The use of hydroxyl radical based reaction (Fenton reaction) for the destruction of organic pollutants has been widely reported in the literature. However, the low pH requirement and rapid hydrogen peroxide consumption rate make the application of conventional Fenton reaction difficult for in-situ treatment. In this study, we conducted a modified Fenton reaction by introducing a chelating agent into the reaction system that could prevent Fe(OH)3 (s) precipitation even at a neutral pH condition and reduce the H2O2 consumption rate by controlling the Fe2+ concentration. A chelating agent (mono-chelate or poly-chelate) combines with Fe2+ or Fe3+ to form stable metal-chelate complexes in solution. This decreases the concentration of Fe2+ in the solution so that reactions can be carried for longer contact times. Experimental results (citrate was the chelating agent) for 2,4,6-trichlorophenol (TCP) showed that TCP degradations were greater than 95% after 2.5 h and 24 h reaction times at fixed pH 5 and 6, respectively. For the same reaction time, the normalized chloride formations were 85% at pH 5 and 88% at pH 6. Several other chlorinated organic compounds were also chosen as the model compounds for detoxification studies because of their chemical structures: trichloroethylene (unsaturated hydrocarbon), carbon tetrachloride (highly oxidized compound), 2,2-dichlorobiphenyl, and biphenyl (a dual-aromatic ring structure). Poly-chelating agents (such as polyacrylic acid-PAA) provide multiple Fe2+/Fe3+ binding sites in the modified Fenton reaction for the oxidation of contaminants (2,2-dichlorobiphenyl, and biphenyl) at a neutral pH environment. Numerical simulation based on the kinetic model developed from the well known Fenton reaction and iron-chelate chemistry fits experiment data well for both standard and chelate modified Fenton reactions. In this dissertation, it was proven that both monomeric (citrate) and polymeric (PAA) chelate modified Fenton reactions were effective for dechlorination of carbon tetrachloride from aqueous phase by the superoxide radical anion. On the other hand, PAA (a poly-chelating agent) can also be used for solid surface modification by polymerization of acrylic acid (monomer). The successful degradations of biphenyl and trichloroethylene by the PAA functionalized silica particles/membrane demonstrate the versatile applications of the chelate modified Fenton reaction.

The road transportation is a big source for the release of NOx emissions. NOx has been confirmed to cause negative affect on the air-quality especially in the urban areas, there are therefore regulations for allowed released amount from vehicles. The most adopted technology used for the reduction of these NOx emissions from the diesel exhaust gas is the ammonium selective catalytic reduction (NH3-SCR) using a Cu-zeolite as the catalyst in the system. The SCR catalyst can be deactivated through different mechanism, whereas poisoning by sulfur has been documented to be an important factor for the deactivation. The degree of deactivation of the catalyst has been suggested to vary depending on the catalytic material and which sulfur conditions the catalyst is exposed to, where SO3 has been indicated to cause more sever deactivation compared to SO2.  The aim of this project has been to investigate the deactivation mechanism of Cu-zeolites at different SOx conditions and evaluate potential regeneration mechanism. The project was carried out by evaluating the catalysts, Cu-BEA and Cu-SSZ-13, over different reactions that occurs in the SCR system, investigating the deactivation effect caused by SO2 poisoning and the regeneration potential. The project was then continued with the focus on the Cu-SSZ-13 catalyst investigating different SOx poisoning and regeneration conditions were investigated. In order to investigate the SO3 poisoning a generator using oxidation of SO2 to SO3 was successfully build during this project.  A kinetic model over the Cu-SSZ-13 NH3-SCR reactions was also built based on literature studies and the experimental data obtained. The results from the sulfur poisoning of Cu-BEA are based on the master thesis by Maria Arvanitidou. The fresh samples Cu-Beta and Cu-SSZ-13 exhibited similar activity, with the exception of the high formation of N2O observed over Cu-Beta under SCR conditions. The SO2 causes deactivation, especially at low temperatures. Cu-SSZ-13 exhibited more loss in activity but was able to recover more through the elevated SCR regeneration steps than the Cu-Beta. When SO2 exposure was performed together with NH3, larger deactivation was observed, likely due to ammonium sulfate species formed on the surface. The ammonium sulfate species were less thermally stable than copper sulfates, making it easier to recover the loss of activity in the Cu-SSZ-13. SO3 caused a much more sever deactivation of the SCR reactions than that of the SO2 poisoning and continued to show the lowest NOx removal activity after the regeneration process.  A difference in initial deactivation and recovery of activity between standard and fast SCR reactions was observed, indicating that the different mechanisms used are affected differently by the poisoning. The kinetic model for NH3-SCR over the Cu-SSZ-13 was successfully created when compared to the experimentally obtained data.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The piggery for many years was characterized as a waste-generating activity of high polluter, but in recent decades many studies are responsible for changing this concept. The use of biodigester is well disseminated to lessen the impacts generated by this activity, gaining encouragement deployment in recent years, by encouraging the use of renewable energy. The biodigester is responsible for the production of biogas used as alternative energy on farms that have the digesters system. We observed few studies that investigate the geometry of the digesters and its effects on anaerobic digestion process. This work aimed to study the partitioning of the Canadian model digester anaerobic digestion of swine waste applied to evaluating the degradation (removal) of the physic-chemical parameters (temperature, pH, COD, BOD5, total nitrogen, total phosphorus, total solids, total fixed solids and total volatile solids), and determining a kinetic model describing the biogas produced in each of the compartments of the digesters. For the study were built three reactors in bench scale: the first with a partitioning which caused variation of the horizontal flow, the second with partitioning which flux change generated in the vertical and third, without fragmentation, to be used as a reactor testimony. The analyzes of the physicchemical parameters were made according to Standard Methods for the Examination of Water and Wastewater, since the determination of the kinetic model was done considering the existence of a plug flow (tubular reactor) to each of the reactors constructed and to qualification of biogas was use a gas chromatograph. On the analysis of physic-chemical was second reactor (flow variation vertically) that showed that showed a significant difference in the efficiency of COD removal and pH values, and this reactor also showed better removal of solids and BOD5. Already temperature, showed similar behavior in the three reactors, characterizing the anaerobic digestion occurred primarily in the mesophilic range. Considering the BOD5 as a substrate was obtained as rate constant 0.021 d-1, 0.025 d-1 and 0.024 d-1, respectively for the first, second and third reactor. However, considering the COD as a substrate was obtained 0.032 d-1, and 0.034 d-1, 0.027 d-1 for each of the reactors. Kinetic models had a higher correlation with the experimental data when considering the COD as substrate, and was the second reactor with the highest correlation (R2 = 0.599). In the evaluation of biogas the three reactors not showed difference between them. / A atividade suinícola por muitos anos foi caracterizada como uma atividade geradora de resíduos de alto índice poluidor, porém nas últimas décadas muitos são os estudos responsáveis por mudar esse conceito. O uso de biodigestor está bem disseminado para diminuir os impactos gerados por essa atividade, ganhando estímulo de implantação nos últimos anos, pelo incentivo ao uso de energia renovável. O biodigestor é responsável pela produção do biogás, usado como energia alternativa em propriedades rurais que possuem o sistema de biodigestores. Observam-se poucos trabalhos que pesquisam a geometria dos biodigestores e seus efeitos no processo de digestão anaeróbia. Esse trabalho objetivou o estudo da compartimentação do biodigestor modelo canadense no processo de digestão anaeróbia aplicada a resíduos da suinocultura, avaliando a degradação (remoção) dos parâmetros físico-químicos (temperatura, pH, DQO, DBO5, Nitrogênio total, Fósforo total, sólidos totais, sólidos fixos totais e sólidos voláteis totais), determinando um modelo cinético e qualificando o biogás produzido em cada um dos compartimentos dos biodigestores. Para o estudo foram construídos três reatores em escala de bancada: o primeiro com uma compartimentação que provocava variação de fluxo na horizontal, o segundo com uma compartimentação, a qual gerava variação de fluxo na vertical e o terceiro, sem compartimentação, para ser utilizado como um reator testemunho. As análises dos parâmetros físicoquímicos foram realizadas de acordo com o Standard Methods for Examination of Water and Wastewater, já a determinação do modelo cinético foi realizada considerando a existência de um fluxo pistão (reator tubular) para cada um dos reatores construídos e para a qualificação do biogás utilizou-se um cromatógrafo a gás. Quanto à avaliação dos parâmetros físico químicos, foi o segundo reator (variação de fluxo na vertical) que apresentou diferença significativa na eficiência de remoção de DQO e nos valores de pH, sendo que esse reator também apresentou melhor remoção de DBO5 e sólidos. A temperatura apresentou comportamento semelhante nos três reatores, caracterizando que a digestão anaeróbia ocorreu prioritariamente na faixa mesofílica. Considerando a DBO5 como substrato obteve-se como constante de velocidade 0,021 d-1; 0,025 d-1 e 0,024 d-1, respectivamente para o primeiro, segundo e terceiro reator. Todavia, considerando a DQO como substrato obteve-se 0,032 d-1; 0,034 d-1 e 0,027 d-1 para cada um dos reatores. Os modelos cinéticos apresentaram uma maior correlação com os dados experimentais quando considerada a DQO como substrato, sendo que foi o segundo reator que apresentou maior correlação (R2 = 0,599). Na avaliação do biogás os três reatores não apresentaram diferença entre si.

A pesquisa propôs avaliar o desempenho e o comportamento de reatores seqüenciais em batelada com biomassa suspensa e imobilizada, em escala de bancada, na remoção de compostos de nitrogênio. Tais sistemas foram testados como tratamento complementar de reatores sulfetogênico e metanogênico utilizados no tratamento de água residuária industrial com alta concentração de sulfato e amônia. Visou o desenvolvimento de uma estratégia de operação que viabilizasse o uso dos próprios constituintes da água residuária para a maximização da eficiência do tratamento. O estudo foi dividido em 3 etapas principais. Na etapa 1 (181 dias de operação), o reator com biomassa suspensa foi mantido com 4 fases alternadas aeróbio/anóxico e ciclo de 24 horas, e verificou-se a presença da desnitrificação endógena (eficiência de remoção de nitrogênio de 65 \'+ OU -\' 27%). Para a etapa 2 (127 dias de operação), o reator de biomassa suspensa foi submetido ao tempo de ciclo de 12 horas, com uma fase aeróbia (6 horas) e com posterior fase anóxica (6 horas). Nessa etapa adicionou-se efluentes dos reatores metanogênico e sulfetogênico, ricos em ácidos voláteis (ácido acético), com intuito de acelerar o processo desnitrificante. Os resultados obtidos foram baixos em termos de remoção de nitrogênio (42 \'+ OU -\' 21%). Para a etapa 3 (134 dias de operação), foram ensaiados vários meios suportes, através de técnica de microsensores de oxigênio dissolvido, a fim de verificar a formação de biofilme específico (nitrificante/desnitrificante) e optou-se pelo uso do carvão mineral no reator com biomassa imobilizada. Nesta última etapa, foi mantida a estratégia operacional adotada na etapa 2 (ciclo 12 horas), bem como a adição de parcela do afluente na fase anóxica. A remoção de nitrogênio, com períodos aeróbio e anóxico e ciclo de 12 horas, mostrou-se viável no reator com biomassa imobilizada (eficiência de remoção de nitrogênio de 72 \'+ OU -\' 13%). Ao final dos ensaios experimentais, realizaram-se modelagens cinéticas que permitiram a compreensão dos processos convencionais e não convencionais ocorridos nas várias etapas para remoção de nitrogênio, tais como desnitrificação em fase aeróbia e o processo ANAMMOX. / The purpose of this research was to evaluate the performance and the behavior of sequential batch reactors with suspended and immobilized biomass, in benches scale, for the nitrogen composite removal. Such systems had been tested as sulphetogenic and methanogenic reactors complementary treatment, used in an industrial waste water treatment with high sulphate and ammonia concentrations. The research aimed for the development of an operation strategy that could make possible the use of the proper waste water constituent for the improvement of the treatment efficiency. The study was divided into 3 main stages. In stage 1 (181 days of operation), the reactor with suspended biomass was kept with 4 alternating phases aerobic/anoxic and a 24-hour cycle was used, and the endogenous denitrification was verified (nitrogen removal efficiency of 65 \'+ OU -\' 27%). For stage 2 (127 days of operation), the suspended biomass reactor was submitted to a cycle of 12 hours, with an aerobic phase (6 hours) and posterior anoxic phase (6 hours). In this stage effluent of the methanogenic and sulphetogenic reactors, rich in volatile acid (acetic acid), was added to accelerate the denitrify process. The achieved results had been low in terms of nitrogen removal(42 \'+ OU -\' 21%). For stage 3 (134 days of operation), some supports media was tested through dissolved oxygen microsensors technique, in order to check the specific biofilm formation (nitrificant/denitrificant) and the mineral coal was opted to be used in the immobilized biomass reactor. In this last stage it was adopted an operational strategy similar in stage 2 (12 hours cycle), as well as the addition of part of the affluent in the anoxic phase. The nitrogen removal, with aerobic and anoxic periods and 12 hours cycle, revealed feasible in the reactor with immobilized biomass (nitrogen removal efficiency of 72 \'+ OU -\' 13%). In the end of the experimental tests, kinetic modelings were done and had allowed the understanding of conventional and not conventional processes occurred in the stages for nitrogen removal, such as desnitrification in aerobic phase and ANAMMOX process.

This research investigated life cycle environmental impacts and benefits of an integrated microalgae system with wastewater treatment system using an integrated process modeling approach combined with experimentation. The overall goal of this research is to understand energy, carbon and nutrient balances in the integrated system and to evaluate the environmental impacts and benefits of the integrated system from a carbon, nutrient, and energy perspective. In this study, four major research tasks were designed to contribute to a comprehensive understanding of the environmental and economic sustainability of the integrated system, which included development of an integrated co-limitation kinetic model for microalgae growth (Chapter 2), kinetic parameter estimation models for anaerobic co-digestion (Chapter 3), development of an integrated process model (Chapter 4), and life cycle environmental and economic assessments of the integrated system (Chapter 5). The integrated co-limitation kinetic model was developed to understand microalgae growth in the centrate from dewatering of anaerobically digested sludge. This growth kinetic model considered four major growth factors, including Nitrogen (N), dissolved carbon dioxide (CO2) concentrations, light intensity, and temperature. The model framework was constructed by combining threshold and multiplicative structures to explain co-limitation among these factors. The model was calibrated and validated using batch studies with anaerobically digested municipal sludge centrate as wastewater source, and the model was shown to have a reasonable growth rate predictor for Chlorella sp. under different nutrient levels of the centrate. Anaerobic co-digestion was used for energy conversion process in the integrated system. To estimate methane production of anaerobic co-digestion, kinetic models commonly applied. To apply the kinetic model, determining kinetic parameters for anaerobic co-digestion of microalgae and waste activated sludge (WAS) is essential, and this research introduced two potential regression-based parameter estimation models to estimate the kinetic parameters. Using the estimation models presented, the kinetic parameters for co-digestion was able to be determined for different ratios of co-substrates with limited experiments. In this research, the integrated process model was developed to simulate the dynamic behavior of the integrated system. The model included the microalgae cultivation, harvesting, and anaerobic co-digestion processes in the integrated system to provide a comprehensive understanding of the integrated system. For cultivation, the integrated co-limitation kinetic model was applied to estimate microalgae productivity, while the regression-based parameter estimation model was used to determine the first order kinetic parameter to estimate methane production rates for anaerobic co-digestion. The simulated microalgae productivity results were comparable to typical microalgae productivity in open pond systems. For the integrated system, removal of NH4-N by microalgae was not efficient. In particular, the NH4-N removal was minimal during the winter season due to low microalgae growth. As the microalgae productivity increased, the CH4 and biosolids production increased as a result of the increased amount of the substrates from the harvested microalgae biomass. The increase of CH4 and biosolids productions, however, was minor because of the small amount of microalgae biomass for the co-digestion. Based on simulated data for integrated process modeling, the life cycle environmental and economic impacts of the integrated system (with different CO2 supply areas) were evaluated and compared to the conventional wastewater treatment system. The integrated systems had a lower carbon footprint, cumulative energy demand, and life cycle cost than the conventional system. The integrated system with 10% CO2 sparging area was able to achieve the lowest carbon footprint. Without CO2 addition during microalgae cultivation, the integrated system had the lowest energy balance and life cycle cost. However, there is no significant difference between the integrated and conventional systems for eutrophication potential because these systems had the same effluent quality. In terms of an energy saving with the integrated systems, the benefit of energy reduction for the wastewater treatment was greater than the energy production from the anaerobic co-digestion, compared to the conventional system. Overall, the integrated system can improve the carbon balance by reducing the life cycle energy required in the conventional system.

Nitrogen-alloyed austenitic stainless steels are becoming increasingly popular, mainly due to their excellent combination of strength and toughness. Nitrogen desorption to the atmosphere during the autogenous welding of these steels is often a major problem, resulting in porosity and nitrogen losses from the weld. In order to counteract this problem, the addition of nitrogen to the shielding gas has been proposed. This study deals with the absorption and desorption of nitrogen during the autogenous arc welding of a number of experimental stainless steels. These steels are similar in composition to type 310 stainless steel, but with varying levels of nitrogen and sulphur. The project investigated the influence of the base metal nitrogen content, the nitrogen partial pressure in the shielding gas and the weld surface active element concentration on the nitrogen content of autogenous welds. The results confirm that Sievert's law is not obeyed during welding. The weld nitrogen content increases with an increase in the shielding gas nitrogen content at low nitrogen partial pressures, but at higher partial pressures a dynamic equilibrium is created where the amount of nitrogen absorbed by the weld metal is balanced by the amount of nitrogen evolved from the weld pool. In alloys with low sulphur contents, this steady-state nitrogen content is not influenced to any significant extent by the base metal nitrogen content, but in high sulphur alloys, an increase in the initial nitrogen concentration results in higher weld nitrogen contents over the entire range of nitrogen partial pressures evaluated. A kinetic model can be used to describe nitrogen absorption and desorption during welding. The nitrogen desorption rate constant decreases with an increase in the sulphur concentration. This is consistent with a site blockage model, where surface active elements occupy a fraction of the available surface sites. The absorption rate constant is, however, not a strong function of the surface active element concentration. Alloys with higher base metal nitrogen contents require increased levels of supersaturation prior to the onset of nitrogen evolution as bubbles. These increased levels of supersaturation for the higher-nitrogen alloys is probably related to the higher rate of nitrogen removal as N2 the onset of bubble formation. Given that nitrogen bubble formation and detachment require nucleation and growth, it is assumed that a higher nitrogen removal rate would require a higher degree of supersaturation. Nitrogen losses from nitrogen-alloyed stainless steels can be expected during welding in pure argon shielding gas. Small amounts of nitrogen can be added to the shielding gas to counteract this effect, but this should be done with care to avoid bubble formation. Supersaturation before bubble formation does, however, extend the range of shielding gas compositions which can be used. Due to the lower desorption rates associated with higher surface active element concentrations, these elements have a beneficial influence during the welding of high nitrogen stainless steels. Although higher sulphur contents may not be viable in practice, small amounts of oxygen added to the shielding gas during welding will have a similar effect. / Dissertation (PHD)--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / unrestricted

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<p>This dissertation describes an investigation into the free radical batch polymerization of methyl methacrylate to high conversion. The overall objective was to develop a kinetic model to accurately predict conversion and molecular weight distribution for the polymerization. The dissertation is divided into three self-contained parts.</p> <p>Part I describes the development and testing of the kinetic model. New gel permeation chromatograph (GPC) data interpretation methods (developed in Part I I), the free volume concept of diffusion theory, and newly obtained isothermal kinetic data, are combined with computer implemented optimization techniques, to show that classical kinetics apply to high conversions.</p> <p>Part II details the development of three new GPC interpretation techniques. The two most recent are evaluated in Part I.</p> <p>The third has been used by other workers. Other interpretation methods are also evaluated and discussed. Part I I I describes the development of a high shear concentric cylinder viscometer and its use with Newtonian standards. This is a prelude to future studies in polymer rheology and polymerization under shear conditions.</p> / Doctor of Philosophy (PhD)

Fuel comprised of thorium has been explored since the early development of nuclear energy in the 1960s. In the last decade, there has been a renewed interest in thorium fuel and it has now become a primary focus in studies and proposed in next-generation nuclear reactors. This has been prompted by a limited supply of uranium in the foreseeable future and an abundance of thorium resources. Additionally, when compared to natural uranium (NU), thoria (ThO$_2$) produces substantially less long-lived radioactive waste and the fissile content can be reprocessed for additional fuel cycles. The CANDU 6 reactor has a unique ability to harvest thorium fuels because of its superior neutron economy. Thorium requires a driving isotope to sustain neutron fission until the long absorption chain produces viable amounts of U-233. Previous studies have investigated many different practical fissile isotopes and core modeling techniques that would make thorium feasible in a CANDU 6 reactor. This thesis focuses on a safety evaluation of thorium fuel compared to NU fuel in a lattice cell and full core configuration. \\ DRAGON 3.06 and SERPENT 2 are used to examine the infinite lattice cell containing NU and homogeneous thorium fuel enriched with 2.0\% U-235, emphasizing the relationship between multiple nuclear libraries. This configuration is used to determine the enrichment concentration, temperature coefficient, coolant void reactivity, and the power relationship. Thorium fuel exhibits a higher negative temperature coefficient, a lower coolant void reactivity, and a greater reactivity change when simulated at different powers. If the lattice cell is simulated at 75\% nominal power there is an 11 mk adjustment for thorium fuel, whereas the adjustment is only three mk for NU fuel. This is related to the extensive cross section of Th-232 and the long fertile absorption chain results in a sizeable inventory of the intermediate isotope Pa-233. The fissile content of the fuel bundle after exiting the reactor will continue to accumulate U-233 and should be monitored and properly stored. \\ A full core evaluation in a CANDU 6 reactor is performed in DONJON 4. Thorium fuel has an inferior reactivity worth for the control mechanism than does NU fuel in an operating CANDU 6 reactor. The reactivity worth of leakage and absorption in the reactor is estimated to be slightly lower for the thorium fuel. \\ This thesis presents a new computational model for analyzing full core power transients built upon previous results. The approximation model utilizes many assumptions to develop an expeditious code for analyzing the infinite square lattice retaining the isotopic densities. This model has demonstrated the ability to accurately emulate the reactivity of a lattice cell at different powers and power transients formed in DRAGON. The model is coupled with a point kinetic code to perform power transients in a CANDU 6 reactor. \\ Load following operations are performed in cycles of 24 hours examined at 80\%, 60\%, and 40\% full power. Power adjustments are performed in increments of 10 minutes, two hour, or four hour periods with a constant reactivity input. The power adjustment time has minimal effect on the reactivity perturbations and only influences the rate of reactivity. Thorium fuel has enhanced load following capabilities compared to conventional NU fuel.\\ The long-lasting effects of Pa-233 introduces safety concern when reducing power or reactor shutdown scenarios. Reactivity transformation within the first two days of immediate power reduction will yield similar results for both fuels. Excess reactivity in the thorium fuel will continue to accumulate and eventually double the reactivity peak of NU fuel in the following 90 to 120 days. A shutdown simulation is performed in incremental power reduction steps of 20\% for a range of different days. It is found that NU fuel can adequately control the additional reactivity in this simulation. Thorium fuel maintains a disconcerting amount of excess reactivity that will need to be addressed accordingly. The protactinium transient highlights the need to adequately monitor the buildup of Pa-233 for thorium-based fuels in a reactor. / Thesis / Master of Applied Science (MASc)