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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

Reductive dechlorination of chlorinated aliphatic hydrocarbons by Fe(ii) in degradative solidification/stabilization

Jung, Bahng Mi 25 April 2007 (has links)
This dissertation examines the applicability of the iron-based degradative solidification/stabilization (DS/S-Fe(II)) to various chlorinated aliphatic hydrocarbons (CAHs) that are common chemicals of concern at contaminated sites. The research focuses on the transformation of 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2,2-tetrachloro-ethane (1,1,2,2-TetCA) and 1,2-dichloroehtane (1,2-DCA) by Fe(II) in cement slurries. It also investigates the degradation of 1,1,1-TCA by a mixture of Fe(II), cement and three iron-bearing phyllosilicates. Transformation of 1,1,1-TCA and 1,1,2,2-TetCA by Fe(II) in 10% cement slurries was characterized using batch reactors. Dechlorination kinetics of 1,1,1-TCA and TCE* (TCE that was produced by transformation of 1,1,2,2-TetCA) was strongly dependent on Fe(II) dose, pH and initial target organic concentration. Degradation of target organics in DS/S-Fe(II) process was generally described by a pseudo-first-order rate law. However, saturation relationships between the rate constants and Fe(II) dose or between the initial degradation rates and target organic concentration were observed. These behaviors were properly described by a modified Langmuir-Hinshelwood kinetic model. This supports the working hypothesis of this research that reductive dechlorination of chlorinated ethanes occurs on the surface of active solids formed in mixtures of Fe(II) and cement. Transformation products for 1,1,1-TCA and 1,1,2,2-TetCA in mixtures of Fe(II) and cement were identified. The major product of the degradation of 1,1,1-TCA was 1,1-DCA, which indicates that the reaction followed a hydrogenolysis pathway. However, a small amount of ethane was also observed. TCE* was rapidly produced by degradation of 1,1,2,2-TetCA and is expected to undergo β-elimination to produce acetylene. Dechlorination of 1,1,1-TCA in suspension of Fe(II), cement and three soil minerals (biotite, vermiculite, montmorillonite) was characterized using batch reactors. A first-order rate model was generally used to describe the dechlorination kinetics of 1,1,1-TCA in this heterogeneous system. The rate constants for 1,1,1-TCA in mixtures of Fe(II), cement and soil minerals were influenced by soil mineral types, Fe(II) dose and the mass ratio of cement to soil mineral. It was demonstrated that structural Fe(II) and surface-bound Fe(II) in the soil minerals affect dechlorination kinetics and the effects vary with mineral types. Furthermore, it suggests that the reductant formed from Fe(II) and cement hydration components is also effective in systems that include soil minerals.
22

Some Aspects of Neutral Systems: Stability Analysis and Stabilization

Fan, Kuo-Kuang 28 October 2002 (has links)
ABSTRACT In this dissertation, the stability analysis and stabilization problems of neutral systems are investigated. Firstly, the stability analysis of various classes of neutral systems, including discrete and distributed time-delay systems, are investigated by using Lyapunov functional approach. Delay-dependent and delay-independent criteria are proposed. Secondly, we consider the stability problems of neutral systems by using the powerful LMI tools. In this part, we also provide delay-dependent and delay-independent criteria for the stability of neutral systems under consideration. Finally, the stabilization problems of neutral systems are considered. We will propose stabilizability criteria for neutral systems with multiple time delays and with input delay, respectively. We will provide an observer-based controller design method. The improvements of our results over those results recently published in related literature are illustrated if the comparisons are possible. Examples are given in appropriate places to illustrate our main results.
23

Characterization and stabilization of arsenic in water treatment residuals

Wee, Hun Young 15 November 2004 (has links)
The characterization of water treatment residuals containing arsenic was investigated in the first study. Arsenic desorption and leachability from the residuals were the focus of this study. Arsenic leaching from water treatment residuals was found to be underestimated by the toxicity characteristic leaching test (TCLP) due to the pH of the leachates being favorable for As(V) adsorption. Competitive desorption of arsenic with phosphate was significant because phosphate tends to compete with As(V) on the surface of the metal hydroxide for adsorption sites. However, arsenic desorption by the competition of sulfate and chloride was found to be negligible. The pH in the leachate was a critical variable in controlling arsenic stability in the residuals. The release of arsenic from the residuals was elevated at low and high pH due to the increase dissolution of the adsorbents such as Fe and Al hydroxides. In the second phase of the study, the stabilization techniques for arsenic contained residuals and were examined to develop methods to suitably stabilize arsenic to eliminate and/or minimize leaching. A decrease of arsenic leaching was achieved by the addition of lime to the residuals and believed to be due to the formation of less soluble and stable calcium-arsenic compounds. However, it is suggested that the ordinary Portland cement (OPC) should be added with the lime for the long term stabilization because lime can be slowly consumed when directly exposed to atmospheric CO2. The solidification and stabilization (S/S) technique with lime and OPC was shown to be successfully applied by the immobilization of a wide variety of arsenic tainted water treatment residuals.
24

Reductive dechlorination of chlorinated aliphatic hydrocarbons by Fe(ii) in degradative solidification/stabilization

Jung, Bahng Mi 25 April 2007 (has links)
This dissertation examines the applicability of the iron-based degradative solidification/stabilization (DS/S-Fe(II)) to various chlorinated aliphatic hydrocarbons (CAHs) that are common chemicals of concern at contaminated sites. The research focuses on the transformation of 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2,2-tetrachloro-ethane (1,1,2,2-TetCA) and 1,2-dichloroehtane (1,2-DCA) by Fe(II) in cement slurries. It also investigates the degradation of 1,1,1-TCA by a mixture of Fe(II), cement and three iron-bearing phyllosilicates. Transformation of 1,1,1-TCA and 1,1,2,2-TetCA by Fe(II) in 10% cement slurries was characterized using batch reactors. Dechlorination kinetics of 1,1,1-TCA and TCE* (TCE that was produced by transformation of 1,1,2,2-TetCA) was strongly dependent on Fe(II) dose, pH and initial target organic concentration. Degradation of target organics in DS/S-Fe(II) process was generally described by a pseudo-first-order rate law. However, saturation relationships between the rate constants and Fe(II) dose or between the initial degradation rates and target organic concentration were observed. These behaviors were properly described by a modified Langmuir-Hinshelwood kinetic model. This supports the working hypothesis of this research that reductive dechlorination of chlorinated ethanes occurs on the surface of active solids formed in mixtures of Fe(II) and cement. Transformation products for 1,1,1-TCA and 1,1,2,2-TetCA in mixtures of Fe(II) and cement were identified. The major product of the degradation of 1,1,1-TCA was 1,1-DCA, which indicates that the reaction followed a hydrogenolysis pathway. However, a small amount of ethane was also observed. TCE* was rapidly produced by degradation of 1,1,2,2-TetCA and is expected to undergo β-elimination to produce acetylene. Dechlorination of 1,1,1-TCA in suspension of Fe(II), cement and three soil minerals (biotite, vermiculite, montmorillonite) was characterized using batch reactors. A first-order rate model was generally used to describe the dechlorination kinetics of 1,1,1-TCA in this heterogeneous system. The rate constants for 1,1,1-TCA in mixtures of Fe(II), cement and soil minerals were influenced by soil mineral types, Fe(II) dose and the mass ratio of cement to soil mineral. It was demonstrated that structural Fe(II) and surface-bound Fe(II) in the soil minerals affect dechlorination kinetics and the effects vary with mineral types. Furthermore, it suggests that the reductant formed from Fe(II) and cement hydration components is also effective in systems that include soil minerals.
25

Taiwan ren kou yu jiu ye qing kuang fen xi

Qin, Dacheng. January 1900 (has links)
Thesis (M.A.)--Guo li zheng zhi da xue zheng zhi yan jiu suo. / Cover title. Includes bibliographical references.
26

Removal of algae from facultative pond effluent

Miqdadi, Issam Mahmoud Ahmad January 1992 (has links)
Wastewater stabilization ponds have gained popularity as a means of secondary wastewater treatment because of their low cost and simplicity of operation and maintenance, in addition to several other advantages. However, the presence of algae in the effluent from facultative ponds may cause undesirable environmental impacts, such as DO depletion or eutrophication, in water bodies to which this effluent is discharged. Thus, regulations and/or the adverse environmental impacts of effluents containing algae sometimes necessitate reduction or removal of algae from pond effluents. Many methods have been used for the purpose of removal of algae from wastewater stabilization pond effluent. Upflow rock filtration and coagulationsedimentation have been investigated in this research. In the past, mechanisms of removal of algae in rock filters and factors that affect the removal process have not been well explained. Design of these filters has not been related mathematically to the operating variables. Three pilot rock filters were built for the purpose of this research. The first filter was filled with rock of 1 cm average diameter, the second and third filters were filled with 5 cm and 10 cm average diameter rock, respectively. Five different hydraulic loadings were applied to these filters, with variable influent characteristics and under different environmental conditions. The results of this research have shown that gravitational settling and hydrodynamic forces are the most important mechanisms affecting removal of algae in upflow rock filters. Also, a method of design of unisize-media upflow rock filters for removal of algae from facultative pond effluent has been established. The cost of coagulant has been the main disadvantage of the process of coagulation-sedimentation for algae removal from wastewater stabilization pond effluent. In this research, jar tests were carried out to determine the effect of settling time and/or addition of kaolinite or bentonite with the primary coagulant, alum, on the optimum dose of this primary coagulant required for removal of algae from facultative pond effluent. Both increase in settling time and coagulant aids, namely kaolinite and bentonite, have reduced optimum alum dose. Kaolinite and bentonite, applied as low-cost primary coagulants, were also effective in removing algae from facultative pond effluent. From the very limited experiments carried out at the end of this research, it was shown that crossflow microfiltration has some potential as a process for algae removal from facultative pond effluent. A mathematical model has been developed in this work to describe the eutrophic state of King Talal Reservoir in Jordan. The model predicts that even elimination of phosphorus from the effluent of Al-Samra Wastewater Stabilization Ponds will not bring the reservoir into an oligotrophic state.
27

AN EVALUATION OF THE EFFECT OF GEOFABRICS ON STRESSES AND DISPLACEMENTS IN BURIED CULVERTS

Sanan, Bal Krishan January 1980 (has links)
The results of a study to evaluate the behavior of a flexible culvert with the inclusion of a goefabric above the culvert are presented. In the soil-fabric-culvert system the geofabric becomes an interactive stress-carrying component of the system. Insight into the phenomenon of the stress-attenuation due to the inclusion of a semimechanical reinforcement, like geofabric, is also obtained from this research. The numerical technique of the finite element method is used for the analysis of the soil-fabric-culvert system. In the finite element model, two-dimensional triangular and quadrilateral elements having nonlinear, stress-dependent material properties are used for representing the soil. Beam elements are used to model the culvert, no-compression bar elements are used for the fabric, and two-dimensional interface elements for the contact surfaces between the soil and fabric. Incremental construction sequence and approximate nonlinear geometry are adapted in the analysis. Because of the relatively recent usage of fabrics for engineering purposes, no information regarding their employment as an inclusion in a soil-culvert system is available in the open literature. However, a review of the literature is conducted to bring out the current state of understanding of the behavior of soil-culvert systems without the presence of a fabric. The classical design concepts which reflect the development of the design methodology for flexible culverts are reviewed. The phenomenological concepts of soil-culvert interaction, particularly those of arching in the soil above the culvert and buckling of the soil-surrounded culvert wall are discussed. The burial depths of D/2 and D are considered for the horizontal configuration of the fabric when D = diameter of culvert. A burial depth of 2D is considered for the inclined configuration of the fabric. The following surface concentrated loading conditions are considered for the horizontal configuration of the fabric. Loads of 10 kip are placed symmetrically at S/D = 1/4, 1/2, 1, or 2 and 20 kip load at S/D = 0 (S = distance from vertical centerline of culvert). For the inclined configuration of the fabric above culvert, 50 kip surface concentrated loads are placed at S/D = 0, 1/4, and 1/2 simultaneously. This study shows that the fabric alters the stresses in the soil-fabric-culvert system by two mechanisms: the fabric can carry part of the load in tension and/or it can distribute the load more uniformly over a wider area. Under most practical conditions, the inclusion of fabric causes a significant reduction in the magnitudes of the following culvert design parameters: maximum axial force, maximum moment, vertical crown deflection, and horizontal springline deflection. The presence of fabric is more effective in attenuating the culvert design parameters for the location of surface loads within the horizontal projection of the culvert and for shallow depths of soil cover.
28

COMPRESSIBILITY AND REBOUND CHARACTERISTICS OF COMPACTED CLAYS

Massanat, Yousef Matri, 1944- January 1973 (has links)
No description available.
29

SOME FACTORS AFFECTING SOIL FLEXIBILITY

Duffy, Dennis Michael, 1942- January 1977 (has links)
No description available.
30

Rain erosion control of compacted soils

Liu, Hon-ho, 1947- January 1972 (has links)
No description available.

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