In recent years, the majority of research on surface patterning, as a means of precisely controlling cell positioning and adhesion on surfaces, has focused on eukaryotic cells. Such research has led to new insights into cell biology, advances in tissue engineering, and cell motility. In contrast, considerably less work has been reported on tightly-controlled patterning of bacteria, despite its potential in a wide variety of applications, including fabrication of in vitro model systems for studies of bacterial processes such as quorum sensing and horizontal gene transfer. We report a rapid and convenient method to generate patterned bacterial co-cultures using surface chemistry to regulate bacterial adhesion and liftoff patterning for controlling cellular positioning at the surface. A mannoside-terminated SAM formed an adhesive surface for bacterial monolayer formation, allowing fabrication of patterned regions using a subtractive microcontact printing process with a hydrogel stamp. The patterned substrates were subsequently inoculated with a second strain of bacteria from solution which deposited onto the unpatterned regions, forming a robust micropatterned coculture, providing platforms for spatially controlled studies of conjugation between donor and recipient bacterial cells. Towards this aim, donor cells were transformed with a modified conjugative plasmid that would bind fluorescent molecules and become visible upon entering a recipient cell. We discovered during the course of the project that bacterial co-cultures on metal surfaces exhibit slower growth rates than on semi-solid agar, and as such the time scale required for efficient conjugation lead to photobleaching of fluorescent foci. However, we were able to demonstrate through cultivation techniques that conjugation could occur in these micropatterned co-cultures after three hours.

This thesis covers extraction of hay with NaOH to produce foaming solutions which might be used to substitute or reduce the need for, oil based surfactant in detergents. Extraction time, temperature and NaOH concentration were found to have varying levels of influence on the properties of the extract solutions. Models were constructed to describe their effects on the% mass extracted from the hay, as well as extract solution absorbance, viscosity, and contact angle using response surface, experimental design methodology. The hay extract foam was examined along with other types of foaming solutions, using cryogenic SEM. Hay, rice straw and horse chestnut leaf extract foams were found to be particle stabilised and interesting images were captured showing their microstructures. Foaming was found to be due to lignin-carbohydrate complexes in hay extract solutions and proteins in horse chestnut leaf extract solutions. Finally correlations were sought between foaming of hay extract solutions and their other properties, e.g. Foaming of the hay solutions is due to lignin derivatives, hence solution absorbance correlates positively with foaming; and foaming is improved by increased solution viscosity hence its positive correlation with solution viscosity and % mass extracted from hay.

The Sonolator liquid whistle is an industrial inline mixer used to create complex multiphase mixtures which form components of high value added liquid products. Despite its wide use, this device’s mechanism of operation is not well understood which has led to this combined experimental and computational study to elucidate key phenomena governing drop and jet break-up. The work has focused on single phase Particle Image Velocimetry (PIV) measurements of a model device to validate single phase Computational Fluid Dynamics (CFD) simulations to gain basic understanding of the flow fields which are responsible for the breakage behaviour, assuming dilute dispersions. Multiphase pilot plant experiments on a silicone oil-water-SLES emulsion have been used to characterise the droplet size reduction in a pilot scale Sonolator for both dilute and medium concentrations of the dispersed phase. An empirical model of droplet size was constructed based on pressure drop, dispersed phase viscosity and surfactant concentration. This empirical model was compared with the droplet breakage theories of Hinze, Walstra and Davies. Extra work mentioned in the appendices includes studies on cavitation in the Sonolator, with the cavitating flow conditions identified and the contribution to emulsification considered, and the usage of population balance methods to simulate droplet breakup in the environment indicated by CFD/PIV studies in order to investigate how the droplet size distributions measured in pilot plant studies came about.

Although there has been ongoing research on fluidised beds for the past 70 years, the interaction between particles and rising bubbles and the general solids motion in bubbling fluidised beds are still not fully understood. The work presented in this thesis uses the method known as Positron Emission Particle Tracking (PEPT) to track the motion of a single radioactively labelled particle inside a fluidised bed. Recent developments in PEPT include new ways of labelling micron sized tracer particles that can be as small as 60 μm and the new mobile camera system also known as the Modular PEPT camera that can follow particle trajectories in equipment of various sizes and geometries. So far, PEPT has only been used to investigate fluidised beds of Geldart group B and D particles due to the previous limitation in the size of tracer particles. The results outlined in the thesis include group A particles (aluminium oxide) fluidised at atmospheric pressure in an 8 cm internal diameter bed and at elevated pressure in a 15 cm internal diameter bed and group B particles (sand) fluidised at atmospheric pressure in a 15 cm internal diameter column. The three areas that have been investigated are the use of particle trajectories to measure the properties of rising bubbles and the dispersion and general solids motion together with solids circulation as a measure of particle mixing. The protocols required to process the PEPT data used in the thesis were originally set by Stein (1999) but modified and improved versions are proposed and used. The PEPT results are in general agreement with existing models and results published by other researchers. A set of Matlab programs to analyse the results of PEPT experiments and which can be readily used by other users is presented.

The results of the catalytic oxidation in supercritical water of two non-biodegradable and highly toxic nitrogen-containing organic compounds (DBU and quinoline) are presented. The reactions were studied in a tubular xed-bed reactor over three catalysts: Pt/Al\(_2\)O\(_3\), CuO/Al \(_2\)O\(_3\) and MnO\(_2\)/CuO. The effect of operating conditions, namely temperature, pressure, oxygen concentration and initial concentration of the organic compounds were studied to evaluate their influence on its removal. Reaction rates were calculated from the experimental data collected. In addition, the selectivities and stabilities of the catalysts were investigated. Before conducting the experimental study the isothermal and isobaric operation of the reactor was veried together with the complete decomposition of hydrogen peroxide to oxygen and water in the preheating section and the reproducibility of experimental data was verified. Absence of external concentration gradients was determined experimentally for each reaction. The results showed that temperature was the main controlling variable of the catalytic oxidation. On the contrary, the effect of pressure depended on the catalyst used. Increasing the concentration of the organic compound did not aect their oxidation. Meanwhile, oxygen concentration above a stoichiometric ratio of two did not considerably improve the reaction. A power-law kinetic model was proposed to quantify the oxidation reaction. Three Langmuir-Hinshelwood-Hougen-Watson reaction rates were also explored to the experimental data. In the absence of a specic reaction mechanism the kinetic data were best represented by the power-law kinetic model. CO2 was the main carbon product of the reaction with small amounts of inorganic carbon species dissolved in the liquid effluent. Meanwhile, NH\(_4\), NO\(_3\) and NO\(_2\) ions were the only nitrogen species detected in the liquid effluent. Pt/Al\(_2\)O\(_3\) proved to be the most effective catalyst because it promoted faster reactions rates, had higher selectivity towards CO2 and produced lower nitrogen species. Surface analysis of the spent catalysts identied that the loss of activity was due to the 23 reduction of surface area. Leaching of active metals and chemical changes on the surface of the active metals and support of the catalyst were found for CuO/Al \(_2\)O\(_3\) and MnO \(_2\)/CuO. To conclude, it was demonstrated that catalytic supercritical water oxidation is a feasible and effective alternative for the destruction of contaminants in water. The thesis also includes suggestions for further research to continue the development of this technology and consolidate the process at industrial scale.

This work investigates the effect of fat crystal-stabilised interfaces on the transport of solutes between the two aqueous phases in W1/O/W2 emulsions. The aim is to separate solutes (NaCl or KCl) between the two aqueous phases. Fat crystals are used to stabilise the primary emulsion interface. Fat crystals are seeded at the interface during emulsion production using monoglycerides. Subsequently they sinter to form "shells" around the water droplets. It is shown that these "shells" are capable of retaining salt encapsulated within the aqueous phase despite the application of osmotic pressure gradients. The W1/O primary emulsions are incorporated into a double structure. It is shown that primary emulsion droplets retain their structure during the secondary emulsification step, although the shear may cause some damage to their protective "shells". Salt is retained within W1 as long as the primary interface is crystalline. The choice of secondary emulsifier is important to double emulsion stability. The double structure is not stable if small molecule surfactants are used to stabilise the secondary interface. Protruding fat crystals from primary emulsion droplets cause coalescence of double globules and lead to phase separation. The double emulsions are stable if proteins or particles are placed at the secondary interface.

The iodide/iodate reaction scheme was used to study the effect of gas sparging and/or solid particles on micromixing in a stirred vessel. A literature review illustrated the need for focused work on this matter and gave valuable ideas for the experiments. For this, the experimental method was first validated for using the added gaseous and solid phases air and glass beads, respectively. The experiments covered a range of conditions for micromixing in single-phase, for validation, in gas-liquid, solid-liquid and gas-solid-liquid systems: power inputs up to 1.94 W/kg, gas sparge rates up to 1.5 vvm and up to 11.63 wt.% solids with diameters from 150 to 1125 μm. For comparison, the power inputs from the impeller were kept constant when affected by the added phase(s). In order to allow better quantification of the experimental data, variations of the Incorporation model were evaluated for taking recent suggestions for the reaction scheme into consideration. The second dissociation of sulphuric acid was included in the model and different kinetic rate laws from the literature on the Dushman reaction were implemented. These variations allowed order-of-magnitude estimates and further comparisons of local specific energy dissipation rates.

Fuel cells are becoming increasingly important in the conversion of our society to clean, and renewable energy sources. However, there are some technical, as well as commercial barriers, which remain to be overcome before the fuel cell industry may be counted a success. One such problem is that of nonlinear current fluctuations, which have been observed under quite general conditions, in solid oxide fuel cells. This thesis attempts to elucidate the mechanisms driving this undesirable be- haviour, by developing a rational mathematical model based on fundamental chemical kinetics, and mass transfer effects, which take place within the porous anode of the fuel cell. A system of nonlinear, coupled ordinary differential equations is derived to describe the reaction and transfer processes associated with this fundamental model. This system is then rationally reduced to a planar dynamical system and the cases of weakly and fully humidified fuel streams are considered. Self-sustained, temporal oscillations are shown to arise through Hopf bifurcations in each case, and key parameter regimes leading to oscillatory behaviour are identified. Experiments have been conducted on commercial fuel cells, with results presented in Chapter 5.

This thesis presents an investigation into the use of four biochars (wood, rapeseed, miscanthus and sewage sludge) to generate a hydrogen-rich syngas that can be utilised in solid oxide fuel cells. Experimental investigations are split into three sections; (i) biochar characterisation, (ii) biochar gasification and (iii) the use of syngas in a single, microtubular solid oxide fuel cell. Characterisation revealed that wood biochar had the highest carbon content at 71.58%, sewage sludge had the lowest at 30% and rapeseed had the highest mineral content. The effects of temperature on gasification were investigated over a temperature range of 650 - 850°C at a steam flow of 172 g min\(^-\)\(^1\) kg\(^-\)\(^1\) biochar and effects of steam flow at 850°C over a steam flow range of 54 - 277 g min\(^-\)\(^1\) kg\(^-\)\(^1\) biochar. Results revealed the transient behaviour of the process as well as the effects of temperature and steam flow. Dry gas yield increases with both temperature and steam flow, with wood biochar giving maximum values of 2.58 m\(^3\) kg\(^-\)\(^1\) at 850°C and 277 g min\(^-\)\(^1\) kg\(^-\)\(^1\) biochar. Hydrogen content decreases at high temperatures and peak hydrogen content, 58.7%, was achieved at 750°C from the rapeseed biochar. Syngas from wood and rapeseed biochars was collected and used in a microtubular solid oxide fuel cell. Gas from rapeseed had a negative effect on the fuel cell performance, leading to a 28% decrease in the performance over the 30 minutes of potentiostatic operation of 0.7 V. Gas from wood biochar was more suitable and was used in the solid oxide fuel cell for approximately 500 minutes, giving an initial electrical efficiency of 16.8% at 0.7 V.

Gas-liquid mass transfer, agitator power consumption, rheology, gas-liquid mixing and gas hold-up have been studied in an agitated, sparged vessel of diameter, T = 0.3 m, with a liquid capacity of 0.02 m\(^3\), unaerated liquid height = 0.3 m. The solutions of sodium carboxymethylcellulose used exhibit moderate viscoelasticity and shear thinning behaviour, obeying the power law over the range of shear rates studied. The gas-liquid mass transfer was studied using a steady state technique. This involves monitoring the gas and liquid phase oxygen concentrations when a microorganism (yeast) is cultured in the solutions of interest. Agitator power consumption was measured using strain gauges mounted on the impeller shaft. Various agitator geometries were used. These were: Rushton turbines ( D = T/3 and D = T/2 ), used singly and in pairs; Intermig impellers ( D = 0.58T ), used as a pair; and a 45° pitched blade turbine ( D = T/2 ), used in combination with a Rushton turbine. Gas hold-up and gas-liquid flow patterns were visually observed. In addition, the state of the culture variables, (oxygen uptake rate and carbon dioxide production rate), were used to provide a respiratory quotient, the value of which can be linked to the degree of gas-liquid mixing in the vessel. Measurement of point values of the liquid phase oxygen concentration is also used to indicate the degree of liquid mixing attained. The volumetric mass transfer coefficient, k\(_L\)a, was found to be dependent on the conditions in which the yeast was cultivated, as well as being a function of time. These variations were associated with variations in solution composition seen over the course of each experiment. Steps were taken to ensure that further k\(_L\)a values were measured under identical conditions of the culture variables, in order to determine the effect on k\(_L\)a of varying viscosity, agitator speed and type and air flow rate. Increasing solution viscosity results in poorer gas-liquid mixing and a reduction in k\(_L\)a, as has been found by earlier workers. Thus high agitator speeds and power inputs are required to maintain adequate mass transfer rates. In the more viscous solutions used, large diameter dual impeller systems were required, to mix the gas and liquid phases. Of these a pair of Rushton turbines ( D = T/2 ) gave the highest k\(_L\)a values at a given power input. In these solutions the dependence of k\(_L\)a on the gassing rate, which is seen in intermediate and low viscosity solutions, virtually disappears, with k\(_L\)a highly dependent on the power input and the apparent viscosity. At intermediate viscosities a smaller pair of Rushton turbines showed the most efficient mass transfer characteristics, here k\(_L\)a is dependent on the power input and the gassing rate, but independent of viscosity. This is linked to the flow regime force in the vessel, which at intermediate viscosities lies in the transition region between the laminar and turbulent flow regimes. Variations in gas hold-up, rising then falling with increasing impeller speed, were linked to variations in the gassed power number, falling then rising with increasing impeller speed. These effects are considered to be due to variations in the size of the gas filled cavities behind the impeller blades.