Matching Items (7)

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Model Membrane System to Determine Water Permeability of Linde Type A Zeolite

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In this research, construction of a model membrane system using Polyvinylidene Chloride-Co Acrylonitrile and Linde Type A zeolites is described. The systems aims to separate out flow through zeolite pores

In this research, construction of a model membrane system using Polyvinylidene Chloride-Co Acrylonitrile and Linde Type A zeolites is described. The systems aims to separate out flow through zeolite pores and flow through interfaces between zeolites and polymers through the use of pore filled and pore open zeolites. Permeation tests and salt rejection tests were performed, and the data analyzed to yield approximation of separated flow through zeolites and interfaces. This work concludes the more work is required to bring the model system into a functioning state. New polymer selections and new techniques to produce the membrane system are described for future work.

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  • 2014-05

THE EFFECT OF POLYMER FILM ROUGHNESS ON THE PERFORMANCE OF POLYAMIDE REVERSE OSMOSIS MEMBRANES

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The scarcity of fresh water worldwide has necessitated improved technology for desalinating sea water. Reverse osmosis membranes are currently limited by their inclination for fouling, in which a layer forms

The scarcity of fresh water worldwide has necessitated improved technology for desalinating sea water. Reverse osmosis membranes are currently limited by their inclination for fouling, in which a layer forms on the surface of the membrane and impedes water flux. This yields shortened membrane lifespan and increased energy costs. Current technology uses interfacially polymerized polyamide thin film composite membranes, which form nodules, leaves, and other structures that lead to rough film surfaces and may contribute to fouling propensity. In this study, polyamide latex was designed in order to cast a smoother membrane with comparable performance. Polyamide latex particles were formed using a modified procedure based on Lind et. al [10] and characterized for sphericity using scanning electromagnetic microscopy (SEM).

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  • 2015-05

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Analysis of the Reverse Osmosis Process

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This paper considers the state of desalination today and explores improvement of the reverse osmosis process via exergy analysis. Various methods of desalination in place today were explored, along with

This paper considers the state of desalination today and explores improvement of the reverse osmosis process via exergy analysis. Various methods of desalination in place today were explored, along with the proportion of each of those methods in use today. From literature reviews, it was found the reverse osmosis (RO) and multi-stage flash (MSF) desalination were the main methods of desalination in use today. Desalination is an energy intensive process and so this paper aimed to address this issue in three ways: by exploring various coupling with renewable energy sources, carrying out an exergy analysis on the MSF and RO processes, and finally exploring conceptual methods of interest. It was found that concentrated solar power was best suited for the MSF process, since the MSF process require direct heat. Wind energy was best suited for the RO process, since RO was less energy intensive and so could account for wind variability. The exergy analysis demonstrated very low second law efficiency for both desalination processes (~4%), with most of the exergy being destroyed in the separation process (~75%). The RO process also demonstrated a higher efficiency and lower exergy destruction, reinforcing the conlcusion that RO is the less energy intensive of the two. Based on the analysis, it was found throttling valves account for the next highest exergy destruction after the separation process. An alternate plant design was proposed to fully utilize wasted pressure, which resulted in less energy consumption. Finally, two conceptual methods, a mobile desalination plant and the Hybrid process, were explored that could potentially make the RO process a more valuable asset to society and more economically viable with a higher yield

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  • 2015-05

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Comparison of four methods to assess silver release from nano impregnated reverse osmosis membranes

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With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers.

With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane.

This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.

The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.

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  • 2017

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Electrospun Pretreatment Membranes

Description

Managing water resources has become one of the most pressing concerns of scientists both in academia and industry. The reverse osmosis (RO) water treatment process is a well-researched technology among

Managing water resources has become one of the most pressing concerns of scientists both in academia and industry. The reverse osmosis (RO) water treatment process is a well-researched technology among the pressure driven processes to produce potable water. RO is an energy intensive process and often RO membranes are susceptible to fouling and scaling that drives up operational cost and hinder the efficiency. To increase the performance of RO membranes the feed water is pretreated to remove pollutants before desalination. This work aims to fabricate pretreatment membranes to prevent the effects of fouling and scaling by introducing hydrophilic character to membrane. This work explores electrospinning, a cost-effective and scalable technique, to blend two polymers into a nonwoven membrane comprised of fibers ~100 nm - 10 µm in diameter.

A rotary drum collector holding the mat was used to simultaneously collect the electrospun hydrophobic poly(vinyl chloride) (PVC) and hydrophilic poly(vinyl alcohol) (PVA) fibers from two separate solutions. The hydrophilicity of the resulting membrane was tuned by controlling the relative deposition rate of PVA onto the co-spun mat. Fiber diameter and morphologies were characterized by scanning electron microscopy, and Fourier-transform infrared spectroscopy and Confocal fluorescence microscopy further confirmed the presence of both polymers. Moreover, a rigorous analysis to map the PVA/PVC concentration was established to accurately report the relative concentrations of the two polymers on the co-spun mat. After electrospinning, the PVA in the co-spun mats were cross-linked with poly(ethylene glycol) diacid to impart mechanical strength and tune the porosity.

EDS analysis revealed inconsistencies in the mass deposition of both polymers suggesting an improvement in the current experimental design to establish a meaningful relationship between PVA concentration and hydrophilicity. However, tensile test revealed that co-spun mats with high mass flow ratios of PVA possessed high mechanical strength showing a significant improvement in the Young’s Modulus. Furthermore, the co-spun mats were challenged with filtration experiments expecting a positive correlation of flux with PVA concentration. But it was found that with increased concentration, crosslinked PVA constricted PVC fibers minimizing the pores causing a lower flux and a dense membrane structure suitable for filtration.

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  • 2020

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Flux performance and silver leaching from in-situ synthesized silver nanoparticle treated reverse osmosis point of use membranes

Description

Drinking water filtration using reverse osmosis (RO) membranes effectively removes salts and most other inorganic, organic, and microbial pollutants. RO technologies are utilized at both the municipal and residential scale.

Drinking water filtration using reverse osmosis (RO) membranes effectively removes salts and most other inorganic, organic, and microbial pollutants. RO technologies are utilized at both the municipal and residential scale. The formation of biofilms on RO membranes reduces water flux and increases energy consumption. The research conducted for this thesis involves In-Situ coating of silver, a known biocide, on the surface of RO membranes. This research was adapted from a protocol developed for coating flat sheet membranes with silver nanoparticles, and scaled up into spiral-wound membranes that are commonly used at the residential scale in point-of-use (POU) filtration systems. Performance analyses of the silver-coated spiral-wound were conducted in a mobile drinking water treatment system fitted with two POU units for comparison. Five month-long analyses were performed, including a deployment of the mobile system. In addition to flux, salt rejection, and other water quality analyses, additional membrane characterization tests were conducted on pristine and silver-coated membranes.

For flat sheet membranes coated with silver, the surface charge remained negative and contact angle remained below 90. Scaling up to spiral-wound RO membrane configuration was successful, with an average silver-loading of 1.93 g-Ag/cm2. Results showed the flux of water through the membrane ranged from 8 to 13 liters/m2*hr. (LMH) operating at 25% recovery during long-term of operation. The flux was initially decreased due to the silver coating, but no statistically significant differences were observed after 14 days of operation (P < 0.05). The salt rejection was also not effected due to the silver coating (P < 0.05). While 98% of silver was released during long-term studies, the silver release from the spiral-wound membrane was consistently below the secondary MCL of 100 ppb established by the EPA, and was consistently below 5 ppb after two hours of operation. Microbial assays in the form of heterotrophic plate counts suggested there was no statistically significant difference in the prevention of biofouling formation due to the silver coating (P < 0.05). In addition to performance tests and membrane characterizations, a remote data acquisition system was configured to remotely monitor performance and water quality parameters in the mobile system.

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Date Created
  • 2017

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Investigation of Water Permeation through Molecular Sieve Particles in Thin Film Nanocomposite Membranes

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Nanoporous materials, with pore sizes less than one nanometer, have been incorporated as filler materials into state-of-the-art polyamide-based thin-film composite membranes to create thin-film nanocomposite (TFN) membranes for reverse osmosis

Nanoporous materials, with pore sizes less than one nanometer, have been incorporated as filler materials into state-of-the-art polyamide-based thin-film composite membranes to create thin-film nanocomposite (TFN) membranes for reverse osmosis (RO) desalination. However, these TFN membranes have inconsistent changes in desalination performance as a result of filler incorporation. The nano-sized filler’s transport role for enhancing water permeability is unknown: specifically, there is debate around the individual transport contributions of the polymer, nanoporous particle, and polymer/particle interface. Limited studies exist on the pressure-driven water transport mechanism through nanoporous single-crystal nanoparticles. An understanding of the nanoporous particles water transport role in TFN membranes will provide a better physical insight on the improvement of desalination membranes.

This dissertation investigates water permeation through single-crystal molecular sieve zeolite A particles in TFN membranes in four steps. First, the meta-analysis of nanoporous materials (e.g., zeolites, MOFs, and graphene-based materials) in TFN membranes demonstrated non-uniform water-salt permselectivity performance changes with nanoporous fillers. Second, a systematic study was performed investigating different sizes of non-porous (pore-closed) and nanoporous (pore-opened) zeolite particles incorporated into conventionally polymerized TFN membranes; however, the challenges of particle aggregation, non-uniform particle dispersion, and possible particle leaching from the membranes limit analysis. Third, to limit aggregation and improve dispersion on the membrane, a TFN-model membrane synthesis recipe was developed that immobilized the nanoparticles onto the support membranes surface before the polymerization reaction. Fourth, to quantify the possible water transport pathways in these membranes, two different resistance models were employed.

The experimental results show that both TFN and TFN-model membranes with pore-opened particles have higher water permeance compared to those with pore-closed particles. Further analysis using the resistance in parallel and hybrid models yields that water permeability through the zeolite pores is smaller than that of the particle/polymer interface and higher than the water permeability of the pure polymer. Thus, nanoporous particles increase water permeability in TFN membranes primarily through increased water transport at particle/polymer interface. Because solute rejection is not significantly altered in our TFN and TFN-model systems, the results reveal that local changes in the polymer region at the polymer/particle interface yield high water permeability.

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Date Created
  • 2018