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Concerns regarding climate change are becoming a driver behind legislation at both UK and EU levels, and also on the wider, planetary scale. This is the case with emissions from landfills where the release of methane is being targeted for reduction. This thesis uses an integrative approach, incorporating concepts of hierarchy from systems theory, to model landfill as a complex biophysical technology. It assesses the contribution to carbon deposition and global warming of landfill through changes to that technology itself and through changes in the waste stream caused by potential waste policies. The thesis develops an holistic, conceptual model of the landfill system, mapping flows and transformations of carbon within that system. It further develops this conceptual model into a calculating model of landfill as a waste management technology incorporating measurements taken to provide new data and validate published data to calibrate the model. It thus applies modelling techniques to a biophysical technology, producing an integrated model of the landfill that allows the knowledge gained from other research to be used to explore engineering and operational decisions on landfills. The thesis includes results from measurements of the composition of household waste, and of the biochemical methane potential (BMP) of fractions of that waste. It includes measurements of the residual BMP in samples of excavated waste and measurements of gas flows. The main results suggest the following: • Early capping of landfilled waste is important in reducing the global warming impact; • If the rate of degradation of the waste is accelerated in the drive towards sustainability, capping should be carried out even earlier if the global impact is not to be increased; • Although recycling parts of the degradable elements of the waste stream has the effect of reducing the global impact, extensive recycling has implications for landfill engineering.

Philosophiae Doctor - PhD / Geomechanical analysis and integrity assessment of hydrocarbon reservoirs upon depletion and injection are crucial to ensure that CO2 storage projects can be safely implemented. The Bredasdorp Basin in South Africa has great potential for CO2 storage, given its hugely available exploration data. However, there has not been any geomechanical characterization carried out on this basin to determine its integrity issues. This study aims to investigate the feasibility of a carbon storage project in the E-M depleted gas field. The preliminary geological assessment demonstrates that Zone 2 and Zone 3 display acceptable injectivity for CO2 injection of the E-M gas field. Seismic lines display faults that could affect the caprock's integrity during depletion and carbon storage. Geomechanical characterization provides a guideline as to how geomechanical analysis of depleted fields can be done for a safe CO2 sequestration practice. The geomechanical model constructed at a depth of 2570 m indicated that the magnitudes of the principal vertical, minimum, and maximum horizontal stresses in the field are respectively 57 MPa, 41 MPa, and 42-46 MPa. Fault and fracture stabilities were examined before and after depletion. It was found that faults and fractures in compartments C1 and C2 of the reservoir are stable before and after depletion, while normal faults (FNS8 and FNS9) in compartment C3 dipping SW were critically stressed. The minimum sustainable pressure of the reservoir determined by simulating depletion is 6 MPa. Below that, pressure depletion causes normal faulting in reservoir compartments C1 and C2. The maximum sustainable pressure, on the other hand, was found to be 25 MPa. The geomechanical studies also reveal that it is possible that the reservoir experienced compaction of 8 cm during depletion and will experience an uplift of 3.2 cm during 71 years of injection. The economic model of a CO2-enhanced gas recovery project in E-M gas field, the annual expenses (Aexp) of carbon capture and storage range between Zar20 3.31 × 109 and Zar20 4.10 × 109. The annual revenues (RA) were estimated to be Zar20 1.42 × 1010. The cash flow analysis derived from Aexp and RA confirms that enhanced gas recovery could partially offset the cost of CO2 storage if a minimum of 5 % of CO2 fraction is allowed in the natural gas recovered. Geological and geomechanical studies have demonstrated that carbon storage is physically feasible in the E-M gas field. However, the project's completion lies in the among the gas recovered to balance the cost of CO2. http://

Intensive agriculture, coupled with an increase in nitrogen fertilizer use, has contributed significantly to the elevation of atmospheric greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Rising GHG emissions usually mean a decrease in soil carbon. Currently, soil C is twice that of all standing crop biomass, making it an extremely important player in the C cycle. Fortunately, agricultural management practices have the potential to reduce agricultural GHG emissions whilst increasing soil C. Management practices that impact GHG emissions and soil C include various tillage practices, different N fertilization amounts and treatments (synthetic N, cattle manure, or a combination of both), the use of cover crops, aeration, and water levels. Employing agricultural best management practices (BMPs) can assist in the mitigation and sequestration of CO2, N2O and soil C. Measuring soil carbon storage and GHG emissions and using them as metrics to evaluate BMPs are vital in understanding agriculture's role in climate change. The objective of this research was to quantify soil carbon and CO2 and N2O emissions in agroecosystems (dairy, crop, and meat producing farms) under differing management practices. Three farms were selected for intensive GHG emissions sampling: Shelburne Farm in Shelburne, VT, a dairy in North Williston, VT, and Borderview Farm in Alburgh, VT. At each site, I collected data on GHG (CO2 and N2O) emissions and soil carbon and nitrogen storage to a depth of 1 meter. Soil emissions of CO2 and N2O were taken once every two weeks (on average) from June 2015 through November, 2015 using static flux chambers and a model 1412 Infrared Photoacoustic Spectroscopy (PAS) gas analyzer (Innova Air Tech Instruments, Ballerup, Denmark). Fluxes were measured on 17 dates at Shelburne Farms, 13 dates at the Williston site, and 13 dates in the MINT trial. Gas samples were taken at fixed intervals over a 10-14 minute time frame, with samples normally taken every one or two minutes. I also measured soil carbon to a depth of 1m in six BMPs at Borderview Farm. Overall, I found that manure injection increased N2O and CO2 emissions, but decreased soil C storage at depth. Tillage had little to no impact on N2O emissions, except at Shelburne Farms, where aeration tillage decreased N2O emissions (marginally significant, P < 0.1). No-till did, however, decrease CO2 emissions relative to other conservation tillage practices (strip and vertical tillage) but we were unable to detect a significant change in soil C due to tillage practices. At Borderview farm, N2O emissions increased with soil NO3 and soil moisture, while CO2 emissions increased with soil temperature and nitrate. At Williston, CO2 emissions only increased with temperature; at Shelburne CO2 emissions increased with nitrate. N2O fluxes at Shelburne and Williston were not associated with any of the measured covariates.

A principle concern for engineered CO2 storage is long-term security. Surface leakage (‘seepage’) of injected CO2 to the surface is economically and environmentally undesirable. Italy is a region of intense natural CO2 degassing; 308 CO2 seeps are catalogued which exhibit different surface characteristics, and a number CO2 rich reservoirs were discovered when drilling for hydrocarbons. These seeps and reservoirs provide excellent natural analogues for seeps that might arise from breached carbon stores. This thesis explores the geological controls on the crustal plumbing of CO2 fluids to model the processes governing CO2 seep locations and distribution, and characteristics; and their consequences on human health risk. Risk of human death from accidental CO2 poisoning at all seep types is low (10-8 yr-1) and several factors influence risk of human mortality. Seeps distribute on two spatial scales; on a local scale (<5 km) seeps are clustered and aligned with subsidiary geologic structures, while on large scales seep clusters are discrete, and align with regional structures. Within clusters, seep locations are influenced by fault maturity, the presence of lithological boundaries and seep manifestation, which is determined by the flow properties of the outcropping lithology and local topography. Sealing and seeping CO2 reservoirs are identified, and their geological characteristics compared. Italian reservoirs successfully retain large CO2 columns at a range of reservoir conditions. Reservoirs which have hydrostatic pressure conditions in the overburden, determined from well logs, are located close to surface CO2 seeps and recent extensional faults. Where there is significant overpressure above hydrostatic in the overburden, there are no seeps present above the reservoir structure. Overpressure of reservoir fluids may enhance fluid flow rates but is not a necessary condition for CO₂ leakage. Geothermal conditions influences the style of leakage at depths and towards the surface. Total CO2 degassing from dry Italian CO2 seeps is 3.5 ± 0.5 Mt(CO2)yr-1. It would take thousands of years for the effectiveness of a commercial scale store to be significantly reduced if it leaks to form a single seep with the mean flux rates modeled in Italy. If a seep cluster develops, the storage effectiveness will reduce more rapidly, and could negate engineered CO₂ storage as a climate mitigation strategy. The research presented in this thesis contributes to a body of knowledge which directly informs site selection procedure for carbon storage and maximise the long term storage potential for CCS. Thorough scientific understanding of the geological processes governing fluid escape is crucial to assure the scientific, political and public communities that safe, long-term carbon storage can be realised as an effective climate mitigation technology.

Floodplain fens represent an important component of the global carbon cycle through their role in carbon sequestration. Peat development depends upon rate of production exceeding rate of decomposition, yet there is little understanding of the effects of sea-level rise on these processes in lowland environments. This thesis investigates the impacts of projected sea-level rise from climate change on carbon storage in floodplain fens, using a combination of field, laboratory and simulation modelling techniques. A gradient of saline influence was determined for the Broads, UK, based on analysis of water chemistry and published water level data, allowing for the application of a space-for-time substitution technique. Increased water level had a positive effect on above-ground production of Phragmites australis (cav.) Trin. Ex Steud. (1841) - perhaps because water stress limits important photosynthetic processes. An increase in salinity had a negative effect on the growth of P. australis, probably due in part to osmotic stress. Previous management practice significantly impacted on production - as uncut vegetation became less productive with time. There was evidence to suggest that sea-level rise may lead to faster decay rates, but this will be partially offset by litter quality. Saline influenced sites had lower carbon accumulation potentials. Radiometric dating confirmed that these sites have lower carbon sequestration rates - probably as a result of increased mineral deposition in floodwaters. Carbon stock ranged between 33 and 144 kt C but depended greatly on peat depth and bulk density. Results from both field data and the model indicated that peat accretion in the Broads would not offset projected sea-level rise. Floodplain fen development under the influence of sea-level rise will be dependent on the majority of assimilate being allocated to above-ground vegetation.

Des résultats récents ont montré que les podzols équatoriaux stockent d’importantes quantités de carbone dans leurs horizons Bh profonds. Cette constatation amène deux questions principales : (1) comment et à quel rythme se sont formés ces sols (2) dans quelle mesure le changement climatique pourrait induire une production par ces sols de carbone atmosphérique susceptible d’impacter le système climatique mondial.Dans ce contexte, nous avons réalisé un modèle qui permet de contraindre les flux de carbone à la fois par les stocks observés et leur âge 14C. En situation suffisamment simplifiée, nous avons établi une relation formelle entre l’évolution des stocks et l’âge 14C de celui-ci. Appliqué aux podzols amazoniens, notre modèle a apporté des résultats nouveaux et inattendus. Il a permis de montrer que ce sont les horizons de surface des aires podzolisées les plus hydromorphes qui sont les plus gros contributeurs de MOD transférée vers le réseau hydrographique et la mer. On observe que la formation des Bh n’est possible qu’en envisageant deux compartiments, rapide et lent. Une estimation basse de leur temps de formation permet de différencier des podzols relativement jeunes (temps de formation de l’ordre de 15 103 - 25 103 ans), développés sur des sédiments Holocènes relativement récents, et des podzols âgés (temps de formation de l’ordre de 180 103 - 290 103 ans), développés sur des sédiments plus anciens. Le taux d’accumulation du carbone dans les podzols étudiés varie de 0,54 à 3,17 gC m-2 an-1, ce qui correspond à une séquestration de carbone de l’ordre de 3 1011 gC an-1, faibles à l’échelle annuelle, mais significative aux échelles géologiques.Les expérimentations de percolation en colonne nous ont permis de montrer la réactivité du Bh et la présence, malgré des rapports C/N très élevés (63 en moyenne), d’une activité bactérienne significative qui modifie la nature de la MOD qui le traverse. Cette dernière a la capacité de transporter Al et Fe sous forme de complexes organo-métalliques, complexes susceptibles de migrer à travers des matériaux très kaolinitiques. Ces résultats participent à la compréhension des transferts de MOD d’origine pédologique dans les nappes profondes.Dans l’hypothèse de l’apparition d’un climat à saisons contrastées, nous avons pu montrer qu’une durée sans pluie de 90 jours après disparition de la nappe perchée ne permettrait pas d’atteindre le point d’entrée d’air par assèchement des horizons superficiels. Néanmoins, dans l’hypothèse d’une entrée d’air, l’extrapolation des taux de minéralisation mesurés expérimentalement en conditions oxiques aboutit à une production de C atmosphérique de l’ordre de 2,0 1014 g de CO2 par an, ce qui peut impliquer une rétroaction positive du système climatique mondial. / Recent results have shown that equatorial podzols store large amounts of carbon in their deep Bh horizons. This leads to two main questions: (1) how and at what kinetics these soils were formed, (2) how climate change could induce atmospheric carbon production that could impact the global climate system.In this context, we have developed a model that allows to constrain carbon fluxes both by the observed C stocks and their 14C age. In a sufficiently simplified situation, we have established a formal relationship between the C stock evolution and its 14C age. Applied to Amazonian podzols, our model has brought new and unexpected results. It has been shown that the surface horizons of the most hydromorphic podzolized areas are the largest contributors of MOD transferred to the hydrographic network then to the sea. It is observed that the formation of Bh is only possible by considering two compartments, fast and slow. The estimate of their formation time (low estimate) allowed to differentiate between relatively young podzols (formation time 15 – 25 ky) developed on relatively recent Holocene sediments and old podzols (formation 180 – 290 ky) developed on older sediments. The carbon accumulation rate in the studied podzols ranges from 0.54 to 3.17 gC m-2 y-1, which corresponds to a carbon sequestration around 3 1011 gC an-1, which is significant at the geological scales.Column percolation experiments allowed us to show the reactivity of the Bh material and the presence, despite very high C/N ratios (63 on average), of a significant bacterial activity which modifies the nature of the MOD which percolates through it. This MOD has the capacity to transport Al and Fe in the form of complex organometallic complexes capable of migrating through very kaolinitic materials. These results contribute to the understanding of the transfers of pedologically formed MOD in the deep aquifers.Under the hypothesis of the appearance of a climate with contrasting seasons, we have been able to show that a 90-day period without rain after the disappearance of the perched water-table would not allow to reach the point of entry of air by drying of superficial horizons. Nevertheless, assuming an air entry, the extrapolation of the experimentally measured mineralization rates under oxic conditions results in a production of atmospheric C around 2.0 1014 g of CO2 per year, which may involve a positive feedback from the global climate system.

<p>The changes to the environment caused by anthropogenic climate change pose major challenges for energy production in the next century. Carbon Capture and Storage (CCS) is a group of technologies that would permit the continued use of carbon-intense fuels such as coal for energy production while avoiding further impact on the global climate system. The mechanism most often proposed for storage is injection of CO2 below the surface of the Earth in geological media, with the most promising option for CO2 reservoirs being deep saline aquifers (DSA's). Unlike oil and gas reservoirs, deep saline aquifers are poorly characterized and the variability in their properties is large enough to have a high impact on the overall physical and economic viability of CCS. Storage in saline aquifers is likely to be a very high-capacity resource, but its economic viability is almost unknown. We consider the impact of geological variability on the total viability of the CO2 storage system from several perspectives. First, we examine the theoretical range of costs of storage by coupling a physical and economic model of CO2 storage with a range of possible geological settings. With the relevant properties of rock extending over several orders of magnitude, it is not surprising that we find costs and storage potential ranging over several orders of magnitude. Second, we use georeferenced data to evaluate the spatial distribution of cost and capacity. When paired together to build a marginal abatement cost curve (MACC), this cost and capacity data indicates that low cost and high capacity are collocated; storage in these promising areas is likely to be quite viable but may not be available to all CO2 sources. However, when we continue to explore the impact of geological variability on realistic, commercial-scale site sizes by invoking capacity and pressure management constraints, we find that the distribution costs and footprints of these sites may be prohibitively high. The combination of issues with onshore storage in geological media leads us to begin to evaluate offshore storage potential. By considering the temperature and pressure regimes at the seafloor, we locate and quantify marine strata that has "self-sealing" properties, a storage option that we find is plentiful off the coasts of the United States. We conclude that further research into transport optimization that takes into account the true variation in geological media is necessary to determine the distribution of costs for carbon capture and storage to permit the full evaluation of CCS as a mitigation option.</p> / Dissertation

The efficiency of one fluid displacing another in permeable media depends greatly on the pore-scale dynamics at the main wetting front. Experiments have shown that the frontal dynamics can result in two different flow regimes: a stable and an unstable front. In stable displacements, any perturbation of the front will diminish with time and the effect of variation in permeability will be lessened. In contrast, in unstable displacements any perturbation of the front will grow with time and any variation in permeability will be magnified. In this dissertation, the stability of two different displacement processes are contemplated; a) vertical infiltration of dense liquid into dry sand from above and b) horizontal displacement of nanoparticle suspension with high pressure liquid CO₂. Significant insights are obtained by measuring the in-situ flow patterns in real time with a light transmission method and CT scanning. Vertical infiltration of dense fluid into dry sands from above is often observed to be unstable and produce gravity driven fingers. The formation of gravity fingers can have large consequences on the sweep efficiency of a displacement. Infiltration experiments showed that gravity driven fingers have a unique saturation profile known as saturation overshoot with a higher saturation at the finger tips than the saturation at the finger tail. Despite the vast number of theoretical and experimental investigations, conditions under which the front is unstable, remain unclear. To determine what controls the saturation overshoot and how it relates to the dynamics at the initial wetting front, saturation overshoot was measured as a function of flux for seven different liquids. These liquids gave a range of molecular weights, viscosities, and vapor pressures. It is found that for each fluid there is a flux (called overshoot flux) below which saturation overshoot ceases and the front is diffuse. The magnitude of the overshoot flux depends inversely on the invading fluid's viscosity and shows little or no dependence on the invading fluid's surface tension, vapor pressure, or miscibility with water. Since the saturation overshoot is not described by the continuum multi-phase flow models, the experimental results are used to develop a semi-continuum model that bridges the continuum-scale and pore-scale physics. The proposed model predicts the observed dependence of overshoot on media permeability and invading fluid properties. At the planned depth for CO₂ injection, either as an enhanced oil recovery technique or for CO₂ storage, CO₂ is typically less dense and less viscous than the in-situ fluid. Therefore, CO₂ injection is unstable and produces viscous fingers. This can greatly reduce the efficiency of a CO₂ flood or CO₂ storage capacity of an aquifer. To remedy this behavior, surface treated nanoparticles were used to reduce the mobility of injected CO₂. Displacement experiments were performed at low pressure with a CO₂ analogue (n-octane) fluid and at high pressure with liquid CO₂. Saturation distributions and pressure drops were measured in real time with the CT scanner when high pressure liquid CO₂ or n-octane was used to displace brine in different cores with and without suspended nanoparticles. In the presence of nanoparticles, the displacement front is more spatially uniform with a later breakthrough compared to the same experiment with no suspended nanoparticles. These observations suggest that nanoparticle stabilized foam, which forms during the displacement, acts to suppress the instability. It is argued that the generation of droplets occurs at the leading front of all drainage displacements. In the presence of nanoparticles, these droplets are preserved when nanoparticle adhere at the fluid-fluid interface. The new mechanism for foam generation described here, provides an interesting alternative for mobility control in CO₂ floods. Moreover, the same mechanism can potentially a) increase the CO₂ storage capacity of an aquifer, b) enhance the CO₂ capillary trapping, and c) provide an engineered barrier to CO₂ leakage from a storage sites, thereby alleviating the risk of contaminating the overlying fresh groundwater resources for CO₂ storage projects. / text