This thesis presents the methodology and results of research undertaken into the rates and mechanisms of iron oxidation both in field and laboratory environments. The field based aspects of the research entailed the collection and analysis of hydrological, hydrogeochemical, and mineralogical data from two parallel treatment systems. Both systems were treating identical ferruginous, circum-neutral, coal-mine drainage, from the Taff Merthyr site, South Wales. During this study a novel pilot scale passive Vertical Flow Reactor (VFR) was trialled against a conventional settlement lagoon and the performance of both systems was compared. The second research aspect focuses on the determination of heterogeneous Fe(II) oxidation rates under laboratory conditions. Experiments were carried out under varying pH, and catalytic surface concentration and type. An analytical method was developed which allowed for the determination of both dissolved and sorbed Fe(II). The results of the field study have shown that the VFR system is capable of removing Fe at a rate greatly in excess of a conventional settlement lagoon. This therefore drastically reduces the treatment area required. In addition, due to the heterogeneous method by which the VFR operates (passing mine- water down through a bed of ochre solid), highly efficient manganese removal was also achieved. The laboratory study has shown that significant catalysis of Fe(II) oxidation can be achieved under mildly acidic pH conditions making Fe(II) oxidation (and therefore passive mine-water treatment) feasible under these conditions. Evidence is also presented for the adsorption of non-oxidisable Fe(II) onto Fe(III) (hydroxy)oxides under mildly-acidic pH conditions. A comparison was then made between field and laboratory results and a conceptual model was produced to describe the observed adsorption and oxidation characteristics.

This thesis presents an investigation into the enhanced natural attenuation of organic chemicals in groundwater. The focus of the research was directed towards the organic chemicals benzene, ethylbenzene, styrene, 1,2- dichloroethane and vinyl chloride, which were found to exist at a contaminated site located in the United Kingdom. A conceptual model was developed for the study site, based on the findings of previous consultant studies and investigations which were carried out solely for the purposes of this research. Sample collection and analytical procedures were designed to yield results, which could further define contamination issues at the study site, so that remedial measures could be appropriately developed. Lab-based microcosm treatability studies were carried out in order to determine the degradation potential of DCA, benzene and ethylbenzene under various enhanced conditions. The enhancements were selected in order to facilitate different degradation mechanisms for the organic contaminants, including aerobic respiration and reductive dechlorination. The microcosms were monitored for chemical and microbiological changes. A hydrogen release compound (HRC ) treatment was found to effectively degrade DCA and benzene under anaerobic conditions. A microorganism containing genetic sequence similarities with Desulfitobacterium dichloroeliminans bacteria was detected within the HRC -enhanced microcosms, indicating that reductive dechlorination was the likely degradation mechanism for DCA. The use of HRC is recommended as an enhancement for the natural attenuation of organic contaminants at the study site.

Source terms models for superheated releases of hazardous liquefied chemicals such as LPG have been developed, governing both upstream and downstream conditions. Water was utilised as the model fluid, not least for reasons of safety, but also for its ability to be stored at conditions that ensure it is superheated on release to atmosphere. Several studies have found that at low superheat jet break-up is analogous to mechanical break-up under sub-cooled conditions. Hence, a non-dimensionalised SMD correlation for sub-cooled liquid jets in the atomisation regime has been developed, based on data measured using a Phase Doppler Anemometry (PDA) system, for a broad range of initial conditions. Droplet SMD has been found to correlate with the nozzle aspect ratio and two non-dimensionalised groups i.e. the liquid Reynolds number and Weber number. An adaptation of the Rossm-Rammler distribution has been proposed for jets undergoing mechanical break-up. Through a high-speed photographic study (1000fps), three distinctive break-up regimes of superheated jets have been identified. Mechanical break-up has been confirmed to dominate jet disintegration at low superheat. Criteria for transition between regimes have been established based on the liquid Jakob number and Weber number. Using a PDA system, droplet SMD data has been produced for fully flashing jets at two sets of initial conditions and three axial downstream locations, with radial measurements performed at each position. Droplet SMD has been found to increase with nozzle diameter. An adaptation of the Rossm-Rammler distribution has been proposed for fully flashing jets. The proposed correlation for sub-cooled break-up, the PDA data for superheated releases and the established transition criteria have been compiled to produce a complete SMD model governing transition from mechanical break-up to full flashing. The model has been validated against three previous studies of flashing jets. An additional high speed photographic study (up to 50,000fps) of the upstream flow structure of superheated jets has been performed using Perspex nozzles. The downstream break-up regime has been found to depend on both the upstream bubble growth rate and concentration.

In Aberdeenshire, approximately 25,000 people rely on potable water from private water supplies. Many of these supplies are of questionable quality with regards to microbiological contamination, which is often due to a lack of maintenance and protection of these supplies. Agricultural practices such as the spreading of slurry and grazing animals in the proximity of supplies all increase the risk of contamination. The presence of coliform bacteria and in particular E. coli, in private water supplies is an indication of the potential for the water supply to be contaminated with pathogenic microorganisms. With the increasing occurrence of severe illness from pathogens such as E. coli O157, which have been found in a number of private water supplies, there is an increasing concern with regards to groundwater quality. This study was conducted initially to determine the magnitude of private water supply contamination in Aberdeenshire and to investigate any links between this contamination with seasonality and rainfall. To enable analysis of a large number of water samples to be carried out within an accepted timeframe, Colilert 18™ was validated for the detection and enumeration of coliform bacteria in potable water and was compared to the accepted standard method, membrane filtration. Colilert 18™ was further validated for use with soil samples to allow the study of factors affecting coliform survival in water and soil to be carried out. Coliform survival in ii soil was found to be influenced particularly by temperature and soil texture. The transport of coliform bacteria in soil was investigated using repacked and undisturbed soil columns, with transport enhanced by rainfall. However even with heavy rainfall coliform bacteria can become attached to or trapped within the soil structure. It was evident from these studies that coliform bacteria and therefore pathogenic microorganisms have the potential to survive in the environment and to travel through the soil structure and enter groundwater.

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Human demand for clean water has increase drastically in the past centuries, mainly due its demographic growth. The sources of clean drinking water have been continuously reduced due to depletion or contamination with one example being the extensive use of fertilizers in agriculture, which can lead to leaching of nitrates into groundwater and hence into surface water. The gravity of the situation was expressed by European Environmental Agency in 1998, revealing that, 87% of agricultural areas in the European Union (EU) have nitrate concentrations in groundwater above the guide level (25 ppm). Catalytic hydrogenation is one potential solution if an appropriate active, selective catalyst could be identified. One of the major drawbacks of the hydrogenation approach is the absence of robust studies which clearly describe what happens during reaction, essential for full understanding of the process. It was decided to use FTIR under operando conditions to try to disclose what happens in the catalyst surface during reaction. Pd/TiO2 catalysts were selected one. Upon adsorption at Lewis acid sites (oxygen vacancies), the nitrates are reduced by the electron enriched titania species, most likely Ti4O7 as identified by electron microscopy, which lead to the formation of nitrites, generally detected in solution during the hydrogenation tests and expected assuming a stepwise mechanism exists. The rather weak adsorption of nitrate onto the catalysts surface allied to their stability might be the reasons for their low reactivity, i.e., limiting step of the hydrogenation process. The nitrite reduction occurs essentially on Pd sites however their adsorption site is Lewis acid sites. NO is adsorbed and reduced exclusively on the noble metal. The order of reactivity of the surface species decreases with the decrease in the oxidation state of the nitrogen, i.e., NO3- NO2- NO. High surface concentration of nitrite leads to the formation of N2O, while ammonia is formed via consecutive hydrogenation of Nads. originating from the dissociation of NO. Ammonia formation takes place over Pd and is dependent on the hydrogen availability and presence of water. Ever since Becquerel discovered the photoelectric effect back 1839, researchers and engineers have been infatuated with the idea of converting light into electric power or chemical fuels. Photocatalysis is also particularly suitable for the abatement of contaminants since it offers potentially high conversions at low cost. Two aspects have dominated the research of photocatalysts, namely improvement of catalytic performances under visible light and the minimization of charge recombination. The latter can be improved by a decrease in the particle size and/or by the addition of small metal clusters of elements such as Cu that operate as electrons sinks thus allowing the system to be employed in processes such as N03- reduction. The addition of metal to TiO2 P25, led to a significant enhancement in the photocatalytic activity of the catalyst. The overall process was found to be dependent on the temperature of reaction media, and the nature and concentration of the hole scavenger, and on the metal loaded. In the case of Hombikat, the metal-free support appeared to operate better possibly as a consequence of its greater surface area as this would hinder, to a certain extent, the charge recombination process. EPR and FTIR experiments under UV irradiation carried out using the metal clusters (Au, Ag and Cu) supported on TiO2, revealed that the presence of the metal leads to the loss of signal related to the stabilized electrons on the pure TiO2 when a hole scavenger such as hydrogen is present. The Fermi level equilibration process, in a semiconductor - metal nanocomposite system, is a clear indication of the presence of electron transfer process between support and metal. Addition of the metal did not, however, modify the band gap energy of the studied semiconductor. In the generality of the cases studied, the photocatalytic approach was found to have much higher activities when compared to the hydrogenation process.

Discolouration of surface waters in upland catchments (with associated costs of water treatment and resources) has increased particularly since the severe droughts in the 1970s and mid 1990s. Such discolouration is a major concern for many water companies whose catchment areas include upland moorland, particularly those areas located on deep blanket peat soils. The principal aim of this study was to evaluate the role of catchment management in the production of discoloured surface runoff and DOC flux from catchments used as gathering grounds for public water supply. The investigation focused on blanket peat moorlands in the Ladybower catchment from which water is treated at Bamford Treatment Works. Whilst other workers have considered management techniques for water colour amelioration at laboratory and plot scale, no previous study had evaluated the impact of these approaches at a catchment scale with a sufficient degree of experimental control. Baseline relationships between meteorological inputs and hydrological responses were established during a calibration period prior to intervention in management. Six catchments were instrumented and the relationships between water discolouration and hydrological and land management characteristics were identified. Suitable pairings of catchments were determined with similar characteristics. One catchment was then treated to a management practice, whilst the management on another was not affected. It was then possible to assess the impact of management on the treated catchment in comparison with the untreated catchment. Following controlled intervention in management on three of the catchments (gullies blocked, cessation of burning and removal of grazing), all study sites were monitored for a further three years to identify and quantify changes in hydrological response, water discolouration and DOC flux and predict responses post-management intervention. The results found that water colour and DOC flux increased on all catchments irrespective of changes in land management, although in the final year there was some recovery. On the paired control sites, where management was not manipulated and similar meteorological conditions prevailed; there were no statistically significant changes from that predicted for true colour and runoff. On the manipulated catchments there were significant changes from that predicted by the control which suggests that management practices contributed to changes on these catchments. Whilst the true colour increased at the gully-blocked site (p = 0.09), the observed colour was lower than predicted on the catchments where burning had ceased (p = 0.891) and grazing was removed (p<0.01). On all catchments there was a reduction in runoff and DOC flux from that predicted; significant at the gully-blocked catchment and where grazing was removed (p<0.01), but where burning ceased the change was only weakly significant (p = 0.085) or not significant (p = 0.4) respectively. Although the results have identified changes in hydrological conditions and colour/DOC response following the manipulation of practices, there is an on-going need for investigation of longer term effects of such interventions, to identify sustainable catchment management practices and to ameliorate further deterioration of surface water quality.

Spent mushroom compost (SMC) is an agricultural waste disposed of in an unsustainable and environmentally degrading manner - mainly in landfills. For every 1 kg of mushrooms grown, approximately 5 kg of SMC is produced, where current generation in the UK is 200,000 tJa. Coal tailings, an industrial by-product from coal mining, are also discarded untenably in lagoons; removing these deposits will eliminate the associated environmental hazards. This project aimed to combine these waste materials into a suitable 'green' fuel for industry through thermal treatment, to produce energy from a sustainable source. Not only will this alleviate the issues regarding existing waste management strategies, but will also attempt to mitigate the environmental impacts of energy generation from nonrenewable sources, such as anthropogenic climate change, through the generation of renewable energy. This PhD research has shown that both materials had high moisture contents, which negatively impacted the calorific value (CV). Drying, though expensive, would thus be required prior to pelletisation and thermal treatment. Key pelletisation parameters were identified and manipulated to control product quality. Optimal values were experimentally-determined for pellet composition (50:50 wt% SMC:coal tailing ratio), moisture (10.5 %) and pressure (6000 psi/41 MPa); such pellets had a NCV of 16.11 MJ/kg. As these pellets were still friable, additional studies were carried out to further improve pellet quality, in tenns of density, tensile strength and durability. Elevated temperatures and steam were considered, in addition to the use of starch and caustic soda binders, which were all successful to varying degrees. Combustion, gasification and pyrolysis tests compared the raw SMC to SMC-coal tailing pellets, where pellet combustion performed better than the SMC alone, and fluidised-bed combustion was more efficient than the packed-bed. Although pyrolysis worked well, the CV of the fuel products were low, whereas gasification was unsuccessful. Consequently, in-depth studies into pellet combustion in a laboratory scale fluidised-bed were perfonned, examining: (i) combustionl fluidisation air flowrates (4.9-10.7 kg/hr); (ii) fuel pellet feedrates (2.02-4.58 kg/hr); and (iii) sand bed depths (0.22-0.30 m). The impacts on temperatures, combustion efficiency and gas concentrations, including acid gas species were analysed. The most favourable operating conditions resulted in high temperatures for efficient energy recovery, with minimal pollutants, although the addition of secondary air jets could further improve the already high combustion efficiencies. While gaseous pollutants are unlikely to be an issue, as the emissions produced generally conformed to the Waste Incineration Directive, efficient particulate collection will be required to remove flyash from the gas stream prior to release to the atmosphere. Industrial implications were explored for heat and power generation, where mass and energy balances for a theoretical furnace, boiler and turbine set-up were completed for various fuel throughputs. Excess heat from the process could be utilized to dry the initial materials, but the economic analysis showed this would be costly - totalling 7) of overall pelletisation expenses. Assuming an overall process efficiency of 18.6 %, a steam turbine could generate over 10 MWe, based on an SMC-coal tailing pellet feedrate of 400,000 tJa - to simulate a large, centralised energy-from-waste facility. FLUENT, a mathematical model, was able to effectively replicate the results of the experimentation and was then used to model particle elutriation and entrainment to assess the suitability of the transport disengagement height provided.