• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 403
  • 222
  • 66
  • 28
  • 16
  • 13
  • 9
  • 7
  • 7
  • 6
  • 6
  • 5
  • 5
  • 5
  • 4
  • Tagged with
  • 960
  • 298
  • 220
  • 209
  • 191
  • 181
  • 159
  • 106
  • 70
  • 70
  • 69
  • 61
  • 59
  • 56
  • 54
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

The effect of metal speciation of the biodegradation of nitrilotriacetic acid

White, Victoria Elizabeth January 1998 (has links)
No description available.
92

Ozone initiated oxidation of organic pollutants, m-xylene and 2-chloroethanol.

Gounden, Asogan Nokan. January 2010 (has links)
A variety of hazardous organic compounds are present in leachate from landfill sites that accept medical and industrial chemical waste. Most of these compounds find their way into nearby streams, rivers and dams, posing a threat to the ecosystem. In the present work two hazardous organic compounds, namely, m-xylene and 2-chloroethanol were chosen to react with ozone gas at different experimental conditions. The ozone initiated oxidation of m-xylene and 2-chloroethanol in solvent free conditions were investigated as a function of time. Gas chromatographic analysis of ozonated m-xylene, showed an increase in the conversion of substrate from about 1 % after 3 hours to about 14 % after 24 hours. Some of the ozonation products identified were formic acid, acetic acid, 3-methylbenzylalcohol, 3-methylbenzaldehyde and 3-methylbenzoic acid. The presence of acetic acid, ethyl acetate or acetone during ozonation significantly improved the percent conversion of m-xylene relative to similar products obtained under solvent free conditions. The presence of activated charcoal during ozonation of m-xylene showed marginal improvement in percent conversion compared to solvent free ozonation. The oxidation of 2-chloroethanol was followed by monitoring the consumption of the halogenated organic substrate which showed an increase in conversion from about 2 % after 3 hours to about 46 % after 12 hours. Ozonated products contained a mixture of acetaldehyde and acetic acid. It was also found that the ozonation of 2-chloroethanol yielded quantitative amounts of chloride ions. The percent conversion of 2-chloroethanol in the presence of acetic acid and ethyl acetate were higher than those under solvent free conditions. The use of activated charcoal during ozonolysis of 2-chloroethanol showed a significant increase in percent conversion of the substrate. Since 2-chloroethanol has a higher solubility in water than m-xylene the effects of solution pH, activated charcoal and hydrogen peroxide on ozone initiated reactions were studied. Solutions of 2-chloroethanol maintained at pH level 4 and 7 showed marginal changes in percent conversion compared to ozonation alone, however percent conversion improved significantly when the pH of the solution was increased to 10. The ozonation of 2-chloroethanol in the presence of 5 % hydrogen peroxide in water at pH levels 4 and 7 showed marginal changes in percent conversion compared to ozonation alone, however, percent conversion and product yields improved significantly, when the pH of the solution was increased to 10. Increasing the strength of the hydrogen peroxide in the reaction mixture from 5 % to 10 % had very little effect in the percent conversion of 2-chloroethanol and product formation. Based on the experimental findings the overall reaction mechanism for the reaction of both m-xylene and 2-chloroethanol with ozone is described. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.
93

Evaluation of the environmental impact of trace elements in the Zarqa River using chemometric analysis of inductively coupled plasma optical emission spectroscopy data (ICP-OES)

Al-Sheraideh, Mohammed Sharif January 1999 (has links)
No description available.
94

The measurement and characterisation of aerosol in the urban atmosphere (PM10) and an evaluation of the sources of these particles by number

Dye, Andrew Lindsay January 1998 (has links)
The Measurement and Characterisation of Aerosol in the Urban Atmosphere (PM 10) and an Evaluation of the Sources of these Particles by Number Andrew Lindsay Dye Abstract The link between human health and the mass of fine particulate matter below 10 tm (PM10) in air is well documented. Current research suggests that the number, size and shape of particles may be of most concern and that in the urban atmosphere combustion sources of PM10, especially diesel engine sources, dominate the fine (< 1µm) and ultra-fine (<0.1 µm) particles. Despite this, the number, size and shape of particles in urban air has not been reported to any great extent or detail, and the percentage contribution to the numbers of particles from different sources is largely unknown. The objectives of this research were to characterise fine particles with respect to their morphology and thus apportion the sources of particles by number. Urban aerosol above 1 µm was initially examined to study the fluctuations in PM10 number and make retrospective analysis of periods of elevated PM10 for source identification in Plymouth, UK. Aerosol was collected via a Burkard spore trap and examined using light microscopy with image analysis between 16 March 1995 and 31 August 1996, at a background site in Plymouth, UK. Two periods, 19 Januamy-4 February and 10-25 March 1996, identified as UK wide PM 10 episodes, were retrospectively studied and compared with PM10 mass measurements. The mean number count for the whole period was 10.5 x 104 ± 7.9 x 104 particles m-3 . The two PM10 episodes had elevated average number concentrations of 13.5 x 104 ± 7.6 x 104 particles m-3 for 19 January - 4 February 1996, and 13.0 x 104 ± 9.7 x 104 particles n13 for 10-25 March 1996. During the periods of elevated PM10 the tapered element oscillating microbalance (TEOM) mass of particles had a low correlation with the particles less than 5 µm and an increased correlation to the particles greater than 5 µm in size. Outside of these peak periods the PM10 TEOM mass was most closely correlated with the number of particles less than 5 µm in size. This work shows the difference in urban aerosol during periods of air quality guideline exceedence. These findings agree with literature that an aged continental aerosol source has a key role in the generation of UK wide PM10 mass exceedances. Further analysis of the fine urban aerosol (< 1 µm) was made using direct sampling of urban aerosol on to porous carbon films (PCF) developed in this research. The efficiency of collection was low (ca 5%) but the samples were representative and enabled transmission electron microscopy (TEM) for sub-micron particle analysis. Measurement was made of the fractal dimensions and diameter of particles. This was used to identif' any ageing and ultimately the sources of aerosol. PCF were used in the simultaneous collection of urban roadside and background aerosol, on seven dates between December 1996 and August 1997 in Plymouth, UK. The average perimeter fractal dimension (PFD) of aerosol was consistently significantly greater at the roadside than the background (+ 0.02), indicative of a smoother, aged aerosol at the background site. The sampling of a variety of combustion engines was made for source identification purposes. The particle morphology produced from the diesel engines showed great uniformity of particle morphology with varying speed and load; no consistent significant differences were found. The morphology results were comparable to other density fractal dimensions and penmneter fractal dimension values found in other studies for diesel. A natural log relationship between the median particle size and the median PFD was found for the diesel engine sources but not in petrol samples. This natural log trend was considered as a tentative 'fingerprint' of diesel engine combustion and was in harmony with literature values of PFD for diesel engine particles. Using the fractal measures, size and particle classification the bulk of aerosol was identified as from hydrocarbon combustion sources; ca. 88-92% of the roadside and ca. 77-86% of background. A component of carbon ceno-spheres were identified contributing ca. 6-12% of both the roadside and background aerosol. Non-combustion particles increased from ca. 1-4% of the roadside to ca. 7-9% of the background, as did the proportion of aged combustion particles, from 0-1% of roadside to 2-3% of the background aerosol. A strong correlation for the median size vs. PFD morphology curve between, the roadside and diesel sources (0.93 - 0.95) and the background and petrol sources was found (0.95). The roadside aerosol was significantly different to the petrol source in the 120-220nm size range (p=O.007) and there was a low correlation of the petrol and the roadside size vs. morphology curve (0.66). This suggests the domination of roadside aerosol by diesel engine particles. The background aerosol was similar to both diesel and petrol engine sources, especially from a dilution tunnel, thus indicative of a mixture of sources and an aged combustion aerosol. Roadside sources thus dominate the fine and ultra fine urban aerosol by number as compared to most other studies which have only apportioned the sources of particles in the air by mass.
95

Application of cyclodextrin nanoporous polymers in the removal of organic pollutants from water

30 April 2009 (has links)
M.Sc. / The removal of organic pollutants from industrial and municipal water is a great challenge to water providers worldwide. Some of these pollutants are very toxic and pose serious health risks to both humans and animals. Additionally, the presence of organic pollutants in the water often leads to the corrosion of turbines used for power generation at power stations. This obviously makes the power generation process less efficient and thus has cost implications, especially for the end user. Besides the corrosion of turbines, organic water pollutants impact on the cost of generating clean water. To this end, municipalities and industries sourcing water from Rand Water’s treatment plants and Eskom’s power stations (coal-fired power station) may be plagued by high water costs. Geosmin and 2-MIB are detectable by the human nose at concentration levels as low as 10 ng/L. These common water pollutants and are renowned for causing bad taste and odour in drinking water. Although geosmin and 2-MIB do not pose any serious health risks to humans, they impact on the aesthetic and consumer acceptability of drinking water. Currently available technologies such as activated carbon are unable to remove these pollutants to low levels (i.e. ppb levels). In our laboratories, we have found cyclodextrin-based polyurethanes to be effective in the removal of a range of organic pollutants from water to the desired ppb levels. However, these investigations were confined to water samples deliberately spiked with specific pollutants and have not been proven with "real" water samples. We sought to integrate data accumulated in the laboratory by testing and applying these polymers on a larger scale and on real systems. Cyclodextrin (CD) polymers were employed in the removal of 2-MIB, geosmin and other organic pollutants from water. The water was sampled from a coal-fired power station and Zuikerbosch Water Treatment Plant (Rand Water). After using Solid Phase Microextraction (SPME) for the extraction of organic pollutants from the water samples the organic pollutants were identified and quantified using Gas chromatography-mass spectrometry (GC-MS). The new cyclodextrin polymer technology was compared with treatment methods currently applied at both the power station and treatment plant. To determine the environmental friendliness of this technology, polymer degradation studies were also carried out. These entailed performing soil burial tests prior to the characterization of the polymers. Thermogravimetric analysis (TGA), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and Braunner Emmet Tellet (BET) analysis were used for the characterization of the polymers. The techniques were also used to determine if any degradation modifications occurred on the polymeric material. The findings of the study are summarized below: • SPME extraction and GC-MS analyses of geosmin, 2-MIB and other pollutants were successfully accomplished. • The cyclodextrin polymers were effective in the removal of geosmin and 2-MIB (up to 90%) from water sampled at Zuikerbosch water treatment plant. The polymers remained effective (90%) in the absorption of geosmin and 2-MIB even when the water samples were spiked with a competing pollutant (i.e. humic acid). Activated carbon has been noted to have reduced adsorption capacity when humic acid is present in water. • The polymers demonstrated the ability to remove as much as 90% of organic pollutants from raw water compared to the 50% removed by the polyelectrolyte and optimum minimal polyaluminium chloride employed at the coal-fired power station. Analyses of the samples using TOC before and after treatment were accomplished. Reduction in the TOC was noted at the different sampling points after Eskom’s water treatment regime. • Results from the study indicated that the β-CD TDI polymers underwent a greater weight-loss during soil burial when first digested in sulphuric acid (ca. 50% maximum mass loss). On the other hand, β-CD HMDI polymers appeared to be unaffected by predigestion and experienced the same amount mass loss for the digested and undigested polymers (ca. 30% maximum mass loss). SEM studies revealed changes in the surface morphology of the polymers. Moreover, thermogravimetric analysis (TGA) gave an indication of polymer degradation under all soil burial conditions the polymer was subjected to.
96

Die Verteilung von Schadstoff durch rotierende Aufwinde in der konvektiven atmosphärischen Grenzschicht unter verschiedenen Turbulenzannahmen

Cieszelski, Rolf 25 October 2016 (has links) (PDF)
Der Einfluß der Turbulenzstruktur rotierender Aufwinde auf die räumliche Schadstoff verteilung in der konvektiven atmosphärischen Grenzschicht über Land wurde untersucht. Für die Simulation der Aufwinde wurde ein dreidimensionales nicht-hydrostatisches Gitterpunktsmodell verwendet. Die Simulationsergebnisse, die mit verschiedenen Turbulenzparametrisierungen erzielt wurden, zeigen, daß organisierte subskalige Turbulenz zu Änderungen der skaligen Schadstoffverteilungen führen kann. Die Energie- und Helizitätsflüsse zwischen skaligem und subskaligem Regime bei der jeweiligen Turbulenzparametrisierung werden verglichen und die Konsequenzen für die Naßphasenchemie werden diskutiert. / The influence of the turbulence structure of rotating thermals on the spatial pollutant distributions in the convective boundary layer over land was examined. For the simulation of thermals, a threedimensional non-hydrostatic grid point model was used. Simulation results found with different turbulence parametrisations indicate that organized subgrid scale turbulence may lead to alterations of the resolved pollutant distributions. Energy and helicity fluxes between the resolved and subgridscale regime of each turbulence parametrization are compared and the consequences on wet phase chemistry are discussed.
97

Erfassung des atmosphärischen Trübungszustands und seiner zeitlichen Veränderung infolge von Emissionsabnahmen auf Grund sich vollziehender Strukturveränderungen in Mitteldeutschland

Hoyningen-Huene, Wolfgang von, Stettler, M. 27 October 2016 (has links) (PDF)
In the SANA project (Scientific Attandance Program for the Rehabilitation of the Atmospheric Environment in the German New Federal Lands) different kinds of turbidity measurements are used to characterize the change of the turbidity state of the atmospheric boundary layer produced by atmospheric aerosols within the time span between 1990 and 1995. For this characterization the following turbidity measurements are used: 1.) continuous measurements of the humidity corrected aerosol extinction coefficient obtained with a He-Ne-Lasertransmission path (length: 810 m, wavelength: 0.633 μm) within the urban boundary layer ofLeipzig, 2.) direct measurements ofthe particilate matter (PM10) concentration, 3.) combined measurements of spectral aerosol optical thickness (within the spectral range of0.35 - 1.1 μm) and sky brightness in the solar almucantar plane for cloud free situations, 4.) integrated radiation flux density measurement (Globalradiation). In all measurements a decrease of the atmospheric aerosol turbidity could be stated in the time span of 1990/91 to 1995: for the extinction coefficient and the particulate matter within the boundary layer of approximately 60 %, the turbidity coefficient derived from the spectral aerosol optical thickness ( corrected for the influence of the stratospheric volcanic aerosol by the Pinatobo) give a reduction of 57 %. The combined measurements of spectral aerosol optical thickness and the sky brightness are used for the determination of the main climate-relevant aerosol parameters: aerosol phase function, asymmetry parameter, columnar aerosol size distribution and apparent columnar refractive index. The largest change in the columnar aerosol size distribution could be stated in the size range of 0.2 - 0.8 μm (radius), also a reduction of approximately 60 %. Together with the measurements of the downwelling flux density an estimation of the aerosol absorption in kind of the imaginary part of the refractive index is made. The imaginary part is reduced in the same way: 1991: k = 0.021, 1994 and 1995 k = 0.008. A first estimation of the anthropogenic shortwave radiative forcing produced by the old East German air pollution of the on the basis of these data gives a change in the shortwave radiative balance of approximately -8 W/m2. / Im Rahmen des SANA Projekts (Wissenschaftliches Begleitprogramm zur Sanierung der Atmosphärenumwelt) wurden verschiedene Trübungsmessungen verwendet, um die Veränderungen im Trübungszustand in der atmosphärischen Grundschicht, hervorgerufen durch Aerosole, im Zeitraum von 1990 bis 1995 charakterisieren zu können. Dazu wurden folgende Trübungsmessungen verwendet: 1.) kontinuierliche Messungen des feuchtekorrigierten Aerosolextinktionskoeffi.zienten mit Hilfe einer Laser- Transmissionsstrecke (Länge 810 m, He-Ne-Laser Wellenlänge: 0.633 μm) in der urbanen Grundschicht von Leipzig, 2.) direkte Messungen der Schwebstaubkonzentration, 3.) kombinierte Messungen von spektraler optischer Dicke des Aerosols (im Spektralbereich von 0.35 - 1.1 μm) und Himmelshelligkeitsfunktion im Almukantar unter wolkenfreien Bedingungen, 4.) integrale Strahlungsflußdichtemessungen (Globalstrahlung). In allen Messungen konnte im Zeitraum 1990/91 bis 1995 eine Abnahme der Aerosoltrübung festgestellt werden: Für den Extinktionskoeffi.zienten und die Schwebstaubkonzentration in der urbanen Grundschicht ungefähr 60 %, für den aus den spektralen optischen Dicken des Aerosols abgeleiteten Trübungskoeffizienten (korrigiert um den Beitrag des stratosphärischen Vulkanaerosols des Pinatubo) 57 %. Die kombinierten Messungen von spektraler optischer Dicke des Aerosols und der Himmelshelligkeitsfunktion dienten der Bestimmung der wesentlichen klimarelevanten Aerosolparameter: Aerosolphasenfunktion, Asymmetrieparameter, columnarer Aerosolgrößenverteilung und columnarer Brechungsindex des Aerosols. Die größte Änderung in der columnaren Aerosolgrößenverteilung ist im Radienbereich 0.2 - 0.8 μm festgestellt worden, ebenfalls eine Reduktion von ungefährt 60 %. Zusammen mit den Messungen der abwärtsgerichteten Strahlungsflußdichte wurde eine Abschätzung der Aerosolabsorption in Form des Imaginärteils des Brechungindex vorgenommen. Der Imaginärteil verringert sich in gleicher Weise: 1991: k = 0. 021, 1994 und 1995: k = 0. 008. Auf der Grundlage dieser Daten konnte der anthropogene Anteils des kurzwelligen Strahlungsforcings, das durch die Luftverunreinigung unter den alten Ostdeutschen Bedingungen hervorgerufen wird, mit ungefähr -8 W/m2 Änderung in der kurzwelligen Strahlungsbilanz abgeschätzt werden.
98

(1-3)-B-D glucan exposure assessment in poultry farms in South Africa

Dayal, Payal 13 April 2015 (has links)
Introduction: Poultry workers have an increased risk of respiratory symptoms associated with various irritant and allergenic exposures causing airway inflammation. This study investigated the levels of (1-3)-β-D glucan exposure in several poultry farming processes. The objectives involved categorising the different tasks undertaken in the poultry industry. After which a method was established and validated to detect and quantify the levels of (1-3)-β-D glucan using the Glucatell assay. This assay was used to measure the amount of (1-3)-β-D glucan poultry farm workers were exposed to using personal sampling. Thereafter, general respiratory symptoms were described briefly via the administration of a respiratory questionnaire. Method: A total of 308 personal air samples were collected from several poultry farming processes (rearing, laying, hatchery, broilers, catching) of a large poultry farm in the North West Province. A walkthrough checklist was used to obtain information on various exposure determinants such as farm size, number of chickens, ventilation system, bedding material used and poultry feed used. The Glucatell assay (Associates of Cape Cod, East Falmouth, MA, USA) was used to quantify the concentration of (1-3)-β-D glucans in the air samples. Results: The geometric mean concentrations of (1-3)-β-D glucans ranged from 24.38 to 645.98 ng/m3 across the various poultry farming processes investigated. Workers in the broiler farms were exposed to two times higher levels of (1-3)-β-D glucans compared to those in the breeding farms. The sizes of the broiler farm houses as well as the age of the chickens were among the main determinants of exposure. The larger broiler farm houses (GM=5.2 ng/m3, GSD=3.74) had significantly (p<0.05) lower levels than the smaller broiler farm houses (GM=6.4 ng/m3, GSD=2.14) whilst houses with older chickens had higher (1-3)-β-D glucan levels (G=5.8 ng/m3,
99

Kinetics and mechanisms of methoxide substitution and electroreduction of hexachlorobenzene

Sidhu, Jeswant K., University of Western Sydney, Faculty of Informatics, Science and Technology January 2000 (has links)
Hexachlorobenzene (HCB) is a pollutant, and there is an urgent need to degrade it. Two methods of degrading HCB to ethers are nucleophilic substitution and electroreduction, chosen for their viability and safety. The kinetics of substitution of HCB by potassium hydroxide and methanol were examined. The substitution of HCB by methoxide produced 1,2,3,5-tetrachloro-4.6-dimethoxybenzene (1,2,3,5-TCDMB) as the major substitution product, and side reactions produced extra chloride due to other substitution products. Thus, the proposed reaction mechanism is complicated due to the formation of ethers and phenols due to consecutive and parallel reactions. The substitution products of HCB were uncatalytically and catalytically electroreduced. Products with increasingly more methoxy substituents had lower electron affinities and increasing positive free energies. Catalysed electroreduction was more effective than uncatalysed electroreduction in dechlorinating the HCB substitution products to aromatic ethers. The most effective organic catalysts were those that possessed the lowest electron affinity as reflected in the reduction potential. A combination of nucleophilic substitution and electroreduction of HCB and its substitution products produced mono-, di- and trimethoxide chloroaromatic ethers and phenols. These products, particularly the ethers, may have future applications as fragrance ingredients / Doctor of Philosophy (PhD)
100

A predictive model for environmental fate and transport of the toxicity of leachates from highway construction and repair materials

Quigley, Marcus M. 14 April 1998 (has links)
Recent concern over the potential environmental impact of highway construction and repair materials on surface and ground waters has lead to extensive laboratory screening and subsequent testing of a set of new materials and waste amended mixes. As part of Phase II of a three-phase project for the National Cooperative Highway Research Program, a fate and transport model for the assessment of this impact has been written. The model predicts concentrations and loads of contaminants as well as toxicities for the leachates in both surface and subsurface environments. The model addresses four specific "reference environments": an impermeable highway surface, a permeable highway surface, a vertical piling, and a filled borehole. Six materials are examined in detail: crumb rubber asphalt concrete. SEMASS asphalt concrete, foundry sand asphalt concrete, ammonical copper zinc arsenate treated wood, and methyl methacrylate deck sealer. A statistical approach to relating toxicity to the concentration of a chemical "surrogate" forms the basis for prediction of toxicity in the leachates. All fate and transport prediction methods are based on physical and mathematical descriptions of the near-highway environment. Surface runoff is calculated using kinematic wave theory coupled with leaching, photolysis and volatilization, flow through pavement cracks is based on continuity, and subsurface transport is based on a plug flow model with linear or Freundlich sorption and biodegradation. Explicit finite difference numerical methods are used for both surface leaching and subsurface transport. A search engine is provided for examination of all laboratory results. / Graduation date: 1999

Page generated in 0.0357 seconds