1,181 research outputs found
Determining Potassium (K+) Release, Crop Availability and Uptake from Three Red Algal (Rhodophyta) Species.
Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017
Fluoride Removal from Contaminated Water by Limestone Reactor and Phosphate Rock Reactor
Fluorosis, which results in mottling of teeth enamel, softening of bones, ossification of tendons and ligaments, and even neurologic damage, is endemic in many mid-latitude regions. It is caused by the long-term ingestion of high fluoride (F) drinking water, and the World Health Organization (WHO) recommends that drinking water have fluoride concentrations < 1.5 mg/L. The most common technologies to remove fluoride from wastewaters are precipitation and sorption. The sorption methods are more effective in reducing fluoride concentration than precipitation methods. However, they typically require initial high setup costs and supervision. Therefore, the development of a simple, passive and inexpensive technology to reduce fluoride concentrations in waters to recommended drinking water limits is of significant benefit to communities affected by fluorosis world-wide. Three reactors were developed in this research and the fluoride removal efficiencies were evaluated.
The first reactor was composed of two columns of limestone granules and one column of calcium citrate powder. This reactor was developed based on a cost-effective reactor developed by Reardon and Wang, which is composed of two columns of limestone gravel. The reactor functions by adding carbon dioxide to inflowing water, which forces calcite (CaCO3) to dissolve and thus fluorite (CaF2) to precipitate in the first column. The exiting water then degasses by unsaturated flow through the second column of limestone gravel which results in a precipitation of the calcite that dissolved in the first column. In this study, a column containing quartz sand/calcium citrate mixture was introduced and connected between the original two columns. Citrate and additional calcium ions were brought into the solution through saturated flow. The feedwater then entered the second column of limestone gravel, where citrate promoted the incorporation of fluoride ions into calcite. This study examines the known role of citrate ion to induce fluoride ion to co-precipitate in calcite, and evaluates its effectiveness to improve the passive, two-column reactor of Reardon and Wang to attain drinking water quality fluoride concentrations.
The results of this study indicate that the limestone reactor designed in this study reduced fluoride concentration from up to 150 mg/L to below the maximum contaminant level (4 mg/L) at the residence time of 4 h. When the residence time was 24 h, fluoride concentration was reduced to below the drinking water standard (1.5 mg/L). This fluoride removal efficiency was higher than with the limestone reactor of Reardon and Wang (by a further reduction of 1.19 mg/L fluoride in total) yet still lower than the predicted efficiency. One important reason of the lower fluoride removal efficiency than with prediction is that the citrate ions suppressed the precipitation of calcite. In addition, a short residence time of the experiment decreased the removal efficiency of the limestone reactor and a longer residence time results in high removal efficiency. An improvement to this reactor was to inject a slurry containing CaF2 into the upper port of the first column, which further decreased fluoride concentration by 0.420 mg/L.
The second reactor was composed of two columns of dolomite granules and one column of calcium citrate powder. The results in the dolomite reactor experiments indicate that this reactor was only able to reduce the fluoride concentration to 4.30 mg/L at a residence time of 4 h. The three main reasons are the slow dissolution rate of dolomite, negative effect of magnesium on the precipitation of fluorite in column 1 and suppression effect of citrate on precipitation of calcite in column 2. However, the present of magnesium promoted more fluoride to co-precipitate in fluorite in column 2 than that in a limestone reactor.
Accurate determination of the fluoride concentration is critical in this research. Three commonly used fluoride determination techniques including SPADNS, IC and fluoride electrode methods were investigated on their sensitivities and interference from citrate. The results indicate that citrate has a significant interference on the SPADNS method, and the addition of a pH buffer does not eliminate the interference. In addition, citrate has a minor effect on the determination of fluoride using fluoride electrode and no effect on using IC method, since the peaks of the fluoride and citrate were well separated. However, the running time is long for each sample with IC analysis, and the cost is much higher than with the fluoride electrode method. Consequently, fluoride electrode method was used throughout this research for determination of fluoride.
The third reactor was a single column of crushed phosphate rock from four sources: Carbonatite, Tennessee Brown, and two types of PSP with different particle sizes. Each of these materials was assessed as treatment options for fluoride. From mineralogical analysis, the results indicate that the major active mineral compositions among the four tested phosphate rocks are calcite, apatite and quartz. The results indicate that PSP rock, which contains the highest percentage of hydroxyapatite, is the best choice for fluoride remediation among the four. It can reduce fluoride concentration from 10 mg/L to 1.5 mg/L for up to 120 pore volumes. However, after 120 pore volumes the fluoride concentration continuously increased with adsorption sites becoming saturated over time. This outcome indicates a mechanism of adsorption rather than precipitation. The results from batch tests also provide evidence that adsorption contributed much more than precipitation for removal of fluoride.
Future work should be devoted to improvement of the removal efficiency of the limestone/ dolomite reactor: one is to evaluate a single reactor incorporating both calcite and dolomite with a reasonable ratio of the two minerals, and the other is to consider and assess organic ligands other than citrate to more efficiently promote the incorporation of fluoride in calcite precipitates. In addition, future work should be done on improving the fluoride removal ability of the phosphate rocks. Investigation should be done on understanding the dissolution process of the calcite and apatite within the phosphate rocks in the columns, and methods should be developed to simulate the precipitation of fluorite in the columns of the reactor. Constant monitoring of the heavy metals in the effluent from the reactor is also recommended.4 month
Spectrophotometric determination of sulphide and fluoride.
Ho Chak Ming.Thesis (M.Phil.)--Chinese University of Hong Kong, 1994.Includes bibliographical references (leaves 122-126).Acknowledgment --- p.iTable of contents --- p.iiList of figures --- p.ivList of tables --- p.vAbstract --- p.ixChapter Part I --- Determination of sulphideGeneral introduction --- p.1Spectrophotometric determination of sulphide --- p.5Chapter 1. --- Introduction --- p.5Chapter A. --- Review of the reported methods for the determination of sulphide --- p.5Chapter B. --- General description of the proposed method --- p.13Chapter 2. --- Experimental section --- p.18Chapter A. --- Preservation of samples --- p.18Chapter B. --- Sample pre-treatment --- p.19Chapter C. --- Separation/preconcentration of sulphide --- p.19Chapter D. --- Spectrophotometric determination of sulphide by proposed method --- p.24Chapter E. --- Spectrophotometric determination of sulphide by standard methylene blue method as the counter-check method --- p.32Chapter 3. --- Results and discussions --- p.34Chapter A. --- Optimization of the proposed spectrophotometric method --- p.34Chapter B. --- Optimization of the separation/preconcentration methods --- p.45Chapter C. --- Construction of the calibration graph for the spectrophotometric determination of sulphide and determination of the molar absorptivity coefficient --- p.53Chapter D. --- Precision and detection limit of the proposed spectrophotometric method --- p.54Chapter E. --- Interferences studies of the proposed method --- p.56Chapter F. --- Spectrophotometric determination of sulphide in water --- p.60Chapter G. --- Spectrophotometric determination of sulphide in beers --- p.63Chapter H. --- Spectrophotometric determination of sulphide in orange juices --- p.66Chapter 4. --- Conclusions --- p.68References --- p.70Chapter Part II --- Determination of fluorideGeneral introduction --- p.75Spectrophotometric determination of fluoride --- p.78Chapter 1. --- Introduction --- p.78Chapter A. --- Review of the reported methods for the determination of fluoride --- p.78Chapter B. --- General description of the proposed scheme for the spectrophotometric determination of fluoride in animal feeds --- p.84Chapter 2. --- Experimental Section --- p.87Chapter A. --- Ashing of the animal feed samples --- p.87Chapter B. --- Reduction of interferences in the ashed sample solutions using anion exchange resin --- p.89Chapter C. --- Preparation of solutions for the calibration graph and the ashed sample solutions for the spectrophotometric measurement --- p.90Chapter D. --- Spectrophotometric determination of fluoride in the ashed samples --- p.92Chapter E. --- Potentiometric determination of fluoride in the ashed sample solutions by the FISE method as the counter-check method --- p.93Chapter 3. --- Results and discussions --- p.94Chapter A. --- Ashing conditions of the animal feed samples --- p.94Chapter B. --- Removal of the interferences in the ashed sample solutions --- p.99Chapter C. --- Construction of the calibration graph for the spectrophotometric determination of fluoride --- p.112Chapter D. --- Precision of the spectrophotometric method --- p.113Chapter E. --- Spectrophotometric determination of fluoride in animal feeds --- p.114Chapter F. --- Potentiometric determination of fluoride in animal feeds by the FISE method as the counter-check method --- p.117Chapter 4. --- Conclusions --- p.120References --- p.12
Flow potentiometric detection of ions using metallic and coated wire electrodes in single and multiple cell designs
Application of membrane technologies in water purification
The world is facing a serious water crisis due to rapid population growth, industrialization and climate change. Water purification using membrane technologies provides a promising solution to address this problem. This thesis investigated the feasibility of membrane technologies in a wide range of applications covering drinking water purification and wastewater treatment. Target contaminants included fluoride, natural organic matter (NOM), emerging contaminants bisphenol A (BPA) and cimetidine, and the waterborne parasite Cryptosporidium. The first part of the thesis explored the solute-solute interactions of fluoride and humic substances (HS) in order to understand the behaviour of fluoride in natural water and during membrane filtration processes. It is shown that, at low pH and high ionic strength, fluoride ions are temporarily trapped inside the structure of HS aggregates. The second part of the thesis examined the feasibility of nanofiltration (NF) and reverse osmosis (RO) in treating challenging natural waters in Tanzania containing high fluoride and NOM concentrations, with the aim to increase the availability of drinking water sources. Fluoride retention was found to be dependent on ionic strength and recovery, which was predominantly due to a solution-diffusion mechanism. NOM retention was independent of water matrices but was governed by a size exclusion mechanism. NOM was observed to have a positive impact on fluoride removal. The third part of this work evaluated the on-site performance of a pilot-scale renewable energy powered membrane system in remote areas under varying solar conditions. While the technology is well established, the adaptation to remote areas is far from achieved. The system used in this study reliably produced high-quality drinking water despite of solar fluctuations. This area requires further work in terms of integration, technology adaptation and operation and maintenance schemes. The last part of the thesis reported the development of a series of novel photocatalytic polymers and tested their capabilities in removing wastewater contaminants. The photoactive polymers were highly capable of degrading BPA and cimetidine, as well as inactivating Cryptosporidium. These are very promising materials for simultaneous decontamination and disinfection of wastewater. The results obtained from this thesis provide new insights into solute-solute interactions, solute transport mechanisms, decentralized membrane system and novel membrane materials, which are hoped to contribute to advancements in current membrane technologies
Fabrication and use of new solid state phosphate ion selective electrodes for monitoring phosphorylation and dephosphorylation reactions
Highly selective and sensitive phosphate sensors have been fabricated by constructing a solid membrane disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO4) and powdered copper (Cu). Both binary and ternary electrode systems are produced depending on their composition. The ternary membranes exhibit greater selectivity over a wide range of concentrations. The ternary electrode with the composition 25% AlPO4, 25% Cu and 50% Al was selected as our preferred electrode. The newly fabricated ternary membrane phosphate selective electrodes exhibited linear potential response in the concentration range of 1.0 × 10−6 to 1.0 × 10−1 mol L−1. The electrodes also exhibit a fast response time of <60 s. Their detection limit is 1.0 × 10−6 mol L−1. The unique feature of the described electrodes is their ability to maintain a steady and reproducible response in the absence of an ionic strength control. The electrodes have a long lifetime and can be stored in air when not in use. The selectivity of the new phosphate selective electrodes with respect to other common ions is excellent. The results obtained provide further insight into the working principles of the newly fabricated phosphate selective electrodes.
Dephosphorylation and phosphorylation reactions were monitored using the preferred phosphate selective electrode. The following reactions were studied and inferences drawn; (a) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[OH(PO2O)]2- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[OH(PO2O)]2- ratios.(b) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[O2NC6H4PO2(O)(OH)]- for
1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[O2NC6H4PO2(O)(OH)]- ratios. (c) the
reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)2O]2- for 1:1, 2:1 and
3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)2O]2- ratios, and (d) the reactions
between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)3O2]3- for the 1:1, 2:1 and 3:1
[{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)3O2]3- ratios. Further insight into
dephosphorylation and phosphorylation reactions is unravelled by the novel
phosphate selective electrode monitoring.
*For clarity of the complexes utilized, see chapter 4, table 4.1.
KEY WORDS; Dephosphorylation, phosphorylation, ion selective electrodes,
phosphate ion selective electrode, decontamination, electromotive force, potential
difference, activity, concentration, selectivity coefficient, calibration, ionic strength,
hydrolysis, inorganic phosphates, nitrophenylphosphate, pyrophosphate,
tripolyphosphate, organophosphate esters.ChemistryD. Phil (Chemistry
An inter-laboratory comparative study of fluoride determination in water
South Africa is on the brink of implementation of mandatory fluoridation of municipal water following the final approval by Parliament in 2001. The ability to accurately measure fluoride in water is an obvious prerequisite for the safe and effective implementation of water fluoridation. This paper evaluates the current status of fluoride determination in water in South Africa. The study was undertaken by the University of Johannesburg in collaboration with the South African Bureau of Standards as part of their ongoing Water-Check Programme. River water, borehole water, and synthetic water samples were sent to 66 participating laboratories in South Africa in March 2004. The results obtained from the analysis of 7 fluoride-containing
samples with varying matrix composition, show that 50% of the laboratories could achieve results that fall between a lower limit of -20% and an upper limit of +20% relative to the true value. The precision (%RSD) for the determination of samples with fluoride concentration at the important level below 0.5 mg/ℓ was poor, ranging from ±20% at 0.5 mg/ℓ to ±100% at 0.1 mg/ℓ. The two major analytical techniques used by the participating South African laboratories were ISE (40%) and IC (36%).. Water SA Vol.32 (3) 2006: pp.365-37
Evaluation of Aluminum Speciation Using Synthetic and Natural Samples: Final Report
published or submitted for publicationis peer reviewedOpe
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The Dental Fluoridation Potential of Drinking Water
Water fluoridation is considered one of the top ten greatest health achievements of the twentieth century due to its effectiveness in reducing the prevalence of dental caries. However, despite extensive research on the subject, there is little information currently available about how the constituents of drinking water affect the uptake of fluoride by tooth enamel. This study investigated how several key components and characteristics of drinking water influence fluoride uptake and developed a corresponding model system for testing fluoride uptake. The experimental variables included the concentration of calcium and magnesium ions, degree of water hardness, and pH and buffer strength; a final geographical experiment was also performed that analyzed the effectiveness of fluoride uptake in several different municipal water samples. Overall, standard levels of calcium and magnesium ions, water harness, and buffer strength did not affect fluoride uptake, and a pH of 6.0 was optimal for fluoride uptake. Notably, there was no significant difference in fluoride uptake between the water samples from different regions, indicating fluoride is a resilient ion likely be incorporated in enamel if originally present in the water
Distribution and causes of high fluoride groundwater in the western Bushveld area of South Africa
Includes bibliography.Dental fluorosis is endemic in the western Bushveld of South Africa. This study investigated the occurrence of fluoride (Fˉ) in groundwater in the area. It was hypothesised that fluoride in groundwater originated from the dissolution of fluorine-bearing minerals, principally fluorite, mica, amphibole and apatite, and that high F- groundwater would be hosted in rocks with a high fluorine (F) content. It was further hypothesised . that groundwater residence time, rare F-bearing minerals, ion exchange reactions and evaporation affected the Fˉ concentration of groundwater. These hypotheses were investigated by analysing data on Fˉ concentrations in groundwater, paired rock and soil samples, and selected minerals. Three hundred and thirty eight samples of groundwater from the field area were analysed for Fˉ by both Fluoride Ion Selective Electrode and High Pressure Ion Chromatography. The results were added to a database of three thousand water samples covering the western Bushveld and together provide the first complete picture of the distribution of high Fˉ groundwater in the area
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