Browsing by Subject "Fluoride"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
Item Biodegradation Potential of Perfluorooctanoate and Perfluorooctane Sulfonate(2012-10-19) Thelakkat Kochunarayanan, ParvathyPerfluorooctanoate (PFOA) and Perfluorooctane sulfonate (PFOS) are two environmentally persistent perfluorinated compounds widely used for many industrial and consumer products due to their high thermal, oxidative resistance and surface repellence to water and oil. Their reproductive and developmental toxicity in lab animals and their persistence in environment have raised a serious concern for humans and animals. Trace amounts of these compounds have been found in water bodies, human blood, and wildlife samples. PFOA and PFOS are currently listed in Environmental Protection Agency's drinking water Contaminant Candidate List and in the list of Persistent Organic Pollutants in the Stockholm Convention. The strong covalent bond between carbon and fluorine present in PFOA and PFOS makes them stable and resistant to conventional treatment processes. Several advanced chemical processes can degrade PFOA and PFOS under high temperatures and pressures or other extreme conditions. However, the potential of biodegradation as a treatment technology for these compounds hasn't been developed successfully. This thesis focuses on evaluating the biodegradation potential of PFOA and PFOS. Fluoroacetate dehalogenase is an enzyme capable of defluorinating fluorinated aliphatic compounds. In this study, the potential of fluoroacetate dehalogenaseexpressing microorganisms to biodegrade PFOA and PFOS is examined. Two known fluoroacetate dehalogenase-expressing strains and fluoroacetate-degrading mixed cultures were used. The effect of ammonia in the enzyme activity was extended to study its effect on the biodegradation of PFOA and PFOS. Fluoride ions released during the mineralization of the PFOA and PFOS was used as a proof of biodegradation. The experiments with fluoroacetate dehalogenase-expressing strains and mixed culture consortia enriched from soil showed an increase in fluoride concentration in the solution thus indicating the possibility of successful biodegradation of PFOA and PFOS. Based on the fluoride ion content, it was also concluded that ammonia inhibits the enzyme activity in one of the two pure strains.Item Cationic Main Group Compounds as Water Compatible Small Anion Receptors(2013-05-06) Leamer, Lauren AnneThe fluoride anion plays an important role in dental health and as a result is added to drinking water at low concentrations. If the concentration of fluoride is too high however, skeletal fluorosis can occur. Because of this, there has been significant interest in the development of water compatible anion sensors that can sense fluoride at the ppm level. This is made difficult by the high hydration enthalpy of fluoride (?H0 = -504 KJ/mol) which significantly lowers the reactivity of this anion in water. For this reason it has become the goal of the Gabba? group, as well as other research groups to develop fluoride sensing small molecules. Such molecules should possess sufficient Lewis acidity to overcome the hydration enthalpy of the fluoride anion. A significant amount of research has been conducted on triarylboranes containing cationic moieties such as ammonium, phosphonium, and sulfonium groups. This thesis will describe additional examples of such species, including a series of ammonium boranes of the general formula [p-(Mes2B)C6H4(NMe2R)]+. As indicated by anion complexation studies, the R group present in these molecules has a notable effect on the anion affinity of the somewhat distant boron center. Another component of this thesis deals with the chemistry of newly synthesized stiboranes that are also decorated by peripheral ammonium groups. As observed for the ammonium boranes mentioned above, the ammonium groups present in these stiboranes drives anion capture, leading to zwitterionic ammonium antimonite formation.Item Defluoridation and natural organic matter removal in drinking waters by alum coagulation(2014-05) Stehouwer, Mark Lawrence; Lawler, Desmond F.; Katz, Lynn E.Fluoride naturally occurs in some ground and surface waters at high concentrations all around the world. Due to increasing health concerns about over-exposure to fluoride in drinking water, the United States Environmental Protection Agency (USEPA) has begun to review fluoride as a drinking water contaminant. Should the USEPA decide to lower the fluoride maximum contaminant limit (MCL), many water systems in addition to those already struggling to meet the fluoride MCL will require defluoridation as part of their drinking water treatment process. Alum coagulation was investigated as a defluoridation treatment strategy in this research project. Surface and blended (ground/surface) drinking water sources with high fluoride concentrations pose a unique challenge to defluoridation by alum coagulation because of the presence of both natural organic matter (NOM) and fluoride. Defluoridation of synthetic and natural waters using jar tests elucidated interactions of fluoride, NOM, and aluminum during alum coagulation. Alum coagulation was able to remove 80% of fluoride from natural waters with a 500 mg/L alum dose; however, 50% fluoride removal was observed to be possible with an alum dose of 150-170 mg/L. The optimum pH for fluoride removal in synthetic and natural waters was observed to be approximately 6.5 and was found to be an important factor in determining the overall performance of alum coagulation. The presence of fluoride during alum coagulation was found to reduce the removal of three low molecular weight (LMW) organics, acting as surrogates for NOM, to different extents depending on their functionality. The presence of LMW organic acids in synthetic waters did not impact the removal of fluoride; however, increasing NOM concentrations in the natural waters likely accounted for decreasing fluoride removals observed in the natural waters. Additional jar tests with natural waters revealed that pH adjustment was unnecessary for defluoridation of high pH and high alkalinity waters and that an enhanced precipitation effect occurred at low alum doses when no pH adjustment was made during alum coagulation. The enhanced precipitation effect caused comparable or enhanced removals of fluoride and NOM to be observed despite system pH values being higher than the optimal defluoridation pH of 6.5. Lower aluminum residuals were also observed as part of the enhanced precipitation effect, suggesting that when precipitation begins under high pH conditions, fluoride interference does not occur and therefore promotes more precipitate formation with greater available surface area for adsorption. However, as precipitation occurs, pH drops, and fluoride increasingly interacts with the aluminum precipitate resulting in greater overall fluoride removals.Item Drinking water treatment by alum coagulation : competition among fluoride, natural organic matter, and aluminum(2012-12) Alfredo, Katherine Ann; Lawler, Desmond F.; Katz, Lynn Ellen; Liljestrand, Howard M.; Holcombe, James A.Some community water systems using sources containing elevated levels of fluoride, in the United States and worldwide, struggle to treat their drinking water to healthy fluoride concentrations. Many treatment plants in the U.S. currently use aluminum based salts, such as aluminum sulfate and polyaluminium chloride, as coagulants during conventional treatment for removal of particles from drinking water sources. Moreover, enhanced aluminum sulfate, or alum, coagulation requires higher concentrations of aluminum added to the process and has been shown to be effective for removal of disinfectant byproduct precursors, i.e., natural organic matter (NOM). The presence of fluoride may interfere with the formation of aluminum hydroxide precipitates, and interrelationships among NOM, aluminum precipitation and fluoride removal are not well understood. A fundamental understanding of how fluoride alters the properties of aluminum precipitates and how fluoride and NOM molecules compete as ligands interacting with soluble aluminum species is lacking. As a result, the development of guidelines for implementation and optimization of a treatment scheme that uses aluminum in the presence of fluoride requires a multi-faceted approach in which the development of a mechanistic understanding of these interactions is conducted in concert with macroscopic experiments to identify optimum conditions for simultaneous removal of fluoride and NOM. To date, little research has looked at the efficiency of removing both fluoride and organics from the perspective of the precipitation process. To provide a foundation for revising treatment techniques, this research evaluated the effect of co-precipitating aluminum in the presence of fluoride, organics, and in multi-ligand systems to characterize the solid precipitate and removal competition. This research verified the formation of a co-precipitate in the presence of fluoride and certain low molecular weight organics. Co-precipitation from organics and fluoride competes for removal, especially at low alum coagulant doses, complicating treatment for resource limited areas.Item Fluoride, natural organic matter, and particles : the effect of ligand competition on the size distribution of aluminum precipitates in flocculation(2016-05) Herrboldt, Jonathan Philip; Lawler, Desmond F.; Katz, Lynn EllenFluoride occurs at elevated concentrations naturally in surface and ground waters around the world. If consumed at low concentrations in drinking water (< 1.5 mg/L), fluoride is shown to reduce the occurrence of dental caries and the Centers for Disease Control and Prevention named fluoridation of public water systems one of the 10 Great Public Health Achievements of the 20th Century (CDC, 1999). However, prolonged exposure to high concentrations of fluoride (> 2.0 mg/L) causes adverse health effects to teeth and bones. For this reason the United State Environmental Protection Agency (USEPA) enacted a maximum contaminant level (MCL) for fluoride at 4.0 mg/L. This rule is currently under review following a recent risk assessment and may be lowered. If the MCL were lowered, water systems previously meeting treatment standards would suddenly find themselves out of compliance and will need to implement additional treatment to meet the new standard. Defluoridation by alum coagulation is a proposed defluoridation method. However, the interaction between fluoride and natural organic matter (NOM) and their effects on the particle size distribution of aluminum precipitates is not well understood. Because the particle size distribution of aluminum precipitates is an important parameter in the efficiency of sedimentation and filtration systems, a thorough understanding of these interactions and their potential effect on sedimentation and filtration is needed to inform the implementation of defluoridation by alum coagulation. This work utilized a series of jar tests on synthetic surface water to determine the effect of fluoride and NOM on the particle size distribution of aluminum precipitates. It was found that fluoride caused the volume distribution of aluminum precipitates to shift toward smaller particle sizes. However, NOM caused the formation of a larger number of aluminum precipitates, which resulted in a dramatic increase in the total volume of precipitates. When both fluoride and NOM were in the system, a combination of the two effects was observed: the volume distribution shifted toward smaller particle sizes but the peak of the distribution shifted toward a greater volume, indicating both smaller particles were being formed and a greater overall volume of particles precipitated.Item The high pressure synthesis, crystal growth and physical properties of transition metal perovskites(2013-12) Marshall, Luke Gordon; Goodenough, John B.; Zhou, JianshiThe perovskite structure has an incredible versatility that results in myriad compounds with varied and eccentric behaviors. Perovskite oxides have been extensively studied and used for over 60 years. In order to expand on our already thorough knowledge of these compounds, it is necessary to use modern and creative experimental techniques. High-pressure synthesis and high oxygen-gas pressure annealing techniques are used to synthesize oxygen stoichiometric RNiO₃ (R = lanthanide). The particularly rich phase diagram of this compound allows for the study of the crossover from localized to itinerant electronic behavior and from an enhanced Pauli to a Curie-Weiss law paramagnetism. Single crystals of RFeO₃ are grown in order to analyze the spin canting in these antiferromagnetic samples. The size of the rare earth-cation is used to tune the magnitude of octahedral-tilt distortions. This tuning allows distinguishing between the two possible drivers for spin canting and weak ferromagnetism in these compounds, the octahedral-tilt-dependent single-ion anisotropy and the octahedral-tilt-independent Dzyaloshinskii-Moriya interaction. Although it is a fluoride compound, KCuF₃ has been used as an analogue to transition-metal oxide perovskites such as LaMnO₃ because of the similarity of their orbital ordering. Through the use of high-temperature neutron diffraction, it is shown that the orbital ordering and Jahn-Teller distortion in this compound are not lifted at the predicted temperature. Another mechanism for orbital ordering is identified. La₂[subscript-x] Sr [subscript x] CuO₄ has long been of interest as the progenitor system of the highTc superconductors. Despite having an exceedingly well-studied phase diagram in the over-doped region of its superconducting dome, little is known about this system in the region x > 0.3 because of the difficulty of synthesizing fully oxygen-stoichiometric samples. With high-oxygen-gas-pressure annealing and high-pressure synthesis, the completion of the phase diagram up to x = 1.0 is attempted. Finally, like many iridates, post-Perovskite CaIrO₃ exhibits a very strong spinorbit coupling of its 5d electrons. Because its magnetism is very weak, traditional methods to measure the magnitude of its orbital moment and spin-orbit coupling, such as neutron powder diffraction, are not viable. In order to address this issue, direct measurement of the orbital moments was conducted by using x-ray absorption spectroscopy and x-ray magnetic circular dichroism techniques.Item Mechanisms of ligand removal and competition in aluminum salt coagulation systems : insights using ATR-FTIR spectroscopy(2016-05) Bartolo, Mitchel Joseph; Lawler, Desmond F.; Katz, Lynn EllenFluoride, while beneficial in moderate to low doses, has detrimental health effects associated with chronic exposure to elevated concentrations from sources such as drinking water. Natural organic matter (NOM) is ubiquitous in many drinking water sources and can contribute to the formation of carcinogenic disinfection by-products (DBPs). In an era marked by increasing concerns for drinking water quality and increased costs to produce high quality drinking water, small water systems (SWSs) are the most vulnerable due to their lack of financial and operational resources. Aluminum salt coagulation processes have the potential to remove both fluoride and NOM, and would be advantageous to a SWS since the technology has been widely used for decades. However, the removal mechanisms and interactions among competing contaminants remain poorly understood. This study aims to elucidate the mechanisms of removal and better understand the competition that occurs in a coagulation system by using a combination of spectroscopic insights at the solid surfaces and macroscopic insights from aqueous removal levels. Attenuated total reflectance Fourier transform infrared spectroscopy provided insights at the solid-aqueous interface where it was concluded that sulfate and pyromellitate (an NOM surrogate) adsorb via outer-sphere complexation while fluoride, silicate, and carbonate create inner-sphere surface complexes. It was also evident that silicate accumulated and polymerized at the aluminum hydroxide surface with time. Both fluoride and pyromellitate exhibited greater removal efficiencies in waters containing sulfate versus chloride, suggesting that sulfate has a higher affinity for the surface than chloride. Fluoride and pyromellitate removals were also reduced at the higher pH of 7.5 due to increased aluminum solubility and competition with inner-sphere complexed carbonate. Pyromellitate removal is significantly impacted by the presence of fluoride whereas fluoride removal is marginally impacted by the presence of pyromellitate. This was explained by the inner-sphere complex that fluoride forms in comparison to the weaker electrostatic interaction of pyromellitate. Silicate was observed to reduce fluoride and pyromellitate removals both initially and with time due to competition for surface bonding sites. Over time, the accumulation and polymerization of silicate is believed to be responsible for desorption of fluoride and pyromellitate.