<p> This thesis focuses on the thermal plasma treatment of non-point source pollutants accumulating in stormwater ponds. Stormwater ponds are constructed as a part of urban non-point source pollution control systems. Pollutants from various sources are collected in the stormwater ponds as sediments. In this work, stormwater sediments were first separated by a filter with an opening of 208μm. The filtered sludge-water was subjected to pulsed arc electrohydraulic discharge (PAED) treatment while the solid part (i.e., wet sludge and dried PAED treated sludge) was subjected to thermal plasma treatment under non-DC transferred and partial transferred operation modes. The results from the PAED sludge-water treatment show that the reduction of TOC in sludge-water was approximately 80% and was greater than 90%, respectively, after 5 minutes and 2 hours of PAED treatment. The accumulated gaseous concentrations of CxHy, CO, C02, S02, H2S and NO emission from sludge-water treatment were 8.2, 3.1, 1.9, 0.32, 0.29 and 0.07 mg/L, respectively, after 2 hours of PAED treatment. The concentrations of volatile elements in sediments such as S, Br, Cl and K decreased approximately 80, 90, 30 and 20% respectively. The solid-phase carbon was observed to be approximately completely removed after treatment. Based on the above results, it can be concluded that PAED successfully degraded organic compounds into C02, CO and CxHy, and converted sulfur and nitrate compounds into S02, HzS and NO. </p> <p> Thermal plasma wet-sludge treatments showed that a reduction of TOC was approximately 52% with argon plasma gas and air flow rates (in the reaction zone) of 24 and 2.4 L/min, respectively. Based on SEM images, wet sludge was melted under partial transferred mode. Thirteen elements with concentration relationships of 0 > Si > Al > Ca > S >Fe> K > Mg > Na > Cu > C > Ti > Cl were quantified by the X-ray energy dispersion technique. The elemental weight percentages of Si, K, Fe and 0 increased with increasing reaction zone air flow rate, while Ca and Cu decreased with increasing air flow rate. Thirty two elements were quantified by Neutron Activation Analyses (NAA) but only 27 elements were above the detection limits. Major elements (concentration> 1000 ppm) with relative concentrations of Ca > Al >Fe> K > Mg > Na > Ti > Cl; minor elements (100 - 1000 ppm) with relative concentrations of Mn > Ba > Sr > Zn; and trace elements(< 100 ppm) with relative concentration were Mo > V > Cr > Br >La> As > Sc > Th> As > Co > Dy > W > Sb > Eu; were determined. Concentrations of Zn, La and Co were enriched 90, 50 and 30% on average respectively, while concentrations of Br, W and As decreased by 80, 50 and 20% on average respectively. The chemical compositions in sludge were quite different after thermal plasma treatment. The average percentages of sand (Si02) and calcite (CaC03) decreased 35 and 10% respectively, while compounds such as KAlSi08, Fe304, NaCl and CaS04 were formed after thermal plasma treatment. Gaseous hydrocarbons, H2S, CO and NO were emitted continuously during the thermal plasma treatment of sludge. Higher reduction of organics and sulfur compounds and suppression of NOx formation were observed in the thermal plasma treatment of wet sludge. The integrated system consisting of PAED sludge-water treatment and thermal plasma wet sludge treatment under partial transferred mode may provide a potential for stormwater pond sediment treatment control. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

Biofilms are colonies of bacteria attached to the surface at a solid-fluid interface. Bacteria in biofilm produce exopolysaccharides (EPS) that form a gel-like matrix in which the bacteria are embedded. Biofilms have numerous consequences in industrial and medical settings, both positive (bioreactors, digestion) and negative (blocking, as corrosive damage of materials/devices, food contamination, clinical infection). The use of antibiotics or mechanical clearing can be effective at removing biofilms, but such treatments are not always effective or appropriate in all situations. Recently, non-thermal atmospheric plasma treatments have been proposed as an alternative (or complementary) form of treatment, that can target sites of infection with minimal damage to the surroundings (e.g. host cells in a clinical setting). These plasmas generate a multitude of chemical species, most of which are very short lived, that can infiltrate and diffuse into the biofilm killing the bacteria within. The aim of this thesis is to develop a multi-dimensional mathematical model to investigate the effect of a non- thermal plasma on biofilms in time and space and to identify key factors that determine effectiveness of the treatment. Most of the chemical products of cold plasmas are too short lived, or too reactive, to be effective in killing the biofilms, it is the longer live species, e.g. ozone, hydrogen peroxide, acid species, that penetrated the biofilm and do the most damage. However, the EPS in biofilms is an effective barrier against ozone and hydrogen peroxide. No published biofilm model combines multi-dimensional growth with a detailed description of EPS production, hence a new mathematical model is developed and applied to simulating plasma treatment. The thesis is split broadly into two parts. The first part presents a new biofilm model framework that simulates growth in response to any number of substrates (e.g. nutrient, oxygen). The model combines an Individual based model (IbM) description of bacteria (individuals or clusters) and substrates are described as a continuum. Novel features of the framework are the assumption that EPS forms a continuum over the domain and the explicit consideration of cellular energy (ATP). Simulations of this model demonstrate the contrast between biofilm grown with topical nutrient sources (forming irregular, bumpy biofilm) and basal nutrient source with topical oxygen such as biofilm grown on agar (forming regular spatially uniform biofilms). The former is in broad agreement with experiments whilst the latter, to our knowledge, has been the subject of very little experimental study. The second part extends the modelling framework to consider the effect of the plasma species. The simulations demonstrate that penetration is a key factor in their effectiveness, for which EPS plays a key role in preventing spread within and beyond the plasma treated zone. The simulations provide estimates of the timescale of equilibration of the main plasma species, predict the effect of combining these species and demonstrate how the constituents of the biofilm can change following treatment. A number of recommended suggestions for future theoretical and experimental study are discussed in the conclusions.

No description available.

abstract: High photoluminescence (PL) quantum yields reported from amorphous (a-Si) and crystalline (c-Si) nanoparticles have opened up lots of possibilities for use of silicon in optical applications such as light emitting diodes (LEDs), photonics and solar cells with added processing and cost benefits. However, the PL response and the mechanisms behind it are highly dependent on the matrix in which the nanoparticles are grown and on the growth method. While, the bottom-up approach for deposition of free standing nanoparticles seem to be perfectly suited for large area deposition for LED and solar cell applications, the dominant growth techniques (laser ablation and pyrolysis) have been shown to suffer from limitations in control over size distribution of nanoparticles and the requirement of equipment capable of withstanding high temperature. This led to the exploration of plasma based synthesis methods in this work. Towards this effort, the development and automation of a novel tool “Anny” for synthesis of silicon nanoparticles using non-thermal plasma chamber is reported. These nanoparticles are then accelerated due to choked flow through a nozzle leading to substrate independent deposition. The nanoparticle properties are characterized against precursor gas flow rates and RF power to identify the optimum growth conditions for a stable, continuous deposition. It is found that amorphous nanoparticles offer a wide variety of chamber conditions for growth with a high throughput, stable plasma for continuous, long term operations. The quantum confinement model for crystalline and spatial confinement models for amorphous nanoparticles in our size regime (6-8nm) are suggested for free standing nanoparticles and we report a high PL output from well passivated amorphous nanoparticles. The PL output and its dependence on stability of surface hydrogen passivation is explored using Fourier Transform Infrared spectroscopy (FTIR). It is shown that the amorphous nanoparticles have a better and more stable passivation compared to crystalline nanoparticles grown under similar conditions. Hence, we show a-Si nanoparticles as exciting alternatives for optical applications to c-Si nanoparticles. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

Actuellement et en raison de la diminution des ressources pétrolières pour les années à venir, l’hydrogène ou le gaz de synthèse (H2 + CO) sont considérés comme des vecteurs énergétiques qui pourraient permettre de répondre aux enjeux environnementaux et besoins énergétiques. L’exploitation de la biomasse constitue une réserve de carbone et d’hydrogène pouvant être transformée en carburant utilisable. Le travail de cette thèse s’inscrit dans le cadre des recherches concernant la thématique de la conversion de biomasse par plasma non thermique. L’objectif de ce travail a été d’évaluer l’efficacité d’un réacteur plasma spécifique appelé "Statarc" pour la production de gaz de synthèse à partir de composés issus de la biomasse. Afin de caractériser le comportement du réacteur "Statarc", une étude physique de la décharge dans la vapeur d'eau a d’abord été effectuée. Ce travail préliminaire a été considéré comme une base de référence pour l’interprétation des différents résultats obtenus avec des molécules issues de la biomasse : méthanol, éthanol et phénol. Dans tous les cas étudiés, la concentration en Hydrogène obtenue dans les gaz secs ne dépasse pas 66 %. Des bilans énergétiques et chimiques ont été établis afin d’évaluer les différentes pertes dans notre système. Des essais sur le traitement de l’ammoniaque, représentatif d'autres sources hydrogénées, ont montré l’efficacité de notre réacteur plasma pour la production de gaz de synthèse. Un traitement direct du bois nous a permis de déduire que le traitement plasma génère un mélange gazeux libérant plus d’énergie que celle fournie par la combustion du bois consommé. Afin d’obtenir une meilleure compréhension des phénomènes qui se produisent dans le réacteur plasma, un modèle chimique a été élaboré dans le cas des mélanges méthanol – eau. Les résultats expérimentaux obtenus au cours de ce travail ouvrent des perspectives pour de futures modélisations. / Currently and due to the decrease of oil resources for coming years, hydrogen or syngas (CO + H2) are considered as energy vectors to environmental issues and energy needs. The exploitation of biomass provides a reserve of carbon and hydrogen which can be converted into usable fuel. The present work of this thesis is part of research on the topic of the biomass conversion by non-thermal plasma. The objective of this study is to evaluate the efficiency of a specific plasma reactor called "Statarc" for the production of syngas from biomass. To characterize the behaviour of the Statarc reactor, the physical study of the discharge in water vapour was first performed. This preliminary work is considered to a baseline to understand the results obtained with methanol, ethanol and phenol mixtures. In all the cases studied, the concentration obtained of H2 in the dry gas does not exceed 66%. Chemical and energy balances are establish to evaluate the losses in our system. Experiments on the treatment of ammonia, representing other hydrogenated compounds, have shown the efficiency of our plasma reactor to produce syngas. Direct treatment of wood has allowed us to deduce that the plasma treatment produces a gas mixture releases more energy than that provided by the combustion of consumed wood. To obtain a better understanding of phenomena that occur in a plasma reactor, a simple chemical model was developed in the case of the mixture of methanol - water. The experimental results obtained in this work imply perspectives for modeling.

In this report we establish cyclohexasilane (CHS) as a reliable precursor for non-thermal plasma synthesis of high quality photoluminescent silicon nanocrystals (SiNCs). We demonstrate that this synthesis approach can produce high quality, size tunable silicon quantum dots with quantum yields exceeding 60% as synthesized (subsequent work in our group has measured over 70% quantum yield after density gradient ultracentrifugation size purification).After a brief background on non-thermal plasma synthesis, the characterization methods used in this study, and an overview of CHS, we report at length on our development of the apparatus used, and our exploration of the controllable processing parameters of the synthesis method. We describe our successes and challenges with size tuning, sample collection, and passivation. Finally, we discuss preliminary studies we performed to identify promising future research areas. Novel reactor designs, blue light passivation, and magnetic confinement of plasma are described briefly to entice future researchers.

Today we face the formidable challenge of meeting the fuel needs of a growing population while minimizing the adverse impacts on our environment. Thus, we search for technologies that can provide us with renewable fuels while mitigating the emission of global pollutants. To this end, use of non-thermal plasma processes can offer novel methods for efficiently and effectively converting carbon dioxide and water vapor into synthesis gas for the production of renewable fuels. Particularly, non-thermal plasma technologies offer distinct advantages over conventional methods including lower operating temperatures, reduced need for catalysts and potentially lower manufacturing and operation costs. The non-thermal plasma reactors have been studied for ozone generation, material synthesis, decontamination, thruster for microsatellites, and biomedical applications. This dissertation focuses on producing synthesis gas using a non-thermal, microhollow cathode discharge (MHCD) plasma reactor. The prototype MHCD reactor consisted of a mica plate as a dielectric layer that was in between two aluminum electrodes with a through hole. First, electrical characterization of the reactor was performed in the self-pulsing regime, and the reactor was modeled with an equivalent circuit which consisted of a constant capacitance and a variable, negative differential resistance. The values of the resistor and capacitors were recovered from experimental data, and the introduced circuit model was validated with independent experiments. Experimental data showed that increasing the applied voltage increased the current, self-pulsing frequency and average power consumption of the reactor, while it decreased the peak voltage. Subsequently, carbon dioxide and water vapor balanced with argon as the carrier gas were fed through the hole, and parametric experiments were conducted to investigate the effects of applied voltage (from 2.5 to 4.5 kV), flow rate (from 10 to 800 mL/min), CO₂ mole fraction in influent (from 9.95% to 99.5%), dielectric thickness (from 150 to 450 [mu]m) and discharge hole diameter (from 200 to 515 [mu]m) on the composition of the products, electrical-to-chemical energy conversion efficiency, and CO₂-to-CO conversion yield. Within the investigated parameter ranges, the maximum H2/CO ratio was about 0.14 when H2O and CO₂ were dissociated in different reactors. Additionally, at an applied voltage of 4.5 kV, the maximum yields were about 28.4% for H2 at a residence time of 128 [mu]s and 17.3% for CO at a residence time of 354 [mu]s. Increasing residence time increased the conversion yield, but decreased the energy conversion efficiency. The maximum energy conversion efficiency of about 18.5% was achieved for 99.5% pure CO₂ at a residence time of 6 [mu]s and an applied voltage of 4.5 kV. At the same applied voltage, the maximum efficiency was about 14.8% for saturated CO₂ at a residence time of 12.8 [mu]s. The future work should focus on optimizing the conversion yield and efficiency as well as analyzing the temporal and spatial changes in the gas composition in the plasma reactor. / text

L’étude présentée ici entre dans la problématique générale des arcs électriques intervenant dans des applications industrielles telles que le soudage, le découpage, le traitement des déchets. Ce travail constitue une première phase de modélisation de cette étude générale. Le plasma est décrit par un ensemble d'équations de conservation de fluide et de l’électromagnétisme, complétés par des propriétés thermodynamiques et des coefficients de transport appropriés, en formant un système d’équations non linéaires fortement couplées. Ces équations sont écrites en supposant l’équilibre thermodynamique local, une symétrie cylindrique et un écoulement laminaire stationnaire. Ce système d’équations est résolu à l’aide du logiciel commercial FLUENT de type CFD fondé sur l’approche des volumes finis. Pour pouvoir utiliser la partie solveur nous avons résolu notre modèle en utilisant les routines UDF Users-Defined-Function. Dans une première partie, nous présentons la validation du modèle à deux dimensions et à 100 A dans l’argon par des résultats de la littérature. Cette comparaison laisse apparaître un accord satisfaisant sur les profils de température dans la colonne de plasma et des différences dans les zones proches des électrodes dues aux conditions aux limites. Dans une deuxième partie, nous présentons une étude expérimentale, à l’issue de laquelle on constate que les profils de température expérimentaux sont en accord avec ceux du modèle dans la zone de colonne positive. / The study presented here enters the general problem of electric arc involved in industrial applications such as welding, cutting, waste treatment. This work constitutes the first numerical phase of modeling of this general study. The plasma is described by a set of fluid conservation equations, electromagnetic equations complemented by suitable thermodynamic and transport properties, forming a strongly coupled non-linear system. These equations are written assuming local thermodynamic equilibrium, a cylindrical symmetry and steady laminar flow. This system of equations is solved using commercial software FLUENT CFD-type based on finite volume algorithm. To use the solver part we solved our model using UDF macro Users-Defined-Function. In the first part, we present the validation of the two dimensional model in and 100 A in argon with the literature results. A detailed analysis of various characteristic quantities is presented. This comparison reveals a good agreement of the temperature profiles in the column plasma and differences in electrode areas due to boundary conditions. In a second part, we present an experimental study, the experimental temperature profiles are consistent with the model in the column area which means that the model is validated in the column of plasma.

<p>This dissertation was undertaken to study two different subjects both related to molecular decomposition by applying a shock tube and non-thermal plasma to decompose selected hydrocarbons. The first approach to molecular decomposition concerned thermal decomposition and oxidation of highly diluted nitromethane (NM) in a shock tube. Reflected shock tube experiments on NM decomposition, using mixtures of 0.2 to 1.5 vol% NM in nitrogen or argon were performed over the temperature range 850-1550 K and pressure range 190-900 kPa, with 46 experiments diluted in nitrogen and 44 diluted in argon. By residual error analysis of the measured decomposition profiles it was found that NM decomposition (CH₃NO₂ + M -> CH₃ + NO₂ + M, where M = N₂ /Ar) corresponds well to a law of first order. Arrhenius expressions corresponding to NM diluted either in N₂ or in Ar were found as k_N2 = 1017.011×exp(-182.6 kJ/mole / R×T <cm³/mole×s> and k_Ar = 1017.574×exp(-207 kJ/mole / R×T )<cm3^/mole×s>, respectively. A new reaction mechanism was then proposed, based on new experimental data for NM decomposition both in Ar and N₂ and on three previously developed mechanisms. The new mechanism predicts well the decomposition of NM diluted in both N₂ and Ar within the pressure and temperature range covered by the experiments.</p><p>In parallel to, and following the decomposition experiments, oxidative experiments on the ignition delay times of NM/O₂/Ar mixtures were investigated over high temperature and low to high pressure ranges. These experiments were carried out with eight different mixtures of gaseous NM and oxygen diluted in argon, with pressures ranging between 44.3-600 kPa, and temperatures ranging between 842-1378 K.</p><p>The oxidation experiments were divided into different categories according to the type of decomposition signals achieved. For signals with and without emission, the apparent quasi-constant activation energy was found from the correlations, to be 64.574 kJ/mol and 113.544 kJ/mol, respectively. The correlations for the ignition delay for time signals with and without emission were deduced as τemission = 0.3669×10^-2×[NM]^-1.02[O₂]^-1.08×[Ar]^1.42×exp(7767/T) and τno emission = 0.3005×10^-2×[NM]^-0.28[O₂]^0.12×[Ar]^-0.59×exp(13657/T), respectively.</p><p>The second approach to molecular decomposition concerned the application of non-thermal plasma to initiate reactions and decompose/oxidize selected hydrocarbons, methane and propane, in air. Experiments with a gliding arc discharge device were performed at the university of Orléans on the decomposition/reforming of low-to stoichiometric concentration air/CH₄ mixtures. The presented results show that complete reduction of methane could be obtained if the residence time in the reactor was sufficiently long. The products of the methane decomposition were mainly CO₂, CO and H₂O. The CH₄ conversion rate showed to increase with increasing residence time, temperature of the operating gas, and initial concentration of methane. To achieve complete decomposition of CH₄in 1 m³ of a 2 vol% mixture, the energy cost was about 1.5 kWh. However, the formation of both CO and NOx in the present gliding discharge system was found to be significant. The produced amount of both CO (0.4-1 vol%) and NO_x (2000-3500 ppm) were in such high quantities that they would constitute an important pollution threat if this process as of today was to be used in large scale CH₄ decomposition. Further experimental investigations were performed on self-built laboratory scale, single- and double dielectric-barrier discharge devices as a means of removing CH₄ and C₃H_{8 f}rom simulated reactive inlet mixtures. The different discharge reactors were all powered by an arrangement of commercially available Tesla coil units capable of high-voltage high-frequency output. The results from each of the different experiments are limited and sometimes only qualitative, but show a tendency that the both CH₄ and C₃H₈are reduced in a matter of a 3-6 min. retention time. The most plausible mechanism for explaining the current achievements is the decomposition by direct electron impact.</p>