Thesis (M.S.)--Florida State University, 2006. / Advisor: Jeffrey Chanton, Florida State University, College of Arts and Sciences, Dept. of oceanography. Title and description from dissertation home page (viewed Sept. 26, 2006). Document formatted into pages; contains ix, 84 pages. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 149-154).

Submitted in fulfillment of the requirements of the degree of Masters of Engineering: Chemical Engineering, Durban University of Technology, Durban, South Africa, 2018. / The anaerobic process is increasingly becoming a subject for many as it reduces greenhouse gas emissions and recovers carbon dioxide energy as methane. Even though these benefits are attainable, proper control and design of the process variables has to be done in order to optimize the system productivity and improve stability. The aim of this research was to optimize methane and biogas yields on the anaerobic co-digestion of sewage sludge using bio-chemical substrates as co-substrates. The first objective was to find the bio-chemical substrate that will generate the highest biogas and methane yields. The anaerobic digestion of these substrates was operated using 6 L digesters at 37.5℃. The substrate which generated the highest biogas and methane yield in the first batch experiment was then used for the second batch test. The objective was to optimize the anaerobic conditions (substrate to inoculum ratio, co-substrate concentration and temperature) in-order to optimize the biogas and methane yields. The second batch test was achieved using the conventional One-Factor-At-A-Time (OFAT) and the Design of Experiment (DOE) methods. Final analysis showed that the bio-chemical substrates could be substrates of interest to biogas generators. Amongst the substrates tested in the first batch experiment glycerol (Oleo-Chemical Product waste) generated the highest methane and biogas yields of 0.71 and 0.93 L. (g volatile solids added)-1, respectively. It was believed that glycerol contains significant amount of other organic substances such as lipids that have higher energy content than the other bio-chemical substrates, thus generating larger biogas and methane yields. Moreover, digestion of sewage sludge alone produced biogas yields of 0.19 L /g VS and 0.33 L/g COD, and methane yields of 0.16 L/g VS and 0.28 L/g COD. Generally, co-digestion yields were higher than digestion yields of sewage alone. Using the OFAT method the results of the second batch test on glycerol demonstrated highest amounts of volatile solids (VS) reduction, chemical oxygen demand (COD) reduction, biogas yield and methane yield of 99.7%, 100%, 0.94 L (g VS added)-1 and 0.75 L (g VS added)-1 at a temperature, substrate to inoculum ratio and glycerol volume of 50℃, 1 (on VS basis) and 10 mL, respectively. Above 22 mL and substrate to inoculum ratio of 1, the process was inhibited. The DOE results suggested that the highest methane and biogas yields were 0.75 and 0.94 L (g VS added)-1, respectively. These results were similar to the OFAT results, thus the DOE software may be used to define the biogas and methane yields equations for glycerol. In conclusion, anaerobic co-digestion of bio-chemical substrates as co-substrates on sewage sludge was successfully applied to optimize methane and biogas yields. / M

No description available.

Albany thicket is prevalent in the Eastern Cape Province of South Africa. Its spread has diminished through overgrazing and heavy browsing by animals, land clearance and urban expansion. The result is highly degraded land characterized by invasion of alien species. There is a wealth of documented evidence on the high carbon sequestration ability of thicket biome, but not much has been done to assess its effect on carbon dioxide emissions from the soil. Given that the concentration of atmospheric greenhouse gases has been constantly rising since the industrial era, it is imperative to assess the influence of thicket biome as a source or sink of these gases. There is evidence of shifts in the climate in southern Africa as reflected by changes in rainfall patterns, increased temperatures, recurrent droughts and fires. As such, the historical rainfall variability in an Albany thicket region and its interaction with the temporal land use / cover changes was studied. This served to give some background information about the study area for more detailed study on C and carbon dioxide effluxes in thicket vegetation under different levels of degradation. This study thus aimed to determine the influence of thicket vegetation at various levels of degradation on soil carbon and carbon dioxide fluxes. The impact of plant photosynthetic pathway on soil C residence time and gas effluxes were analysed to elucidate on the land-use and cover patterns occurring in the area. All this was done to shed some light on the role of soil and thicket vegetation on carbon dioxide emissions and C storage in the spectrum of a shifting climate. The main area of research was Amakhala reserve in an Albany thicket in Eastern Cape Province; and it concentrated on three land cover types namely intact thicket, degraded thicket and grassland. The objectives mentioned above were achieved by assessing historical rainfall variability from 1970 to 2010 through trend and time series analysis at nine rainfall stations located at Amakhala reserve, Grahamstown, Bathurst, Port Alfred, Uitenhage and Port Elizabeth. The land use changes that have occurred in the Albany thicket region covering Amakhala reserve, Grahamstown, Bathurst and Port Alfred were also assessed for 1989, 1999 and 2009 through satellite image analysis with Idrisi Andes GIS software; then their interaction with rainfall variability were determined. To elucidate on the vegetation species composition and land use / cover changes that have occurred in the study area, plant biomass as well carbon (C) and nitrogen (N) isotope measurements were done. Plant biomass was assessed for the dominant species through use of pre-existing allometric equations that required data on plant basal diameter, canopy area, stem numbers and height. The plant carbon was then estimated through use of a conversion factor of 0.48 on above-ground biomass, while soil organic C was determined through the modified Walkely - Black method. Carbon and N isotope ratios were determined from the foliar material of three replicate samples of dominant plant species then analyzed through mass spectrometry. Soil carbon dioxide effluxes were then monitored in each of the intact thicket (IT), degraded thicket (DT) and grassland (G) over a 10 month period; by measuring the net carbon dioxide exchange rate (NCER) through the dynamic chamber method. An automated carbon dioxide exchange analyzer, coupled to a soil temperature probe and photosynthetic active radiation (PAR) sensor was used; with NCER measurements taken every 20-30 days. Soil temperature, moisture, penetration resistance and PAR readings were taken during each assay and later used to interpret the NCER. Results showed that long term variability in annual rainfall had a declining trend at Grahamstown (r = -0.59), Uitenhage and Bathurst stations (r = -0.32 at both stations), but was not significant at Amakhala, Port Alfred and Port Elizabeth stations. Most reductions in rainfall occurred in the 1980s and 1990s with the autumn, winter and summer rainfalls, the daily rainfall index and the daily rainfall subclasses of 10 mm and above showing a similar trend. The land use change detection gave a significant increase in proportion of degraded and transformed (moderately degraded) land between 1989 and 2009 with most of the increases occurring from 1989 to 1999, while farmland area decreased by 1.8 percent over the years. Thus the Albany region had over 30 percent of its land occupied by transformed vegetation, with heavy browsing and uncontrolled grazing being attributed to the destruction of pristine vegetation. Land-use change to game ranching and goat pastoralism was attributed to the reduction in farmland. Rainfall variability – land use change linkages were most significant in 1999 that recorded the least rainfall and had the lowest mean, maximum and sum of the NDVI. Grahamstown had the most significant rainfall-NDVI trends as it had the lowest NDVIs in 1999 when rainfall was lowest, the highest NDVI in 1989 when rainfall was highest and moderate NDVIs in 2009 when rainfall was moderate. Vegetation at the IT was characterized by a dense thicket with diverse growth forms of canopy trees, woody shrubs, succulent shrubs and ephemerals which mostly had the C3 type of pathway. This was in contrast with the IT soil isotopy that showed more positive C isotope ratios, indicating a switch between C3 and CAM photosynthesis in original vegetation. Most of the canopy trees had disappeared in the DT to be replaced by herbs, shrubs and grasses. As such, there was a huge difference in isotope ratios between DT plants and soils with the plants having mostly C3 metabolism while the soil showed a predominance of CAM plants in previous vegetation, indicating significant changes in land cover. The G site mostly comprised the grasses Themeda triandra and Panicum maximum and a few herbs. It maintained a dominance of C4 metabolism in both plants and soils showing very little change in species composition over the years. Because of the higher species diversity at IT, its soil organic C was quite high reaching levels of 3.4 percent (i.e. 3.4 t C / ha) in the top 10 cm then decreasing with depth (p < 0.001); but was moderate at DT (1.1-1.3 percent) and very low at G ( 0.5 percent C) (p < 0.001). In the same manner above-ground biomass was highest at IT i.e. 330 000 kg/ha; but was only 22 000 kg/ha in DT and as low as 6 700 kg/ha in G vegetation. High biomass at IT was mostly attributed to the succulent shrub Portulacaria afra and the canopy trees Euclea undulate, Rhus longispina and Schotia afra. This above-ground biomass translated to biomass C amounts of 158 000 kg/ha at IT, 10 600 kg/ha at DT and 3 200 kg/ha at G. Thus the IT had the highest while G the least and DT moderate plant and soil C sequestration ability. In all, the conversion of IT to DT led to a net loss of 147 000 Kg of biomass C / ha and 12 000kg less organic C / ha of land. Soil carbon dioxide effluxes were however variable between seasons as they were affected by differences in soil properties and seasonal weather patterns. High soil moisture levels (up to 16 percent gravimetric moisture) resulted in reduced soil penetration resistance (1 to 4 Kg/cm2) which raised effluxes at G and DT sites (up to 1.2 μmols m-2 sec-1) in winter, while low moisture (2 percent) resulted in hard dry soil (14 Kgm-2 penetration resistance) with suppressed CO2 effluxes in spring (0.2 μmols m-2 sec-1) especially in DT and G soils. Rising temperature generally caused accelerated gas emissions but only when moisture was not limiting (as was the case in IT). Thus the high summer temperatures (up to 40oC) gave lower effluxes especially in DT and G (< 1 μm-2sec-1) due to limited moisture supply (< 10 percent); while the Autumn period that had very high temperature (up to 48 oC) and good moisture (up to 16 percent) saw accelerated soil CO2 emissions (averaging 2 μmols m-2 sec-1) from all cover types. The high biomass and litter fall at IT served as ready substrate for soil respiration as long as moisture was not limiting and temperatures were favourable, while reduced cover at DT resulted in poor moisture conservation and creation of hard dry soils in spring and summer with reduced respiration. It was concluded that the DT had high CO2 effluxes in winter and reduced emissions in summer; while the opposite was true for the IT. All the cover types had minimal CO2 effluxes in spring and accelerated emissions in autumn. The grassland on the other hand was a fairly moderate source or sink of CO2 in most seasons compared with the other two covers. It was observed that an environment of good moisture and low-moderate temperatures (such as that in the winter) minimises effluxes while maintaining good plant productivity. It was concluded that thicket vegetation is a good sink of carbon that should be preserved in its natural condition to optimize its carbon sequestration potential. All three land covers served as sources or sinks of CO2 depending on soil and seasonal conditions. Thus high moisture and low penetration resistance generally increased effluxes of thicket ecosystems. The effect of increasing temperature on effluxes was only significant when moisture was not limiting. Conditions of good moisture and low-moderate temperatures gave reasonable amounts of effluxes while maintaining good plant productivity. Though the dry soil conditions significantly reduced effluxes in all land covers; they were not desirable since they decreased plant productivity and ultimately its C sequestration potential. Moreover, prolonged dry conditions only serve to exacerbate recovery of thicket plants as they increase mortality of canopy species in degraded and transformed areas in comparison with intact thicket.

Air pollution is a threat to the environment and human health. Freight trucking in particular is the main source of freight transportation emissions. Heavy-duty trucks emit large amounts of toxic air pollutants that cause serious diseases and harm public health. In addition, heavy-duty trucks emit great amounts of greenhouse gas (GHG), which is the leading cause of global warming. Despite increased environmental restrictions on air pollution and rising trucking greenhouse gas emissions in the past decades, no economic study has examined the potential GHG and air pollution reductions in the trucking sector and the associated private abatement costs to the industry. This study accounts for GHG emissions and toxic air pollutants in measuring and evaluating efficiency and productivity for the trucking industry in the 48 contiguous states. Moreover, the private costs of abatement to the industry were also estimated. When only GHG was incorporated in the production model, the results showed that each state could expand desirable output and reduce GHG by an average of 11 percent per year between 2000 and 2007. The Malmquist-Luenberger productivity indexes showed that omitting or ignoring GHG in trucking service production yielded biased estimates. On the other hand, due to increased environmental regulations, most of the toxic air pollutants decreased dramatically between 2002 and 2005. The analytical results showed that inefficiency decreased during this period. The private costs of abatement averaged $73 million per state in 2005. When GHG and six toxic air pollutants were incorporated in the production model, the estimated private abatement cost was $76 million per state, which was equivalent to 0.7 percent of the industry output in 2005.

Advanced power electronic techniques are crucial to enable high-performance energy conversion systems for the applications of various load and source interfaces, e.g., electric vehicle battery charger, solar power, wind power, motor traction, grid-connection. Also, the improvements on electrification for energy conversion contributes to the Carbon Neutrality with the reduction of fuel combustion. The control and design of the power conversion systems largely determine the efficiency, power density and system cost which typically need specialized design procedures. Since the types of interfaced energy sources may vary, the corresponding control algorithms and hardware configurations will be different. Thus, the power electronics system design is conventionally a specific routine based on the desired source and load requirements. Generally speaking, two main perspectives need to be considered when designing a power conversion system: (1) the power converter circuitry topology with the corresponding hardware components, e.g., low/high power circuits design, passive components design; (2) control algorithms and functions design, e.g., voltage/current control techniques, active/reactive power balancing and adjustment. However, the repetitive and specific power electronics design procedures for different load/source requirements are time-consuming and costly. This thesis proposes a software-defined power electronics concept to develop a generalized auto-converter module (ACM) by leveraging variable-frequency critical-soft-switching, model predictive control techniques and high-performance litz-PCB inductors. The software-defined power electronics techniques can be applied to various types of electrified load/source applications without the need of repetitive hardware components and software algorithms designing procedures. The fundamental unit for the generalized concept, auto-converter module, is a type of MPC-based power module. A hierarchical control architecture is designed to manage the local ACMs and satisfy different load/source energy conversion requirements with high efficiency, high power-density and high-reconfigurability. To achieve high-performance for the software-defined power electronics system, several advanced technologies are developed and integrated including variable-frequency critical-soft-switching, modular model predictive control, litz-PCB inductor design. Firstly, a variable-frequency critical-soft-switching technique is developed to adjust the switching frequency for the zero-voltage soft-switching. Doing so, the switching losses can be largely reduced with high efficiency. Secondly, the critical-soft-switching inductor is designed based on litz-PCB winding structure and neural network model to optimize the inductor losses and reduce the volume for the application of high frequency and large current ripple. Thirdly, a modular model predictive control method is designed for each of the local ACM to improve the dynamic performance and attenuate the oscillation caused by the variable frequency operation. Lastly, a hierarchical control architecture is developed to generalize the software-defined power electronics with multi-layer structure, central control layer, local module control layer and application layer. The hierarchical control architecture can be widely applied to different types of load/source interfaces, e.g., single/three-phase grid-connected inverters, motor traction inverter, battery charger, solar energy and so on. Leveraging the hierarchical control architecture and software-defined power electronics, the repetitive power converter hardware components and software algorithms design procedures can be simplified and standardized. Also, for different power converter applications, the efficiency and power density are both improved with better dynamic performance.

Dry Reforming of Methane (DRM) is a relatively new process technology that provides economic and environmental incentives for several industries that rely heavily on Hydrogen (H₂) and syngas (H₂ and Carbon Monoxide (CO)) utilization. The process utilizes Carbon Dioxide (CO₂) and Natural Gas, containing mainly Methane (CH₄), as a feedstock to produce H₂ and CO. Hydrogen intensive applications and syngas processing facilities benefit mostly by generating new revenue streams as well as achieving a reduced overall carbon footprint of their operations, since CH₄ and CO₂ are both powerful greenhouse gases. This process can be considered on a reactive basis to treat flue gases and emitted streams rich in CO₂, and it also can be a proactive approach to eliminating CO₂ emissions before they occur. The focus in this work is on the latter approach, where DRM, deposited on a low-pressure monolith, is being studied as a relatively new process to produce a pure H₂ gas stream (+99.9% purity) while maintaining carbon neutrality and prove its superiority to the dominating technology today; Steam Methane Reforming (SMR) which utilizes steam (H₂O) as a reactant instead of CO₂, and reacts with Natural Gas to produce H₂ and CO, however, they are accompanied by a large generation of CO₂ emissions. A comprehensive life cycle assessment (LCA) analysis was conducted to compare both technologies, DRM and SMR, and has demonstrated the feasibility of DRM in almost all environmental impact categories with a significant reduction in CO₂ equivalent emissions. This study assessed the performance of SMR and DRM in various indicators, including energy consumption, air emissions, global warming potential, water consumption, wastewater production, solid catalyst utilization and solid waste production. Although DRM requires higher energy in the reformer, its overall energy consumption is lower than SMR since steam generation needed is only roughly one third that of SMR. Harmful components released by DRM in air emissions are lower in all categories which reduces global warming potential to a large extent and in particular, CO₂ is reduced by approximately 61% when compared with SMR. Since SMR relies heavily on steam input and cooling purposes, water consumption and wastewater generation indicators are more adverse compared to DRM. This outcome acts as a strong driver to invest more in this research field and accelerate commercialization of this process technology. The research focus around DRM has been studied for over 20 years focusing on landfill gas (CO₂:CH₄ with a ratio of 0.8) and only few commercial testing facilities exist as of today due to major catalyst stability drawback, due to excess CH₄ causing coking issues. While most of the research body is considering DRM to process landfill gas, this research work has found out that by moving to a coke-free regime, the catalyst retains excellent initial stability properties. Thermodynamic analysis demonstrated that ratios of CO₂:CH₄ equal to and greater than 1.5, solid carbon no longer thermodynamically forms, and indeed, the experimental studies have confirmed the same conclusion evident by stable catalyst performance. Both Nickle (Ni) and Rhodium (Rh) in powder forms exhibited excellent activity and stability levels under a CO₂:CH₄ ratio of 1.5. This was the first and most important stepping stone in constructing a solid argument supporting DRM as a stable process with great potential for commercialization. This ratio is possible when separate sources of CO₂ and CH₄ are available and thus ratios can be adjusted unlike in landfills where CH₄ is always in excess. The work continued in performing several parametric experiments and screening multiple catalysts with different metal loadings. Three active metals were tested, Ni, Rh, and Ruthenium (Ru), and the results concluded that the most promising formulations are 10% Ni on Alumina (Al2O3) and 1% Rh on Al₂O₃. Those were further investigated in details for artificially aging by intentionally forming coke and successfully regenerated by steam gasification. The catalysts were coked and regenerated to essentially fresh activity. Commercial SMR is operated with a packed-bed reactor design and utilizing catalysts (most commonly Ni on alpha Al₂O₃.) in the form of pellets and rings, which lead to large pressure drops and ultimately large reactor design and increased energy requirements. To help overcome the design challenges, this research work has considered monolithic catalysts for testing and scale-up purposes. Monoliths, with their high open frontal areas and large geometric surface areas, overcome the challenges of high pressure drop, experienced in pellets, exhibit solid mechanical strength and provide large geometric surface areas of catalysts (washcoat) contact for reactions to take place, and hence, significantly reduce reactor sizes and eventually, overall capital and operating costs. The monolithic catalysts were prepared by washcoating 10% Ni and separately 1% Rh, both on gamma Al₂O₃. on their walls. The same parametric studies conducted for powders were tested for monolithic catalysts, and the results were positively surprising. Monolithic catalysts possessed extremely high activities, far better than all powders tested even at higher loadings. Moreover, their excellent stability results provide a possible road to a more compact reactor design. One conclusion; monolithic catalysts, or washcoated structured reactors as known in industry, are strong competitors that have the potential to deliver superior results when compared to packed-bed reactors. Therefore, this research is proposing the use of monolithic catalysts working under the favorable thermodynamic environment, as a potential solution to accelerate DRM advanced testing for H₂ production. To further support the thesis argument, a basic process design of the DRM was carried out to understand the various compositions of streams and the material and energy requirements for a feasible commercial plant. The design resembled very closely that of an SMR plant with the major difference in the main reactor, known as the “Reformer”. With this data on hand, a financial modelling was constructed to preliminarily prove the feasibility of this technology when compared to competitors in the market. Consequently, when compared to SMR with and without carbon capture (CC), DRM achieved relatively low H₂ prices in the range of 1.07-1.32 $/kg in the case of a Methanator design case and up to 1.91 $/kg for the CC design case, while SMR exceeded 2.1 $/kg for sustainable H₂ production; indicating that DRM, on preliminary basis, is a very profitable process technology. In conclusion, the laboratory research work combined with process design and financial feasibility, strongly supports the grounds of recommending DRM as a viable H2 production technology for a future pilot plant testing and advancement for commercialization. A more detailed engineering design and financial assessment would provide more accurate results after the successful pilot plant testing.

No description available.

In 1997 industrialized nations, the Third Conference of the Parties to the United Nations Framework Convention on Climate Change, met in Kyoto, Japan to sign a treaty (the “Kyoto Protocol”) in terms of which industrialized nations would be required to reduce their greenhouse gas emission by at least five percent below 1990 levels by the end of the “first commitment period” 2008-2012. South Africa is not regarded as an industrialized nation, but nonetheless acceded to the Kyoto Protocol in 2002. The literature reviewed in the present research reveals that, although idealistic, the Kyoto Protocol has been problematic. Fourteen meetings of the Conference of Parties to the Kyoto Protocol between 1997 and 2011 have achieved little more than to repeatedly defer and redefine Kyoto obligations. This research was undertaken to document the existing environmental taxation policies employed in selected international jurisdictions with a view to providing a framework for environmental tax policy formation in South Africa to assist this country in meeting its “greenhouse gas” emission targets, while at the same time promoting economic growth. A doctrinal research methodology was adopted in this study as it mainly analysed and interpreted legislation and policy documents and therefore the approach was qualitative in nature. An extensive literature survey was performed to document the various environmental policies that have been legislated in the selected jurisdictions. Comparisons were drawn with proposed tax policy measures for South Africa. The literature indicates that in the selected international jurisdictions carbon taxes achieved less-than-optimal results, largely due to political and industry-competitive agendas. With South Africa planning to introduce a carbon tax, it is submitted that the implementation of a carbon tax regime in isolation will be counter-productive, given South Africa’s economic profile. On the basis of the literature reviewed, it was concluded that South Africa should consider “recycling” carbon tax revenues within the economy to fund a broad-based tax incentive regime that will stimulate the change to non-carbon energy whilst promoting growth through sustainable development