The continued depletion of oil reserves, a necessity for energy security and the environmental importance of reducing greenhouse gas emissions has prompted the industrial development of clean, non-conventional, renewable fuels. Transport fuels are currently composed primarily of fossil-derived alkanes and commonly contain a minor biofuel component of bioethanol in gasoline or fatty acid methyl esters (FAMEs) in diesel. Increasing biofuel supply to satisfy governmental targets imposes substantial technological constraints on automobile engine manufacturers and raises controversies over arable land usage. ‘Drop-in’, microbial, alkane biofuels are structurally identical to fossil fuels and their production does not compete directly with arable farming, thereby obviating the problems associated with the manufacture and deployment of bioethanol and FAMEs. This study investigated alkane biosynthesis in two non-photosynthetic bacteria, Mycobacterium sp. NCIMB 10403 and Desulfovibrio desulfuricans, to evaluate their potential for use as biocatalysts in the industrial manufacture of ‘drop-in’ biofuels. This study employed single- and two-dimensional gas chromatography-mass spectrometry as a means to provide a rigorous analysis of alkane biosynthesis in these bacteria. In addition, a microarray analysis was used to develop an understanding of the genes potentially important in regulating alkane production in D. desulfuricans. In contrast to the original reports from the 1960’s, Mycobacterium sp. NCIMB 10403 and D. desulfuricans NCIMB 8307 did not synthesise alkanes. Alkane biosynthesis was confirmed in D. desulfuricans NCIMB 8326 although the alkane quantities and carbon chain length distribution differed significantly to those previously reported. The microarray data gave evidence to suggest that the expression of genes encoding a long chain fatty acid-CoA ligase and an aspartyl/glutamyl-tRNA amidotransferase may be important for regulating alkane biosynthesis in D. desulfuricans. Furthermore, several genes encoding hypothetical proteins were identified as being potentially involved directly in the formation of alkanes.

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A major consideration in the exploitation of microalgae as biotechnology platforms is choosing robust, fast-growing strains that are amenable to genetic manipulation. The freshwater green alga Chlorella sorokiniana has been reported as one of the fastest growing and thermotolerant species, and studies in this thesis have confirmed strain UTEX1230 as the most productive strain of C. sorokiniana with doubling time under optimal growth conditions of less than three hours. Furthermore, the strain showed robust growth at elevated temperatures and salinities. In order to enhance the productivity of this strain, mutants with reduced biochemical and functional PSII antenna size were isolated. TAM4 was confirmed to have a truncated antenna and able to achieve higher cell density than WT, particularly in cultures under decreased irradiation. The possibility of genetic engineering this strain has been explored by developing molecular tools for both chloroplast and nuclear transformation. For chloroplast transformation, various regions of the organelle’s genome have been cloned and sequenced, and used in the construction of transformation vectors. However, no stable chloroplast transformant lines were obtained following microparticle bombardment. For nuclear transformation, cycloheximide-resistant mutants have been isolated and shown to possess specific missense mutations within the RPL41 gene. Such a mutant allele should prove useful as a dominant marker. Genetic engineering of the chloroplast genome has been well established for another microalga Chlamydomonas reinhardtii. This system was exploited in three biotechnological applications: 1) generation of alkane producing strains by introducing genes encoding for acyl reductase and aldehyde decarbonylase. 2) expression of a vaccine candidate major capsid protein L1 of the human papillomavirus. 3) expression of a potent HIV-inactivating protein cyanovirin-N. In all cases, stable transformant lines were obtained and molecular analysis confirmed the successful integration of the transgenes into the genome. The detailed biochemical analysis of the lines is presented in the thesis.

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In the present hydrocarbon economy, energy is primarily derived from fossil fuels, like Coal, Oil and Gas. The petroleum oil obtained from mother earth is further, refined into gasoline, diesel, and natural gas. However, the burning of these hydrocarbon fuels causes the emission of greenhouse gases and other pollutants. Hydrogen the lightest of all gases and the most abundant element in the universe, is being considered for use as an energy carrier (for storing and transporting energy) for future generations. Emphasis on mitigating global climate change and reducing pollution, strengthens the case of hydrogen over other fuels. The environmentally benign nature of hydrogen coupled with the finite supply of fossil fuels supports the hydrogen economy. A possible transition to the full hydrogen economy is envisaged which will take place through several phases. The current work is concerned with the transitional phase and involves an investigation into the possibility of using the existing natural gas infrastructure for transporting hydrogen as a natural gas-hydrogen mixture. Likely impacts on the natural gas infrastructure as a consequence of the introduction of hydrogen are being studied as part of a European Union funded research project called Naturalhy. The work that is the subject of this thesis forms part of the safety work package of the Naturalhy project. In turn the part of the safety work package with which the work of this thesis is concerned is the changes that handling a mixture of natural gas and hydrogen rather than natural gas will have on the risk that will be posed to the general public. In particular, it is concerned with the changes that might result to such parameters as the ease with which mixtures of hydrogen and natural gas might be ignited compared with natural gas and hence the change to the frequency with which such events as explosions within domestic properties might increase. The work commenced with a review of the literature on the subjects of failure probability and ignition probability associated with natural gas infrastructure. The analysis and the outcome of this literature review suggested that the most sensitive area affected by the addition of hydrogen is accidental gas releases into confined enclosures such as domestic property. The presence of hydrogen is likely to increase the probability of fire and/or explosion due to the characteristic properties of hydrogen (wide flammability range, lower minimum ignition energy etc.). The ignition characteristics for the gases (methane, hydrogen and methane-hydrogen mixtures) was studied using an experimental rig based on the principle of capacitive spark discharge. Consequently, the data obtained through experiments was used to calculate the Minimum Ignition Energy (MIE) of a particular gas and the Lowest Ignition Energy at various flammable gas concentrations for a particular gas. The results and observations were further analysed to provide information on the ignition probability associated with various ignition energy values for all the gases. The results for MIE are compared with the available data in the literature for methane and hydrogen gas. Generalised correlations for predicting the ignition energy for pure gases and for two component (methane-hydrogen) gas mixtures were developed. Methane gas release incidents are compared with hydrogen to estimate increases in the probability of fire and/or explosion incidents using a few deterministic release rates for the two gases.

This research investigates specific ash control methods to limit inorganic content within biomass prior to fast pyrolysis and effect of specific ash components on fast pyrolysis processing, mass balance yields and bio-oil quality and stability. Inorganic content in miscanthus was naturally reduced over the winter period from June (7.36 wt. %) to February (2.80 wt. %) due to a combination of senescence and natural leaching from rain water. September harvest produced similar mass balance yields, bio-oil quality and stability compared to February harvest (conventional harvest), but nitrogen content in above ground crop was to high (208 kg ha.-1) to maintain sustainable crop production. Deionised water, 1.00% HCl and 0.10% Triton X-100 washes were used to reduce inorganic content of miscanthus. Miscanthus washed with 0.10% Triton X-100 resulted in the highest total liquid yield (76.21 wt. %) and lowest char and reaction water yields (9.77 wt. % and 8.25 wt. % respectively). Concentrations of Triton X-100 were varied to study further effects on mass balance yields and bio-oil stability. All concentrations of Triton X-100 increased total liquid yield and decreased char and reaction water yields compared to untreated miscanthus. In terms of bio-oil stability 1.00% Triton X-100 produced the most stable bio-oil with lowest viscosity index (2.43) and lowest water content index (1.01). Beech wood was impregnated with potassium and phosphorus resulting in lower liquid yields and increased char and gas yields due to their catalytic effect on fast pyrolysis product distribution. Increased potassium and phosphorus concentrations produced less stable bio-oils with viscosity and water content indexes increasing. Fast pyrolysis processing of phosphorus impregnated beech wood was problematic as the reactor bed material agglomerated into large clumps due to char formation within the reactor, affecting fluidisation and heat transfer.

Aquatic biomass is seen as one of the major feedstocks to overcome difficulties associated with 1st generation biofuels, such as competition with food production, change of land use and further environmental issues. Although, this finding is widely accepted only little work has been carried out to investigate thermo-chemical conversion of algal specimen to produce biofuels, power and heat. This work aims at contributing fundamental knowledge for thermo-chemical processing of aquatic biomass via intermediate pyrolysis. Therefore, it was necessary to install and commission an analytical pyrolysis apparatus which facilitates intermediate pyrolysis process conditions as well as subsequent separation and detection of pyrolysates (Py- GC/MS). In addition, a methodology was established to analyse aquatic biomass under intermediate conditions by Thermo-Gravimetric Analysis (TGA). Several microalgae (e.g. Chlamydomonas reinhardtii, Chlorella vulgaris) and macroalgae specimen (e.g. Fucus vesiculosus) from main algal divisions and various natural habitats (fresh and saline water, temperate and polar climates) were chosen and their thermal degradation under intermediate pyrolysis conditions was studied. In addition, it was of interest to examine the contribution of biochemical constituents of algal biomass onto the chemical compounds contained in pyrolysates. Therefore, lipid and protein fractions were extracted from microalgae biomass and analysed separately. Furthermore, investigations of residual algal materials obtained by extraction of high valuable compounds (e.g. lipids, proteins, enzymes) were included to evaluate their potential for intermediate pyrolysis processing. On basis of these thermal degradation studies, possible applications of algal biomass and from there derived materials in the Bio-thermal Valorisation of Biomass-process (BtVB-process) are presented. It was of interest to evaluate the combination of the production of high valuable products and bioenergy generation derived by micro- and macro algal biomass.

This study investigates the use of Pyroformer intermediate pyrolysis system to produce alternative diesel engines fuels (pyrolysis oil) from various biomass and waste feedstocks and the application of these pyrolysis oils in a diesel engine generating system for Combined Heat and Power (CHP) production. The pyrolysis oils were produced in a pilot-scale (20 kg/h) intermediate pyrolysis system. Comprehensive characterisations, with a view to use as engine fuels, were carried out on the sewage sludge and de-inking sludge derived pyrolysis oils. They were both found to be able to provide sufficient heat for fuelling a diesel engine. The pyrolysis oils also presented poor combustibility and high carbon deposition, but these problems could be mitigated by means of blending the pyrolysis oils with biodiesel (derived from waste cooking oil). The blends of SSPO (sewage sludge pyrolysis oil) and biodiesel (30/70 and 50/50 in volumetric ratios) were tested in a 15 kWe Lister type stationary generating system for up to 10 hours. There was no apparent deterioration observed in engine operation. With 30% SSPO blended into biodiesel, the engine presents better overall performance (electric efficiency), fuel consumption, and overall exhaust emissions than with 50% SSPO blend. An overall system analysis was carried out on a proposed integrated Pyroformer-CHP system. Combined with real experimental results, this was used for evaluating the costs for producing heat and power and char from wood pellets and sewage sludge. It is concluded that the overall system efficiencies for both types of plant can be over 40%; however the integrated CHP system is not economically viable. This is due to extraordinary project capital investment required.

Computational Fluid Dynamics (CFD) has found great acceptance among the engineering community as a tool for research and design of processes that are practically difficult or expensive to study experimentally. One of these processes is the biomass gasification in a Circulating Fluidized Bed (CFB). Biomass gasification is the thermo-chemical conversion of biomass at a high temperature and a controlled oxygen amount into fuel gas, also sometime referred to as syngas. Circulating fluidized bed is a type of reactor in which it is possible to maintain a stable and continuous circulation of solids in a gas-solid system. The main objectives of this thesis are four folds: (i) Develop a three-dimensional predictive model of biomass gasification in a CFB riser using advanced Computational Fluid Dynamic (CFD) (ii) Experimentally validate the developed hydrodynamic model using conventional and advanced measuring techniques (iii) Study the complex hydrodynamics, heat transfer and reaction kinetics through modelling and simulation (iv) Study the CFB gasifier performance through parametric analysis and identify the optimum operating condition to maximize the product gas quality. Two different and complimentary experimental techniques were used to validate the hydrodynamic model, namely pressure measurement and particle tracking. The pressure measurement is a very common and widely used technique in fluidized bed studies, while, particle tracking using PEPT, which was originally developed for medical imaging, is a relatively new technique in the engineering field. It is relatively expensive and only available at few research centres around the world. This study started with a simple poly-dispersed single solid phase then moved to binary solid phases. The single solid phase was used for primary validations and eliminating unnecessary options and steps in building the hydrodynamic model. Then the outcomes from the primary validations were applied to the secondary validations of the binary mixture to avoid time consuming computations. Studies on binary solid mixture hydrodynamics is rarely reported in the literature. In this study the binary solid mixture was modelled and validated using experimental data from the both techniques mentioned above. Good agreement was achieved with the both techniques. According to the general gasification steps the developed model has been separated into three main gasification stages; drying, devolatilization and tar cracking, and partial combustion and gasification. The drying was modelled as a mass transfer from the solid phase to the gas phase. The devolatilization and tar cracking model consist of two steps; the devolatilization of the biomass which is used as a single reaction to generate the biomass gases from the volatile materials and tar cracking. The latter is also modelled as one reaction to generate gases with fixed mass fractions. The first reaction was classified as a heterogeneous reaction while the second reaction was classified as homogenous reaction. The partial combustion and gasification model consisted of carbon combustion reactions and carbon and gas phase reactions. The partial combustion considered was for C, CO, H2 and CH4. The carbon gasification reactions used in this study is the Boudouard reaction with CO2, the reaction with H2O and Methanation (Methane forming reaction) reaction to generate methane. The other gas phase reactions considered in this study are the water gas shift reaction, which is modelled as a reversible reaction and the methane steam reforming reaction. The developed gasification model was validated using different experimental data from the literature and for a wide range of operating conditions. Good agreement was observed, thus confirming the capability of the model in predicting biomass gasification in a CFB to a great accuracy. The developed model has been successfully used to carry out sensitivity and parametric analysis. The sensitivity analysis included: study of the effect of inclusion of various combustion reaction; and the effect of radiation in the gasification reaction. The developed model was also used to carry out parametric analysis by changing the following gasifier operating conditions: fuel/air ratio; biomass flow rates; sand (heat carrier) temperatures; sand flow rates; sand and biomass particle sizes; gasifying agent (pure air or pure steam); pyrolysis models used; steam/biomass ratio. Finally, based on these parametric and sensitivity analysis a final model was recommended for the simulation of biomass gasification in a CFB riser.