This thesis describes an experimental and theoretical investigation of the flow upstream and in the near wake of a fence attached to a plane wall on which exists a turbulent boundary layer. The study is conducted for a fence height comparable with the thickness of the approaching boundary layer. Comparative results were also obtained in the flow upstream of a forward facing step. The experimental investigation consists of measurements of mean flow and turbulent velocities using hot wire probes at selected locations in the flow. The hot wire results were analysed digitally to give all three components of mean velocity and Reynolds normal stress, and two components of Reynolds shear stress. Some flow visualisation studies using smoke were also undertaken. Results are presented of the theoretical investigation which extends through a range of models, including inviscid, laminar and turbulent flow simulations. All the models describe the flow by various forms of the elliptic Navier Stokes equations and solutions are obtained iteratively. It has been found that certain aspects of two-dimensional separation as described in the Stratford-Townsend model are identifiable well up to the separation point. However, additional three-dimensional motion is observed due to the presence of the fence or forward facing step, which induces significant increases in outer flow stress levels. It is suggested that these additional stresses appear in the downstream wake. The theoretical simulations have indicated that the gross features of the flow can be easily predicted, but that a very complex turbulence model would have to be employed to realise fully the flow mechanics observed in the experiment.

Effective management of municipal solid wastes continues to be a major challenge in rapidly growing cities of developing countries. Inadequate waste disposal remains rampant thus posing a serious threat to the environment and public health. The use of biogas technology in the management of municipal solid wastes has become a major focus of interest in developed countries due to its economic value in the generation of energy from biodegradable waste and its ability to divert waste from landfill. The application of the technology in developing countries, in particular sub-Saharan African countries has been a challenge. A major barrier to its implementation in these countries has been attributed to the lack of substantial specific information required in the design of appropriate strategies. This study investigated key factors affecting the application of biogas technology in Kigali City (the capital of Rwanda) with the aim of proffering suitable strategies for effective implementation. The study used an integrated methodological approach interrelating social, technical and economic spheres tools. The study was carried out in three stages. The first stage investigated the availability of suitable feedstock for Anaerobic Digestion (AD) from both domestic and non-domestic sources, household waste management practices and public awareness and attitude towards waste separation at source. Results showed that household food waste was the largest category of waste produced in Kigali City from September 2010 to March 2011, comprising about 74% of total municipal waste produced during this period. This was taken as the average for the City. Socio-economic levels existing in Kigali were found to impact on total waste production with higher production rates occurring in high income households. It was found that households with higher income are more likely to separate waste at source and more willing to pay for waste management services. Incentives, such as free garbage bags, reduced waste charges and economic benefits, with greater focus on poor income communities were found capable of promoting waste separation practice which could effectively enhance the recovery of suitable feedstock. The second stage examined the digestibility and potential energy production from available household food waste and industrial biodegradable feedstocks such as banana and passion fruit wastes. The study also studied the potential effect of operating an AD system under the ambient temperature in Kigali City. Results obtained showed that Kigali ambient temperature of 25oC achieved half methane yields in comparison with the optimum mesophilic operational temperature of 37oC commonly used for large scale AD systems around the world. Results also showed that co-digestion of domestic waste with industrial feedstock can substantially increase biogas yields. The third stage investigated technical requirements and economic viability of operating a biogas plant at 37oC with the available feedstock for the generation of electricity to export to grid and digestate for spreading on land. The annual net energy expected to be generated using the available feedstock was estimated to be 182 kWh/tonne of source-separated waste. Risk analysis revealed that socio-economic needs of communities need to be appropriately integrated to secure the reliability of suitable feedstock in order to ensure project’s viability and profitability. It was also found that the development of biogas technology in Kigali could benefit both technically and economically from current Rwandan National key policy objectives related to municipal waste management. All the above mentioned outcome of the research was used to develop a strategic policy-based operational and investment framework for the application of biogas technology in Rwanda.

This thesis develops and demonstrates an innovative method for adsorbing metals from metal mine drainage in mid-Wales and northern Italy using dealginated seaweed (DS) as a biosorbent. The chemical composition of 15 mine drainages and two receiving waters in Wales was determined over a two year period in relation to precipitation and season. The waters were circum-neutral, iron-poor (<1 mg/L) but metal-rich, dominated by Zn ( 42 mg/L), Cu ( 188 μg/L), Cd ( 99 μg/L) and Pb ( 2.7 mg/L). The chemical composition varied throughout the year, but did not necessarily show clear seasonal variation, with Zn, Cd and Pb tending to show a winter maximum. The physico-chemical adsorption characteristics of the DS were determined. Over 80 % of Zn, Cd and Pb were removed from solution within 15 minutes of contact; adsorption was not affected by pH (between 3.3 and 6.6) nor by additional elements in solution. The adsorption capacity of the DS was Pb > Cd > Zn. The main removal mechanisms were determined to be adsorption and ion exchange with Ca, Na, Mg released from the DS surface. Treatment plants containing DS were deployed at three sites in mid-Wales and one site in Italy. In mid-Wales, Zn, Pb and Cd adsorption peaked within an hour (at ~98 %) associated with a significant release of Ca, Mg and Na. The DS adsorbed Pb > Cd > Zn, with the DS adsorbing ~1 % of its dry weight of Pb, ~0.01 % Cd and ~2 % Zn. The saturation of the DS was dependent on the mine drainage composition, with adsorption continuing for several months when low metal concentration (<1 mg/L) mine drainages were remediated. In Italy, acidic (~pH 2.5), metal-rich ( 120 mg/L Al, 420 mg/L Fe and 99 mg/L Cu) mine drainage required neutralisation and Fe-removal before entering the DS treatment plant to remove the remaining metals. The treatment plants improved the quality of mine drainage and reduced their impact on receiving water courses; the plant was designed to be a practical, low-cost, solution which uses a waste product (from the alginate industry). This thesis demonstrated a novel method for remediation of neutral, low Fe waters, and is applicable as a final ‘polish’ when acidic, Fe-rich water has been neutralised and the Fe removed.

La recarrega artificial de les aigües subterrànies consisteix en infiltrar aigua als aqüífers per mitjà de les instal·lacions dissenyades per a tal fi i representa una eina important en la gestió dels recursos. A més de l’augment dels recursos d'aigües subterrànies, la recàrrega pot suposar una millora natural de la seva qualitat durant el seu pas pel subsòl. Els processos que tenen lloc en el sistema sòl-aqüífer (filtració, adsorció, reaccions de mescla , redox, biodegradació, etc) han demostrat produir una millora integral de la qualitat de l'aigua, eliminant també de manera efectiva una sèrie de contaminants orgànics. En l'actualitat, la qüestió és saber si la contaminació pels microcontaminants orgànics emergents, és a dir, productes farmacèutics, cosmètics, hormones, drogues il·lícites, pesticides i tensioactius, també es poden atenuar de forma natural. Alguns d’aquests compostos no són completament eliminats pels tractaments d'aigua residual convencionals, essent introduïts contínuament en els cursos d’aigua superficials pels efluents de les plantes de tractament. Malgrat la baixa concentració (ng/L i μg/L), la seva presència en el medi ambient és actualment un problema per a la vida aquàtica i la salut humana. En aquest context, la recàrrega artificial pot esdevenir una alternativa potencial o un tractament complementari per a l'eliminació de microcontaminants orgànics de l’aigua. Hi ha evidències que les condicions redox predominants podrien influir en el comportament d’aquests productes en l'aqüífer. No obstant, en el cas dels microcontaminants emergents, el coneixement sobre aquest tema és encara molt limitat. L’objectiu principal d’aquesta tesi és doncs investigar el possible efecte de les condicions redox sobre el destí de microcontaminants orgànics, la majoria dels quals són contaminants emergents. El treball està motivat pels projectes de recàrrega artificial amb aigua del riu Llobregat (Barcelona, Espanya). L’estudi es basa en experiments de laboratori (batch) utilitzant materials naturals de l'aqüífer, microcontaminants en concentracions ambientals (1 μg/L de cada compost), i unes condicions ambientals similars als llocs de recàrrega artificial. Afegint les quantitats adequades d’acceptors i donadors d’electrons s’han obtingut i mantingut les diferents condicions redox anaeròbies en cada conjunt de microcosmos. Els experiments inclouen sèries biòtiques i abiòtiques per separar la biodegradació de contaminants de l’adsorció a la superfície dels sòlids i altres processos abiòtics. També s’ha dut a terme un experiment amb una major concentració de contaminants (1 mg/L de cada compost), per comprovar la representativitat dels estudis convencionals. Els objectius finals del treball són: 1) identificar les condicions redox més favorables per eliminar de l'aigua els compostos seleccionats, a fi de ser promogudes en l’assaig de camp; i 2) mesurar les velocitats de les reaccions de degradació per tal de preveure el comportament dels micrcontaminants en el aqüífer. / La recarga artificial de acuíferos, que consiste en la infiltración de agua subterránea en instalaciones diseñadas para tal fin, constituye una importante herramienta en la gestión de recursos hídricos. Más allá de aumentar los recursos de aguas subterráneas, suscita gran interés la capacidad de tratamiento natural que confiere el tránsito sub-superficial a las aguas. Los procesos que tienen lugar en el sistema suelo-acuífero (filtración, adsorción, mezcla, reacciones redox, biodegradación, etc.) permiten una mejora general de la calidad del agua, eliminando incluso diversos contaminantes orgánicos. En la actualidad, el reto es entender si los microcontaminantes orgánicos emergentes, es decir farmacéuticos, productos de cuidado personal, hormonas, drogas ilícitas, plaguicidas y tensioactivos, puedan también ser atenuados. Muchos de ellos no son completamente eliminados en tratamientos de agua convencionales, siendo introducidos constantemente en aguas superficiales por los efluentes de las plantas de tratamiento de aguas residuales. A pesar de sus baja concentraciones (ng/L and μg/L), su omnipresencia en el medioambiente es actualmente causa de preocupación para la vida acuática y la salud humana. En este contexto, la recarga artificial puede representar un tratamiento alternativo o complementario para la eliminación de microcontaminantes orgánicos de las aguas. Hay evidencias de que las condiciones redox dominantes pueden influenciar el comportamiento de contaminantes orgánicos convencionales en los acuíferos. Sin embargo, en el caso de los microcontaminantes emergentes los conocimientos sobre este tema es todavía limitado. El principal objetivo de esta tesis, motivada por proyectos de recarga artificial con aguas del río Llobregat (Barcelona, España), es investigar el efecto potencial de las condiciones redox sobre el comportamiento de microcontaminantes orgánicos seleccionados (la mayoría de los cuales son contaminantes emergentes) durante la recarga artificial. El estudio se basa en experimentos batch de laboratorio usando material natural del acuífero, microcontaminantes en concentraciones ambientales (1 μg/L cada compuesto), y condiciones verosímiles en enclaves de recarga artificial. Añadiendo cantidades adecuadas de aceptadores y donadores de electrones, fueron establecidas y se mantuvieron diferentes condiciones redox anaeróbicas (condiciones nitrato-, manganeso-, hierro- y sulfato-reductoras) en cada grupo de microcosmos. Se llevaron a cabo series bióticas y abióticas para separar la biodegradación de los contaminantes (mineralización biótica o transformación) de los procesos de adsorción y de otros procesos abióticos. También fue realizado un experimento para alta concentración de contaminantes (1 mg/L cada compuesto), para comprobar la representatividad de los estudios convencionales. El objetivo final de este trabajo es identificar 1) las condiciones redox más favorables para la eliminación del agua de los contaminantes seleccionados, para su posterior simulación en el sitio piloto, y 2) las tasas de eliminación de esos contaminantes, para predecir sus comportamientos en el acuífero. / Artificial recharge of groundwater, consisting in infiltrating water into aquifers by means of properly designed facilities, represents an important tool in water resources management. Beside its quantitative benefits (augmentation of groundwater resources, long term underground storage, etc.), a great interest for this technique is related to the natural treatment provided to water by subsurface passage. The processes occurring in the soil-aquifer system (filtration, sorption, mixing, redox reactions, biodegradation, etc.) have indeed proven to yield an overall improvement of water quality, removing effectively also a number of organic contaminants. At present time, the issue is to understand whether emerging organic micropollutants, i.e. pharmaceuticals, personal care products, hormones, illicit drugs, pesticides and surfactants, can also be removed. A number of these compounds are not completely removed by conventional water treatments, being thus introduced continuously into surface water bodies by the discharge of wastewater treatment plants effluents. In spite of their low concentration (ng/L and μg/L), their ubiquitous presence in the environment is currently a cause of concern for aquatic life and human health. In this context, artificial recharge may represent a potential alternative or complementary treatment for the removal of organic micropollutants from water. Evidences showed that, among the factors influencing the fate of conventional organic contaminants in the aquifer, the predominant redox conditions could play an important role. Yet, in the case of emerging micropollutants the knowledge on this topic is still limited. The main objective of this thesis, motivated by artificial recharge practices using Llobregat river water (Barcelona, Spain), is to investigate on the potential effect of redox conditions on the fate of selected organic micropollutants, most of them being emerging contaminants, during artificial recharge of groundwater. The study is based on batch experiments involving natural aquifer material, micropollutants at environmental concentrations (1 μg/L each compound), and settings feasible at artificial recharge sites. Different anaerobic redox conditions (namely, nitrate-, manganese-, iron- and sulphate-reducing conditions) were promoted and sustained in each set of microcosms by adding adequate quantities of electron donors and acceptors. The experiments included biotic and abiotic series to separate contaminant’s biodegradation (i.e. biotic mineralization or transformation) from sorption and other abiotic processes. An experiment at higher pollutants concentration (1mg/L each compound) was also carried out, to check the representativeness of studies at concentrations easier to be tested and analysed. The ultimate aim of the work is to identify 1) the most favourable redox conditions for the removal of the target compounds from water, for their following stimulation in the field test site, and 2) pollutants’ removal rates, to predict their behaviour in the aquifer.

Access to drinking water is one of the challenges of the 21st century for an increasing number of countries in the world. In Spain, a desalination plant providing between 20% and 30% of Barcelona¿s drinking water has been in operation since summer 2009. The desalination plant¿s Reverse-Osmosis (RO) system processes sea water to produce drinking water and a waste product, concentrated brine, which has a negative impact on the flora and fauna (coral) around the plant outlet pipe. It would be a shame for this waste product with such a high salt concentration (60 g to 80 g of salt per litre, compared to about 30 g per litre in the sea) to go unused. This research explores the possibility to reduce the amount of brine discharged into the sea by the desalination plants by using it in an industrial process. By means of an Electrodialysis (ED) process, the concentration of the discharge from the Reverse- Osmosis process can be increased up to 250 g per litre so the brine can then be purified and used as a raw material in the chlor-alkali industry. Taking these challenges into account, an ED pilot plant using CIMS and ACS Neosepta membranes was built in Barcelona to test concentration of RO brine solutions. The ED pilot was dimensioned to concentrate 500L/h of brine coming from two different configured RO pilot plants. As the ED plant had unlimited access to the feed brine and it did not pretend to desalt this brine, the circuits of diluate and electrolyte were designed in one-single pass. This allowed operating the plant with high current densities, as limiting current density was never achieved. Consequently, higher NaCl concentrations on the concentrate stream were obtained. The results obtained during the start-up and preliminary operation of the pilot plant aredescribed in the current thesis. These experiences showed the concentration feasibility of this technology when reaching 258 g NaCl/L after 35h of operation at 0.4kA/m2 with a power consumption of 0.24 kWh/kg NaCl at 10ºC. Moreover, as the membranes used (Neosepta CIMS and ACS) were mainly selective for univalent ions, polyvalent ions such as calcium and magnesium were partially removed from the brine which represented an advantage for its final reuse in the chlor-alkali industry. However further treatments would be needed to meet the electrolysis requirements. A mathematical model was also developed based on Nernst-Planck equations to predict NaCl concentration performance of the ED pilot plant. Several of the model parameters were obtained experimentally and others were taken from the literature. The model was able to accurately predict the NaCl concentration reached in the concentrate tank along the experiment, as well as the time required to reach maximum concentration and production overflow as a function of the operation conditions such as electrical current intensity and NaCl feed concentration. In this work, the results of the mathematical model are compared with the preliminary experimental results obtained at the pilot plant in order to validate the model. Finally, this pHd aims at evaluating the possibility to use an alternative source of brine in a cost effective way compared to current sources of salt. At the same time it provides a technical solution for the optimal use of natural resources since it minimizes environmental impact of the desalinization process. To meet this challenge, our brine and electrolysis specialists in Italy are collaborating on the project with the Barcelona water company (Aguas de Barcelona - AGBAR) and the Universitat Politècnica de Catalunya (UPC). Finally this thesis brings an interesting step forward in reducing environmental impact of the desalinization process transforming the RO waste into raw material for the Chlor- Alkali Industry. Besides, it helps develop future applications for existing Technologies as the Electrodyalisis. / Para hacer frente al problema de la escasez de agua para el consumo, actualmente se plantea la necesidad de recurrir a recursos no naturales como la desalación por ósmosis inversa, que permite garantizar el suministro de caudales constantes con una alta calidad, independientemente de la climatología. Sin embargo la desalación produce un rechazo salino en cuantía similar a la producción de agua potable. El objetivo de esta tesis es explorar el valor del residuo salino procedente de rechazo de desalación como materia prima para la industria electroquímica, teniendo en consideración que esta salmuera rechazo presenta una concentración de 70 g NaCl/kg, lejos de la concentración de saturación (250 g/kg) necesaria para el proceso electrolítico de la industria cloro-álcali. Tras un análisis de las tecnologías de concentración existentes, la investigación se ha llevado a cabo utilizando la tecnología de la Electrodiálisis (ED) como sistema más eficiente para concentrar la salmuera de rechazo de desaladora. Así, se ha diseñado y construido una planta piloto experimental, necesaria para confirmar la viabilidad técnica y económica de la electrodiálisis como sistema de concentración de salmuera. Dicha planta piloto se ubicó en el Prat de Llobregat (Barcelona), en el centro de investigación de desalación del proyecto SOSTAQUA (www.sostaqua.com) donde DOW y DEGREMONT tienen instaladas sus plantas piloto de Ósmosis Inversa (OI). Los principales hallazgos de la investigación doctoral confirman que la conexión de la planta de electrodiálisis al rechazo de OI para la producción de salmuera destinada a una electrolisis de Cloro-Sosa ofrece las siguientes ventajas competitivas: 1. El acceso ilimitado de salmuera ya pre-concentrada permite trabajar en la configuración de paso directo (One Single Pass). Esto significa que la corriente de diluido no se llega a desconcentrar (pierde 6 g NaCl) en iones Na+ y Cl-, por lo que la resistividad del stack de membranas se mantiene constante (y baja), incluso cuando se aplican densidades de corriente elevadas. 2. Los pre-tratamientos realizados al agua de mar previos a la OI, como la eliminación de materia orgánica, ahorran la etapa de depuración previa a la EDI. Además, el uso de anti-escalantes retrasa la precipitación de sulfatos en la superficie de las membranas. 3. Al ser un proceso de arrastre electroquímico, la EDI no añade reactivos nocivos a la salmuera rechazo de OI; sino todo lo contrario, el rechazo de la EDI es salmuera diluida y el concentrado es el residuo que se pretende valorizar como materia prima para un proceso industrial. 4. La selectividad de las membranas de electrodiálisis consigue una primera etapa de depuración de los iones bivalentes nocivos para el posterior proceso industrial durante el propio proceso de concentración. Al no concentrar los iones Mg2+ y Ca2+ la electrodiálisis resulta una tecnología interesante pues integra una etapa de depuración en iones bivalentes para la aplicación industrial de producción de Cl2 -NaOH. 5. Finalmente, la ventaja competitiva de la electrodiálisis viene por el lado del consumo energético Los resultados experimentales sitúan el consumo energético en torno a 0,2 kWh/kg sal frente a los 8,5 kWh/kg de los sistemas tradicionales de concentración de salmuera por evaporación. Por otra parte, se ha desarrollado un modelo teórico basado en las ecuaciones de Nernst-Planck, que se ha podido validar con resultados experimentales obtenidos en la planta piloto. El modelo resulta ser válido para predecir la evolución temporal de la concentración en NaCl de la solución. Finalmente, en el aspecto ambiental, esta tesis aporta aspectos muy interesantes ya que da salida al rechazo producido en los procesos de desalación de OI como materia prima para la industria y sienta bases para ayudar a desarrollar futuras nuevas aplicaciones a tecnologías existentes.

Urban drainage network models are increasingly used in the water industry for hydraulic and water quality simulation. These models require inputs for energy loss and mixing coefficients to make predictions of head loss and the transport of solutes or dissolved substances across hydraulic structures, such as sewer pipes and manholes. Laboratory-derived head loss and energy loss coefficients for manholes may be used in urban drainage modelling. However, the applicability of the laboratory-scale derived parameters to full-scale structures in the urban drainage system, Le. scalability of these parameters, is not clearly understood. The overall aim of the research was to derive generic scaling methodology to describe the impact of physical scale of manholes on the hydraulic and mixing processes using laboratoryand CFD-based analyses. A 1:3.67 scale model of an 800 mm diameter manhole (the prototype) studied by Guymer et al. (2005) has been constructed in the laboratory. Laboratory experiments were conducted to measure head loss and solute dispersion in the scale model. The solute dispersion results were analysed using advection dispersion equation (ADE) and aggregated dead zone (ADZ) models and comparisons of the results with the prototype experimental data were made. The cumulative temporal concentration profiles (CTCPs) for the scale model were also compared with the prototype profiles. However, analysis of the laboratory-derived data failed to quantitatively identify the scale effects because the recorded data of the two manholes was not directly comparable. Computational fluid dynamics (CFD) was used to investigate the effects of scale in the surcharged manhole. A thorough validation study was conducted to provide confidence in the CFD model predictions. A standard modelling protocol for manhole simulations was developed through the validation study. Three differently sized manholes were created using CFD. The scale effects on the flow field, energy loss and solute transport characteristics were investigated. The findings of the study suggest that scale effects exist in the three manholes; however, the degree of the effects is very small. The scale effects were attributable to the dissimilarity in Reynolds number and that led to different characteristic of the jet in the manhole. Methodologies to scale the hydraulic and solute transport processes in surcharged manholes have been presented.

Surface area and fluid dynamics have always opposed each other in the engineering of improved materials such as catalysts, adsorbents and molecular sieves. Whilst the smallest particle and pore sizes ensure a large contact area, they also cause huge back pressures and hindered flows, impractical for bulk industrial processes. A material that combines several levels of porosity would encompass the positive properties each array can offer. Highly ramified networks of micro- and macro-pores would be desired, so that an easy, rapid access to the active sites on a given surface became possible. Taking these parameters into account, novel hierarchical porous materials were synthesized via hydrothermal growth of faujasite on the surface of diatomite frustules and natural carbons (olive seeds, coconut husk and coconut fibres), previously seeded with nano-zeolite crystals. Seeding was attempted both with freshly synthesised colloidal zeolite Y, as well as finely ground commercial zeolite. For the latter, wet ball milling was applied, successfully reducing particle size to the sub-micron range ( 180nm average). The resulting hierarchical porous materials possessed very high surface areas (up to 600 m2/g), and were successfully tested for the removal of cobalt and arsenic from aqueous solutions. It was found that the efficiency of zeolite Y increased whenever it is supported on a macroporous structure; for some cases, this efficiency is tripled. When working with concentrations of arsenic typically found in extremely polluted streams, a complete removal of the element was achieved, complying with the latest regulations from the USEPA. The supported zeolites proved to have a very high adsorption capacity, thus ensuring their long active life. Cobalt was also removed in significant amounts, and its subsequent vitrification proved to be a practical way to immobilize the ion: no cobalt was released after a 7- day leaching period, even in the presence of exchangeable ions. The application of readily available resources, such as natural carbons and ground nano-zeolites, significantly reduces the production cost of these materials, turning them into alternatives of great potential for the treatment of hazardous effluents.

Climate change mitigation via a reduction in the anthropogenic emissions of carbon dioxide (C02) is the principle requirement for reducing global warming, its impacts, and the degree of adaptation required. Here, the trade-offs between delaying mitigation action and the strength of mitigation action required to meet particular atmospheric CO2 concentrations are explored using a conceptual model of emission trajectories and a simple Earth system model. The results show that avoiding dangerous climate change is more likely if global mitigation action commences as soon as possible and that starting mitigation earlier is also more effective than acting more aggressively once mitigation has begun, given realistic limits of rates of decarbonisation. A detailed examination of the latest datasets on CO2 emissions from the combustion of fossil fuels and cement production show a significant shift in the dominant drivers of global CO2 emissions, with a substantial growth in emissions from coal since 2002, and coal surpassing oil as the main source of emissions from fossil fuels in 2006. When compared to the Intergovernmental Panel on Climate Change (IPCC) scenarios, recent emissions are shown to be higher than five of the six Special Report on Emission Scenarios (SRES) emission scenarios, and the growth rate in emissions for 2000 to 2007 are higher than the growth rates for the current decade, in four of the six scenarios. If the post-2002 emissions continue, driven by a growth in coal which is the most carbon intensive fossil fuel, then the task of mitigation becomes more challenging, the importance of building adaptive capacity more pressing and calls into question whether mitigation alone is sufficient to meet the aspiration of avoiding dangeriiious climate change. Given the significant and widening gap between the current trajectory of CO2 emissions and the trajectory that would provide the greatest probability of avoiding dangerous climate change, there has been a resurgence of interest in geoengineering in recent years. Climate geoengineering seeks to rectify the current radiative imbalance via either (1) reducing incoming solar (shortwave) radiation or (2) removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A critical review of the geoengineering literature shows that shortwave geoengineering can rectify a global radiative imbalance but ocean acidification and residual regional climate changes would still occur and the intervention could bring about unforeseen Earth system responses that may in turn increase the radiative imbalance. Creation of CO2 sinks (longwave geoengineering) involves less risk than shortwave geoengineering, as it acts upon the primary cause of the radiative imbalance and has a more limited capacity for `failure'. Geoengineering does not provide a `solution' to anthropogenic climate change. In order to meet the ultimate objective of the United Nations Framework Convention on Climate Change (UNFCC), demonstrable and significant mitigation action must get under way soon, with the creation of CO2 sinks a potential complement. The necesscity of undertaking geoengineering will ultimately be dicated by the magnitude of climate interference judged to be dangerous and the strength of mitigation agreed and adhered to by the international community in Copenhagen in December 2009

One of the practices for dealing with water pollution from point and non point pollution sources is the use of on-line purification lakes. The Lea Marston lakes were built in the early 1980' s to reduce the pollution load transported by the River Tame to the River Trent. The lakes operate on the principle of particle bound contaminant sedimentation. The lakes were observed to be efficient at reducing suppressed (ATU) biochemical oxygen demand (BOD(ATU)), suspended solids (SS) and metals under dry weather flow and wet weather flow conditions. However, ammoniacal-nitrogen (ammonia) is observed to increase across Lake 1. The dominant mechanism of removal is via sedimentation with greater removal occurring under higher inlet concentrations. The addition of ammonia occurs possibly via diffusion with the bed sediments providing a source of ammonia. The bed sediments were identified as a potential pollution source and processes such as diffusion and resuspension could adversely affect the water quality across Lake 1. Porewater and surface water profiles identify the significance of the bed sediments as a sink for dissolved oxygen and a source of ammonia. A modelling study showed that a River Quality Objective (RQO) of River Ecosystem Class (RE) 2 could be achieved at the lakes inlet by improvements in nearby wastewater treatment works effluent quality and water quality from the upper catchment. However, the outlet water quality would probably be adversely influenced by ammonia released from the lake sediments.

The potential of agricultural drainage ditch sediments to release and retain phosphorus (P) was investigated at six sites in two sub-catchments of the River Blackwater in Counties Monaghan and Armagh, Ireland. The bed sediment was sampled on a fortnightly basis between April 2008 and March 2009: the sediment (top 1 cm) was analysed for total P, individual P fractions (with a modified Psenner sequential extraction scheme), equilibrium P concentration (EPCo), iron (Fe) and manganese (Mn) concentrations; sediment pore water (top 5 cm) and stream water were analysed for soluble reactive P (SRP). In relation to variation in stream discharge, sediment total P (TP) decreased rapidly during the largest storms, followed by calmer hydrological conditions and recovery in sediment TP. This provides field evidence of sediment TP depletion during storms, demonstrating the physical basis of the sediment's net P release in this study. This is also consistent with the interpretation of storm P-discharge hysteresis, where stream P concentration does not follow the rising and falling limbs of the hydrograph, that high discharge events can mobilise P retained in bed sediment. In terms of sediment P fractionation, the reductant-soluble bicarbonate-dithionite (BO) fraction was by far the largest, in terms of concentration and contribution ratio to TP (medians: 41 % - 62%), and the most sensitive to change in discharge, which suggests that the redox-sensitive binding of P to Fe and Mn hydroxides in the BO fraction was the dominant chemical process controlling sediment P. In addition, an inverse relationship was observed between Fe/P ratio in the BO fraction and sediment TP, but the BO-Fe data has been shown to be compromised due to analytical delays and inadequate sample preservation. This observation would have further indicated the chemical basis to sediment P retention during the recovery from storms: a decrease in Fe/P ratio points to the uptake of P by the reductant-soluble amorphous Fe hydroxide in this fraction. The comparison between sediment EPCo (medians: 0.005 - 0.041 mg P L-1 ) and stream P concentration (medians: 0.023 - 0.129 mg P L-1 ) generally indicated potential for sediment P retention. This was in spite of consistently reducing conditions in the bed sediment and the presence of high pore water P concentration at P-enriched sites (highest median: 2.133 mg P L-1 ). No evidence was found that supports the hypothesis that potential sediment P release contributed to the stream water SRP concentration during the stable low flow periods of the summer. This indicates that rural point sources are more likely to be responsible. Therefore, the ditches acted as temporary storage of P from catchment sources, chemically retaining P during low flow periods, before physically releasing the accumulated P load during episodic high discharge events. Under non-storm conditions, the bed sediment was clearly a P sink, mitigating nutrient enrichment in situ and downstream, by removing in-stream P and delaying downstream transport of P loading from catchment sources. There is a need to understand better the potential P release upon physical disturbance by storm flow - in particular the environmental implications of the dominance of the BD-TP fraction and the reductant-soluble Fe-P binding mechanism in the mobilised bed sediment.