Research on the electrocoagulation (EC) of hexane extractable materials (HEM) has been conducted at the University of New Orleans using a proprietary bench-scale EC reactor. The original reactor configuration forced the fluid to follow a vertical upward-downward path. An alternate electrode arrangement was introduced so that the path of flow became horizontal. Both configurations were evaluated by comparing the residence time distribution (RTD) data generated in each case. These data produced indication of internal recirculation and stagnant water when the fluid followed a vertical path. These anomalies were attenuated when the fluid flowed horizontally and at a velocity higher than 0.032 m s-1 . A series of EC experiments were performed using a synthetic emulsion with a HEM concentration of approximately 700 mg l-1. It was confirmed that EC of HEM follows first-order kinetics, and kinetic constants of 0.0441 s-1 and 0.0443 s-1 were obtained from applying both the dispersion and tanks-in-series (TIS) models, respectively. In both cases R2 was 0.97. Also, the TIS model indicated that each cell of the EC behaves as an independent continuous-stirred-tank reactor.

A racionalização dos recursos hídricos tem sido uma das metas das indústrias em vários setores. Tais metas exigem inovações tecnológicas tanto para novos processos produtivos quanto para novas técnicas de tratamento e reutilização de água na cadeia de produção. Os custos elevados de água industrial no Brasil, particularmente nas regiões metropolitanas, têm estimulado as indústrias nacionais a avaliar as possibilidades de reúso. O objetivo deste trabalho é a aplicação do tratamento de águas de processo contendo polipropileno utilizando radiação ultravioleta e peróxido de hidrogênio, isto é, o sistema UV/H2O2, visando adequá-las para reúso no próprio processo, reduzindo a necessidade de captação de água pré-tratada e de descarte de efluente. A primeira parte do estudo consistiu na realização de experimentos em um sistema fotoquímico de batelada, empregando quatro diferentes correntes efluentes de processo, para a avaliação da viabilidade técnico-econômica do tratamento fotoquímico, bem como para a obtenção de dados referentes à cinética das reações fotoquímicas. Com base nas informações obtidas, na segunda parte do estudo foram realizados experimentos em um sistema fotoquímico contínuo, a fim de obter dados para o aumento de escala para aplicação industrial do processo de tratamento contínuo. Os resultados experimentais indicaram a viabilidade técnica de aplicação do sistema UV/H2O2 utilizando fonte de luz artificial para todas as correntes de processo estudadas, tendo sido alcançados níveis de remoção de matéria orgânica acima de 90%. No entanto, sob o ponto de vista econômico, apenas as correntes com baixo teor de carbono orgânico total dissolvido (COT), entre 6 e 12 mgC L-1, mostraram-se adequadas ao reúso, após o tratamento. / Rationalization of water use has been one of the goals in many industrial activities, and, in particular, in the petrochemical industry. Such goals demand technological innovations in the productive processes and in techniques for treatment and reuse of water in the production chain. The high costs of industrial water, particularly in some metropolitan regions, have stimulated the industries to evaluate the possibilities of water reuse. The objective of this work is to evaluate the feasibility of the UV/H2O2 photochemical process applied to the treatment of process waste water containing polypropylene, aiming at the reuse of the waste water in the as process water in the industrial complex, thus reducing the need for tap water supply and waste water generation rate. The first part of this study consisted of laboratory-scale experiments in a batch photochemical reactor with four different waste water streams to perform the technical and economical feasibility of the photochemical treatment, as well to obtain data on the degradation rate. Based on the results of the first part, the second part of this study consisted of experiments in a continuous photochemical reactor, aimed at obtaining experimental data for reactor scale-up. Experimental results indicate that the UV/H2O2 photodegradation process is able to remove more than 90% of the organic compounds contained in the waste water. However, only waste waters containing relatively low contaminant levels (between 6 and 12 mgC L-1) can be treated at economically favourable costs.

No meio científico são bastante utilizados os modelos matemáticos para avaliar as características hidrodinâmicas de reatores, porém a literatura é pobre em informações relativas à aplicação do equacionamento matemático em regime não-permanente. Neste trabalho foi aplicado um modelo matemático simulando a hidrodinâmica de reatores tubulares com dispersão para avaliar o efeito da variação de vazão afluente sobre os parâmetros hidrodinâmicos. As simulações foram efetuadas considerando vazão e volume constantes, vazão e volume variáveis e vazão variável e volume constante. Foi investigada a influência de dois tipos de ensaios estímulo-resposta, pulso e degrau, para aplicação de modelos matemáticos e determinação das curvas de distribuição do tempo de residência (DTR) experimentais. Teoricamente ambos devem fornecer os mesmos resultados embora o ensaio em pulso costume apresentar maior sensibilidade experimental. Conforme esperado, ambos os ensaios apresentaram os mesmos resultados finais. Também foram avaliados os traçadores empregados nos dois tipos de ensaios estímulo-resposta, pulso e degrau. Foram empregados três traçadores diferentes - verde de bromocresol, azul de bromofenol e eosina Y que proporcionaram curvas com diferentes características. Como ferramenta auxiliar da modelação foram estudas a determinação das curvas DTR experimentais com auxílio de duas técnicas distintas. Para calibrar o modelo matemático proposto foram utilizados dados de reatores em escala de bancada com diferentes configurações submetidas a variações de vazões afluentes. Os dados de um reator UASB em escala piloto - submetido a variações cíclicas de vazão afluente de 40 e 60% - foram empregados para calibrar e verificar o modelo matemático proposto. Os resultados encontrados com o modelo matemático proposto nesta pesquisa demonstraram que a variação de vazão afluente não deve ser negligenciada. O modelo utilizado representou adequadamente o reator UASB. Seus resultados, quando comparados aos modelos matemáticos que não consideram a variação de vazão, mostraram que para flutuações de vazão elevadas, vazões com valores até 60% maiores do que a vazão média, os valores dos coeficientes de difusão diferem significativamente em função das hipóteses empregadas no desenvolvimento do modelo matemático. / Mathematical models for hydrodynamic characteristics evaluation of reactors are commonly used however there is a lack of information in the literature concerning the application of mathematical modeling for non-steady state flow. In this thesis, it is presented a non-steady mathematical model to simulate the hydrodynamic behavior of pipe flow reactors with diffusion in order to evaluate the effect of the variation of the influent flowrate in the hydrodynamic parameters. The simulations were performed considering constant flowrate and volume, variable flowrate and volume and, variable flowrate and constant volume. It was investigated the influence of two types of stimulus-response assays, pulse and step function, on the application of mathematical models and the determination of the experimental retention time distribution curves. Theoretically, both tests should provide the same results although the pulse stimulus assay usually presents higher experimental sensitivity. As it was expected, both tests presented the same final results. The tested tracers were also evaluated in relation to the pulse and step stimulus-response tests. Three tracers were tested (bromocresol green, bromophenol blue and eosin Y) and it was shown that they provided different curves. It was studied the construction of the experimental retention time distribution curves using two procedures as an auxiliary tool for modeling. The proposed mathematical model was calibrated with data of bench scale reactors submitted to different cyclical variations of flowrates. Moreover, data of UASB reactor in pilot scale - submitted to 40 and 60% of cyclical variations of flowrates were utilized to calibrate and verify the obtained mathematical model. The results found with the mathematical model proposed in this research showed that the variations in influent flow rate can not be neglected. The model adequately represented a pilot scale UASB reactor. The results showed that the diffusion coefficients differ significantly for high flowrate fluctuations, when compared to other mathematical models that do not incorporate variable flowrate, depending upon the hypothesis used to derive the model.

This study is focused on the flow through the uppermost part of the unsaturated zone in karstified areas. The information about distribution of transit times and chemical reactions taking place in the unsaturated zone is based on isotopic and chemical composition of cave dripwaters, precipitations and water caught by gravitation lysimeters. The water balance was calculated using measurements of intensity of dripwaters and amounts of water caught by lysimeters and rain gauges. The velocity of a hydraulic shockwave between monitored objects was also estimated according to the delay between significant precipitation event and dripwater intensity increase. The field study took place in the Němcova 1 cave in the northern part of Moravian Karst, near the village Suchdol. It was carried out during the hydrological year 2010/2011. The cave is about 13 m under the surface. The information about composition of overlaying rock above the cave was obtained using geoelectrical and electromagnetic measurements. Studied geological environment is built of 0.5 - 1.5 m of soil, 0.5 - 3.5 m of epikarst and a layer of massive limestone as thick as 10 m. About 70 to 90 % of dripwaters have residence time over 4 years. The distribution of transit time of younger water can be described using the exponencial model (well...

L'étude cinétique d'une réaction catalytique permet une meilleure compréhension du mécanisme réactionnel et du fonctionnement du catalyseur. Elle est nécessaire pour le dimensionnement des réacteurs et des procédés. Les modèles micro-cinétiques sont constitués d'une séquence d'étapes élémentaires sans hypothèses sur les étapes cinétiquement déterminantes. Ces modèles sont applicables sur des plages de conditions opératoires plus larges que celles des modèles plus classiques de type Langmuir-Hinshelwood (LH) ou d'Hougen-Watson. Lorsqu'ils sont implémentés dans un modèle de réacteur, ils permettent d'obtenir une plus grande précision vis-à-vis du dimensionnement du catalyseur et du réacteur. Cependant, cette approche nécessite un nombre d'expériences plus élevé pour estimer les nombreux paramètres cinétiques qui le constituent. Ce travail de thèse porte sur le développement de modèles micro-cinétiques de systèmes catalytiques en exploitant les informations obtenues lorsque le catalyseur fonctionne en régime transitoire. En effet, l'expérimentation en régime transitoire, en comparaison avec celle classiquement réalisée en régime stationnaire, permet d'accéder à plus d'informations par une meilleure sensibilisation des réactions mises en jeu. Les études cinétiques en régime permanent sont plutôt adaptées pour des modèles cinétiques globaux qui considèrent un nombre limité d'étapes cinétiquement déterminantes (en général une seule). De ce fait, la compréhension du mécanisme réactionnel [1], la connaissance du nombre de types de sites actifs mis en jeu ou encore la détermination des vitesses de réaction des étapes élémentaires restent imprécises. Afin d'accéder aux différentes vitesses de réaction des étapes élémentaires, il est nécessaire de réaliser un grand nombre d'expériences en régime permanent, ce qui est très coûteux en temps et en argent. L'expérimentation en régime transitoire est donc une alternative qui permet d'accéder à des informations cinétiques détaillées dans un délai plus rapide. Cependant, l'interprétation des expériences est plus fastidieuse puisqu'elle nécessite le développement de modèles dynamiques de réacteur. Ces études consistent à réaliser des perturbations sous forme de pulses, d'échelons ou bien d'oscillations périodiques d'un certain nombre de paramètres d'état tels que la concentration des réactifs, la pression ou encore la température. Dans ces travaux, des oscillations périodiques de concentration sont réalisées en entrée de réacteur. Ce choix permet de réaliser des variations autour de l'état stationnaire, dans des conditions proches des celles utilisées dans l'industrie. La mise en place et la validation de cette méthodologie ont été réalisées pour un système catalytique réactionnel d'intérêt industriel : l'hydrogénation sélective de l'acétylène. Cette réaction a lieu en phase gaz au contact d'un catalyseur solide et présente l'avantage de mettre en jeu peu de composés facilement analysables. Une voie importante pour la production d'éthylène est le vapocraquage. L'éthylène produit par ce procédé contient de faibles quantités d'acétylène qu'il faut éliminer car il constitue un poison pour les procédés catalytiques en aval. Cette élimination se fait par l'hydrogénation sélective de l'acétylène, en présence d'éthylène, en employant un catalyseur à base de palladium. C'est une réaction rapide dont le mécanisme réactionnel n'est pas encore complètement connu.La cinétique transitoire permet non seulement d'étudier les réactions chimiques mais également de caractériser le transport des réactifs et des produits, de l'échelle du lit catalytique à l'échelle des pores du catalyseur. Un modèle de réacteur incluant un modèle cinétique a été développé pour expliquer les données expérimentales obtenues sur un réacteur pilote. Des manipulations en régime transitoires et une modélisation dynamique de l'unité pilote incluant un modèle micro-cinétique sont réalisées [etc...] / Kinetic experiments performed under stationary conditions mainly give information on the rate determining step. Numerous experiments must be done to estimate a limited number of parameters. Unsteady-state experiments, on the other hand, give more detailed information about the kinetics of the different elementary steps with a small number of experiments. In order to work under dynamic conditions, a perturbation of a process variable (concentration, pressure, temperature, etc.) is introduced at the reactor entrance (pulse, step, oscillation ...). This study explores periodic sinusoidal variations of the flow to obtain kinetics for heterogeneous catalytic processes. The kinetic information is contained in the phase lag and the gain change of the oscillations. The oscillations can be kept small and can be performed around steady-state operation, thus studying the kinetics under relevant conditions. First a model able to directly estimate the gain and phase lag has been created. Secondly, simple cases of adsorption have been performed in order to validate the model and to test the experimental set up. To finish, the approach has been applied to the selective hydrogenation of acetylene. Kinetic modeling was carried out in both stationary and dynamic conditions in order to compared the two methodologies

Computer based simulation models have often been used to study the multimodal freight transportation system. But these studies have not been able to dynamically couple the various modes into one model; therefore, they are limited in their ability to inform on dynamic system level interactions. This research thesis is motivated by the need to dynamically couple the multimodal freight transportation system to operate at multiple spatial and temporal scales. It is part of a larger research program to develop a systems modeling framework applicable to freight transportation. This larger research program attempts to dynamically couple railroad, seaport, and highway freight transportation models. The focus of this thesis is the development of the coupled railroad and seaport models. A separate volume (Wall 2010) on the development of the highway model has been completed. The model railroad and seaport was developed using Arena® simulation software and it comprises of the Ports of Savannah, GA, Charleston, NC, Jacksonville, FL, their adjacent CSX rail terminal, and connecting CSX railroads in the southeastern U.S. However, only the simulation outputs for the Port of Savannah are discussed in this paper. It should be mentioned that the modeled port layout is only conceptual; therefore, any inferences drawn from the model's outputs do not represent actual port performance. The model was run for 26 continuous simulation days, generating 141 containership calls, 147 highway truck deliveries of containers, 900 trains, and a throughput of 28,738 containers at the Port of Savannah, GA. An analysis of each train's trajectory from origin to destination shows that trains spend between 24 - 67 percent of their travel time idle on the tracks waiting for permission to move. Train parking demand analysis on the adjacent shunting area at the multimodal terminal seems to indicate that there aren't enough containers coming from the port because the demand is due to only trains waiting to load. The simulation also shows that on average it takes containerships calling at the Port of Savannah about 3.2 days to find an available dock to berth and unload containers. The observed mean turnaround time for containerships was 4.5 days. This experiment also shows that container residence time within the port and adjacent multimodal rail terminal varies widely. Residence times within the port range from about 0.2 hours to 9 hours with a mean of 1 hour. The average residence time inside the rail terminal is about 20 minutes but observations varied from as little as 2 minutes to a high of 2.5 hours. In addition, about 85 percent of container residence time in the port is spent idle. This research thesis demonstrates that it is possible to dynamically couple the different sub-models of the multimodal freight transportation system. However, there are challenges that need to be addressed by future research. The principal challenge is the development of a more efficient train movement algorithm that can incorporate the actual Direct Traffic Control (DTC) and / or Automatic Block Signal (ABS) track segmentation. Such an algorithm would likely improve the capacity estimates of the railroad network. In addition, future research should seek to reduce the high computational cost imposed by a discrete process modeling methodology and the adoption of single container resolution level for terminal operations. A methodology combining both discrete and continuous process modeling as proposed in this study could lessen computational costs and lower computer system requirements at a cost of some of the feedback capabilities of the model This tradeoff must be carefully examined.

Current lean-premixed fuel injector designs have shown great potential in terms of reducing emissions of pollutants, but such designs are susceptible to combustion instabilities in which aerodynamic instability plays a major role and also has an effect on mixing of air and fuel. In comparison to prototype testing with combustors running in operating conditions, computational approaches such as Large Eddy Simulations (LES) offer a much more cost-effective alternative in the design stage. However, computational models employed by LES require validation by experimental data. This is one of the main motivations behind the present experimental study. Combined particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) instrumentation allowed simultaneous measurements of velocity vector and a conserved scalar introduced into the fuel stream. The results show that the inner swirl shear layer features two pairs of vortices, which draw high concentration fuel mixture from the central jet into the swirl stream and causes it to rotate in their wakes. Such periodic entrainment also occurs with the characteristic frequencies of the vortices. This has clear implications for temporal variations in fuel/air ratio in a combusting flow; these bursts of mixing, and hence heat release, could be a possible cause of mixing-induced pressure oscillation in combusting tests. For the first time in such a flow, all 3 components of the turbulent scalar flux were available for validation of LES-based predictions. A careful assessment of experimental errors, particularly the error associated with spatial filtering, was carried out. Comparison of LES predictions with experimental data showed very good agreement for both 1st and 2nd moment statistics, as well as spectra and scalar pdfs. It is particularly noteworthy that comparison between LES computed and measured scalar fluxes was very good; this represents successful validation of the simple (constant Schmidt number) SGS model used for this complex and practically important fuel injector flow. In addition to providing benchmark data for the validation of LES predictions, a new experimental technique has been developed that is capable of providing spatially resolved residence time data. Residence times of combustors have commonly been used to help understand NOx emissions and can also contribute to combustion instabilities. Both the time mean velocity and turbulence fields are important to the residence time, but determining the residence time via analysis of a measured velocity field is difficult due to the inherent unsteadiness and the three dimensional nature of a high-Re swirling flow. A more direct approach to measure residence time is reported here that examines the dynamic response of fuel concentration to a sudden cutoff in the fuel injection. Residence time measurement was mainly taken using a time-resolved PLIF technique, but a second camera for PIV was added to check that the step change does not alter the velocity field and the spectral content of the coherent structures. Characteristic timescales evaluated from the measurements are referred to as convection and half-life times: The former describes the time delay from a fuel injector exit reference point to a downstream point of interest, and the latter describes the rate of decay once the effect of the reduced scalar concentration at the injection source has been transported to the point of interest. Residence time is often defined as the time taken for a conserved scalar to reduce to half its initial value after injection is stopped: this is equivalent to the sum of the convection time and the half-life values. The technique was applied to a high-swirl fuel injector typical of that found in combustor applications. Two test cases have been studied: with central jet (with-jet) and without central jet (no-jet). It was found that the relatively unstable central recirculation zone of the no-jet case resulted in increased transport of fuel into the central region that is dominated by a precessing vortex core, where long half-life times are also found. Based on this, it was inferred that the no-jet case may be more prone to NOx production. The technique is described here for a single-phase isothermal flow field, but with consideration, it could be extended to studying reacting flows to provide more insight into important mixing phenomena and relevant timescales.

No description available.

It is generally accepted that the Marginal Value Theorem (MVT) describes optimal foraging strategies. Some research findings, however, indicate that in natural conditions foragers not always behave according to the MVT. To address this inconsistency, in a series of computer simulations, I examined the behaviour of four types of foragers having specific foraging efficiencies and using the MVT and alternative strategies in 16 simulated landscapes in an ideal environment (no intra- and inter-species interactions). I used data on elk (Cervus elaphus) to construct the virtual forager. Contrary to the widely accepted understanding of the MVT, I found that in environments with the same average patch quality and varying average travel times between patches, patch residence times of some foragers were not affected by travel times. I propose a mechanism responsible for this observation and formulate the perfect forager theorem (PFT). I also introduce the concepts of a foraging coefficient (F) and foragers hub (), and formulate a model to describe the relationship between the perfect forager and other forager types. I identify situations where a forager aiming to choose an optimal foraging strategy and maximize its cumulative consumption should not follow the MVT. I describe these situations in a form of a mathematical model. I also demonstrate that the lack of biological realism and environmental noise are not required to explain the deviations from the MVT observed in field research, and explain the importance of scale in optimal foraging behaviour. I also demonstrate that smart foraging, which is a set of rules based on key ecological concepts: the functional response curve (FRC), satisficing, the MVT, and incorporates time limitations, should allow for fitness maximization. Thus, it should be an optimal behavior in the context of natural selection. I also demonstrate the importance of the FRC as a driver for foraging behaviors and argue that animals should focus more on increasing the slope of their FRC than on choosing a specific foraging strategy. Natural selection should, therefore, favor foragers with steep FRC. My findings introduce new concepts in behavioural ecology, have implications for animal ecology and inform wildlife management.

L'objectif principal de ce travail de thèse concerne l'étude de l' élimination de la DCO et de la nitrification dans une nouveau lit bactérien Multi-Section ( MSB ) . Après une caractérisation de l’hydrodynamique et du transfert d’oxygène de ce lit bactérien, les expériences biologiques menées sous des conditions opératoires contrastées (fortes et faibles charges organiques eteaux usées contenant ou pas des matières particulairs) ont été menées. En parallèle, des simulations avec le logiciel Biowin® ont été réalisées. Les principaux résultats sont résumés en suivant :- La rétention de liquide statique est majoritaire par rapport à la rétention dynamique que ce soit en présence ou en absence de biofilm. Le biofilm joue le rôle d’une "éponge" permettant un maintien de l’humidité du lit même à faible débit. Les expériences de DTS ont montré que le biofilm accroit le temps de séjour du liquide et conduit à une diminution de l’épaisseur du film liquide permettant ainsi de promouvoir le transfert de l'oxygène.- Le réacteur MSB montre une élimination efficace de la DCO (> 95 % ) et de la nitrification ( > 60 % de l’azote entrant), mais une accumulation de DCO particulaire a lieu dans le filtre ce qui conduira à un colmatage à terme. La nitrification cohabite avecl’élimination de la DCO même dans la première section et pour une charge organique élevée ce qui implique une bonne capacité d’oxygénation du MSB par l’aération naturelle.- Un modèle dynamique de MSB a été utilisé implémenté sur le simulateur - BioWin , afin d'obtenir la répartition des biomasses au sein du réacteur et d'évaluer le processus limitant dans chaque section. Le modèle partiellement calibré peut aider à estimer les besoins minimum d'oxygène pour la nitrification et peut rendre compte de la compétition entre la croissance hétérotrophe et la nitrification. / The main objective of this PhD work focused on the study of the COD removal and nitrification in a new designed Multi-Section Bioreactor (MSB). Hydrodynamic characterization of the reactor, biological experiments under contrasted conditions and simulations by Biowin® software were carried out:- Firstly, it was found that static liquid retention is the predominant part both without and with the presence of biofilm. Biofilm acts like a "sponge". RTD experiments showed that biofilm can promote liquid residence time, decrease the liquid film andpromote the oxygen transfer consequently.- Secondly, the MSB operated at contrasted organic loading rate (OLRs) and nitrogen loading rate (NLRs) showed that COD can be effectively removed (removal efficiency > 95%) and nitrification (> 60% of the N removal) occurred in this biofilter.Nitrification is efficient even in the first section implying no drastic oxygen limitation though only natural aeration is occurring.- Thirdly, a TF dynamic model has been used from a simulator - BioWin, in order to get more insights on the biomass distribution in the pilot and to assess the limiting process in each section of the bioreactor. Calibration of the model can help us to estimate theminimum oxygen requirement for nitrification for each zone inside the pilot and it can well represent the competition between heterotrophic growth and nitrification.