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The recent discovery of an 800 million solar mass black hole powering a quasar at a redshift corresponding to 690 million years after the Big Bang is the latest in a growing list of observations of super-massive black holes (SMBHs) that were most likely seeded with masses larger than those expected from the remnants of the first generation of stars. This thesis investigates the consequences of the seeding of SMBHs by massive black holes on galaxy evolution through a combination of analytic modelling techniques. Firstly, I analytically model the growth of gravitational instabilities in an isolated proto-galaxy disc as it progresses into a fully-formed galaxy in the presence of a massive seed black hole formed directly through isothermal collapse. The model shows for the first time how the gravitational effects of a seed black hole lead to an increase in the stability of the disc and an increase in the star formation timescale in the region of the disc close to the black hole. This gravitational imprint of the black hole on the galactic disc has the effect of suppressing star formation. To investigate if this has a lasting effect on the properties of seed hosting galaxies, I evolve the disc galaxy model from the epoch of seed formation down to z ~ 6. I show how star formation in seed hosting galaxies is further regulated by a combination of gravitational stability and the accretion of gas onto the black hole, leading to a scenario where the resulting ratio of black hole to stellar mass at z = 6 is significantly higher than observed in the local universe. I also investigate how the growth of massive seed black holes is regulated by the mass and momentum transport in the disc. The inward accretion of gas towards the central massive black hole and therefore the accretion of gas onto the black hole itself is a function of the stability of the disc. The stabilising effect of the black hole therefore has the potential to regulate the inflow of gas, depending on the relative masses of the galaxy disc and black hole. I find that even in the regime where the inflow rate is not affected by the presence of the black hole, viscosity driven accretion is too inefficient for even massive seeds to grow into a SMBHs by z ~ 6. This indicates the isolated growth of SMBHs is not possible. Indeed, merger events or other processes which are efficient at dissipating angular momentum are required to provide the necessary rapid accretion of gas for SMBHs to form. Finally, I study the dynamical heating of a dark matter halo through the accretion of massive black hole systems. Modelled as both a black hole embedded in its own subhalo and as a naked black hole, the infall of the black hole system acts as a perturber to the density of the central halo, converting potential energy to heat the gas of the central halo through dynamical friction. The timescale over which this infall occurs decreases with a larger perturber mass relative to the central halo mass. The total energy released through black hole accretion during the period of infall is strongly dependent on the black hole growth model. Generally, the total energy from black hole growth exceeds the total energy from dynamical friction. However, the energy released through dynamical friction reaches a maximum when the perturber's proximity to the centre of the central halo is minimised, generally after black hole accretion has ceased. There is therefore a period of time where dynamical friction is the primary source of heating within a halo, potentially contributing to the luminosities of some distant quasars and leading to over-estimates in inferred black hole masses.

Gas turbine engine performance requires effective and reliable internal cooling over the duty cycle of the engine. Understanding the effectiveness of cooling flows when making life predictions for rotating components subject to the main gas path temperatures is crucial. A test facility has been developed at the University of Sussex incorporating a two stage turbine designed to support a European funded research project with the objective of enhancing the understanding of interactions between main annulus gas paths and secondary air systems. This thesis describes the specific contribution of the author to the research conducted at the test facility. Non-invasive gas seeding and concentration measurement techniques together with hot geometry displacement measurements have been developed to meet three distinct objectives: to determine inter-stage seal flows between rotor disc cavities; to provide data to quantify rim seal exchange flows between rotor stator cavities and the main annulus gas path for both bulk ingestion and egress conditions; and, to provide data to quantify the re-ingestion of cooling air egressed into the main annulus gas path. Detailed knowledge of these flows is vital to understanding the flow structures within rotor stator cavities and to optimise coolant delivery methods. Experimental results are presented for a number of cooling flow supply geometries and flow rates. The gas concentration measurement techniques developed and the results obtained are compared to traditional measurements as well as numerical simulations carried out by research project partners. This work develops the measurement techniques of rotor stator cavity flows and provides data suitable for the validation of improved thermo-mechanical and CFD codes, beneficial to the engine design process.

Nutrient rich digestate resulting from the anaerobic digestion of waste from different feedstocks (kitchen waste, manure, agricultural waste, etc.) is mainly used in Northwest Europe as a fertiliser, but its heavy usage has led to soil eutrophication and its spreading onto arable land is now restricted under the Nutrient Vulnerable Zones policy. Consequently, digestate has become an underused resource and novel technologies to remediate this waste are now needed. In this thesis, microalgae were evaluated for their potential to bioremediate digestate, within the context of a circular economy. Chapter 1 presents a summary of digestate characteristics and its current use and discusses the circular economy concept focusing on microalgae as a bioremediation tool. Digestate is characterised by its dark colour and high dry matter content, which can be bottlenecks to light penetration and consequently microalgal growth, hence treatment is essential to allow for microalgal growth on this waste. Chapter 2 investigated mechanical and biological processing of a digestate from kitchen waste and aimed to assess its potential to support microalgal growth. Digestate was shown to be a suitable nutrient source for Chlorella vulgaris, following membrane filtration, which was highly efficient at separating liquid and solid fractions of digestate. 2.5% of digestate was the optimal concentration used in this work, as higher levels could lead to ammonium toxicity, therefore, this chapter also highlighted the bottlenecks of digestate utilisation for microalgal cultivation. To improve digestate uptake by microalgae, chapter 3 tailored different digestate sources to Chlorella vulgaris and Scenedesmus obliquus while maintaining a low pH to increase ammonium availability by reducing evaporation. Digestate from pig manure provided the best growth results in both strains, and while ammonium availability was increased, acclimation of strains to high ammonium levels was still necessary, limiting the use of high concentrations of digestate in cultures. Composition analysis of the microalgal biomass showed that nitrogen starvation, caused by higher pHs and reduced ammonium lead to lipid increase. This chapter demonstrated the importance of digestate and strain pairing to improve remediation and enhance scalability of valorising digestate within a circular economy. Growth of microalgae on digestate was demonstrated in chapters 2 and 3, to pursue the circular economy approach and use the produced biomass, chapter 4 subsequently aimed to assess the feasibility of using a microalgal hydrolysate derived from digestate as a feed ingredient in the feed of Nile tilapia. Enzymatic hydrolysis was used to alleviate palatability issues encountered when whole cells are incorporated into feed. An incorporation of 10% of the waste-derived hydrolysate did not convey advantages in terms of the fish growth but increased fatty acid content demonstrating a commercial advantage of the ingredient in terms of flesh quality. Increasing digestate uptake by microalgae is essential to increase viability of the circular economy concept presented in chapter 2, 3 & 4. Consequently, chapter 5 investigated the potential of microalgae-bacteria consortia for this purpose, by studying the bacterial community associated to Chlorella vulgaris and the influence of nutrient availability on this dynamic association. Sequencing analysis revealed that there was a likelihood of growth-promoting and other advantages conveyed by bacteria growing concomitantly with microalgae and the use of bacteria to increase digestate remediation by microalgae was discussed. The different lines of research investigated in this thesis demonstrated the feasibility of valorising nutrient rich digestate using microalgae by developing a circular economy approach. My thesis has also highlighted some of the bottlenecks to the establishment of a sustainable and commercially viable microalgal industry in the UK and globally, and additional research contributing to bridging this gap were discussed in Chapter 6, giving an outlook on future research prospects in the field of microalgae biorefineries.