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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.
11

Effect of particle size and natural organic matter on the transport and fate of latex nanoparticles in saturated porous media

Pelley, Andrew John. January 2007 (has links)
Colloid filtration experiments were performed using latex particles (50 nm, 110 nm and 1500 nm) in both the presence and absence of 5.0 mg/L humic acid (HAs). At low ionic strengths (1 -- 10 mM KCl), an increase in attachment efficiency (alpha) with increasing particle size was observed, which contrasts with predictions based on DLVO theory. The presence of HAs generally resulted in a decrease in alpha. Characterization experiments to better understand this behaviour included particle sizing using dynamic light scattering (DLS) and zeta potential using laser Doppler velocimetry (LDV). The particles' hydrodynamic diameters were unchanged in the presence of HAs. HAs lead to an increase in absolute zeta potential for the 50 nm and 110 nm colloids and a decrease in zeta potential for the 1500 nm particles. A discussion of the apparent deviations from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and explanations for the observed behaviour are provided.
12

In Situ Groundwater Remediation using Enricher Reactor-Permeable Reactive Biobarrier

Somayajula, Sreerama Murthy Kasi January 2012 (has links)
Permeable reactive biobarrier (PRBB) is a flow-through zone where microorganisms degrade contaminants in groundwater. Discontinuous presence of contaminants in groundwater causes performance loss of a PRBB in removing the target contaminant. A novel enricher reactor (ER) - PRBB system was developed to treat groundwater with contaminants that reappear after an absence period. ER is an offline reactor for enriching contaminant degraders, which were used for augmenting PRBB to maintain its performance after a period of contaminant absence. The ER-PRBB concept was initially applied to remove benzene that reappeared after absence periods of 10 and 25 days. PRBBs without ER augmentation experienced performance losses of up to 15% higher than ER-PRBBs. The role of inducer compounds in the ER to enrich bacteria that can degrade a mixture of benzene, toluene, ethylbenzene, and xylene (BTEX) was investigated with an objective to minimize the use of toxic chemicals as inducers. Three inducer types were studied: individual BTEX compounds, BTEX mixture, and benzoate (a non toxic and a common intermediate for BTEX biodegradation). Complete BTEX removal was observed for degraders enriched on all three inducer types; however, the removal rates were dependent on the inducer type. Degraders enriched on toluene and BTEX had the highest degradation rates for BTEX of 0.006 to 0.014 day-1 and 0.006 to 0.012 day-1, respectively, while degraders enriched on benzoate showed the lowest degradation rates of 0.004 to 0.009 day-1. The ER-PRBB technique was finally applied to address the performance loss of a PRBB due to inhibition interactions among BTEX, when the mixture reappeared after a 10 day absence period. The ER-PRBBs experienced minimal to no performance loss, while PRBBs without ER augmentation experienced performance losses between 11% and 35%. Presence of ethanol during the BTEX absence period increased the performance loss of PRBB for benzene removal. PRBBs augmented with degraders enriched on toluene alone overcame the inhibition interaction between benzene and toluene indicating that toluene can be used as a single effective inducer in an ER. The ER-PRBB was demonstrated to be a promising remediation technique and has potential for applications to a wide range of organic contaminants.
13

Assessment of the potential of selected adsorbents for use in small-scale systems for the removal of uranium from mine-impacted water

Mabape, Kgaugelo Ishmael Smiley January 2017 (has links)
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science, 2017 / The tailoring of zeolites surface properties using organic functionalising agents displaying higher binding affinity for metal ions is a widely explored approach for water treatment. In this study, amine functionalised zeolites and phosphate functionalised zeolites were separately synthesised from similar natural zeolite precursors using reflux methods. The surface composition and morphological elucidations were achieved by characterising the adsorbents using Fourier Transform Infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA), Zeta potential, Point of zero charge (pHPZC), and the Brunauer, Emmett and Teller analysis (BET). In case study 5.1, the sorption mechanisms of the uranyl ion onto amine functionalised zeolites (AMZ), activated carbon (AC) and natural zeolite (NZ) were studied as function of various environmental batch parameters. There was effective adsorption when uranium existed as uranyl ions: UO22+ and UO2OH+. The data fitted numerous kinetic and isotherm models suggesting that the equilibrium mechanisms were characteristic of a combination of chemisorption and physisorption for these three adsorbents. The Dubinin-Radushkevich (DR) model did not fit the data and therefore the energy values derived from it were not used to predict the mechanisms involved. However, the thermodynamic evaluations of parameters ∆H, ΔG and ∆S° showed that equilibrium mechanisms were exothermically, randomly and spontaneously favoured for all adsorbents at temperatures ranging between 22 and 40oC. The adsorption capacity of 0.452 mg g-1 was achieved at pH 3 by 500 mg AC dosage using 20 mL volume of 10 mg L-1 uranyl ion solution after equilibrating for 6 h within the temperature ranges of 22 to 30oC. Under the same conditions of sorbent dosage of 500 mg, uranyl solution volume of 20 mL and 10 mg L-1 U(VI) solution concentration, the maximum adsorption capacity of 0.506 mg g-1 for NZ and 0.480 mg g-1 for AMZ were both achieved at pH 4 after equilibration time of 21 h and 6 h with the optimum temperature range of 22 to 30oC, respectively. The model results predict that intraparticle diffusion thorough pores decreased in the order AC ˃ NZ ˃ AMZ while estimating that chemisorption occurred in a reverse order. On the basis of the modelled data, it was deduced that amine functionalisation of natural zeolites improves their chemisorption capability for uranyl ion and can therefore be used as a cost efficient adsorbent for small-scale remediation of contaminated aquatic systems. In another case study 5.2, the surface properties of successfully prepared aminomethyl phosphonic acid functionalised natural zeolite (APZ) were compared to those of commercial silica polyamine composites (SPC) for uranium uptake in batch aqueous solutions. The FTIR spectrum revealed that (3-aminotrimethyl) phosphonic acid functional groups were successfully grafted onto natural zeolite. The TGA analysis showed that the APZ had higher thermal stability and fewer active sites compared to SPC. The optimum adsorption capacity (qe) of 49 mg g-1 and 44 mg g-1 uranium was achieved using 25 mg SPC and 100 mg APZ, respectively at pH 4, 25oC after 1 and 6 h equilibrating time. The data best fitted the pseudo second-order kinetic model and Freundlich isotherm model. The thermodynamic studies showed that adsorption occurred chemically and exothermically for both APZ and SPC. The overall selectivity order for APZ was; Na ˃ Mn ≥ U ˃ Ca ˃ Fe and for SPC was; Fe ˃ Mn ≥ Ca ˃ U˃ Na. The findings showed that phosphate- and amine-functionalised zeolite bind strongly to uranium compared to the unmodified natural zeolite and other conventional adsorbents such as activated carbon. Their selectivity for this element was commendable. With further improvements in the synthetic protocols e.g. by using microwave-based methods, it should be possible to obtain functionalised zeolite that has superior properties to SPC. / XL2017
14

Laboratory and Field Studies Directed toward Accelerating Arsenic Remediation at a Major US Superfund Site in New Jersey

Wovkulich, Karen January 2011 (has links)
Arsenic is a prevalent contaminant at a large fraction of US Superfund sites. Therefore, establishing techniques for accelerating As remediation could benefit many contaminated sites. Remediation of As contaminated groundwater by conventional methods, i.e. pump and treat (P&T), can be impeded by slow desorption of As from Fe and Al (hydr)oxides in aquifer solids. Through experimentation at different physical scales (grain, bench, and field scale), the potential for chemical additions to increase As release from sediments and possibly accelerate P&T remediation is examined. The work described here focuses on As contamination and remediation at the Vineland Chemical Co. Superfund site in southern NJ. The site is extensively contaminated with As resulting from decades of poor chemical storage and disposal practices by the Vineland Chemical Co., which manufactured As-based biocides from 1949-1994. Despite significant intervention, including groundwater remediation by P&T and treatment of solids via soil washing, sufficient site clean up could require many decades with current technologies. Chemical amendments that either compete with As for sorption sites or dissolve Fe and Al (hydr)oxides can increase As mobility and potentially improve P&T remediation efficiency. Simple extrapolations from bench scale column experiments based on pore volumes suggest that treatment with 10 mM oxalic acid could lower the time necessary for clean up at the Vineland site from 600 years (with current techniques involving just groundwater) to potentially on the order of 4 years. Small scale (<1 mm2) X-ray fluorescence maps from columns performed within the synchrotron beamline showed As release during oxalic acid treatment that was consistent with the bulk column materials and suggested that microscale processes can be predictive of the larger system. Finally, during a 3-month pilot study at the Vineland site, oxalic acid was injected into a section of the aquifer via an injection manifold system that was designed and built for the experiment. Groundwater samples indicate that introduction of oxalic acid led to increased As release at a sampling well and pump and treat recovery well in the study area. Addition of oxalic acid shows promise for accelerating treatment of a highly contaminated site.
15

Uranium and technetium bio-immobilization in intermediate-scale permeable reactive scale barriers

Sapp, Mandy M. 01 December 2003 (has links)
Groundwater at Oak Ridge National Laboratory's Field Research Center (FRC) is contaminated with U(VI) and Tc(VII), has pH values as low as 3.3, and nitrate concentrations as high as 120 mM. The objective of this research was to determine if in-situ bio-immobilization is a viable treatment alternative for this water. A laboratory column packed with crushed limestone and bicarbonate was used to model in-situ pH adjustment. Denitrification and metal reduction were modeled in columns packed with FRC sediment with ethanol as the electron donor. Two intermediate-scale physical models deployed in the field were packed with limestone and sediment and were stimulated with ethanol to support denitrification, U(VI) reduction, and Tc(VII) reduction of FRC groundwater. The limestone/bicarbonate column maintained a pH of above 5 for nearly one hundred pore volumes without significant loss in hydraulic conductivity. The high-nitrate (~120 mM) column study provided rates of denitrification (~15.25 mM/day), ethanol utilization (~13 mM/day), and technetium reduction (~120 pM/day) by sediment microorganisms, but no uranium reduction was detected. Results of the low nitrate (3 mM) column study indicate that once the pH of FRC water is adjusted to pH ~7 and nitrate is removed, uranium (~3 μM) and technetium (~500 pM) reduction occurred with ethanol as the electron donor at rates of 0.5 μM/day and 57 pM/day. Similar results were obtained in two intermediate-scale (~3 m long) physical models. Data from the high-nitrate, low-pH model indicate that the pH was increased and nitrate and technetium reduction were occurring. Decreased U(VI) concentrations were measured in the presence of high nitrate concentrations. Thus, U(VI) precipitates may form or sorption of U(VI) may occur near the inlet in the pH adjustment region. The maximum pseudo-first order rates of reduction measured during the seventh week of model operation were: nitrate at 0.76 day⁻¹, Tc(VII) at 0.28 day⁻¹, and U(VI) at 0.12 day⁻¹. Ethanol concentrations were reduced from ~180 mM to zero in ~10 days during the seventh week of model operation. No Fe(II) production was measured. Concentration data collected from the low nitrate, neutral pH model indicate that nitrate, uranium, and technetium reduction were occurring, though the model had been operational for only ~6 weeks. No Fe(II) production was detected but sulfate reduction was occurring. The results of the laboratory experiments and the performance of the intermediate-scale physical models suggest that bio-immobilization is a viable treatment alternative for the contaminated groundwater at the FRC. / Graduation date: 2004
16

Down-borehole permeable barrier reactor : verification of complete mineralization of pentachlorophenol in a sequential anaerobic-aerobic process

Roberts, David Bradley 10 October 1997 (has links)
Graduation date: 1998
17

Down-borehole permeable barrier reactor : primary substrate selection for aerobic dichlorophenol degradation

Kaslik, Peter J. 14 March 1996 (has links)
In situ bioremediation of pentachlorophenol-contaminated ground water in a sequential anaerobic-aerobic down borehole permeable barrier reactor requires a non-toxic primary substrate for dichlorophenol cometabolism. Serum bottle tests comparing the effectiveness of eight primary substrates for aerobic dichlorophenol degradation showed phenol to be the most effective followed by imitation vanilla flavoring, guaiacol, sodium benzoate, molasses, acetic acid, propylene glycol and ethyl vanillin in propylene glycol. As phenol is a pollutant, imitation vanilla flavoring is the recommended primary substrate for field use. In a second bottle test, 3,4,5-trichlorophenol was not sufficiently biotransformed, emphasizing the need for biotransformation to occur in the anaerobic zone of the reactor. / Graduation date: 1996
18

Environmental impacts of chrome mining on the Assmang Chrome Dwarsriver mine.

Mmbengwa, Tshengedzeni Remember. January 2010 (has links)
Thesis (MTech. : Environmental Management.)--Tshwane University of Technology, 2010.
19

Assessment of permeable reactive barriers alternative media for the remediation of nitrate-contaminated ground-waters.

Zorgani, Abdulmutaleb Esseid. January 2013 (has links)
The increase in the contamination of ground-water (GW) with nitrates in both developing and developed countries mainly results from agricultural activities and improper sanitation systems, and is a recent phenomenon that has become a source of great health concern, particularly in regions where people rely on the ground-water as their primary water source. Due to the advantages of using Permeable Reactive Barriers (PRB) including its cost-effectiveness as well as its capability to remove or mitigate the spread of large spectrum of contaminants (including nitrates), a significant increase has been observed in the use of this subsurface treatment technology compared to other methods. However, identifying more economic and reliable reactive media to be used instead of the costly conventional PRB materials is now of key importance. Two local soils namely Berea Red Sand (BRS) and Umgeni Sand (US) were the main focus of this research. In addition to these soils, Zero Valent Iron (ZVI) was also used in this study. Through the use of batch experiments the feasibility of the nitrate reduction was investigated by five substrates including 100% ZVI, 100% BRS, 100% US, mix of 75% ZVI + 25% BRS, and mix of 50% ZVI + 50% BRS. Five concentrations of nitrate synthetic solution including 10 mg/l, 25 mg/l, 50 mg/l, 100 mg/l, and 500 mg/l were used to simulate nitrate-contaminated ground-water. All the batch experiments were performed under semi-aerobic and uncontrolled pH conditions, and only one solid/liquid ratio of 1:10 was used. The two mixes (mix of 75% ZVI + 25% BRS, and mix of 50% ZVI + 50% BRS) exhibited a nitrate removal efficiency of 100%, with all the different initial concentrations that were used with it; besides these two mixes, none of the other substrates showed this performance. 100% ZVI; however, managed complete nitrate reduction when the 10 mg/l and 25 mg/l concentrations were used. Finally, it was concluded that the benefits of using BRS in combination with other materials such as ZVI in the PRB field are promising. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.
20

Characterization and surfactant enhanced remediation of organic contaminants in saturated porous media

Taylor, Tammy Palmer 08 1900 (has links)
No description available.

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