A urolitíase é um problema recorrente na clínica veterinária considerada como causa de morbidade. As urolitíases são estreitamente associadas ao pH urinário e a nutrição exerce um papel fundamental no controle desta afecção, pois através da manipulação da dieta, pode-se modificar o pH urinário. A dieta possui cátions e ânions na sua composição mineral e a diferença entre íons é medida em miliequivalentes (mEq/kg) e denominado excesso de bases (EB) da dieta, calculado através da equação: (49,9 x Ca) + (82,3 x Mg) + (43,5 x Na) + (25,6 x K) – (64,6 x P) – (62,4 x S) – (28,2 x Cl), sendo a concentração dos elementos em g/kg de MS. A finalidade deste estudo, dividido em dois experimentos, foi avaliar o efeito da adição de fontes de enxofre (S) e cálcio nas dietas de felinos sobre o pH urinário e equilíbrio ácido-básico. A adição de fontes de enxofre objetivou demonstrar a eficácia na acidificação urinária. No primeiro experimento avaliaram-se três diferentes fontes de enxofre: sulfato de cálcio (CaSO4), DL-metionina (DLM) e Metionina hidróxi análoga (MHA) adicionados a uma dieta controle em dois níveis cada um. No tratamento controle não houve adição de acidificantes. No primeiro nível adicionou-se 1,28 g de S/kg e no segundo 2,56 g de S/kg, resultando em sete tratamentos. No segundo experimento duas fontes de cálcio foram avaliadas com o objetivo de pesquisar a eficácia destes sais na alcalinização da urina. No tratamento controle não houve adição de fontes de cálcio. Nos tratamentos 2 e 3 foram adicionados à dieta controle carbonato de cálcio e gluconato de cálcio, respectivamente, nas doses de +160 mEq/kg, resultando em três tratamentos. A urina produzida em cada período de 24 horas teve aferida seu volume, densidade e pH. No segundo experimento foi também medida a excreção urinária de cálcio no período de 72h. O equilíbrio ácido-básico foi avaliado pela hemogasometria de sangue venoso. A DLM no maior nível e o MHA diferiram da dieta controle em relação ao pH urinário (p<0,001) e seu poder acidificante foi maior que o do sulfato de cálcio (p<0,05). As duas fontes de cálcio alcalinizaram a urina, mas o carbonato de cálcio atingiu um pH urinário mais alto que o gluconato de cálcio. Concluiu-se que o efeito diferenciado das fontes de S e cálcio sobre o pH urinário é um indicador de que a participação do cálcio é dependente dos ânions a que está associado, o que leva ao questionamento sobre qual a melhor forma de avaliar sua participação no cálculo do EB. / Urolithiasis is a commom problem in the veterinary clinic considered as a cause of morbidity. The urolithiasis are closely associated with urinary pH and nutrition plays a key role in the control of this disease, because through dietary manipulation, it´s possible modify the urinary pH. The diet has cations and anions in their mineral composition and the difference between ions is measured in milliequivalents (mEq/kg) and called base excess (BE) of the diet, calculated by the equation: (49.9 x Ca) + (82, Mg x 3) + (43.5 x Na) + (25.6 x K) - (64.6 x P) - (62.4 x S) - (28.2 x Cl), being the concentration of elements in g/kg DM. The purpose of this study, divided in two experiments, was to evaluate the effect of addition of sources of sulfur (S) and calcium in the diets of cats on the urinary pH and acid-base balance. The addition of sulfur sources aimed to demonstrate the efficacy in urinary acidification. In the first experiment were evaluated three different sources of sulfur, calcium sulfate (CaSO4), DLMethionine (DLM) and Methionine hydroxy analogue (MHA) added to a control diet at two levels each. In the control treatment there was no addition of acidifying. At the first level was added 1.28 g S/kg and in the second 2.56 g S/kg, resulting in seven treatments. In the second experiment two calcium sources were evaluated in order to research the effectiveness of these salts in alkalinize urine. In the control treatment there was no addition of calcium sources. In treatments 2 and 3 were added to the control diet calcium carbonate and calcium gluconate, respectively, at doses of +160 mEq/kg, resulting in three treatments. The urine produced in each period of 24 hours had measured its volume, density and pH. The second experiment also measured the urinary excretion of calcium in the period of 72 hours. The acid-base balance was evaluated by blood gas analysis of venous blood. The DLM at the highest level and MHA differed of the control diet in relation to urinary pH (p<0.001) and their acidifying power was greater than the calcium sulfate (p<0.05). The two sources of calcium alkalinized the urine, but the calcium carbonate reached a urine pH higher than calcium gluconate. It was concluded that the effect of different sources of S and calcium on urinary pH is an indicator that the participation of calcium is dependent of the anions that is associated, which leads to questions about how is the best way to evaluate its participation in calculation of BE.

Dans un contexte de stress hydrique, la micro-irrigation avec des eaux usées traitées constitue une solution visant à réduire les dépenses en eau. Cependant, le colmatage des goutteurs constitue une contrainte à l’utilisation de ces eaux bien chargées à cause des précipitations chimiques et du développement de biofilm. Les objectifs de cette étude sont de: a) Caractériser la précipitation des sels dissous en fonction des conditions opératoires, b) étudier le développement des biofilms sous différentes conditions hydrodynamiques, c) analyser l’interaction entre le carbonate de calcium et le développement du biofilm. En premier lieu une étude fut conduite sur l’impact de la température le pH et la pression partielle du CO2 sur la précipitation chimique. Cette étude a permis de quantifier l’augmentation de la masse du carbonate de calcium en fonction du pH et de la température. Les résultats expérimentaux ont permis de valider et de calibrer un modèle numérique (PHREEQC) qui permet de prédire la précipitation chimique pour une qualité d’eau donnée dans des conditions opératoire variées. Des expérimentations ont ensuite été réalisées à l’aide d’un banc d’essai d’irrigation pour étudier l’influence du carbonate de calcium sur la croissance des biofilms au niveau des conduites et des goutteurs. En parallèle un réacteur de Taylor-Couette fut utilisé pour étudier l’influence de la contrainte de cisaillement sur le développement des biofilms. Le biofilm a tendance à se développer selon la plus forte contrainte de cisaillement (4.4 Pa comparée à des contraintes de 2.2 et 0.7 Pa). Une précipitation du carbonate de calcium a été observée en interaction avec la croissance du biofilm. / In a context of water stress, micro-irrigation with treated wastewater is a solution to reduce water expenditure. However, the clogging of micro-irrigation systems constitutes a constraint on the use of these well-laden waters due to chemical precipitation and the development of biofilm. The objectives of this study are to: a) characterize precipitation of dissolved salts as a function of operating conditions, b) study the development of biofilms under different hydrodynamic conditions and c) analyze the interaction between calcium carbonate and the development of biofilm. First, a study was conducted on the impact of pH, temperature and partial pressure of CO2 on chemical precipitation. This study permits the quantification of the increase in the mass of the precipitate produced in the form of calcite (calcium carbonate) as a function of the increase in pH and temperature. The experimental results allowed validation and calibration of the modeling of the precipitation under PHREEQC’s software. This numerical model allows prediction and quantification of chemical precipitation for a given water quality under various operating conditions. Experiments were then carried out using an irrigation set-up to study the influence of calcium carbonate on the growth of biofilms inside pipes and drippers. In parallel, a Taylor-Couette reactor was used to study the influence of shear stress on the development of biofilms. Biofilm tends to develop under the highest shear stress (4.4 Pa compared to 2.2 and 0.7 Pa). Precipitation of the calcium carbonate in the form of calcite was observed in interaction with the growth of the biofilm.

A urolitíase é um problema recorrente na clínica veterinária considerada como causa de morbidade. As urolitíases são estreitamente associadas ao pH urinário e a nutrição exerce um papel fundamental no controle desta afecção, pois através da manipulação da dieta, pode-se modificar o pH urinário. A dieta possui cátions e ânions na sua composição mineral e a diferença entre íons é medida em miliequivalentes (mEq/kg) e denominado excesso de bases (EB) da dieta, calculado através da equação: (49,9 x Ca) + (82,3 x Mg) + (43,5 x Na) + (25,6 x K) – (64,6 x P) – (62,4 x S) – (28,2 x Cl), sendo a concentração dos elementos em g/kg de MS. A finalidade deste estudo, dividido em dois experimentos, foi avaliar o efeito da adição de fontes de enxofre (S) e cálcio nas dietas de felinos sobre o pH urinário e equilíbrio ácido-básico. A adição de fontes de enxofre objetivou demonstrar a eficácia na acidificação urinária. No primeiro experimento avaliaram-se três diferentes fontes de enxofre: sulfato de cálcio (CaSO4), DL-metionina (DLM) e Metionina hidróxi análoga (MHA) adicionados a uma dieta controle em dois níveis cada um. No tratamento controle não houve adição de acidificantes. No primeiro nível adicionou-se 1,28 g de S/kg e no segundo 2,56 g de S/kg, resultando em sete tratamentos. No segundo experimento duas fontes de cálcio foram avaliadas com o objetivo de pesquisar a eficácia destes sais na alcalinização da urina. No tratamento controle não houve adição de fontes de cálcio. Nos tratamentos 2 e 3 foram adicionados à dieta controle carbonato de cálcio e gluconato de cálcio, respectivamente, nas doses de +160 mEq/kg, resultando em três tratamentos. A urina produzida em cada período de 24 horas teve aferida seu volume, densidade e pH. No segundo experimento foi também medida a excreção urinária de cálcio no período de 72h. O equilíbrio ácido-básico foi avaliado pela hemogasometria de sangue venoso. A DLM no maior nível e o MHA diferiram da dieta controle em relação ao pH urinário (p<0,001) e seu poder acidificante foi maior que o do sulfato de cálcio (p<0,05). As duas fontes de cálcio alcalinizaram a urina, mas o carbonato de cálcio atingiu um pH urinário mais alto que o gluconato de cálcio. Concluiu-se que o efeito diferenciado das fontes de S e cálcio sobre o pH urinário é um indicador de que a participação do cálcio é dependente dos ânions a que está associado, o que leva ao questionamento sobre qual a melhor forma de avaliar sua participação no cálculo do EB. / Urolithiasis is a commom problem in the veterinary clinic considered as a cause of morbidity. The urolithiasis are closely associated with urinary pH and nutrition plays a key role in the control of this disease, because through dietary manipulation, it´s possible modify the urinary pH. The diet has cations and anions in their mineral composition and the difference between ions is measured in milliequivalents (mEq/kg) and called base excess (BE) of the diet, calculated by the equation: (49.9 x Ca) + (82, Mg x 3) + (43.5 x Na) + (25.6 x K) - (64.6 x P) - (62.4 x S) - (28.2 x Cl), being the concentration of elements in g/kg DM. The purpose of this study, divided in two experiments, was to evaluate the effect of addition of sources of sulfur (S) and calcium in the diets of cats on the urinary pH and acid-base balance. The addition of sulfur sources aimed to demonstrate the efficacy in urinary acidification. In the first experiment were evaluated three different sources of sulfur, calcium sulfate (CaSO4), DLMethionine (DLM) and Methionine hydroxy analogue (MHA) added to a control diet at two levels each. In the control treatment there was no addition of acidifying. At the first level was added 1.28 g S/kg and in the second 2.56 g S/kg, resulting in seven treatments. In the second experiment two calcium sources were evaluated in order to research the effectiveness of these salts in alkalinize urine. In the control treatment there was no addition of calcium sources. In treatments 2 and 3 were added to the control diet calcium carbonate and calcium gluconate, respectively, at doses of +160 mEq/kg, resulting in three treatments. The urine produced in each period of 24 hours had measured its volume, density and pH. The second experiment also measured the urinary excretion of calcium in the period of 72 hours. The acid-base balance was evaluated by blood gas analysis of venous blood. The DLM at the highest level and MHA differed of the control diet in relation to urinary pH (p<0.001) and their acidifying power was greater than the calcium sulfate (p<0.05). The two sources of calcium alkalinized the urine, but the calcium carbonate reached a urine pH higher than calcium gluconate. It was concluded that the effect of different sources of S and calcium on urinary pH is an indicator that the participation of calcium is dependent of the anions that is associated, which leads to questions about how is the best way to evaluate its participation in calculation of BE.

A indústria da construção civil é conhecida como umas das atividades econômicas que causam os maiores impactos ambientais desde o processo de extração da matéria prima até a produção dos produtos, incluindo o transporte e manutenção do ambiente construído. A produção de um dos seus principais componentes, o cimento, é o maior contribuinte para a emissão de gases de efeito estufa, principalmente devido a queima de combustíveis fósseis. Por este motivo, pesquisas na área de biotecnologia sustentável são conduzidas para diminuir e até mitigar os efeitos danosos provocados pelos fatores que compõem a construção civil. Dentre estas pesquisas destacam-se as que se baseiam na Biomimética, que é uma ciência que busca na Natureza as soluções tecnológicas para os problemas que os desenvolvimentos humanos geralmente apresentam: a geração de resíduos poluentes, uso de produtos químicos tóxicos e processos que operam com energia e pressão elevadas. Com base nos conceitos biomiméticos, este trabalho se propôs a estudar a biomineralização, que é um processo que ocorre na Natureza a milhares de anos e é responsável pela formação de muitas estruturas biomineralizadas tanto no ambiente terrestre como aquático. A biomineralização é um fenômeno provocado pela ação de diversas espécies de microrganismos que durante o processo de obtenção de energia reciclam minerais presentes no solo e na água e os precipitam na forma de sais inorgânicos. Este material precipitado age como agente ligante de partículas como no caso de formações geológicas (estromatólitos) ou exoesqueletos de animais marinhos, por exemplo. Neste estudo foi avaliado a biomineralização por biodeposição de carbonato de cálcio precipitado na presença da espécie de bactéria ureolítica (Bacillus subtilis) em ensaios em escala laboratorial utilizando corpos de prova de areia, argamassa e concreto. Os corpos de prova em areia e argamassa foram observados em MEV e EDS permitindo a identificação de células de microrganismos, formação de biofilme e provável formação de cristais de carbonato de cálcio na região de biofilme. Os corpos de prova de concreto foram utilizados para avaliar as consequências da biodeposição na absorção de água por capilaridade do material. Resultados indicam redução de 20% na absorção de água por capilaridade. Com os resultados obtidos é possível concluir que a técnica de biodeposição pode ser uma alternativa ao tratamento superficial de estruturas de concreto, contudo requer estudos posteriores de aplicação técnica e viabilidade econômica. / The construction industry has been known as one of the economic activities that cause the major environment impacts since the process of raw material extraction until the products manufacturing including transport and maintenance of the built environment. The production of one of the main compounds, the cement, is the largest contributor to the greenhouse gas emissions, mainly due to burn fossil fuels. For this reason, researches in sustainable biotechnological area are conducted to minimize and even mitigate the damaging effects either promoted by construction industry factors. Among these ones, it stands out researches based on Biomimetic, which is a science that seeks in Nature the technological solutions for problems that human’s development usually presents: the generation of pollutant residues, the use of toxic chemicals and process that operates in high pressure and energy. Based on biomimetic concepts this research proposes to study the biomineralization, which is a process that has occurred in the Nature for thousands of years and it is responsible for the formation of many structures either in soil and water environments. The biomineralization is a phenomenon caused by several specimens of microorganisms that during the process of obtaining energy, they recycle minerals presents at soil and water inducing precipitation as inorganic salts. This precipitated material works as a binder of particles similar to geologic formations (stromatolites) or exoskeleton of sea animal for example. In this study the biomineralization was evaluated through biodeposition of precipitated calcium carbonate by specimen of ureolytic bacteria (Bacillus subtilis). Essays were held using samples made by sand, mortar and concrete. The samples made by sand and mortar were observed at MEV and EDS, allowing the identification of microorganism cells, biofilm formation and probable formation of calcium carbonate crystals at biofilm region. The concrete samples were used to evaluate the consequences of biodeposition on water absorption by capillarity of the material. The results show reduction of 20% on water absorption by capillarity. According the results achieved it possible to conclude that the biodeposition technique can be an alternative to superficial treatment for concrete structures. However, it will be required more studies to evaluate technical application and economical availability.

Conchas do molusco Physa sp., um gastrópode (caracol) comum de aquários de água doce, serviram como modelo para o estudo de alguns aspectos envolvidos na biomineralização. A concha calcária é constituída por cristais de carbonato de cálcio depositados em associação com uma matriz orgânica. Os componentes cristalinos e a matriz, foram estudados por microscopia eletrônica de transmissão e de varredura, e caracterizados por métodos espectroscópicos e analíticos. A constituição cristalina, em geral, assemelha-se àquela existente na maioria dos moluscos, enquanto a camada nacarada, interna da concha, apresenta comparativamente maiores variações. A matriz orgânica consta de um componente insolúvel, essencialmente constituído por polissacarídeos, enxofre e fósforo; e outro componente solúvel, com predominância de serina, glicina, ácido aspártico e ácido glutâmico. A análise feita por ativação de nêutrons demonstrou maior concentração de cálcio, sódio e estrôncio; estes elementos estão geralmente relacionados à presença de aragonita, em outras conchas de moluscos. O estudo qualitativo da fase cristalina foi realizado por difração eletrônica e por espectroscopia de infravermelho. Para análise quantitativa, usou-se a difração de raios-X, sendo os dados refinados pelo método de Rietveld. Os resultados obtidos demonstram a existência de dois polimorfos do carbonato de cálcio, aragonita e calcita, na concha da Physa. A caracterização qualitativa dos componentes inorgânico e orgânico do material estudado, mostrou semelhanças com relação a outros gêneros de moluscos. Experimentos de cristalização do carbonato de cálcio in vitro produziram aragonita e vaterita em presença de ácido aspártico ou glutâmico. Sob ação de glicina, serina ou quitina, houve formação de calcita. Em presença da matriz orgânica insolúvel, houve cristalização de calcita, enquanto a matriz solúvel induziu a cristalização da aragonita. Analisou-se quantitativamente todas as fases cristalinas obtidas nestes experimentos e estudou-se a morfologia dos cristais formados através da MEV e por MO luz. O resultado comparativo das investigações usando a concha natural, e dos cristais sintetizados, permitiu confirmar o papel fundamental da matriz orgânica no processo de cristalização do carbonato de cálcio. / Shells of Physa sp., a common freshwater gastropod snail, were used as a model for mineralization studies of calcium carbonate. The shell is a biomineral that consists of organized crystalline deposits associated to an organic matrix, both of which were studied by transmission and scanning electron microscopy; they were further characterized by means of pectroscopic and analytical methods. As a whole, its structural organization does not differ greatly from that found in other mollusc shells, except for the innermost, nacreous layer, that lines the shell. The organic matrix in Physa was found to consist of an insoluble fraction, essentially containing a polysaccharide, sulphur and phosphor. In addition, another (soluble) fraction is present, in which serine, glycine, aspartic acid and glutamic acid residues prevail. Neutronic activation analysis demonstrates a high concentration of calcium, sodium and strontium, elements known to be related to the presence of aragonite in other molluscan shells. A qualitative study of the crystalline phase was obtained through use of electron diffraction and FTIR spectroscopy. For quantitative analysis X-ray diffraction was used, as refined by the Rietveld method. Results obtained demonstrate the existence of two calcium carbonate polymorphs, aragonite and calcite in the shell of Physa, Qualitative evaluation of both organic and inorganic material from Physa showed similarities to those found in other mollusk shells. In vitro experiments performed at similar-to-natural conditions, on crystallization of calcium carbonate, did also crystallize aragonite and vaterite, provided aspartic acid or glutamic acid were present; whereas calcite was formed in solutions containing glycine, serine or chitin. Aragonite did crystallize when the soluble organic matrix was added to the solution. All these crystalline phases obtained were quantitatively evaluated, their morphologies being studied through light and electron microscopies. A comparative study of the natural crystals from the shell, and those obtained in laboratory experiments, stresses the fundamental role of the organic matrix on calcium carbonate crystallization

A new design of closely intermeshing co-rotating twin-screw compounding extruder, developed at Brunel University, has been utilized in the development of quantitative techniques for characterization of dispersive and distributive mixing in thermoplastics materials prepared by extrusion compounding. Image analysis procedures were used to quantify mixing of polypropylene composites containing calcium carbonate filler using reflected light microscopy on polished surfaces, and transmitted light microscopy of microtomed pigmented sections. Stereological statistics have been applied to raw sample data; results are discussed in relation to mechanistic phenomena influencing particle agglomeration, dispersion and distribution of fillers in thermoplastics. Dispersive or intensive mixing determined from calcium carbonate filled polypropylene specimens showed that processing parameters had no significant influence except when filler was added midway along the machine although the melting zone was highlighted as having a marked effect on the rate of filler dispersion. Premixing of filler and polymer introduced additional agglomeration into the filler. A series of model experiments were undertaken to assess the influence of specific parameters. In this context moisture content emerged as having the single most important effect on filler compaction. Distributive or extensive mixing of carbon black pigmented specimens was very significantly affected by the presence of segmented disc elements at the end of the screws. These elements produced more than a six-fold increase in distributive mixing in the extrudate.

Abstract Heat exchangers are used in industrial processes to transfer energy from one source to another. Heat exchangers improve the energy efficiency of processes and therefore increase the profitability and decrease the environmental impact of production. Effectiveness of heat exchangers may be diminished by fouling, in which unwanted material deposits on the heat transfer surface reducing the heat transfer and increasing the pressure drop of the system. Due to fouling, the energy demand, and the operation and maintenance costs of industrial processes increase significantly. In addition, fouling causes considerable environmental effects due to the increased energy demand and the use of additives and cleaning chemicals. In this thesis, the crystallization fouling of calcium carbonate on heat transfer surfaces was studied using experimental and modeling methods with the aim to reduce fouling by increasing the understanding of the crystallization fouling phenomenon and providing a validated model for studying crystallization fouling on heat transfer surfaces. The fouling experiments were conducted in a laboratory scale set-up to study the crystallization fouling mechanism under controlled conditions. Based on the knowledge and data gained from the experiments, a crystallization fouling model was developed, and validated in various conditions. As a result, the most important parameters affecting crystallization fouling were identified, and the governing sub-processes were determined. The developed model was used to optimize the surface temperature of a heat exchanger to provide the maximum heat transfer rate when the heat exchanger is subject to fouling at various cleaning intervals. In addition, the used methods were applied in the study of the abatement of fouling by surface modifications. Based on the results, the studied crystallization process is governed by the surface integration sub-process. In addition, the residence time of the fluid at the wall affects the mass deposition. The results showed that the surface temperature and the shear stress are the most important parameters affecting fouling in the studied conditions, and therefore, they should be defined accurately. For this purpose, CFD was found to provide a useful tool. The developed models were found to predict reliably the experimental conditions. Therefore, the thesis shows that the developed model facilitates the design of heat exchangers, but also assists in minimizing the fouling of heat exchangers. / Tiivistelmä Lämmönvaihtimia käytetään teollisissa prosesseissa siirtämään energiaa kohteesta toiseen. Lämmönvaihtimet parantavat prosessien energiatehokuutta ja siten lisäävät tuotannon kannattavuutta ja vähentävät ympäristövaikutuksia. Lämmönvaihdinten energiatehokkuutta heikentää kuitenkin likaantuminen, jossa lämmönsiirtopinnalle muodostuu kerrostuma, joka heikentää lämmönsiirtoa ja aiheuttaa virtausvastusta. Likaantuminen lisää lämmönvaihdinten energiankulutusta ja käyttökustannuksia sekä aiheuttaa merkittäviä ympäristöpäästöjä kasvaneen energiantarpeen sekä lisä- ja puhdistusaineiden käytön vuoksi. Tässä työssä tutkittiin kalsium karbonaatin aiheuttamaa lämmönsiirtopintojen kiteytyvää likaantumista käyttäen sekä kokeellisia että mallinnusmenetelmiä. Työn tavoitteena oli lisätä tietoa kiteytyvästä likaantumisesta sekä kehittää validoitu laskentamalli, jolla voidaan tutkia lämmönsiirtopintojen kiteytyvää likaantumista. Likaantumiskokeet tehtiin laboratoriomittakaavan koelaitteessa, jolla voidaan tutkia likaantumismekanismia hallituissa olosuhteissa. Kokeista saadun tiedon ja aineiston perusteella kehitettiin kiteytyvää likaantumista kuvaava malli, joka validoitiin eri olosuhteissa. Tulosten perusteella identifioitiin tärkeimmät kiteytyvään likaantumiseen vaikuttavat parametrit sekä määritettiin rajoittavat osa-prosessit. Kehitettyä mallia käytettiin lämmönsiirtoprosessin optimoinnissa. Lisäksi käytettyjä metodeja sovellettiin tutkimukseen, jossa likaantumista pyrittiin vähentämään pintamodifikaatioiden avulla. Tulosten perusteella tutkittu kiteytymisprosessi on pinta-integraation rajoittama. Lisäksi havaittiin, että fluidin viipymäaika lämmönsiirtopinnalla vaikuttaa likaantumisnopeuteen. Tulokset osoittivat, että pintalämpötila ja leikkausjännitys ovat tärkeimmät kiteytyvään likaantumiseen vaikuttavat tekijät tutkituissa olosuhteissa. Näin ollen niiden tarkka määrittely on erittäin tärkeää likaantumisnopeuden mallintamiseksi luotettavasti. Virtauslaskenta (CFD) osoittautui hyödylliseksi työkaluksi näiden parametrien määrittämisessä. Tulosten perusteella kehitetty malli ennustaa luotettavasti kokeellisia olosuhteita. Näin ollen tämä työ osoittaa, että kehitettyä mallia voidaan käyttää apuna paitsi lämmönvaihtimien suunnittelussa myös lämmönsiirtopintojen kiteytyvän likaantumisen vähentämisessä.

Le carbonate de calcium précipité (CCP) est un additif multi-fonctionnel que l'on trouve dans de nombreuses applications telles que les peintures, la pharmacie, la cosmétique etc. Il peut être synthétisé industriellement par différents procédés mais la voie la plus commune est la carbonatation. Ce procédé consiste à faire barboter du dioxyde de carbone dans une suspension d'hydroxyde de calcium afin de produire des particules de CCP. Toutefois, la problématique inhérente à la synthèse et à l'utilisation de ce précipité est la maîtrise de l'agglomération des monoparticules. En effet, ces dernières sont de taille nanométrique et s'agglomèrent en structures "ouvertes" de taille micrométrique. Cette agglomération a des conséquences directes sur la conduite du procédé ainsi que sur les propriétés d'usage du produit final. Ainsi, le but de ce travail est d'appréhender les mécanismes de ce phénomène, de déterminer sa cinétique et d'étudier l'impact de différents paramètres opératoires dans des conditions industrielles complexes. Sous réserve que les cinétiques de nucléation et croissance cristalline soient connues, le noyau d'agglomération peut être obtenu grâce à un traitement mathématique des distributions de tailles expérimentales. En faisant varier différents paramètres du procédé, il apparait que la constante d'agglomération augmente avec la température alors qu'il existe un optimum par rapport au taux de cisaillement. En se basant sur cette conclusion, une expression de la constante d'agglomération est proposée en fonction du taux de cisaillement, qui pourra être utilisée pour contrôler l'agglomération dans le réacteur industriel / Precipitated calcium carbonate (PCC) is a mineral additive of various applications in paints, pharmacy, cosmetics, etc. It can be industrially synthesized through several ways but the most common one is the carbonation route. It consists in bubbling carbon dioxide in a suspension of calcium hydroxide to get particles of PCC. However, the challenge related to the synthesis and the use of this precipitate is the control of the agglomeration of the monoparticles. Indeed, they are agglomerated in micrometric "loose" structures. This agglomeration has consequences on the run of the process and the end use properties of the final product. Thus, the aim of this work is to understand the mechanisms of this phenomenon, to determine its kinetics and to study the impact of different process parameters under complex industrial conditions. The method to determine the agglomeration kernel is based on the resolution of a population balance using the moment approach. Provided that the kinetic rates of nucleation and growth are known, the agglomeration kernel can be obtained from a mathematical treatment of the experimental particle size distributions. Thanks to an agglomeration kernel model including the crystal growth, it is possible to determine the value of the agglomeration constant. Finally, by varying different process parameters, it also appears that the agglomeration constant increases with temperature whereas an optimum is observed for the shear rate. Regarding to this fact, we can also propose an expression of the agglomeration constant as a function of the shear rate, which can be used to control the agglomeration in the industrial reactor

“Whiting” is a term used to describe a sharply defined patch of water that contains high levels of suspended, fine-grained calcium carbonate (CaCO3). These features are named for their bright (at times white) appearance when compared to surrounding waters, and have been found to occur globally, persisting for multiple consecutive days. Although whitings have been widely studied using chemical, biological, geological, and physical techniques, there has been little effort to document their spatio-temporal distributions in a systematic way, not to mention the lack of consensus on what generates whitings and allows them to persist for days to weeks at a time. In particular, although fishermen and aircraft pilots have reported whiting-like features off southwest Florida (e.g., a sighting off the Ten Thousand Islands was reported on October 29, 2013), there has been no targeted study on these features in this area. Therefore, the objective of this study is two fold: 1) to document the spatial-temporal distributions of whitings in southwest Florida (SWFL) coastal waters from 2003 through 2015 using satellite imagery to study how their occurrence is related to several environmental variables and 2) to conduct field and laboratory measurements to determine the particle composition and water characteristics in and outside the whiting features. To achieve objective one, a multi-year time series from 2003 through 2015 was developed over SWFL using Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Customized processing was used in order to removed clouds and other artifacts and to delineate the surface whiting features. From this, statistics and distribution maps of whiting occurrence were generated. Annual mean whiting coverage peaked in 2011 (11 km2), when whiting reached a maximum daily visible coverage of 92 km2 on February 23. For the entire time series, the highest daily coverage observed was 126 km2 on December 6, 2008. Over all, whitings had higher spatial coverage during the spring and autumn, with 88% of all whiting coverage occurring within 40 km of the coastline. Images of average seasonal spatial distributions showed that over 90% of whitings located between 40 and 70 km of shore occurred specifically during the winter and autumn. A multivariate linear regression was performed, which found little to no correlation between annual whiting coverage and environmental factors such as sea surface temperature (SST), wind, and river discharge. This analysis was also applied to spatial distributions of whiting events within and outside of 20 km and 40 km from shore. The only statistically significant result was that of SST, as well as SST with river discharge and whiting events distributed more than 20 km from shore. In order to accomplish objective two, several field campaigns were conducted to collect in-situ data and water samples of pre-, post-, and occurring whiting event conditions to provide information on composition, driving forces, and variables that cannot be derived via satellites. Samples were collected for taxonomic identification, chemical analysis, bottom sediment grain size fractionation, in-situ remote sensing reflectance (Rrs), particle backscattering (bbp), chlorophyll-a concentration ([chl-a]), particulate absorption (ap), and gelbstoff (otherwise known as color dissolved organic matter, or CDOM) absorption (ag). Taxonomic identification of marine phytoplankton within whiting water revealed the presence of a dominant, small (<5 >μm), centric diatom species during a sampled whiting event. Through the use of scanning electron microscopy (SEM), these were identified as Thalassiosira sp. Amorphous to fully formed crystals of calcium carbonate were present, attached to cells of Thalassiosira sp., localized to the girdle bands. All other diatom species were devoid of similar growths. In comparing the waters within a whiting area to outside waters, no significant differences were found in ap, ag, nor [chl-a]. The carbonate parameters of whiting water differed from outside water, however due to low sample numbers these results are inconclusive. Average backscattering was twice as high within whiting waters compared to non-whiting water, and measured in-situ Rrs was higher at all wavelengths (400 – 700 nm) within whiting water, with a spectral shape similar to outside waters. Overall, this is the first time that SWFL whiting events have been characterized systematically using satellite imagery, field and laboratory as well as meteorological data to diagnose whiting causes and maintenance mechanisms. Although these results are inconclusive, they add new information to the existing literature on this phenomenon.

The decline of tree islands in the freshwater-Everglades wetland because of hydrologic manipulation, has compromised valuable ecosystem services. Although the role of tree islands in maintaining freshwater quality stems largely from evapotranspiration processes, fundamental questions remain about the effects of different geologic materials on their hydrogeochemical functioning. To reduce this uncertainty, the lithological composition of a set of man-made tree islands was investigated coupled with long-term hydrologic and hydrochemical data. Key results indicate that limestone substrates and peat substrates with elevated proportions of sand, facilitated surface water-groundwater interactions and mineral dissolution. However, limestone-based islands were more effective in lowering the water table and concentrating solutes in response to evapotranspiration during low surface water stages. Additionally, the peat substrate of an island with low sand content favored the thermodynamic conditions for calcite accumulation in the phreatic zone, while phosphorus concentrations in the groundwater were associated with the breakdown of organic matter.