Browsing by Subject "Coagulation"
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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 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.Item Modeling the growth and dissolution of clots in flowing blood(Texas A&M University, 2006-10-30) Mohan, AnandMultiple interacting mechanisms control the formation and dissolution of clots to maintain blood in a state of delicate balance. In addition to a myriad of biochemical reactions, rheological factors also play a crucial role in modulating the response of blood to external stimuli. The broad stimuli for clot formation were laid out, more than a century ago, in, what is now referred to as, Virchow??????s triad. To date, a comprehensive model for clot formation and dissolution, that takes into account the biochemical, medical and rheological factors, has not been put into place, the existing models emphasizing either one or the other of the factors. In this dissertation, a model is developed for clot formation and dissolution that incorporates many of the relevant crucial factors that have a bearing on the problem. The model, though just a first step towards understanding a complex phenomenon goes further than previous models in integrating the biochemical, medical and rheological factors that come into play. The model is tested in some simple flow situations as part of an attempt to elucidate Virchow??????s triad. Extensions to the model, along with detailed numerical studies, will hopefully aid in a clearer understanding of the phenomenon, and in making relevant clinical correlations.Item pH-induced flocculation/deflocculation process for harvesting microalgae from water(2014-08) Choi, Jin-Yong, Ph. D.; Kinney, Kerry A.; Katz, Lynn Ellen; Kinney, Kerry A.; Katz, Lynn E.Historically, the presence of microalgae (algae hereafter) in natural waters has been viewed as a nuisance due to its adverse impact on water quality. More recently, however, algae are being investigated as potential sources of biofuel and a range of natural products. These applications require the development of large-scale cultivation systems for mass production that include growth, harvesting, concentration, and product recovery components. While challenges still remain with respect to many of the processes involved in mass production, one of the most technically and economically challenging steps is harvesting the algae from dilute growth cultures, especially in systems where chemical additives are of concern either within the algae concentrate or the effluent water. For this reason, a pH-induced flocculation/deflocculation method using the hydroxides of alkali or alkaline earth metals (e.g., lime, caustic soda) is of particular interest for algae harvesting as Na, Ca and Mg are typically present in natural waters. The goal of this research was to determine the underlying mechanisms responsible for algae coagulation by magnesium and calcium and to evaluate the potential of these mechanisms for harvesting algae for a range of synthetic and field source water chemistries. In the first two phases of this research, the mechanisms for coagulation with magnesium and calcium were studied independently. A series of bench-scale experiments were designed to isolate the potential mechanisms of algae destabilization associated with each of these cations as a function of water chemistry, and microscopic analyses were performed to characterize the flocculated algae/precipitate mixtures. In the third phase of this research, removal of algae in field source waters was evaluated with respect to the underlying science elucidated in the previous phases. The results indicate that the dominant algae destabilization mechanism associated with magnesium shifts from Mg adsorption/charge neutralization to Mg(OH)₂[subscript (S)] precipitation-enhanced coagulation with increasing pH. Moreover, dissolved Mg²⁺ adsorption to the algae surface led to effective algae coagulation, while minimizing the mass of precipitated Mg(OH)₂[subscript (S)] . For Ca, this research identified the importance of the nucleation process (heterogeneous vs. homogeneous nucleation) on algae removal efficiency. Heterogeneous nucleation is a key factor for optimizing algae removal; thus, the degree of oversaturation with respect to CaCO₃[subscript (S)] is a crucial operating parameter. This research demonstrated that the algae harvesting process using pH-induced flocculation/deflocculation method can be optimized for a wide range of source waters if the water chemistry (e.g. pH, ion concentration, alkalinity, ionic strength) is properly incorporated into the system design.Item Reducing turbidity of construction site runoff via coagulation with polyacrylamide and chitosan(2012-05) Rounce, David Robert; Lawler, Desmond F.; Barrett, Michael E.The U.S. Environmental Protection Agency is in the process of developing a nationwide standard for turbidity in construction site runoff. It is widely expected that this standard cannot be met with conventional erosion and sediment control measures; consequently, innovative practices for managing sediment on construction sites must be developed. The objective of this research was to develop an understanding of how soil characteristics and polymer properties affect the amount of turbidity reduction that can be achieved through flocculation. The polymers used were PAMs, a proprietary product, and chitosan. The charge density of the PAMs ranged from 0% to 50% and the molecular weights ranged from 0.2 to 14 Mg/mol. A protocol for creating modified synthetic stormwater runoff for soil samples was developed and used on soils from seven construction sites. Particle size distributions were used to compare the modified synthetic stormwater runoff with grab samples of stormwater from one site and showed the synthetic runoff was representative of the actual runoff. Flocculation tests were performed on the synthetic runoffs with PAM and chitosan doses from 0.03 to 10 mg/L. The non-ionic PAM, proprietary product, and chitosan were found to be the most effective at reducing the turbidity of all the synthetic runoff below 200 NTU. The high molecular weight anionic PAMs were effective on only two of the seven synthetic runoff samples. Hardness tests were performed indicating interparticle bridging to be the bonding mechanism of the PAM. Electrophoretic mobility tests were performed on two of the soil suspensions and indicated the bonding mechanism of PAM to be interparticle bridging, and the bonding mechanism of chitosan to be a combination of charge neutralization and interparticle bridging. Tests showed as the charge density of the PAM increased, their effectiveness decreased.Item The modeling of arsenic removal from contaminated water using coagulation and sorption(Texas A&M University, 2005-11-01) Kim, Jin-WookTo achieve predictive capability for complex environmental systems with coagulation and arsenic sorption, a unified improved coagulation model coupled with arsenic sorption was developed. A unified coagulation model coupled with arsenic sorption was achieved by the following steps: (1) an improved discretized population balance equation (PBE) was developed to obtain the exact solution of conventional coagulation, (2) the improved PBE was extended to an adjustable geometric size interval having higher numerical stability, accuracy, and computational efficiency than existing models for fractal aggregate coagulation that includes agglomeration and fragmentation, (3) a surface complexation equilibrium model and a sorption kinetic model was introduced to predict arsenic sorption behavior onto hydrous metal oxide surfaces, and (4) an improved discretized PBE was coupled with arsenic sorption kinetics and equilibrium models by aid of collision efficiency ?? depending on surface charge (potential) on the hydrous metal oxide particles, colliding particle size ratio, and fluid strain-rate in applied flow system. The collision efficiency ?? into the improved (r,r)ij(r,r)ijdiscretized coagulation model for fractal aggregate yielded a unified improved coagulation model coupled with arsenic sorption kinetics and the equilibrium model. Thus, an improved unified coagulation model could provide high statistical accuracy, numerical stability, and computational efficiency to enhance predictive capability for behavior of arsenic sorption and fractal colloid particle aggregation and break-up, simultaneously. From the investigation, it is anticipated that the unified coagulation model coupled with arsenic sorption kinetics and equilibrium will provide a more complete understanding of the arsenic removal mechanism and its application to water/wastewater treatment. Further, this coupled model can be applied to other water and wastewater treatment systems combined with sorption and filtration processes. These combined processes can be optimized by the coupled model that was developed in this study. By simulating the arsenic sorption and particle size distribution as a pretreatment before filtration (sand filtration or membrane filtration), the overall arsenic removal efficiency and operation cost can be estimated.