Spelling suggestions: "subject:"ozone."" "subject:"azone.""
351 |
Three Air Quality Studies: Great Lakes Ozone Formation and Nitrogen Dry Deposition; and Tucson Aerosol Chemical CharacterizationFoley, Theresa Anne January 2012 (has links)
The Clean Air Act of 1970 was promulgated after thousands of lives were lost in four catastrophic air pollution events. It authorized the establishment of National Ambient Air Quality Standards or (NAAQS) for six pollutants that are harmful to human health and welfare: carbon monoxide, lead, nitrogen dioxide, particulate matter, ozone and sulfur dioxide. The Clean Air Act also led to the establishment of the United Stated Environmental Protection Agency (US EPA) to set and enforce regulations. The first paper in this dissertation studies ozone in the Lake Michigan region (Foley, T., Betterton, E.A., Jacko, R., Hillery, J., 2011. Lake Michigan air quality: The 1994-2003 LADCO Aircraft Project (LAP). Atmospheric Environment 45, 3192-3202.) The Chicago-Milwaukee-Gary metropolitan area has been unable to meet the ozone NAAQS since the Clean Air Act was implemented. The Lake Michigan Air Directors' Consortium (LADCO) hypothesized that land breezes transport ozone precursor compounds over the lake, where a large air/water temperature difference creates a shallow conduction layer, which is an efficient reaction chamber for ozone formation. In the afternoon, lake breezes and prevailing synoptic winds then transport ozone back over the land. To further evaluate this hypothesis, LADCO sponsored the 1994-2003 LADCO Aircraft Project (LAP) to measure the air quality over Lake Michigan and the surrounding areas. This study has found that the LAP data supports this hypothesis of ozone formation, which has strong implications for ozone control strategies in the Lake Michigan region. The second paper is this dissertation (Foley, T., Betterton, E.A., Wolf, A.M.A., 2012. Ambient PM10 and metal concentrations measured in the Sunnyside Unified School District, Tucson, Arizona. Journal of the Arizona-Nevada Academy of Science, 43, 67-76) evaluated the airborne concentrations of PM10 (particulate matter with an aerodynamic diameter of 10 microns or less) and eight metalloids and metals (arsenic, beryllium, cadmium, chromium, cobalt, lead, manganese, and nickel) in the southern Tucson metropolitan area. A Tucson company that uses beryllium oxide to manufacture thermally conductive ceramics has prompted strong citizen concern. This study found that the study area has good air quality with respect to PM₁₀ and metals, with ambient concentrations meeting US Environmental Protection Agency and World Health Organization standards. Beryllium was detected only once (during a dust storm) and was ascribed to naturally-occurring beryllium in the suspended soil. The third paper (to be submitted to the Journal of Great Lakes Research) studies nitrogen dry deposition over Lake Michigan and Lake Superior. Numerous studies have shown that wet and dry deposition of nitrogen has contributed to the eutrophication of coastal waters and declining productivity of marine fisheries. Nitrogen dry deposition over the Great Lakes themselves, as opposed to the shorelines, has not been documented in the peer-reviewed literature. This paper calculates nitrogen dry deposition over Lake Michigan and Lake Superior, using aircraft measurements from the LADCO Aircraft Study, and finds that over-water, nitrogen dry deposition is a significant source of nitrogen to Lake Michigan and Lake Superior.
|
352 |
Combined Use of Models and Measurements for Spatial Mapping of Concentrations and Deposition of PollutantsAmbachtsheer, Pamela January 2004 (has links)
When modelling pollutants in the atmosphere, it is nearly impossible to get perfect results as the chemical and mechanical processes that govern pollutant concentrations are complex. Results are dependent on the quality of the meteorological input as well as the emissions inventory used to run the model. Also, models cannot currently take every process into consideration. Therefore, the model may get results that are close to, or show the general trend of the observed values, but are not perfect. However, due to the lack of observation stations, the resolution of the observational data is poor. Furthermore, the chemistry over large bodies of water is different from land chemistry, and in North America, there are no stations located over the great lakes or the ocean. Consequently, the observed values cannot accurately cover these regions. Therefore, we have combined model output and observational data when studying ozone concentrations in north eastern North America. We did this by correcting model output at observational sites with local data. We then interpolated those corrections across the model grid, using a Kriging procedure, to produce results that have the resolution of model results with the local accuracy of the observed values. Results showed that the corrected model output is much improved over either model results or observed values alone. This improvement was observed both for sites that were used in the correction process as well as sites that were omitted from the correction process.
|
353 |
Chlorine, Fluorine and Water in the Stratosphere: Chemistry, Transport and Trends based on ACE-FTS measurementsNassar, Raymond January 2006 (has links)
The Atmospheric Chemistry Experiment (ACE) is a satellite mission for remote sensing of the Earth's atmosphere using the solar occultation technique. The primary instrument on this satellite is the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). ACE-FTS retrievals are described with a focus on the creation of <em>a priori</em> temperature and pressure profiles. ACE-FTS measurements are then used to investigate the chemistry, transport and trends of chlorine, fluorine and water in the stratosphere, leading to an improved understanding of processes affecting both stratospheric ozone depletion and global climate change. <br /><br /> Total chlorine (Cl<sub>TOT</sub>) in the stratosphere is determined using ACE-FTS measurements of eleven chlorine-containing species, supplemented by both other measurements and models, to determine Cl<sub>TOT</sub> as a function of altitude in five latitude zones. All resulting Cl<sub>TOT</sub> profiles are nearly linear, with a slight slope. Mean Cl<sub>TOT</sub> for 2004 is determined to be 3. 65 ppbv for both the northern and southern midlatitudes (with a precision and estimated accuracy of ??0. 09 and ??0. 13 ppbv, respectively). A slightly lower value of mean Cl<sub>TOT</sub> is determined for the tropics and slightly higher values at high latitudes. Total fluorine (F<sub>TOT</sub>) in the stratosphere is also determined primarily from ACE-FTS measurements using a similar approach, resulting in stratospheric F<sub>TOT</sub> profiles which are nearly linear with mean values ranging from 2. 50 to 2. 59 ppbv for each latitude zone (with a precision of 0. 04-0. 07 ppbv and an estimated accuracy of 0. 15 ppbv). The observed slopes and pattern of latitudinal variation are evidence of the beginning of a decline in global stratospheric chlorine and of the continuing increase in global stratospheric fluorine levels. <br /><br /> The abundance of water in the stratosphere is investigated for the northern hemisphere midlatitudes in 2004 using ACE-FTS measurements. Potential water is determined as [H<sub>2</sub>O]+2[CH<sub>4</sub>] and from [H<sub>2</sub>O] versus [CH<sub>4</sub>] correlations, resulting in a value of 7. 14??0. 05 ppmv, which is used to determine a value of 3. 65??0. 15 ppmv for the mean abundance of water entering the stratosphere. Both values are compared directly with historical data from the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument (1985-1994) and show a negligible change, implying that the increases observed by ATMOS and other long-term measurements from that time period have not continued. <br /><br /> The removal of stratospheric water in the Arctic vortex is investigated using ACE-FTS measurements. Using derived quantities from a meteorological data assimilation, northern hemisphere occultations from early 2004 are classified as vortex, vortex edge or extravortex. [CH<sub>4</sub>] versus [N<sub>2</sub>O] correlations are used to further classify the extravortex occultations as tropical, subtropical or midlatitude. Comparisons between profiles of [N<sub>2</sub>O], [CH<sub>4</sub>] and [H<sub>2</sub>O] inside and outside the Arctic vortex, give estimates of upper stratospheric and lower mesospheric descent rates, indicating that descent in the winter 2004 Arctic vortex was rapid, with evidence of descent at higher altitudes than in past years. <br /><br /> The dehydration of air in the tropical tropopause layer and mechanisms for the entry of water vapor into the stratosphere are investigated by an analysis of ACE-FTS profiles of temperature, water vapor and [HDO]/[H<sub>2</sub>O]. Month-to-month comparisons for 2004 and 2005 reveal a clear pattern of seasonal variation and a correlation between minimum temperature and maximum HDO depletion. Further interpretation indicates that the gradual dehydration mechanism accompanied by lofting of ice particles in the tropical troposphere is the most likely explanation for the observed seasonal variation and the shape of the [HDO]/[H<sub>2</sub>O] profiles.
|
354 |
Occurrence and removal of emerging contaminants in wastewatersJanna, Hussein January 2011 (has links)
Over the past decade, the occurrence and removal of emerging contaminants in the environment has received much attention. Both natural and synthetic progestogens, which are hormones, and also benzotriazoles are two examples of such emerging contaminants. Sewage treatment works are recognised as one of the main routes of these compounds to the environment. Low concentrations (nanograms per litre) of biologically active chemicals may exhibit an impact on aquatic organisms and human health. This study was undertaken to determine the occurrence and removal of these two classes of chemicals at sewage treatment works, along with an evaluation of the performance of advanced treatment and also to investigate their fate in the aquatic environment. Therefore, field-based sampling campaigns were undertaken at a sewage treatment works, rivers and potable water to achieve these aims. Solid phase extraction and LC/MS/MS were used in order to analyse the samples from these different locations, along with catchment modelling and assessment of how the use of benzotriazoles may contribute to their presence in the environment. The results have demonstrated that progestogens and benzotriazoles are in the sewage system; the natural hormone (progesterone) was the most predominant compound entering the sewage treatment work (46.9 ng/l) among the progestogens while concentrations of the benzotriazoles were two orders of magnitude higher than the progestogens. The conventional sewage treatment works were, to some extent, able to remove these compounds from wastewaters. However, this may not be adequate to afford protection to the environment. The investigation of advanced treatments, ozone, granular activated carbon and chlorine dioxide, indicated no further significant removal of progestogens, probably as a result of concentrations being close to method detection limits. However, there were indications that benzotriazoles were removed. A degradation study demonstrated that the natural hormone (progesterone) was degraded rapidly while benzotriazoles were not degraded. Catchment modelling indicated that high (up to 2,000 ng/l) concentrations of benzotriazoles would be present in surface waters used for potable supply, and consequently benzotriazoles were found in the tap water with mean concentrations of 30.9 ng/l (benzotriazole) and 15.1 ng/l for tolyltriazole. It is therefore apparent that although conventional treatment may be seen as effective, achieving over 90% removal, this may not be good enough. However, before investing in tertiary treatment, a number of factors, such as the effectiveness at different sites, the presence of degradation products and costs, both financial and in relation to energy use, need to be considered.
|
355 |
Bayesian Spatial Quantile Regression.Reich, BJ, Fuentes, M, Dunson, DB 03 1900 (has links)
Tropospheric ozone is one of the six criteria pollutants regulated by the United States Environmental Protection Agency under the Clean Air Act and has been linked with several adverse health effects, including mortality. Due to the strong dependence on weather conditions, ozone may be sensitive to climate change and there is great interest in studying the potential effect of climate change on ozone, and how this change may affect public health. In this paper we develop a Bayesian spatial model to predict ozone under different meteorological conditions, and use this model to study spatial and temporal trends and to forecast ozone concentrations under different climate scenarios. We develop a spatial quantile regression model that does not assume normality and allows the covariates to affect the entire conditional distribution, rather than just the mean. The conditional distribution is allowed to vary from site-to-site and is smoothed with a spatial prior. For extremely large datasets our model is computationally infeasible, and we develop an approximate method. We apply the approximate version of our model to summer ozone from 1997-2005 in the Eastern U.S., and use deterministic climate models to project ozone under future climate conditions. Our analysis suggests that holding all other factors fixed, an increase in daily average temperature will lead to the largest increase in ozone in the Industrial Midwest and Northeast. / Dissertation
|
356 |
Analýza časoprostorové variability koncentrací ozonu v Jizerských horách / Temporal and spatial analysis of ozone in the Jizerske hory Mts.Stoklasová, Petra January 2012 (has links)
The aim of this thesis is to analyze and evaluate temporal and spatial patterns of concentrations of ambient ozone in the CHKO Jizerské hory. The Jizerské hory Mts. are an area where one of the highest concentrations of ambient ozone are measured every year and, therefore, our attention was focused on this area. The measurements were carried out between 2006 and 2010 at 13 sites (714-1000 m n. m.) in the CHKO Jizerské hory. From the input data, which were fortnightly average nitrate concentrations created on the filters of Ogawa passive samplers, fortnightly average concentrations of ambient ozone were computed using the empirical flow. Ambient ozone concentrations ranged from 13,8 ppb (year 2007) to 72,1 ppb (year 2006). From the five-year period under study defy the year 2006, when the highest concentrations of ambient ozone were measured. The lowest concentrations occurred in 2009. In all years, the concentrations of ambient ozone increased with increasing elevation and this gradient ranged from 2,7 to 4,6 ppb on 100 meters altitude. The accuracy and precision of measurement was very good (accuracy: R2 = 82 %; precision: R2 = 98 %). By multiple linear regression it was found, that ambient ozone concentration are influenced, in addition to the altitude, by ozone concentrations from previous...
|
357 |
Flottation réactive à l'ozone de contaminants modèles issus de papiers récupérés : étude hydrodynamique et réactivité / Ozone reactive flotation of model contaminants contained in recovered papers : hydrodynamics and reactivity studyHerisson, Alexandre 25 June 2018 (has links)
La diminution de la qualité des collectes des papiers récupérés ainsi que l’accumulation de substances dissoutes dans les eaux de procédés affecte l’efficacité des lignes de désencrage industrielles et contamine davantage les effluents liquides. Dans ce contexte, le LGP2 a développé depuis quelques années un procédé innovant de désencrage, la flottation réactive à l’ozone, afin de dégrader chimiquement les polluants dissouts en parallèle de l’élimination de l’encre. Afin de mieux comprendre les mécanismes mis en jeu, des essais de flottation à l’air et à un mélange ozone/oxygène, sur trois contaminants modèles, sélectionnés après une étude bibliographique préalable, ont été réalisés dans un milieu diphasique gaz/liquide, en l’absence de fibres cellulosiques. Les expérimentations ont été conduites sur deux pilotes de laboratoire instrumentés : une colonne à bulles fonctionnant avec de l’air uniquement, pour l’étude du comportement hydrodynamique (taille et distribution de bulles, rétention gazeuse) en présence des contaminants dissouts, et une deuxième colonne à bulles, similaire mais conçue avec des matériaux résistants aux gaz corrosifs, dédiée à l’étude des réactions d’oxydation en présence d’ozone. L’examen du comportement hydrodynamique montre que les conditions de débit de gaz et d’injection retenues conduisent à des tailles de bulles optimales pour une flottation efficace, que ce soit en présence ou absence de contaminants. Ces conditions obtenues avec de l’air ont été transposées en première approximation au système ozone/oxygène. L’étude du transfert de l’ozone et de sa réactivité avec les trois contaminants modèles, à différentes températures et concentrations en ozone, a conduit à la détermination des constantes cinétiques de réaction et a montré que les contaminants étaient, selon leur nature, oxydés ou dépolymérisés. Bien que la DCO des solutions traitées diminue très peu après la flottation réactive à l’ozone, la qualité des effluents est améliorée sur le plan de leur biodégradabilité. / The decrease of the recovered paper collection quality and the accumulation of dissolved substances in process water affect the deinking line efficiency and contaminate more and more the liquid effluents. In this context the LGP2 has developed an innovative deinking process, the ozone reactive flotation, to chemically degrade dissolved pollutants in parallel with ink removal. To better understand the mechanisms involved, air and ozone/oxygen flotation trials have been conducted on three model contaminants selected in a preliminary bibliographic review, in a two-phase gas/liquid system, in the absence of fibers. Experiments have been carried out on two instrumented laboratory pilots: a bubble column operating only with air for the study of the hydrodynamics of the reactor (bubbles size and distribution, gas hold-up) in the presence of dissolved contaminants, and a second one, similar in its conception but built using materials resistant to corrosive gas, dedicated to the study of the oxidation reactions with ozone. The evaluation of the hydrodynamics related to gas flow and injection system selected, studied with air but supposed to be the same with ozone/oxygen gas mixture, shows that the bubble size, with or without contaminants, is optimal for an efficient flotation process. The study of ozone mass transfer and reactivity with the three model contaminants, for several temperatures and ozone concentrations, leads to the calculation of kinetic constants and shows that the contaminants, depending on their nature, have been oxidized or depolymerized. Although the COD of the treated solutions does not decrease a lot after the ozone reactive flotation, the effluent quality has been improved in terms of biodegradability since contaminants are partially degraded.
|
358 |
Revisão sistemática de literatura sobre o uso terapêutico do ozônio em feridas / Systematic Literature Review about the therapeutic use of the ozone in woundsOliveira, Juliana Trench Ciampone de 28 November 2007 (has links)
Dentre os tratamentos possíveis para feridas, um deles, ainda pouco discutido e divulgado, é o uso terapêutico do ozônio. A finalidade desta revisão foi verificar se há benefícios neste uso em feridas. Os objetivos foram: buscar evidências científicas sobre estes benefícios por meio da revisão sistemática da literatura científica; realizar levantamento bibliográfico de estudos primários sobre a temática; analisar a qualidade metodológica destes estudos e discutir sobre as evidências de seus resultados. A metodologia utilizada foi a revisão sistemática da literatura científica, de acordo com o preconizado pelo Centro Cochrane do Brasil. Foram selecionadas oito bases de dados eletrônicas que disponibilizam publicações de pesquisas na área da saúde (CINAHAL, COCHRANE, EMBASE, LILACS, MEDLINE, OVID, PubMed, USP/Sibi/DEDALUS). Além destas bases, um estudo foi encontrado em um livro alemão específico sobre a temática. A busca foi feita de acordo com os Descritores em Ciências da Saúde baseado no MESH (Medical Subject Headings of U.S. National Library of Medicine). Foram encontrados 1637 estudos, sendo 55 pré-selecionados, e apenas 23 incluídos para a revisão. Dentre os principais resultados destacam-se: 52,2% dos estudos incluídos foram ensaios clínicos não controlados, 21,7% ensaios clínicos randomizados controlados abertos, 17,4% ensaios clínicos não randomizados controlados e 8,7% relatos de casos. A maioria dos estudos considerou como desfecho a cicatrização total da ferida ou a estimulação do processo de cicatrização, seguidos da melhora do aspecto da ferida, diminuição da dor/sintomas, melhora dos exames laboratoriais e, um deles relatou diminuição de odor da ferida. Foi analisado o quanto cada estudo controlou ou não variáveis intrínsecas e extrínsecas e quem foram os sujeitos de pesquisa em cada um deles. Analisou-se, ainda, se houve estratificação de variáveis entre os grupos controle e experimental nos estudos controlados e aplicou-se a Escala adaptada de Jadad para verificar a validade interna dos estudos randomizados, cujas pontuações obtidas foram inferiores ao mínimo estabelecido para um estudo de alta qualidade. Como conclusão, ao considerar apenas como estudos de qualidade aqueles randomizados, é possível reconhecer evidência forte do benefício do uso do ozônio, o que confirma a hipótese desta revisão. Mas, a partir da análise de sua validade interna, controle de variáveis interferentes e quantidade e tipo de população, os estudos apresentam problemas de condução e não é possível esse mesmo reconhecimento. Não é desprezível, porém, o fato de que todos os estudos obtiveram resultados favoráveis com o uso de ozônio, o que enseja a recomendação de viabilidade de realização de mais estudos, do tipo ensaios clínicos controlados e bem conduzidos, com estratificação de variáveis intrínsecas e extrínsecas e, principalmente, que utilizem como única intervenção o próprio ozônio, sem associar qualquer tipo de método que interfira no processo de cicatrização. Finalmente, considerando todos os aspectos discutidos e a realidade brasileira, o ozônio, poderia ser uma importante opção de tratamento para feridas e trazer diversos benefícios aos seus portadores, caso isso fosse provado por estudos bem delineados e de qualidade / Among the possible treatments for wounds there is one that is still very little discussed and divulged: the therapeutic use of the ozone. The purpose of this review is to verify if there are benefits of that use. These were the following goals: to search for scientific evidence of those benefits through systematic scientific literature review; to the bibliographic research of basic studies related to this theme; to analyze the methodological quality of those studies and to discuss the evidence of their results. The methodology used was the systematic scientific literature review, according to what is stated by the Cochrane Center of Brazil. Eight electronic data bases that contain publications of researches in the health area were selected (CINAHAL, COCHRANE, EMBASE, LILACS, MEDLINE, OVID, PubMed, USP/Sibi/DEDALUS). Apart from those data bases, one study was found in a Germany book specific on that theme. The research was done according to the Health Science Key-words based on the MESH (Medical Subject Headings of U.S. National Library of Medicine). 1637 studies were found, 55 were pre-selected and only 23 were included in the review. The main results were the following: 52,2% of the included studies were non-controlled clinical trials, 21,7% were open-label randomized controlled clinical trials, 17,4% were non-randomized controlled clinical trials and 8,7% were case reports. Most part of the studies considered the complete wound healing or the healing process stimulation as outcomes, followed by improvement of the wound aspects, reduction in the pain/symptoms, improvement on the laboratory exams and one of them reported the wound smell reduction. This review analyzed how many intrinsic and extrinsic variables were controlled and who the subjects were in each study. Besides that, it was analyzed if there were variables stratification among the control and the experimental groups in the controlled trials and the adapted Jadad Scale was applied to verify the internal validity of the randomized trials, whose obtained scores were less than the minimum standardized for a high quality study. To sum up, when only randomized trials are considered as of quality, it is possible to recognize strong evidence of benefit in the use of the ozone, which confirms the hypothesis of this review. But, when analyzing the internal validity, the controlled variables and the number and the kind of subjects, the studies presented execution problems and it is not possible to recognize the same thing. It is needless to say that all studies have obtained favorable results in the use of the ozone, which triggers the need to carry out more related studies, as well as to conduct controlled clinical trials, with intrinsic and extrinsic variables stratification and, mainly, that the ozone without associating any method that can interfere in the wound healing is used as unique intervention. Finally, considering all discussed aspects and the Brazilian reality, the ozone could be an important option of wound treatment and it could bring many benefits to its carriers if this was proofed by well conducted quality studies
|
359 |
Estudo da degradação de fenol em solução aquosa por meio dos processos de oxidação por O3, O3/UV e O3-H2-O2 / Study of phenol degradation in aqueous solution by means of the oxidation processes O3, O3/UV e O3-H2-O2Choquechambi Catorceno, Litzy Lina 12 December 2008 (has links)
Neste trabalho, estudou-se a degradação de fenol em solução aquosa por meio dos processos O3, O3/UV e O3-H2O2. Os experimentos foram realizados em batelada com alimentação de ozônio em um reator fotoquímico de bancada com fonte de radiação UVC (254 nm) anular de imersão. Foram avaliados os efeitos das seguintes variáveis, no intervalo de valores mínimos e máximos: concentração inicial de fenol (TOC0) (100 e 500 mgC L-1); pH (entre 3 e 11); concentração de ozônio (10 e 50 mg L-1) e/ou de peróxido de hidrogênio (0,1 e 10 mM); presença ou não de radiação UVC. Utilizaram-se planejamentos experimentais fatoriais fracionários em dois níveis e apresentam-se análises estatísticas para as respostas (remoções porcentual e absoluta de TOC e taxa de remoção de TOC). Os experimentos resultaram em valores máximos de remoção de TOC iguais a 86% (processo O3-H2O2) e 99% (processo O3/UV), para TOC inicial mínimo (valor nominal igual a 100 mgC L-1); nesse caso, a maior taxa de remoção de TOC foi obtida com o processo O3-H2O2 com máxima concentração de peróxido de hidrogênio e pH 8. Na ausência de H2O2, o aumento da concentração de ozônio e a irradiação UVC apresentaram efeito positivo sobre a remoção de TOC, bem como sobre a taxa de remoção, para menor concentração inicial de fenol. Por sua vez, o aumento da concentração de H2O2 no processo O3-H2O2 favoreceu todas as respostas avaliadas, em particular para a maior concentração de ozônio. Para TOC0 baixo, a comparação entre os processos permite concluir que na grande maioria dos casos o processo O3-H2O2 resultou melhor que os sistemas O3 e O3/UV quanto à taxa de remoção de TOC, para os dois níveis de concentração de H2O2 avaliadas; para a remoção de TOC, porém, há forte dependência de [O3] e [H2O2].Para TOC0 alto, o processo O3-H2O2 mostrou-se sempre mais vantajoso que os processos O3 e O3/UV para todas as respostas. Utilizou-se a técnica de redes neurais artificiais para a obtenção de modelos empíricos para previsão da taxa de remoção de TOC em função do tempo para os sistemas O3, O3/UV e O3-H2O2. Os modelos ajustaram adequadamente os resultados experimentais e podem ser convenientemente acoplados a balanços de massa com a finalidade de simular o desempenho dos processos para diferentes condições das variáveis estudadas. / In this work, the degradation of phenol in aqueous solutions was studied by means of the O3, O3/UV, and O3-H2O2 oxidation processes. Experiments were carried out in batch with ozone feed in a bench-scale photochemical reactor with an annular UVC (254 nm) radiation source. The effects of the following variables were studied, according to their minimum and maximum levels: phenol initial concentration (TOC0) (100 and 500 mgC L-1); pH (between 3 and 11); ozone concentration (10 and 50 mg L-1) and/or hydrogen peroxide concentration (0.1 and 10 mM); presence or absence of UVC radiation. Fractional factorial designs at two levels were employed, and statistical analyses for the responses (percent and total TOC removals, TOC removal rate) are presented. The experiments resulted in maximum TOC removals of 86% (O3-H2O2) and 99% (O3/UV) for the minimum initial TOC (reference value, 100 mgC L-1). In this case, the highest TOC removal rate was obtained with the O3-H2O2 process with maximum hydrogen peroxide concentration and pH 8. In the absence of H2O2, the increase in ozone concentration and UVC irradiation showed a positive effect upon TOC removal and TOC removal rate, for the lowest initial phenol concentration. On the other hand, the increase in H2O2 concentration in the O3-H2O2 process favored all measured responses, particularly for the highest ozone concentration. For low TOC0, the comparison of the processes studied enabled to conclude that in most cases the O3-H2O2 process revealed to perform better than the O3 and O3-UV systems in terms of the TOC removal rate for the two H2O2 concentration levels; for the TOC removal, however, a strong dependence on [O3] and [H2O2] was verified. For higher TOC0 values the O3-H2O2 process showed a better performance than the others for all responses.The artificial neural networks methodology was used to obtain empirical kinetic models for the prediction of TOC removal rate as a function of reaction time for O3, O3/UV, and O3-H2O2 systems. The models adequately fitted experimental results and can be conveniently coupled with mass balances to simulate the process performance for different sets of values for the input variables.
|
360 |
Radiação ultravioleta e ozônio aplicados como métodos alternativos de desinfecção de efluentes secundários de esgoto sanitário / Alternatives methods for the disinfection of wastewater secondary effluents applying ultraviolet radiation and ozoneDias, Virgínia Dantas 29 June 2001 (has links)
A cloração é largamente utilizada para a desinfecção de águas de abastecimento e residuárias, porém o potencial de toxicidade da cloração por seus subprodutos torna o processo menos atrativo. O dióxido de cloro surge como alternativa de desinfecção, porém a sua geração envolve reações bastante dependentes das concentrações de reagentes, das condições físico-químicas, podendo gerar também subprodutos prejudiciais à saúde humana. Outras tecnologias alternativas, como o ozônio e a radiação ultravioleta apareceram como processos tecnicamente viáveis. Neste trabalho buscou-se realizar revisão crítica da literatura existente sobre a desinfecção realizada com radiação ultravioleta e ozônio, bem como investigar e interpretar os aspectos relevantes do desempenho da desinfecção de efluentes de esgoto sanitário com ozônio e com radiação ultravioleta na inativação de coliformes totais e coliformes fecais. Na parte experimental avaliou-se as doses de 80, 95 e 120 mg/L e tempos de contato de 20, 30 e 35 minutos para a desinfecção com ozônio. Na desinfecção com radiação ultravioleta, utilizou-se de tempos de exposição de 10, 30, e 60 segundos, mantendo-se a mesma intensidade média de radiação e variando-se a espessura de lâmina líquida. Nos aspectos observados no decorrer desta pesquisa, verificou-se que para as condições analisadas, a desinfecção com radiação ultravioleta mostrou-se como técnica mais simples e eficaz para a inativação de coliformes fecais e coliformes totais quando comparada à ozonização, apresentando assim vários aspectos favoráveis no que concerne ao modo de operação, a influência da qualidade do efluente bruto, ao controle do processo, entre outros. / The Chlorinate is widely used for the disinfection of waste and drinking water, however the toxicity potential by the by-products of chlorinate renders the process less attractive. The chlorine dioxide comes up as a disinfection alternative, but its production involves highly reagent concentration and physical-chemical condition dependant reactions, also being able to create human health hazardous by-products. Other alternative technologies, like ozone and ultraviolet radiation have risen as technically viable processes. It this work, is has been attempted to review critically the existing literature about the effluent disinfection of sanitary waste, using a comparative approach between the disinfection in which ozone and ultraviolet radiation were used, as well as to investigate and interpret the relevant aspects of sanitary waste effluents disinfection with ozone and ultraviolet radiation on the inactivation of otal and fecal coliforms. In the experimental part doses of 80, 95 and 120 mg/L and contact times of 20, 30 and 35 minutes have been evaluated for the ozone disinfection process. For the ultraviolet method, exposure times of 10, 30 and 60 seconds have been used, keeping the same mean intensity of radiation and varying water layer thickness. With regard to the observed of thios research, is has been verified that, for the analyzed conditions, the ultraviolet disinfection has showed the simplest and most effective method of the inactiviation of fecal andtotal coliforms when compared the ozone method, thus showing several favorable aspects concerning the operation mode, the wal effuent quality influence, the process control, among others.
|
Page generated in 0.0366 seconds