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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.
41

Developing Improved Strategies of Remediating Arsenic Contaminated Aquifers

Sun, Jing January 2015 (has links)
Groundwater arsenic contamination is currently a global problem, and also a concern at numerous former industrial sites, agricultural sites, landfill sites and mining operations in the U.S. This dissertation aims to develop improved strategies of remediating these arsenic contaminated aquifers. It focuses on two distinct approaches of remediation: (1) mobilizing arsenic from contaminated aquifer sediments to decrease the quantity of arsenic at the source of contamination; and (2) immobilizing arsenic in situ, to decrease the mobility and bioavailability of this arsenic. Optimal remediation may well involve combinations of these two approaches. Arsenic mobilization using oxalic acid is effective because oxalic acid dissolves arsenic host minerals and competes for sorption sites on those minerals. In this dissertation, oxalic acid treatment was tested using sediments with contrasting iron mineralogies and arsenic contents from the Dover Municipal Landfill and the Vineland Chemical Company Superfund sites. Oxalic acid mobilized arsenic from both sites and the residual sediment arsenic was less vulnerable to microbial reduction than before the treatment. Oxalic acid thus could improve the efficiency of widely used pump-and-treat remediation. Oxalic acid did not remove all of the reactive iron(III) minerals in Vineland sediment samples, and thus released significant quantities of arsenic into solution under reducing conditions than the Dover samples. Therefore, the efficacy of pump-and-treat must consider iron mineralogy when evaluating its overall potential for remediating groundwater arsenic. Arsenic immobilization occurs by changing the chemical state, or speciation, of arsenic and other elements in the system. Arsenic is often assumed to be immobile in sulfidic environments. In this dissertation, sulfate reduction was stimulated in sediments from the Vineland Superfund site and the Coeur d'Alene mining district. Sulfate reduction in the Coeur d'Alene sediments was more effective at removing arsenic from solution than the Vineland sediments. The Vineland sediments initially contained abundant reactive ferrihydrite, and underwent extensive sulfur cycling during incubation. As a result, arsenic in the Vineland sediments could not be effectively converted to immobile arsenic-bearing sulfides, but instead a part of the arsenic was probably converted to soluble thioarsenates. Therefore, coupling between the iron and sulfur redox cycles must be fully understood for arsenic immobilization by sulfate reduction to be successful. Arsenic can also be immobilized by retention on magnetite (Fe3O4). Magnetite is stable under a wide range of aquifer conditions including both oxic and iron(III)-reducing environments. In this dissertation, a series of experiments were performed with sediments from the Dover and Vineland Superfund sites, to examine the potential of magnetite for use in arsenic immobilization. Our data suggest that the formation of magnetite can be achieved by the microbial oxidation of ferrous iron with nitrate. Magnetite can incorporate arsenic into its structure during formation, forming a stable arsenic sink. Magnetite, once formed, can also immobilize arsenic by surface adsorption, and thus serve as a reactive filter when contaminated groundwater migrates through the treatment zone. Reactive transport modeling is used for investigating the magnetite based arsenic immobilization strategy and for scaling laboratory results to field environments. Such modeling suggests that the ratio between iron(II) and nitrate in the injectant regulates the formations of magnetite and ferrihydrite, and thus regulates the long-term evolution of the effectiveness of the strategy. The results from field-scale models favor scenarios that rely on the chromatographic mixing of iron(II) and nitrate after injection. The studies in this dissertation demonstrate that the environmental fate of arsenic depends on the biogeochemical cycling of arsenic, iron, and to a lesser extent, sulfur. The development of effective groundwater arsenic remediation strategies depends on a good understanding of each of the involved processes, and their combinations.
42

Numerical simulation of anaerobic reductive dechlorination of CAHs in continuous flow systems

Mustafa, Nizar Ahmad 14 December 2011 (has links)
Halogenated organic compounds have had widespread and massive applications in industry, agriculture, and private households, for example, as degreasing solvents, flame retardants and in polymer production. They are released to the environment through both anthropogenic and natural sources. The most common chlorinated solvents present as contaminants include tetrachloroethene (PCE, perchloroethene) and trichloroethene (TCE). These chlorinated solvents are problematic because of their health hazards and persistence in the environment, threatening human and environmental health. Microbial reductive dechlorination is emerging as a promising approach for the remediation of chlorinated solvents in aquifers. In microbial reductive dechlorination, specialized bacteria obtain energy for growth from metabolic dechlorination reactions that convert PCE to TCE, cis-1,2-dichloroethene (cDCE), vinyl chloride (VC), and finally to benign ethene. Field studies show incomplete dechlorination of PCE to ethene due to lack of electron donors or other populations competing for the electron donor. Mathematical models are good tools to integrate the processes affecting the fate and transport of chlorinated solvents in the subsurface. This thesis explores the use of modeling to provide a better understanding of the reductive dehalogenation process of chlorinated solvents and their competition with other microorganisms for available electron donors in continuous flow systems such as a continuous stirred tank reactor (CSTR) and a continuous flow column. The model is a coupled thermodynamic and kinetic model that includes inhibition kinetics for the dechlorination reactions, thermodynamic constraints on organic acids fermentation and has incorporated hydrogen competition among microorganisms such as homoacetogenesis, sulfate reducers and ferric iron reducers. The set of equations are coupled to those required for modeling a CSTR. The system of model equations was solved numerically using COMSOL 3.5 a, which employs finite-element methods. The kinetic model was verified by simulation results compared to previously published models and by electron balances. The simulation process progressed by simulating the anaerobic reductive dechlorination, coupled with thermodynamic limitation of electron donor fermentation in batch systems to the modeling of CSTR, and finally to simulate anaerobic reductive dechlorination in continuous flow column, aquifer column including the processes of advection, dispersion and sorption along with the microbial processes of dehalogenation, fermentation, iron and sulfate reduction. The simulations using the developed model captured the general trends of the chemical species, and a good job predicting the dynamics of microbial population responses either the CSTRs or continuous flow column. Although, the kinetic of anaerobic dechlorination processes of chlorinated solvents in those systems have been researched in the past, little progress has been made towards understanding the combined effects of the dechlorination and thermodynamic constraints in continuous flow systems. This work provides a rigorous mathematical model for describing the coupled effects of these processes. / Graduation date: 2012
43

The use of radiorespirometry for evaluation of subsurface biodegradation

Langschwager, Eugene M. January 1985 (has links)
Current use of alcohols as neat automotive fuels or as inexpensive octane enhancers in gasoline-alcohol blends, in addition to their uses as solvents and starting materials in manufacturing, have created a concern due to the increased potential for groundwater contamination. Adsorption and water solubility are primarily responsible for separating gasoline-alcohol blend components in soils and would allow alcohols to move ahead of the remaining gasoline components (e.g., benzene). The presence of alcohols would be difficult to detect, and levels hazardous to humans or animals could be reached readily. The primary objective of this study was to investigate the use of a ¹⁴C-tracer technique for evaluation of subsurface biodegradation of groundwater contaminants. A modification of the heterotrophic activity assay, the radiorespirometric method, was employed as the ¹⁴C-tracer technique. The microorganisms used were those present in soil sampled aseptically at locations in Pennsylvania and Virginia. Both saturated and unsaturated zone soils were used. The alcohols used were methanol and tertiary-butanol. Methanol was easily degraded under both aerobic and anoxic conditions up to approximately 3000 mg/L. Tertiary-butanol was degraded very slowly under both aerobic and anoxic/anaerobic conditions, and an inhibitory concentration was not readily apparent. Tertiary-butanol was degraded at rates approximately 10² slower than methano1. The data generated in this study compare favorably with data obtained by oxygen-uptake and static-microcosm methodologies. / Master of Science / incomplete_metadata
44

Synthesis, characterization and performance evaluation of groundwater defluoridation capacity of smectite rich clay soils and Mn-modified bentonite clay composites

Mudzielwana, Rabelani 05 1900 (has links)
MENVM / Department of Ecology and Resource Management / See the attached abstract below
45

Investigation of factors influencing borehole yields in the Nzhelele-Makhado Area in Limpopo Province, South Africa

Mukheli, Azwindini 21 September 2018 (has links)
MESMEG / Department of Mining and Environmental Geology / This dissertation focused on the assessment of borehole yields within the Nzhelele- Makhado area, which is located in the northern part of South Africa within the Vhembe District Municipality of Limpopo Province. The aim of the study was to identify factors that influence the yields of water supply boreholes within the study area. This information will be used to improve the groundwater resource knowledge required in assessing the potential of groundwater resources in augmenting the Nzhelele Regional Water Supply Scheme. The study area is mostly underlain by the ‘hard rock’ formations of the Soutpansberg Group, which practically has no primary porosity. The groundwater is residing mainly within the weathered and fractured or discontinuities, considered being secondary porosities. Due to the complexity of the underlying fractured and hard rock aquifer systems and the fact that most of the boreholes drilled in the area were not scientifically sited, the study area is dominated by very low yielding boreholes. Majority (48%) of the boreholes were drilled into the Nzhelele formation due to the fact that it occupies the central, relatively flat and low lying sections of the study area. The variations in average yields in boreholes drilled in different formations within the study area is relatively low suggesting that the difference in lithology of different formations do not to have any major influence in the yields of boreholes. The topographical settings of the area do not have any influence in the borehole drilling depths and yields. The high borehole yields in shallow boreholes located in mountainous areas is due to local groundwater systems, which recharges and discharges locally. Mapped lineaments are slightly low yielding (average yield of 0.32 l/s) compared to the faults (average yield of 0.43 l/s) within the study area. Boreholes drilled along the NE-SW trending lineaments support double the yields (0.41 l/s) on average of those along the SE-NW (0.28 l/s) and W-E (0.20 l/s) trending lineaments. The high yields in boreholes closer to non-perennial streams compared to perennial rivers is due to the fact that non-perennial streams are comprised of thick layer of overburden capable of supporting high yielding boreholes, whereas the overburden along the perennial rivers are washed away during rainy season leaving bedrock exposed or covered with thin layer of sediments. The proximity to the young faults trending SE-NW and dry non-perennial streams has proved to be the most the favourable areas for development of high yielding boreholes in the study area, compared to lithological difference and topographical settings of the area. However, it should be noted that there are no simple relationship between various factors that control the yield of the boreholes in the area. Despite the similarities in some factors that influence borehole productivity on a regional scale such as faults and drainage systems, the complexity of the weathered-fractured aquifer system suggests an over-riding influence of local features, which results in significant variations in yield and response to abstraction. / NRF
46

Enhanced adsorption of base metal, phenol and aldehyde from aqueous solutions on low-cost activated carbon.

Mukosha, Lloyd. January 2014 (has links)
D. Tech. Chemical Engineering / Aims of this research project was to add value to largely wasted South African sawdust by development of low-cost AC of high efficiency for removal of toxic Cr (VI), phenol and glutaraldehyde from dilute aqueous media. The main objectives of the research project were: a) To develop low-cost AC based on South African P. patula sawdust using economical physical superheated steam activation.Characterization of carbon samples for selection of optimum preparation conditions for development of low-cost AC of effective microporosity mesoporosity and surface functionality for enhanced adsorption capacity of Cr (VI) and/or phenol and/or glutaraldehyde from dilute aqueous solution. Acid-amine surface groups modification of optimally developed AC for further enhancement of adsorption capacity for mixed polarized glutaraldehyde molecules from aqueous solution. b) To evaluate the aqueous phase batch adsorption properties of developed AC for Cr (VI) and phenol and, of acid-amine modified developed AC for glutaraldehyde. Determination of optimum pH for adsorption; accurate adsorption isotherm modelling for determination of maximum adsorption capacity, comparison of maximum adsorption capacities for Cr (VI) and phenol of developed AC with commercial AC and literature ACs, and attempt to establish average micropore size for enhanced capacity for Cr (VI) and phenol from dilute aqueous solution.Kinetics reaction and diffusion modelling for determination of adsorption rate constants and diffusion parameters; and determination of adsorption thermodynamic parameters.Evaluation of equilibrium selectivity of developed AC for Cr (VI) and/or phenol in binary aqueous solutions. c) To evaluate aqueous phase fixed-bed adsorption characteristics of developed AC for single Cr (VI) and mixed solution using Rapid Small Scale column Tests (RSSCTs). Generation of breakthrough curves at optimum adsorption conditions for evaluation of column performance indicators at different process conditions, bed regeneration-reusability potential, and dynamic adsorption selectivity of developed AC for Cr (VI) from solution of base metals. Determination of column diffusion parameters; accurate mass transfer and empirical modelling of breakthrough data; determination of applicable RSSCT scaling equation; and optimization of breakthrough data for accurate RSSCT scale-up.
47

Groundwater purification using functionalised magnetic nanoparticles (electromagnetic separation)

Aigbe, Uyiosa Osagie 01 1900 (has links)
Most developing countries are faced with drinking water problems, with conditions becoming more severe due to water pollution. Meeting the growing demands for clean water in most countries, there are difficult challenges as the availability and supply of drinkable water are diminishing. Due to economic and environmental concerns, development of additional physical means for the removal of organic compounds from wastewater using permanent magnets, electromagnetic coils, electrodes and ultrasonic pretreatment is desirable. Improving the adsorption and separation process, magnetic field exposure method has progressively drawn consideration. Magnetic field exposure method has demonstrated its capacity for increasing the adsorptive elimination of contaminants from water as static magnetization is suitable, simple and cost-effective. The polypyrrole magnetic nanocomposite use for adsorption experiments influenced by exter-nal magnetic field was prepared using the in-situ polymerization method, which was charac-terized using TEM, SEM, EDX, XRD, BET, FTIR, VSM, and ESR spectrophotometers. The magnetic nanocomposite (PPy/Fe3O4) was observed to have an average particle size of 10 nm with the elementary composition of carbon, oxygen, nitrogen, chloride and iron. The magnetic nanocomposite had a crystalline structure of face-centred cubic lattice of Fe3O4, an adsorption-desorption isotherm shape indicating a typical type-IV mesoporous material with a surface area of 28.77 m2/g. Characteristic peaks of Fe3O4 and PPy were also observed using FTIR spectro-photometer. From the VSM and ESR characterization, the synthesized superparamagnetic ma-terial was shown to have a saturation magnetization of 23 emu/g and an effective g-value of 2.25 g which was attributed to Fe3+ spin interaction. An enhanced removal of Cr(VI), fluoride and congo red dye were observed under the influence of magnetic field, with parameters like pH, adsorbent dosage, the initial concentration of ad-sorbate, magnetic field and magnetic exposure time been varied. The enhanced adsorption of contaminants using magnetic field is attributed to the increase in the magnetic field induced on the particles over a magnetic exposure time, resulting in the rotating particles forming aggre-gates due to the increased magnetic force and torque on the particles from the PSV results. This leads to increase in the chain collision and area of particle interaction with the aqueous solution of hexavalent chromium, fluoride and congo red dye. / Physics / Ph. D. (Physics)
48

Clay polymer nanocomposites as fluoride adsorbent in groundwater

Nengudza, Thendo Dennis 18 May 2019 (has links)
MENVSC / Department of Ecology and Resource Management / Fluoride is one of the anionic contaminants which is found in excess in groundwater because of geochemical reaction or anthropogenic activities such as the disposal of industrial wastewaters. Among various methods used for defluoridation of water such as precipitation, ion-exchange processes, membrane processes, the adsorptions process is widely used. It offers satisfactory results and seems to be a more attractive method for the removal of fluoride in terms of cost, simplicity of design and operation. In this work, the preparation of clay polymer nanocomposites (CPNCs) used in defluoridation began by modifying the original natural Mukondeni clay to render the layered silicate miscible with the chosen polymer, microcrystalline cellulose. Clay polymer nanocomposites (CPNCs) were synthesized using the melt intercalation method. Mukondeni black clay with microcrystalline cellulose as polymers was melt mixed at 220 °C for 10 minutes in an extruder for exfoliation of the resulting composite. Physicochemical characteristics and mineralogical characteristics of the CPNC was determined using XRD, XRF, BET, FTIR and SEM. Batch adsorption experiments were conducted to determine the efficiency of CPNCs in defluoridation of groundwater. The pH, EC, TDS and fluoride concentration of field water was determined using the CRISON MM40 multimeter probe and the Orion versastar fluoride selective electrode for fluoride concentration. Elemental analysis revealed that CPNC 1:1 is mainly characterized of cellulose, Quartz and Albatite as the major minerals with traces of Montmorillonite, Ednite and Magnesium as minor minerals constituting CPNC 1:1. The structure of 1:4 CPNC was partially crystalline and partially amorphous showing increased cellulose quantity (1:4 clay to cellulose) as compared 1:1 CPNC, 1:2 CPNC and 1:3 CPNC. Maximum adsorption of fluoride was attained in 10 minutes using 0.5g of 1:4 CPNC removed 22.3% of fluoride. The initial fluoride concentration for the collected field groundwater was 5.4 mg/L, EC 436 μS/cm, and TDS 282 mg/L. The regeneration potential of CPNCs was evaluated through 3 successive adsorption desorption cycles. Fluoride removal decreased after the first cycle for all ratios of CPNCs, a continued decreased can be observed following the second cycle. CPNC 1:2 decreased from 9.32 % at the 1st cycle to 2.84 % and 0.56 % on the 2nd and 3rd cycle respectively. CPNC 1:4 decreased from 8.22 % at the 1st cycle to 4.80 % and 0.72 % on the 2nd and 3rd cycle respectively. The fluoride-rich Siloam groundwater had a slightly alkaline pH of 9.6. iv The low adsorptive characteristic displayed by all 4 CPNCs can be deduced from the BET analysis that revealed low surface area, pore volume, and pore size, it is evident from the BET analysis that less fluoride will be absorb as adsorption sites will be limited. Based on the findings of this study, recommendations are designing of correct preparation techniques to obtain nanocomposites with desirable properties, polymer melting points and evaporation point of the binder should be taken into consideration. / NRF

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