Increases in atmospheric C have resulted in concerns about global warming and interest in finding means to sequester atmospheric C through land management strategies. The purpose of this study was to (i) compare changes in mineral soil C after a 30-year interval and (ii) examine the role of inorganic-N, soil texture, and topography in these changes. Soil samples were collected at permanently identified points on the Camp Branch Watershed, a second growth oak forest on the Cumberland Plateau in central Tennessee, in July of 1976 and archived. These points were re-sampled in July of 2006 and both archived and new samples of the 0 to 10 cm increment of the mineral soil were analyzed for C and N using the same procedures. Paired comparisons revealed changes in C and N were distinct to each of the 8 soil series. Comparison of 2006 samples to 1976 samples indicated changes in C concentration ranged from -13.1% to +12.0%. Changes in C mass ranged from -11.3% to +8.3%. Increases in C were most closely associated with increases in the C/total-N ratio. C was positively correlated to exchangeable inorganic-N in 1976 (r2 = 0.387) and 2006 (r2 = 0.107). Regression analysis revealed C increased with increasing azimuth and decreasing elevation in 1976 (r2 = 0.140). C was predicted only by clay content in 2006 (r2 = 0.079) and exhibited a negative relationship. Since topography was no longer a predictor of mineral soil C in 2006, we speculate that changes in forest cover also influenced changes in mineral soil C. / Master of Science

In the wake of concerns about the long-term integrity and containment of sub-surface CO₂ sequestration reservoirs, many efforts have been made to improve the monitoring, verification, and accounting methods for geo-sequestered CO₂. This Ph.D. project has been part of a larger U.S. Department of Energy (DOE) sponsored research project to demonstrate the feasibility of a system designed to tag CO₂ with radiocarbon at a concentration of one part per trillion, which is the ambient concentration of ¹⁴C in the modern atmosphere. Because carbon found at depth is naturally free of ¹⁴C, this tag would easily differentiate pre-existing carbon in the underground from anthropogenic, injected carbon and provide an excellent handle for monitoring its whereabouts in the subsurface. It also creates an excellent handle for adding up anthropogenic carbon inventories. Future inventories in effect count ¹⁴C atoms. Accordingly, we developed a ¹⁴C tagging system suitable for use at the part-per-trillion level. This tagging system uses small containers of tracer fluid of ¹⁴C enriched CO₂. The content of these containers is transferred into a CO₂ stream readied for underground injection in a controlled manner so as to tag it at the part-per-trillion level. These containers because of their shape are referred to in this document as tracer loops. The demonstration of the tracer injection involved three steps. First, a tracer loop filling station was designed and constructed featuring a novel membrane based gas exchanger, which degassed the fluid in the first step and then equilibrated the fluid with CO₂ at fixed pressure and fixed temperature. It was demonstrated that this approach could achieve uniform solutions and prevent the formation of bubbles and degassing downstream. The difference between measured and expected results of the CO₂ content in the tracer loop was below 1%. Second, a high-pressure flow loop was built for injecting, mixing, and sampling of the fast flowing stream of pressurized CO₂ tagged with our tracer. The laboratory scale evaluation demonstrated the accuracy and effectiveness of our tracer loops and injection system. The ¹⁴C/¹²C ratio we achieved in the high pressure flow loop was at the part per trillion level, and deviation between the experimental result and theoretical expectation was 6.1%. Third, a field test in Iceland successfully demonstrated a similar performance whereby ¹⁴CO₂ tracer could be injected in a controlled manner into a CO₂ stream at the part per trillion level over extended periods of time. The deviation between the experimental result and theoretical expectation was 7.1%. In addition the project considered a laser-based ¹⁴C detection system. However, the laser-based ¹⁴C detection system was shown to possess inadequate sensitivity for detecting ambient levels of ¹⁴CO₂. Alternative methods for detecting ¹⁴C, such as saturated cavity absorption ring down spectroscopy and scintillation counting may still be suitable. In summary, the project has defined the foundation of carbon-14 tagging for the monitoring, verification, and accounting of geological carbon sequestration.

In order to reduce the rate of climate change, particularly global warming, it is imperative that industries reduce their carbon dioxide (CO2) emissions. A promising solution of CO2 emission reduction is Carbon dioxide Capture and Storage (CCS) by sequestration, which involves isolating and extracting CO2 from the flue gases of various industrial processes, and thereafter burying the CO2 underground. The capture of CO2 proved to be the most challenging aspect of CCS. Thus, the objective of this research was to identify the most promising solution to capture CO2 from industrial processes. The study focussed on capturing CO2 emitted by coal power plants, coal-to-liquids (CTL) and gas-to-liquids (GTL) industries, which are common CO2 emitters in South Africa. This thesis consists firstly of an extensive literature review detailing the above mentioned processes, the modes of CO2 capture, and the various CO2 capture methods that are currently being investigated around the world, together with their benefits and drawbacks in terms of energy penalty, CO2 loading, absorption rate, capture efficiency, investment costs, and operating costs. Modelling, simulation, and pilot plant efforts are also described. The study reviewed many CO2 capture techniques including solvent absorption, sorbent capture, membrane usage, hydrate formation, and newly emerging capture techniques such as enzyme based systems, ionic liquids, low temperature cryogenics, CO2 anti-sublimation, artificial photosynthesis, integrated gasification steam cycle (IGSC), and chemical looping combustion The technique of solvent absorption was found to be the most promising for South African industries. Vapour-liquid-equilibrium (VLE) measurements of solvent absorption using amine blends were undertaken, using blends of methyl-diethanol amine (MDEA), diethanol amine (DEA) and water (H2O) with composition ratios of 25: 25: 50 wt% and 30: 20: 50 wt% respectively, and with CO2 and N2 gases at CO2 partial pressures of 0.5 to 10.5 bar. Experiments were conducted under system pressures of 5 to 15 bar and temperatures of 363.15 and 413.15 K, using a static analytic apparatus. CO2 liquid loading results were analysed and discussed. The experimental data were regressed in Matlab (R2009b) using the Posey-Tapperson-Rochelle model and the Deshmukh-Mather model. The Matlab programmes are presented along with the regressed binary interaction and model parameters. The accuracy of model predictions are discussed. Thereafter an Electrolyte-NRTL model regression and simulation of the absorption process was conducted using Aspen Plus V 7.1. for flue gas compositions, solvent compositions, temperature, and pressure conditions similar to that of process operating conditions. CO2 loading, design factors, CO2 recovery, and CO2 purity results were analysed and compared where appropriate, with experimental results. Finally a general preliminary energy efficiency and cost analysis was conducted based on the simulation results. The main conclusions reached are that the amine solvent blend containing 25:25:50 wt% of MDEA:DEA:H2O, produced higher CO2 loadings for its respective system conditions than other solvents studied and those found in literature. However, absorption of CO2 was found to be highly dependent on system temperature and pressure. The Deshmukh-Mather model provided higher accuracy than the Posey-Tapperson-Rochelle model, producing CO2 loading predictions with a relative error not exceeding 0.04%, in 1.5 to 3 minutes using a dual core processor. Aspen absorption simulations provided significantly lower CO2 loading results than those experimentally obtained, due to the low contact time achieved and higher temperature dependence in the proposed absorption process. Process improvements were highlighted and implemented to increase CO2 recovery and purity. Energy penalty values were found to be higher than those found in literature, but room for process and design improvement was identified and recommendations were given. Investment cost estimates were found to be justifiable and within reason. Limitations of the simulation were also identified and discussed. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Water management that alters riverine ecosystem processes has strongly influenced deltas and the people who depend on them, but a full accounting of the trade-offs is still emerging. Using palaeoecological data, we document a surprising biogeochemical consequence of water management in the Colorado River basin. Complete allocation and consumptive use of the river's flow has altered the downstream estuarine ecosystem, including the abundance and composition of the mollusc community, an important component in estuarine carbon cycling. In particular, population declines in the endemic Colorado delta clam, Mulinia coloradoensis, from 50-125 individuals m(-2) in the pre-dam era to three individualsm-2 today, have likely resulted in a reduction, on the order of 5900-15 000 tCyr(-1) (4.1-10.6 mol Cm-2 yr(-1)), in the net carbon emissions associated with molluscs. Although this reduction is large within the estuarine system, it is small in comparison with annual global carbon emissions. Nonetheless, this finding highlights the need for further research into the effects of dams, diversions and reservoirs on the biogeochemistry of deltas and estuaries worldwide, underscoring a present need for integrated water and carbon planning.

Doctor of Philosophy / Department of Agronomy / Ganga M. Hettiarachchi / Soil carbon (C) sequestration has been recognized as one of the most effective potential mitigation options for climate change. Underlying mechanisms of soil C sequestration/preservation is poorly understood, even after decades of soil C research. The main research objectives of this dissertation were three-fold: (1) enhancing our understanding in mineralogical and physicochemical mechanisms of soil C sequestration in microaggregates, (2) understanding the chemistry of organic C sequestered in soil aggregates, and (3) to determine the resilience of C to different temperature-moisture regimes and physical disturbance in a six-month incubation. An integrated approach was used in obtaining a better picture on mechanisms of C preservation. Two long-term agroecosystems located at the North Agronomy Farm, Manhattan, KS (Mollisols) and the Center of Experimentation and Research Fundacep in Cruz Alta-RS, Brazil (Oxisols) were used. Main plots of both systems were till and no-till. Mollisols consisted of three fertilizer treatments; control, manure/compost and urea. Oxisols had three different crop rotations; simple, intermediate, and complex. Submicron level information gathered by spectromicroscopy approaches, identified the direct preservation of OC structures with the original morphology; suggesting that the preservation of OC is a primary mechanism of C sequestration in these soils. Physical protection and organo-mineral associations seemed to also be involved in OC preservation. Manure/compost addition and no-till favored labile C preservation in aggregates of Mollisols. Significant associations observed between reactive minerals and C pools in Mollisols indicated the significance of organo-mineral associations in OC preservation. Large microaggregates exerted strong C preservation through physical protection and organo-mineral associations. Unlike in Mollisols, Oxisols showed a poor correlation between reactive mineral fraction and organic C which indicated the significance of physical protection over organo-mineral associations. Resilience of sequestred C was significantly affected by temperature across both temperate and tropical soil ecosystems, directly and indirectly. High temperature influenced soil acidity and reactive minerals, ultimately affecting organo-mineral associations. Macromolecular propeties of humic acid fraction showed changes after six months. Overall, direct and indirect evidence from this study suggested that the preservation of SOC is an ecosystem property supporting the newly proposed theories in soil C dynamics.

Soil organic carbon (SOC) is important not only for improving soil quality but also for contributing to climate change mitigation in agriculture. However, net greenhouse gas (GHG) balances, including methane (CH4) and nitrous oxide (N2O), need to be considered, as practices that increase SOC might increase GHG emissions. Sustainable use of soil resources needs to be assessed over long time periods and across spatial scales; biogeochemical models are useful tools to estimate GHG emissions and corresponding mitigation potentials. A process-based, ecosystem model DayCent that simulates soil carbon and nitrogen dynamics from diverse agroecosystems, has been applied to observe SOC sequestration, GHG emissions and yield in a contrasting climatic region UK and Bangladesh agriculture. The study mainly focus on determination of GHG mitigation potentials under improved management practices in rice based cropland Bangladesh. We hypothesized that alternative management would increase SOC and reduce net GHG emissions. As crop yield is the most important variable for Bangladesh, it was includes in the simulations. Since site test simulations under different management using the DayCent model were satisfactory, the model was used to simulate GHG covering 64 districts of Bangladesh, considering climate, soil and SOC content for the period 1996-2015. An integrated management scenario consisting of irrigation, tillage with residue management, reduced mineral nitrogen fertilizer and manure application increased annual SOC stocks, and offset net GHG emissions while maintaining yield. The model outcome suggests that the “4 per mille” target is feasible for Bangladesh. It is also possible to contribute to the GHG reduction target by 2030 set by policy makers.

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 100-106). / Climate change is a threat that could be mitigated by introducing new energy technologies into the electricity market that emit fewer greenhouse gas (GHG) emissions. We face many uncertainties that would affect the demand for each of these technologies in the future. The costs of these technologies decrease due to learning-by-doing as their capacity is built out. Given that we face uncertainties over future energy demands for particular technologies, and that costs reduce with experience, an important question that arises is whether policy makers should encourage early investments in technologies before they are economically competitive, so that they could be available in the future at lower cost should they be needed. If society benefits from early investments when future demands are uncertain, then there is an option value to investing today. This question of whether option values exist is investigated by focusing on Coal-fired Power Plants with Carbon Capture and Storage (CCS) as a case study of a new high-cost energy technology that has not yet been deployed at commercial scale. A decision analytic framework is applied to the MIT Emissions Prediction Policy Analysis (EPPA) model, a computable general equilibrium model that captures the feedback effects across different sectors of the economy, and measures the costs of meeting emissions targets. Three uncertainties are considered in constructing a decision framework: the future stringency of the US GHG emissions policy, the size of the US gas resource, and the cost of electricity from Coal with CCS. The decision modeled is whether to begin an annual investment schedule in Coal with CCS technology for 35 years. Each scenario in the decision framework is modeled in EPPA, and the output measure of welfare is used to compare the welfare loss to society of meeting the emissions target for each case. The decision framework is used to find which choice today, whether to invest in CCS or not, gives the smallest welfare cost and is therefore optimal for society. Sensitivity analysis on the probabilities of the three uncertainties is carried out to determine the conditions under which CCS investment is beneficial, and when it is not. The study finds that there are conditions, specified by ranges in probabilities for the uncertainties, where early investment in CCS does benefit society. The results of the decision analysis demonstrate that the benefits of CCS investment are realized in the latter part of the century, and so the resulting optimal decision depends on the choice of discount rate. The higher the rate, the smaller the benefit from investment until a threshold is reached where choosing to invest becomes the more costly decision. The decision of whether to invest is more sensitive to some uncertainties investigated than others. Specifically, the size of the US gas resource has the least impact, whereas the stringency of the future US GHG emissions policy has the greatest impact. This thesis presents a new framework for considering investments in energy technologies before they are economically competitive. If we can make educated assumptions as to the real probabilities we face, then extending this framework to technologies beyond CCS and expanding the decision analysis, would allow policymakers to induce investment in energy technologies that would enable us to meet our emissions targets at the lowest cost possible to society. / by Eleanor Charlotte Ereira. / S.M.in Technology and Policy

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 138-140). / Carbon capture and sequestration (CCS) technology has the potential to be a key CO2 emissions mitigation technology for the United States. Several CCS technology options are ready for immediate commercial-scale demonstration, but three obstacles to commercial deployment remain: the lack of a clear legal and regulatory framework for sequestration, the lack of a demonstration phase, and most importantly, the lack of a market for CCS. A successful demonstration phase will achieve the goal of technology readiness. The demonstration phase should be organized so as to share costs and risks between public and private actors. Project selection responsibility should be assigned to a dedicated private board and project management responsibility to private companies. This analysis recommends a combination of the Boucher Bill proposal for a CCS demonstration phase, as incorporated in the American Clean Energy and Security Act (ACES Act) of 2009, and a continuation of the DOE Clean Coal Power Initiative program. This combined approach can provide productive competition between public and private demonstration programs. Achieving technology readiness will not on its own lead to commercial deployment of CCS. Two additional policy objectives for the commercial deployment phase are considered: market penetration and cost reduction. Market penetration can be ensured through strong market pull policies, but this may be a very expensive policy approach in the long run. A more prudent goal is long-term cost reduction of CCS. Unlike the market penetration goal, the cost reduction goal will not guarantee that CCS will become a major contributor to carbon emissions mitigation, but it will provide a more cost-effective path. Achieving the cost reduction goal will require strong market pull policies for the short and medium term, together with a focus on technology push policies over the entire period. In the long term, market pull policies for CCS should be eliminated; if CCS is not economically competitive with alternative technologies, it should not be deployed on a significant scale. The ACES Act provides a good policy framework to achieve technology readiness through a demonstration phase and to pursue the long-term goal of cost reduction for commercial deployment of CCS technology. This approach will provide a cost-effective strategy for ensuring that CCS, a major scalable option for carbon emissions mitigation, is given the best chance of success in the long term. / by Michael Roberts Hamilton. / S.M.in Technology and Policy

The reduction and stabilization of atmospheric CO2 concentration is currently one of the most challenging problems being investigated. Carbon mineralization has recently received much attention as one of the most promising options for CO2 sequestration. The engineered weathering of silicate minerals as a means of permanent carbon storage has unique advantages such as the abundance of naturally occurring calcium and magnesium-bearing minerals and the formation of environmentally-benign and geologically stable solids via a thermodynamically favored carbonation reaction. However, several challenges need to be overcome to successfully deploy carbon mineralization on a large-scale. The current limitation of the carbon mineralization scheme for permanent storage of anthropogenic CO2 is the slow reaction kinetics, since the natural weathering of silicate minerals occurs on geological time-scales. Another problem of mineral carbonation is that the cost of the carbon mineralization process for sequestration is dominated by up front energy costs during the mineral processing and carbonation. In this study, chemically enhanced mineral dissolution via various chelating agents was investigated to accelerate the overall reaction rate of ex-situ and in-situ mineral carbonation. To reduce the overall cost of the carbon mineralization process, the utilization of solid products as value-added materials, e.g. precipitated magnesium carbonates (PMC) and precipitated calcium carbonates (PCC), was studied. Wollastonite (CaSiO3) and antigorite, which is a kind of serpentine (Mg3(OH)4(Si3O5)) group minerals, were selected for this work. They are representative of calcium silicate minerals and magnesium silicate minerals, respectively. This work starts with development of an experimental framework for the systematic investigation of mineral dissolution and carbonation behaviors with mineral pre-processing considerations (e.g., the removal of fines (< 5 μm) to standardize the reaction surface of the minerals), experimental set-up (e.g., syringe pump reactor for the investigation of mineral dissolution and high temperature, high pressure batch reactor for the study of direct aqueous mineral carbonation) and post reaction analyses (e.g., the evaluation of various carbon analysis techniques for the accurate estimation of the extent of carbon mineralization). Accelerated wollastonite weathering is experimentally studied first. For large scale carbon mineralization, generally Mg-bearing silicate minerals such as serpentine or olivine (Mg2SiO4) are the most suitable minerals due to not only their significant abundance in nature but also their high capacity. New York State, however, has one of the largest deposits of wollastonite in the United States and is considered to be a suitable place to adapt CO2 mineralization using Ca-bearing minerals as a CO2 storage option. Moreover, the technologies developed for enhancing carbonation of Ca-bearing minerals can also be applied to the industrial wastes with similar chemistry, such as steel slag and cement kiln dust. The effect of various types of chelating agents on the dissolution rate of wollastonite minerals is explored to accelerate its weathering rate. It is found that chelating agents such as acetic acid and gluconic acid can significantly improve the dissolution kinetics of wollastonite even at a much diluted concentration of 0.006 M by complexing with calcium in the mineral matrix. Calcium extracted from wollastonite is then reacted with a carbonate solution to form PCC, and the study shows that by controlling the reaction temperature, the morphological structure of the synthesized PCC can be tuned for various applications (i.e., paper fillers, plastic fillers and construction materials). Microbial and chemical enhancement of ex-situ and in-situ antigorite carbonation is investigated as well as synthesis of PMC to mimic commercially available CaCO3-based filler materials. The effect of various chelating agents, including volatile fatty acids produced via anaerobic digestion of food waste, on antigorite dissolution is investigated in a syringe pump reactor. It is found that oxalate performs best among over fifteen kinds of chelating agents on accelerating dissolution rate of antigorite minerals. Among the volatile fatty acids, valerate works best on antigorite dissolution followed by acetate. The concentration of valerate, however, is very low in the produced mixture of volatile fatty acids via anaerobic digestion. On the other hand, acetate is the dominant component in the mixture, so it is considered as the most valuable product of anaerobic digestion of food waste. Magnesium extracted from antigorite is then reacted with carbonates to form precipitated magnesium carbonates. The effects of various chelating agents, reaction time, reaction temperature and pH on the mean particle size, particle size distribution, composition, and particle morphological structures of precipitated magnesium carbonates are systematically studied. Finally, the effect of volatile fatty acids on direct aqueous mineral carbonation is studied in a high temperature, high pressure batch reactor with antigorite and olivine minerals to predict the effect of volatile fatty acids on in-situ mineral carbonation. Volatile fatty acids can enhance the overall reaction rate via direct aqueous mineral carbonation route slightly. Volatile fatty acids may be not good enough for accelerating ex-situ direct aqueous mineral carbonation. However, they may be suited to in-situ mineral carbonation, which takes years.

To sustain future population and economic growth, the global energy supply is expected to increase by 60% by 2040, but the associated CO₂ emissions are a major concern. Converting CO2 into a commodity through a CO₂-neutral process has the potential to create a sustainable carbon energy economy; however, the high stability of CO₂ requires the discovery of active, selective and stable catalysts. To initially probe the performance of catalysts for CO₂ reduction, CO₂ is activated with H₂, which produces CO and CH₄ as the primary products. For this study, CO is desired for its ability to be used in the Fischer-Tropsch process, while CH₄ is undesired because of its low volumetric energy density and abundance. Precious bimetallic catalysts synthesized on a reducible support (CeO₂) show higher activity than on an irreducible support (γ-Al₂O₃) and the selectivity, represented as CO:CH₄ ratio, is correlated to electronic properties of the supported catalysts with the surface d-band center value of the metal component. Because the high cost of precious metals is unsuitable for a large-scale CO₂ conversion process, further catalyst development for CO₂ reduction focuses on active, selective and low-cost materials. Molybdenum carbide (Mo₂C) outperforms precious bimetallic catalysts and is highly active and selective for CO₂ conversion to CO. These results are further extended to other transition metal carbides (TMCs), which are found to be a class of promising catalysts and their activity is correlated with oxygen binding energy (OBE) and reducibility as shown by density functional theory (DFT) calculations and in-situ measurements. Because TMCs are made from much more abundant elements than precious metals, the catalysts can be manufactured at a much lower cost, which is critical for achieving a substantial reduction of CO₂ levels. In the aforementioned examples, sustainable CO₂ reduction requires renewable H₂, 95% of which is currently produced from hydrocarbon based-feedstocks, resulting in CO₂ emissions as a byproduct. Alternatively, CO₂ can be reduced with ethane from shale gas, which produces either synthesis gas (CO + H₂) or ethylene with high selectivity. Pt/CeO₂ is a promising catalyst to produce synthesis gas, while Mo₂C based materials preserve the C-C bond of ethane to produce ethylene. Ethylene and higher olefins are desirable for their high demand as commodity chemicals; therefore, future studies into CO₂ reduction must identify new low-cost materials that are active and stable with higher selectivity toward the production of light olefins.