of the ketonic portion of biomass pyrolysis vapour – mesityl oxide – was carried out. The aim of this study was to understand the mechanistic changes that occur, which could lead to improved bio-oil yields and more directed fuel properties of the pyrolysis oil. While HZSM-5 and Cu ZSM-5 showed no activity for hydrogenation and little activity for oligomerisation, Pd ZSM-5 led to near-complete selective hydrogenation of mesityl oxide to methyl isobutyl ketone, though this reduced at higher temperatures. At lower temperature (150-250 °C), a small amount of useful oligomerisation was observed, which could potentially lead to a selective pyrolysis oligomerisation reaction pathway.

Over recent years microbial oil has attracted much attention due to its potential to replace traditional oil sources in the production of biofuels and nutraceuticals. Its advantages arise from its independence of the food supply chain and its ease of production compared to conventional plant oils. Also, as concerns for the environment grow, microbially-synthesized oil emerges as potential competitor for the sustainable production of biodiesel. However, the high cost of its production currently hinders its large scale application. The bottlenecks to industrial microbial oil production are the cost of substrate and cultivation. Current research is focusing on process improvements to make microbial oil more competitive and worthwhile to produce. Several types of microorganisms have been explored so far and waste substrates have been utilised as cheap feedstocks. The overall cost is affected by the fermentation stage, therefore it is imperative to design cultivations with little operating requirements and high yields. Consequently, the present thesis aims to contribute to the field by developing and investigating a simple process for oleaginous yeast cultivation, focusing mainly on enhancing the yields during the bioreactor stage. Oleaginous yeasts were screened for their ability to grow on glycerol and the most promising strain was selected for further research. Then, the necessary conditions for its growth and oil accumulation were defined. Shake-flask cultivations showed that the specific growth rate and glycerol consumption of Rh. glutinis were higher at lower glycerol concentrations (smaller or equal to40 g/L), while higher C/N elemental ratios enhanced oil content. Experimental data were used to construct an unstructured kinetic model to describe and predict the system's behaviour. The Monod-based model took into account double substrate growth dependence and substrate inhibition. Following that, bioreactor cultivations extended the range of parameters studied, to include the influence of aeration rate and oxygen supply on cellular growth and microbial oil production. Cultivations at different air flow rates were performed in a 2 L bioreactor and showed that a low aeration rate of 0.5 L/min gave the best glycerol and nitrogen uptake rates, resulting in a concentration of biomass of 5.3 g/L with oil content of 33% under simple batch operation. This was improved by 68% to 16.8 g/L (cellular biomass) with similar oil content (34%) by applying a fed-batch strategy. Finally, different glycerol feeding schemes were evaluated in terms of their effect on oil accumulation. The concept of targeting first a cell proliferation stage, limited by the availability of nitrogen, followed by a lipid accumulation stage, fuelled by glycerol was tested. Continual feeding and pulsed feedings, delivering the same total amount of nitrogen (and glycerol), resulted in similar elevated values of both cellular biomass (~25 g/L) and oil content (~40%). Addition of glycerol at higher rates but giving the same total amount of nitrogen led to a further increase in oil content to 53%, resulting in an overall oil yield of more than 16 g/L (the highest achieved throughout the project). With comparable yields to those reported in the literature but achieved with a much poorer medium, there is every reason to be optimistic that microbial oil production from glycerol could be commercially viable in the future.