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  • 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.
21

Destruction of polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons in soil using ball milling

Magoha, Happy Steven Unknown Date (has links)
This study involves the use of ball mill as a mechanochemical reactor in the destruction of environmental contaminants. Although the technology has the potential to be used for a wide range of organic contaminants, this study focused on polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons. There are different methods for the remediation of the environmental contaminants such as biological, chemical and thermal techniques, most of which are costly. The ball mill is less costly as it involves low technology and little or no other chemicals seem to be needed to give complete destruction of the substances investigated. The mill is relatively easy to construct and can be made in different designs and dimensions to fit its intended purpose i.e. they can range from a laboratory scale to a very large industrial mill for the continuous processing of tonnes of material at a time. The process can be sealed so pollution from the mill is easy to control. In this study two classes of environmental contaminants were investigated. PAH's are common by-products of combustion and are found as contaminants in many soils. The other compounds investigated were the larger aliphatic hydrocarbons. These were chosen as being representative of the evaporated residues from fuel spills or leaks. A laboratory scale centrifugal ball mill with capacity of approximately 200 g was used for the study. The PAH's investigated were naphthalene, anthracene and phenanthrene. The aliphatic hydrocarbons n-eicosane and n-octacosane were used as the model compounds for hydrocarbon residues. Different soil types (scoria, clay soil, silica sand and slag) were spiked with a known amount of these contaminants. The ball milling was done under different milling conditions i.e. with different ball ratio and with different milling duration. In some experiments there was an addition of materials such as a potential free radical trap or metals to investigate the effect on the mechanochemical reaction. The samples were analysed using an ultrasonic extraction method (EPA METHOD 3550C) with GC and GC-MS analysis of the extract for the quantification of the residual contaminant in the soil and identification of possible secondary products and reaction intermediates. It was found that high destruction efficiency was achieved using milling times of between 120 and 150 minutes and high ball to soil ratios for example 7:1 ball mass to soil mass ratio. Also it was found that different type of soil had an influence on the mechanochemical reaction. A silica matrix was found to have a better destruction rate compared to scoria and clay soil. It was also found that the PAH compounds were more rapidly destroyed by ball milling than were aliphatic hydrocarbons. The addition of BHT was found to reduce destruction rate of both PAH's and aliphatic hydrocarbons. This suggests the mechanism of destruction may involve a free radical mechanism. Aluminium metal was observed to have no significant effect in the destruction. The presence of lubricants such as waxes in the contaminated soil appeared to inhibit the mechanochemical reaction although the mechanism is still uncertain. From this study it was concluded that, the ball mill has considerable potential as an effective, low cost method for the destruction of certain environmental contaminants.
22

Persistence and spatial range of environmental chemicals new ethical and scientific concepts for risk assessment /

Scheringer, Martin. January 1900 (has links)
Based in part on the author's thesis (Ph.D.--ETH Zürich, 1996). / Includes bibliographical references and index.
23

Performance of vegetated roadsides in removing stormwater pollutants

Rammohan, Pavitra 16 August 2006 (has links)
Stormwater runoff from highways can contain pollutants such as suspended solids, nitrogen and phosphorus, organic material, and heavy metals. Growing awareness leading to regulatory requirements reflects the need to protect the environment from highway runoff effects. The management practice discussed in this study is the use of vegetated roadsides. The primary objective of this research is to document the potential treatment values from vegetated roadsides typical of common rural highway cross sections in two Texas cities: Austin and College Station. Three sites in each city were examined in this study over a 14-month monitoring period. No significant difference between the edges of pavement pollutant concentrations were observed at any of the research sites in the two study areas. This allowed for direct comparisons of the vegetated roadsides and their associated site characteristics such as annual daily traffic (ADT), dry period, and rainfall intensity. The scatter plots of College Station data show that concentrations of total suspended solids (TSS), total Pb, and chemical oxygen demand (COD) in runoff are dependent on the antecedent dry period and decrease with longer dry periods. The results show that pollutant concentrations are not highly dependent on ADT. However, the results show that the number of vehicles during the storm (VDS) was evaluated and accepted as a satisfactory independent variable for estimating the loads of total Pb and TSS. The results of correlation analysis show that the concentrations of total Pb and chemical oxygen demand are significantly correlated with TSS levels. The findings indicate that nitrate concentrations in runoff is most dependent on the average daily traffic using the highway during the preceding dry period as well as the duration of that dry period. Sites 2 and 3 in College Station are steeper but outperformed Site 1 which has much flatter slopes. This could be accounted for by the poor vegetative cover (brown patches) at Site 1. In the Austin sites, the permeable friction course appeared to have a significant impact on the quality of runoff leaving the road surface. On the whole, the results of this study indicate that vegetated roadsides could be used as a management practice for controlling and treating stormwater runoff from Texas highways.
24

Performance of vegetated roadsides in removing stormwater pollutants

Rammohan, Pavitra 16 August 2006 (has links)
Stormwater runoff from highways can contain pollutants such as suspended solids, nitrogen and phosphorus, organic material, and heavy metals. Growing awareness leading to regulatory requirements reflects the need to protect the environment from highway runoff effects. The management practice discussed in this study is the use of vegetated roadsides. The primary objective of this research is to document the potential treatment values from vegetated roadsides typical of common rural highway cross sections in two Texas cities: Austin and College Station. Three sites in each city were examined in this study over a 14-month monitoring period. No significant difference between the edges of pavement pollutant concentrations were observed at any of the research sites in the two study areas. This allowed for direct comparisons of the vegetated roadsides and their associated site characteristics such as annual daily traffic (ADT), dry period, and rainfall intensity. The scatter plots of College Station data show that concentrations of total suspended solids (TSS), total Pb, and chemical oxygen demand (COD) in runoff are dependent on the antecedent dry period and decrease with longer dry periods. The results show that pollutant concentrations are not highly dependent on ADT. However, the results show that the number of vehicles during the storm (VDS) was evaluated and accepted as a satisfactory independent variable for estimating the loads of total Pb and TSS. The results of correlation analysis show that the concentrations of total Pb and chemical oxygen demand are significantly correlated with TSS levels. The findings indicate that nitrate concentrations in runoff is most dependent on the average daily traffic using the highway during the preceding dry period as well as the duration of that dry period. Sites 2 and 3 in College Station are steeper but outperformed Site 1 which has much flatter slopes. This could be accounted for by the poor vegetative cover (brown patches) at Site 1. In the Austin sites, the permeable friction course appeared to have a significant impact on the quality of runoff leaving the road surface. On the whole, the results of this study indicate that vegetated roadsides could be used as a management practice for controlling and treating stormwater runoff from Texas highways.
25

Development of polyaniline nanotube electrocatalysts and sesor devices for phenolic-pollutants.

Klink, Michael John. January 2007 (has links)
<p>As a source of life, water is one of the most precious commodities for all living organisms. Water resources are reported to be declining in numbers or the amount of water present and the existing onses are being polluted as a result of negligent human activities and intense industrialisation. thus, there is an ever increasing demand to monitor the quality of portable and waste water in our surroundings in real time. This study has been directed towards the prepaparation of polyanilines.</p>
26

Interactions between polycyclic aromatic hydrocarbons and humic substances in the aqueous phase and bound to clay surfaces

Jones, Kim David 12 1900 (has links)
No description available.
27

Effects of chronic cadmium exposure on macrophage function in mice

Haider, Syed Raza January 1989 (has links)
No description available.
28

Development of polyaniline nanotube electrocatalysts and sesor devices for phenolic-pollutants.

Klink, Michael John. January 2007 (has links)
<p>As a source of life, water is one of the most precious commodities for all living organisms. Water resources are reported to be declining in numbers or the amount of water present and the existing onses are being polluted as a result of negligent human activities and intense industrialisation. thus, there is an ever increasing demand to monitor the quality of portable and waste water in our surroundings in real time. This study has been directed towards the prepaparation of polyanilines.</p>
29

Destruction of polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons in soil using ball milling

Magoha, Happy Steven Unknown Date (has links)
This study involves the use of ball mill as a mechanochemical reactor in the destruction of environmental contaminants. Although the technology has the potential to be used for a wide range of organic contaminants, this study focused on polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons. There are different methods for the remediation of the environmental contaminants such as biological, chemical and thermal techniques, most of which are costly. The ball mill is less costly as it involves low technology and little or no other chemicals seem to be needed to give complete destruction of the substances investigated. The mill is relatively easy to construct and can be made in different designs and dimensions to fit its intended purpose i.e. they can range from a laboratory scale to a very large industrial mill for the continuous processing of tonnes of material at a time. The process can be sealed so pollution from the mill is easy to control. In this study two classes of environmental contaminants were investigated. PAH's are common by-products of combustion and are found as contaminants in many soils. The other compounds investigated were the larger aliphatic hydrocarbons. These were chosen as being representative of the evaporated residues from fuel spills or leaks. A laboratory scale centrifugal ball mill with capacity of approximately 200 g was used for the study. The PAH's investigated were naphthalene, anthracene and phenanthrene. The aliphatic hydrocarbons n-eicosane and n-octacosane were used as the model compounds for hydrocarbon residues. Different soil types (scoria, clay soil, silica sand and slag) were spiked with a known amount of these contaminants. The ball milling was done under different milling conditions i.e. with different ball ratio and with different milling duration. In some experiments there was an addition of materials such as a potential free radical trap or metals to investigate the effect on the mechanochemical reaction. The samples were analysed using an ultrasonic extraction method (EPA METHOD 3550C) with GC and GC-MS analysis of the extract for the quantification of the residual contaminant in the soil and identification of possible secondary products and reaction intermediates. It was found that high destruction efficiency was achieved using milling times of between 120 and 150 minutes and high ball to soil ratios for example 7:1 ball mass to soil mass ratio. Also it was found that different type of soil had an influence on the mechanochemical reaction. A silica matrix was found to have a better destruction rate compared to scoria and clay soil. It was also found that the PAH compounds were more rapidly destroyed by ball milling than were aliphatic hydrocarbons. The addition of BHT was found to reduce destruction rate of both PAH's and aliphatic hydrocarbons. This suggests the mechanism of destruction may involve a free radical mechanism. Aluminium metal was observed to have no significant effect in the destruction. The presence of lubricants such as waxes in the contaminated soil appeared to inhibit the mechanochemical reaction although the mechanism is still uncertain. From this study it was concluded that, the ball mill has considerable potential as an effective, low cost method for the destruction of certain environmental contaminants.
30

Recovery of precious metals from automotive catalytic converters /

Wu, Kuo-ying Amanda. January 1993 (has links)
Thesis (Ph.D.)--University of Tulsa, 1993. / Includes bibliographical references (leaves 172-181).

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