Carbon Capture and Storage is a nascent technology developed with the intention of collecting carbon dioxide emissions from the flue gasses of point source producers, such as power stations or cement works. The carbon dioxide is then stored in underground geological reservoirs so that it does not reach the atmosphere, reducing the rate at which greenhouse gasses accumulate and influence climate change. However, as with all nascent technologies, the benefits of these developments and concepts must be weighed against the risks of serious and long-term environmental impact should an accidental release occur. The aim of this thesis is to study the potential for environmental damage caused by a release of carbon dioxide into the marine environment from a sub-seabed carbon dioxide reservoir generated through carbon capture and storage development. The quantification of the rate of change caused by such an accidental release of carbon dioxide will be studied, as will the rate at which natural conditions are re-established upon cessation of the release.

Titanium oxide has found different applications in environmental pollution remediation through its use as a photocatalyst for the purification of air and water. However, despite many advantages of TiO2, its use in unmodified form for photocatalytic reactions is hampered by a number of inherent physicochemical properties. The research in this thesis shows that TiO2 containing either copper (Cu) alone or combined copper-activated carbon (Cu-AC) are active in the simultaneous photocatalytic remediation of nitrate and oxalic acid, while pure titania and titania-activated carbon (TiO2/AC) composites found inactive for the reaction. In the case of photocatalytic removal of phenol, titania-thermally reduced graphene oxide (TiO2-TGO) exhibited superior photocatalytic performance than titania-graphene oxide (TiO2-GO) and pure TiO2.

The biogeochemical behaviour of plutonium and americium was investigated in contaminated soils from the UK to help determine possible remediation and management options. Stimulating anoxic sediments from Aldermaston, through the addition of a carbon substrate (glucose), induced reducing conditions resulting in a negligible change in Pu mobility. This was despite a substantial shift in the bacterial profile from a diverse community to one dominated by fermentative Beta proteobacteria and Clostridia. The latter group also includes organisms associated with metal reduction, such as close relatives to Clostridium species, reported previously to facilitate the reduction of Pu(IV) to Pu(III). A sequential extraction was performed on soils from Aldermaston and the Esk Estuary to identify which selected fractions the Pu and Am are most strongly associated with. The majority of Pu was associated with the 'residual fraction': 63.8 – 85.5 % and 91.9 – 94.5 % in the Aldermaston and Esk Estuary soils respectively. Metals associated with this fraction are highly recalcitrant and are unlikely to be released into solution over a significant time span under most geological conditions. The Am was more evenly distributed with the 'organic fraction' being the most dominant. Degradation of organic matter under oxidising conditions may result in mobilization of metals associated with this fraction. The Aldermaston soil was also subjected to bioleaching using a sulfuric acid producing microbial community, which resulted in a maximum 0.18 % of Pu released into solution. However, up to 12.5% of Am was found in solution suggesting Am is more susceptible to mobilization than Pu. The potential for Pu mobilization through abiotic oxidative leaching was investigated using permanganate. Even when carbonate was added to act as a potential complexant for the Pu, less than 1% of the Pu was leached. Greater success was observed when leaching was attempted using citric acid; an estimated 25 – 30% of Pu was released into solution offering a potential route for remediation of Pu-contaminated soils. These data would suggest that the Pu is highly recalcitrant, and may exist in a small particulate form in the Aldermaston soils, possibly in the oxide form, and is unlikely to mobilize under natural biogeochemical conditions.

In this EngD project I developed a new, analytic equation of state for use in the area of CCS pipeline transport. It was my aim to design a model which would exhibit a high degree of accuracy within the anticipated window of operation of CCS pipelines; from 260 to 335K and 1 to 200bar, whilst simultaneously retaining a simplicity and ease-of-use, a lack of which made some other available equations particularly unwieldy. Having conducted a comprehensive literature review and attended many academic and industrial conferences throughout this project, I felt that there was a need for an equation of state which could perform both these functions. This was the key motivation for my work, and the model presented in this thesis was developed in order that it might contribute towards negating the many concerns that currently surround the pipeline transport stage of CCS. I aimed for the proposed model to display a complexity approaching that of some of the simpler equations currently available, whilst incorporating sucient flexibility to give thermodynamic predictions to a standard approaching that of those which are more complicated. I defined criteria by which the proposed model could be judged, so that it could be applied with condence in the determination of the physical properties of carbon dioxide mixtures during CCS pipeline transport. Work was carried out by fitting the parameters of the proposed model to experimental data gathered from the literature, so that it would be able to determine the homogeneous phase pressure and vapour-liquid equilibrium behaviour of carbon dioxide and other relevant gas mixtures. The project yielded a number of excellent outputs, not least the satisfaction of the primary aim which was the proposal of a model, which through this EngD, I demonstrated had the ability to meet the demands that were set. In carrying out this work, I also developed several highly useful auxiliary mathematical methods which helped in ensuring the proposed model was as accurate as possible. For the case of modelling pure carbon dioxide, the proposed equation worked exceptionally well, providing highly accurate predictions for homogeneous density and vapour liquid equilibrium, which were well within the targets set. A paper on this was published in May 2013. In extending the model to incorporate some binary mixtures I again found that it demonstrated a clear ability to capture the necessary physical behaviours within the target range. I concluded with suggestions as to ways in which the work presented here could be developed further, as well as the many avenues for future work in other areas that this EngD project had opened up.

The continuing need for improved assessment of risk from heavy metal contamination of the environment has prompted scientific interest in quantifying and predicting metal solubility, ‘lability’ and bioavailability. This has led to the development of new techniques to fractionate and speciate trace metals in soils. The objectives of the current study were to increase understanding of the effects of (i) soil properties, (ii) contaminant source and (iii) contact time on metal lability and solubility in soils. Multi-stable isotope dilution (ID) methods were used to determine the lability (E-values) of Ni, Cu, Zn, Cd and Pb in soils, alongside more traditional approaches employed for metal fractionation including single and sequential extraction procedures. Most of the work was undertaken using (i) archived soils amended by metal salts (MA soils; n=23) and (ii) topsoils collected from Nottingham, Wolverhampton and London (Urban soils; n=100). The resulting data was used first to quantify the factors affecting trace metal lability in the MA soils using a logistic (S-shape) model which described metal E-value primarily as a function of soil pH with secondary influences from other soil properties. It was apparent that mineral oxides were important fixation phases for Ni, Zn and Cd while Pb was strongly affected by organic matter in soils. This model, parameterised on soils contaminated originally by metal nitrate solution, was then applied to the Urban soils to reveal the extent to which contaminant source still controlled metal lability. A further investigation of the long-term effect of metal source on metal lability was pursued through a third dataset of rural roadside soils (n=42) which had received Pb mainly from petrol-derived and geogenic sources, defined by their isotopic signature. It was demonstrated that petrol-derived Pb remained more labile than Pb from the parent material, despite decades of contact, although both petrol-derived and geogenic Pb contributed to both the labile and non-labile fractions. In a fourth dataset, soils that had received Pb from sewage sludge amendment (n=16), the co-existence of high phosphate concentration from sewage sludge limited the magnitude and range of Pb lability, probably through formation of Pb-phosphate minerals. No consistent agreement was found between labile fraction of Pb and any single sequential extraction (SEP) fraction in all soils contaminated by Pb from multiple sources. Both empirical equations (extended Freundlich) and mechanistic models (WHAM-VII) were used to predict metal solubility in the MA and Urban soils. The advantage of using E-values (ME) over metal extractable by dilute nitric acid (MExt) to represent the reactive metal fraction in predictions of solubility was very clear for WHAM-VII, but not for the ‘locally parameterised’ Freundlich model. This was almost certainly due to the strong links between pH and E-value becoming subsumed into the coefficient nominally describing the direct influence of pH on metal solubility in the extended Freundlich equation. However, overestimation of the solution concentration from WHAM-VII was observed for all five metals, and strongly correlated with soil pH. Fractionation information from WHAM suggested that the source of the model’s underestimation of metal binding most likely lay with errors in the description of metal binding by Fe and Mn oxides for Ni, Zn and Cd and humic acid (HA) for Cu. An additional factor is the absence of potential binding phases in the WHAM model, such as particulate CaCO3, and the greater diversity of active adsorbents in soils at high pH values. WHAM is based on the assumption that all metal bound to HA is labile. However, in the current study, ‘non-labile’ Cu, Zn and Pb fractions were observed in suspensions of HA extracted from grassland and peat soils. These were quantified by measuring metal E-values and EDTA-extraction of HA-bound metal using size-exclusion chromatography (SEC) coupled to ICP-MS to separate free and HA-complexed metal forms. Evidence of time-dependent metal fixation by HA was found for all three metals during the course of a 40 and 160 day incubation study. The proportion of non-labile Cu held by HA could be 40-50%. The presence of a non-labile metal fraction held by HA may substantially invalidate the assumption of reversible equilibrium which is central to all current geochemical models of metal binding to humic substances.

The performance and sustainability of ground source heat systems is dependent on the thermal behaviour of neighbouring ground. This thesis describes a comprehensive experimental and numerical investigation into the ground behaviour in response to horizontal ground source heat systems. Experimental investigations comprised of a field-scale monitoring scheme, designed and implemented in a horizontal ground source heat system providing space heating to a domestic property located in Mid-Wales, UK. A high resolution ground temperature data-set has been compiled over a 13 month period via 112 thermistors buried in the ground. Further data-sets representing the climatic variables and heat pump behaviour were also compiled over the same period, facilitating a thorough investigation of the ground behaviour in response to heat extraction at the site. Soil properties were also measured at the site as part of a larger site investigation undertaken. The numerical model applied is a coupled thermal-hydraulic (TH) model previously developed at the Geoenvironmental Research Centre (GRC). The GRC’s current model was extended to include developed boundary conditions for the TH simulation of horizontal ground source heat systems, describing the soil’s interaction with the ground-loop and atmosphere. Developments were subject to rigorous validation including comparisons with ground-data collected at the experimental site. The validated model was applied to investigate the long-term ground behaviour at the monitoring site and the effects of different surface materials on the ground behaviour including the recharge process. Finally, the model was applied to investigate the validity of an existing design code for ground source heat system design. The resolution and duration of the collated data-set facilitated extensive analysis, including a thorough investigation of the ground thermal distributions resulting from heat extraction and recharge. Findings indicated unsymmetrical distributions, highlighting potential avenues for system optimisation. Further to this it can be said that the data-set, in its own right, is a significant contribution to the scientific community and is able to provide a means of validation for future models. Results from the numerical investigation indicated that the ground thermal behaviour exhibits an annual cyclic pattern after approximately 3 years. From a holistic perspective, the results demonstrate that horizontal ground source heat systems can provide a sustainable means of providing space heating. Further long-term studies investigating the effects of surface materials show that more thermal energy can be sustainably extracted from systems with urban surface types (i.e. asphalt and brick). Investigations into an existing design code revealed that a ground-loop designed to meet the loads of the monitoring site resulted in unsustainable heat extraction, in doing so demonstrating the simplification of ground-loop burial depth within the current design process. Knowledge regarding the ground response to horizontal ground source heat systems has been furthered through the collection and analysis of field-scale data within this study. Further to this, the boundary developments and validation undertaken have allowed for a more thorough investigation of the long-term ground behaviour than previous studies.

This thesis has addressed several gaps in the knowledge with regards to the calcium looping cycle for carbon dioxide capture, including identification of engineering challenges associated with the scale-up of the technology to pilot scale and beyond; assessment of changes in sorbent morphology during the pilot scale capture process; and partitioning of elemental impurities in the limestone between the solid and gaseous phase during the carbon dioxide capture process. Hydrodynamic investigations identified the optimum superficial velocities required for the reactor in order to optimise solids entrainment and flux, and to minimise gas bypassing. Estimations made in determining how particle attrition would affect minimum fluidisation velocity confirmed a decrease of approximately 0.09m/s for every 5 % reduction in particle size. Amendments made to the exhaust diameter and position, and the loop seals, improved the pressure balance of the system thus enhancing solids transfer. Reactor and process modifications, including modification of carbonator temperature, and maintenance of temperature above 420°C in standpipes resulted in improved carbon dioxide capture %. Increasing bed inventory had a positive effect of carbon dioxide capture % due to an increased Ca looping ratio. Steam addition also benefitted the carbonation process, due to improved sorbent morphology and therefore carbon dioxide diffusion into the sorbent. Sulfur dioxide was considered to have a detrimental effect on carbon dioxide capture due to pore pluggage, although burner- derived steam had a positive effect in maintaining capture %. Gaseous elemental emissions from the process were low for all elements, but concentrations of elements in the solid sorbent phase were influenced by bed inventory, implying that filtering systems may be required in industry for the large masses of sorbent required. Concentrations of elements in the sorbent were identified to be below levels typical of cement, with the exception of Ni, implying that there is potential for spent sorbent to be used in the cement industry with adequate mitigation measures in place.

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