Browsing by Subject "Desalination"
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Item A Systems-Integration Approach to the Optimal Design and Operation of Macroscopic Water Desalination and Supply Networks(2012-02-14) Atilhan, SelmaWith the escalating levels of water demand, there is a need for expansion in the capacity of water desalination infrastructure and for better management and distribution of water resources. This dissertation introduces a systems approach to the optimization of macroscopic water desalination and distribution networks to tackle three problems: 1. Optimal design of desalination and allocation networks for a given demand, 2. Optimal operation of an existing infrastructure of water desalination, distribution, and storage, 3.Optimal planning for expanding the capacity of desalination plants to meet an increasing water demand over a time horizon. A source-interception-sink representation was developed to embed potential configurations of interest. Mathematical programming was used to model the problem by studying different objective functions while accounting for constraints the supply, demand, mass conservation, technical performance, and economic aspects. Such approach determines the type of technologies to be selected, the location and capacity of the desalination plants, and the distribution of the desalinated water from sources to destinations. For the operation and planning problems, the planning horizon was discretized into periods and a multi-period optimization approach was adopted with decisions made for each period. Short- and long-term water storage options (e.g., in storage tanks, aquifers) were included in the optimization approach. Water recycle/reuse was enhanced via the use of treated water and its utilization was improved by minimizing the losses observed in discharged water resulting from the linkage of power plants and thermal desalination plants and the lack of integration between water production and consumption. Several case studies were solved to demonstrate the applicability of the devised approaches.Item An Advanced Vapor-Compression Desalination System(Texas A&M University, 2006-04-12) Lara Ruiz, Jorge Horacio JuanCurrently, the two dominant desalination methods are reverse osmosis (RO) and multi-stage flash (MSF). RO requires large capital investment and maintenance, whereas MSF is too energy intensive. An innovative vapor-compression desalination system is developed in this study. A comprehensive mathematical model for the heat exchanger/evaporator is described. The literature indicates that extraordinarily high overall heat transfer coefficients for the evaporator are possible at selected operating conditions that employ dropwise condensation in the steam side and pool boiling in the liquid side. A smooth titanium surface is chosen to promote dropwise condensation and to resist corrosion. To maximize energy efficiency, a combined-cycle cogeneration scheme is employed composed of a gas turbine, a heat recovery boiler, and a steam turbine that drive a compressor. The combined-cycle power source is oversized relative to the needs of the compressor. The excess power is converted to electricity and sold to the open market. A three-effect evaporator is employed. It is fed with seawater, assumed to be 3.5% salt. Boiling brine (7% salt) is in the low pressure side of the heat exchanger and condensing steam is in the high-pressure side of the heat exchanger. The condensing steam flows at 1.52 m/s (5 ft/s), which maximizes the heat transfer coefficient. The plant is sized to produce 37,854 m3/d (10 mill gal/day) and is assumed to be financed with a 5%, 30-yr municipal bond. Two economic cases were emphasized: the United States and the Middle East. For the United States, the fuel costs $5/GJ ($5.27/mill Btu) with the latent heat exchanger at ( ) 1.11 K 2.00 F T ?? = ?? . The required compressor energy is 14 MJ/m3 (14.7 kW h/thous gal). The capital cost for the U.S. is $884 d/m3 ($3,342/thous gal) and the delivered water selling price is $0.47/m3 ($1.79/thous/gal). For the Middle East, the fuel costs $0.5/GJ ($0.53/mill Btu) with the latent heat exchanger at K T 33 . 3 = ?? ( ) F 00 . 6 ?? . The required compressor energy is 26 MJ/m3 (27.3 kW h/thous gal). ). The capital cost for the Middle East is $620 d/m3 ($2,344/thous gal), and the delivered water selling price is $0.25/m3 ($0.95/thous/gal). In all cases, the water selling price is attractive relative to competing technologies.Item An evaluation of membrane materials for the treatment of highly concentrated suspended salt solutions in reverse osmosis and nanofiltration processes for desalination(2009-05-15) Hughes, Trenton WhitingThis thesis presents a study to enhance and improve a zero liquid discharge (ZLD) reverse osmosis process that uses seed crystals to promote crystallization of the dissolved salts in the residual brine while it is being treated by identifying those membrane materials that are most suitable for the process. In the study, a one plate SEPA Cell module by GE Osmonics was used to determine which membranes were most susceptible to fouling and/or membrane hydrolysis. A cellulose acetate (CA), polyamide (PA) low MWCO, and PA high MWCO membrane were tested under reverse osmosis conditions. The CA and thin film (TF) membranes were also tested for nanofiltration. The cell was operated under conditions that were determined to be optimum for each membrane by the manufacturer, GE Osmonics. A high pressure, low flow, positive displacement diaphragm pump circulated the saturated calcium sulfate solution with 2 % suspended solids through the cell while the reject and permeate were recycled back to the feed, thereby preserving a saturated solution to promote crystal growth and simulate the seeded reverse osmosis process. The temperature was maintained constant by adding an ice pack to the feed vessel when necessary. The transmembrane pressure differential was maintained constant by adjusting a back pressure valve on the concentrate outlet. The results illustrate that if potable drinking water is the intended use, then the nanofiltration cellulose acetate membrane should be used. If irrigation is the desired use, then the nanofiltration thin film membrane should be used. Overall, the reverse osmosis cellulose acetate membrane was observed to outperform all membranes when all performance parameters were normalized. However, this membrane was observed to be prone to degradation in a seeded slurry and therefore its lifetime should be analyzed further. The polyamide membrane initially had a high water transport coefficient, but fouling led to its rapid decline which was attributed to the membrane?s rough and protrusive surface. A lifetime test on the thin film and cellulose acetate revealed that when operated at their maximum pressure specified by GE Osmonics for a duration of 8 hours that no decrease in rejection occurred.Item Desalination of seawater using a high-efficiency jet ejector(Texas A&M University, 2005-08-29) Vishwanathappa, Manohar D.The ability to produce potable water economically is the primary focus of seawater desalination research. There are numerous methods to desalinate water, including reverse osmosis, multi-stage flash distillation, and multi-effect evaporation. These methods cost more than potable water produced from natural resources; hence an attempt is made in this research project to produce potable water using a modified high-efficiency jet ejector in vapor-compression distillation. The greater efficiency of the jet ejector is achieved by properly mixing propelled and motive streams. From experiments conducted using air, the pressure rise across the jet ejector is better in case of one or two mixing vanes and the highest back pressure (pinch valve closed 83.33%). At other pinch valve closings, the air velocity through the jet ejector was high, so the extra surface area from the mixing vanes caused excessive friction and lowered the efficiency.Item Desalination Using Vapor-Compression Distillation(2010-07-14) Lubis, Mirna R.The ability to produce potable water economically is the primary purpose of seawater desalination research. Reverse osmosis (RO) and multi-stage flash (MSF) cost more than potable water produced from fresh water resources. As an alternative to RO and MSF, this research investigates a high-efficiency mechanical vapor-compression distillation system that employs an improved water flow arrangement. The incoming salt concentration was 0.15% salt for brackish water and 3.5% salt for seawater, whereas the outgoing salt concentration was 1.5% and 7%, respectively. Distillation was performed at 439 K (331oF) and 722 kPa (105 psia) for both brackish water feed and seawater feed. Water costs of the various conditions were calculated for brackish water and seawater feeds using optimum conditions considered as 25 and 20 stages, respectively. For brackish water at a temperature difference of 0.96 K (1.73oF), the energy requirement is 2.0 kWh/m3 (7.53 kWh/kgal). At this condition, the estimated water cost is $0.39/m3 ($1.48/kgal) achieved with 10,000,000 gal/day distillate, 30-year bond, 5% interest rate, and $0.05/kWh electricity. For seawater at a temperature difference of 0.44 K (0.80oF), the energy requirement is 3.97 kWh/m3 (15.0 kWh/kgal) and the estimated water cost is $0.61/m3 ($2.31/kgal). Greater efficiency of the vapor compression system is achieved by connecting multiple evaporators in series, rather than the traditional parallel arrangement. The efficiency results from the gradual increase of salinity in each stage of the series arrangement in comparison to parallel. Calculations using various temperature differences between boiling brine and condensing steam show the series arrangement has the greatest improvement at lower temperature differences. The following table shows the improvement of a series flow arrangement compared to parallel: ?T (K) Improvement (%)*1.111 2.222 3.333 15.21 10.80 8.37 * Incoming salt concentration: 3.5% Outgoing salt concentration: 7% Temperature: 450 K (350oF) Pressure: 928 kPa (120 psig) Stages: 4Item Design and control of an integrated wind-water desalination system for an inland municipality(Texas Tech University, 2008-08) Noll, Dennis D.; Ewing, Bradley T.; Song, Lianfa; Swift, Andrew H. P.; Chapman, Jamie C.Current water pricing standards do not take economic responsibility for dwindling potable water aquifer resources. By only incorporating financial, but not true economic costs of these scarce resources, serious depletion of these often slow-recharging groundwater resources has occurred in many areas in the United States. Aquifer depletion for some areas looms on a 50-year or closer horizon, and many municipalities in the Southwest and elsewhere face potential distress due to lack of sustainable fresh water availability. In order for these cities to remain economically and physically viable, alternative water resources must be found. An affected West Texas inland municipality will become the subject of research to evaluate the technology and economics of a full-scale, integrated, wind-powered reverse osmosis water purification system. The integrated system will be applied to produce potable water from a brackish aquifer using renewable energy to reduce the energy costs of the system. An adaptive and intelligent control algorithm will control the integrated wind-water system. The algorithm will process streaming real-time water use and electrical demand data in combination with wind speed measurements in order to determine the best use of the energy produced by a turbine array: either for water purification or for displacing conventional power on other municipal loads. The end product of this system is a water purification process that will utilize a brackish water aquifer for all of the city‘s potable water needs, and wind energy for all associated pumping, reverse osmosis, distribution and other electrical loads.Item Electrode separation effects in capacitive deionization desalination systems(2012-08) Pierce, Kena Marie; Crawford, Richard H.; Hidrovo, Carlos H.A more energy efficient and sustainable method of desalinating water is needed due to increasing water shortages and contamination of current freshwater sources. Capacitive deionization (CDI), a new emerging technology, is a type of electric desalination that uses an applied voltage to pull the salt ions out of the salty solution and store the ions in porous carbon electrodes. CDI uses less applied energy than more commonly used methods of desalination like reverse osmosis and multi-flash distillation and has the added advantage of energy recovery. This report details experiments conducted to analyze the effect of different separation distances between the electrodes on salt ion adsorption for a high concentration solution under various flow rates and a 1 V voltage potential difference. The testing was performed in the Multiscale Thermal-Fluids Laboratory at The University of Texas at Austin using a uniquely fabricated CDI cell. Voltage, elapsed time, and electrical conductivity measurements were taken during the testing. Electrical conductivity was used to signify salinity of the solution. Two different separation distances were created by placing either one 2mm mesh between the electrodes or by using two 2 mm meshes between the electrodes. The results did not agree with the expectation that the one-mesh tests would adsorb twice the amount of salt ions as the two-mesh tests because of the differences in the electric field between the two types of tests. This is believed to be due to the high concentration tested. Future testing should include repeating these tests to verify the results and performing the tests for lower concentrations to see if they followed the expectation.Item The energy water nexus : increasing water supply by desalination integrated with renewable power and reducing water demand by corporate water footprinting(2013-08) Clayton, Mary Elizabeth; Webber, Michael E., 1971-Growing populations and periodic drought conditions have exacerbated water stress in many areas worldwide. Consequently, it would be valuable to manage both supply and demand of water to fully address water sustainability. Additionally, the inextricable link of water and energy -- energy is required to pump, treat, and distribute water and water is often used in the production of energy -- creates the need to study the use of these resources together. In response to water stress, some municipalities have considered desalination of saline water as a freshwater supply. Unfortunately, desalination requires a sizeable energy investment and causes significant carbon emissions with conventional approaches. However, renewable energy technologies can be paired with desalination to mitigate concern over the environmental impacts of increased energy use. At the same time, desalination can be operated in an intermittent way to match the variable availability of renewable resources. Both wind and brackish groundwater resources are plentiful in the Panhandle region of West Texas, making an integrated wind-powered desalination facility an option for meeting increasing water demands. Integrating wind power and brackish groundwater desalination generates a high-value product (drinking water) from two low-value resources (saline water and wind power without storage). This thesis presents a thermoeconomic, geographic, and operational analysis of an integrated wind-powered reverse osmosis facility treating brackish groundwater in West Texas. The results demonstrate the favorability of the integrated facility under certain economic, geographic, and operating conditions. Also in response to water stress, corporations are becoming increasingly interested in identifying water vulnerabilities in their operational portfolios to minimize physical, reputational, regulatory, and financial risks associated with potential water shortages. The water footprint is one tool available to assess water use, identify vulnerabilities, and guide mitigation strategies. This thesis provides an accounting methodology for water reporting that includes direct water uses and indirect (embedded in energy, services, and products) water uses in the operations. Further, a case study is considered to illustrate the methodology by assessing the water impact of a mixed-use facility in Palo Alto, California. The results demonstrate the importance of considering the indirect water uses, which requires a more exhaustive analysis.Item The energy-water nexus : an analysis and comparison of various configurations integrating desalination with renewable power(2015-05) Gold, Gary M.; Webber, Michael E., 1971-Water stress is a worldwide reality. Planners and managers of water resources around the world are tasked with finding new, creative, and innovative solutions to challenges posed by growing populations and declining water supplies. Securing safe drinking water, however, has impacts beyond the water sector. In particular, the connection between energy and water must be carefully considered to avoid unwelcome increases in energy consumption as a result of new water management strategies. One strategy that is gaining increasing attention is desalination of brackish groundwater. However, desalination is an energy-intensive process and could have negative impacts in the energy sector if conventional approaches are used. Relying on fossil fuels for desalination could drive up carbon dioxide emissions associated with water treatment and increase the cost required to produce drinking water. Integrating desalination with renewable power sources such as wind and so- lar energy can mitigate concerns regarding the energy intensity of desalination. By coupling water treatment with non-carbon emitting sources of power, it is possible to meet growing water demands in a sustainable manner. At the same time, water pro- duction offers an opportunity to address problems associated with the intermittent nature of wind and solar power production. Desalination is a time-flexible process that pairs well with wind and solar power, two sources of energy that are limited in application by their daily and seasonal variability. Integrating desalination with wind and solar power offers a solution to energetic challenges of water production while using wind and solar power for desalination offers a solution to challenges associated with the intermittent nature of renewable power. Additionally, utilizing photovoltaic-thermal (PVT) solar modules in an inte- grated facility could be advantageous to both the water and solar power production processes. Brackish groundwater, which is at a relatively cool temperature, can be used to cool solar panels, which suffer from losses in efficiency associated with tem- perature increases. At the same time, solar panels can be used to preheat feed water, a process that reduces the energetic requirement for reverse osmosis desalination. Us- ing the temperature difference between brackish groundwater and solar panels to an engineering advantage can be beneficial for the production of both solar power and drinking water. This thesis offers an investigation of desalination powered by wind and solar energy, including a study of a configuration using PVT solar panels. First, a water treatment was developed to estimate the power requirement for brackish groundwa- ter reverse-osmosis (BWRO) desalination. Next, an energy model was designed to (1) size a wind farm based on this power requirement and (2) size a solar farm to preheat water before reverse osmosis treatment. Finally, an integrated model was developed that combines results from the water treatment and energy models. The integrated model uses optimization to simulate the performance of the proposed facil- ity by maximizing daily operational profits. Results indicate that integrated facility can reduce grid-purchased electricity costs by 88% during summer months and 89% during winter when compared to a stand-alone desalination plant. Additionally, the model suggests that the integrated configuration can generate $574 during summer and $252 from sales of wind- and solar-generated electricity to supplement revenue from water production. These results indicate that an integrated facility combin- ing desalination, wind power, and solar power can potentially reduce reliance on grid-purchased electricity and advance the use of renewable power. In addition, this analysis fills a knowledge gap in understanding the advantages and tradeoffs between using wind power, solar power, and a combination of wind and solar power for desali- nation. By providing insight into the potential operations of an integrated facility, the investigation discussed in this report aids to the understanding of the water-energy nexus associated with new sources of drinking water. Results from this thesis indicate that integrating desalination with renewable power provides an opportunity for collaboration that can be mutually beneficial to both the water and energy sectors. In particular combining desalination, wind power, and solar power can overcome challenges associated with each of these technologies and may be preferable to stand-alone water or power producing facilities.Item Feasibility of brackish water desalination as an alternative water supply in the Barton Springs/ Edwards Aquifer conservation district(2015-05) Barraza, Alan; King, Carey Wayne, 1974-; Kreitler, Charles W.Growing demands for water across the State of Texas has prompted many entities to take into consideration alternative means of obtaining water. The Edwards Aquifer within the Barton Springs/Edwards Aquifer Conservation District (BSEACD) has long been an invaluable and reliable resource in providing high quality water at a low cost. The continued population growth within the BSEACD along with continued drought conditions have strained the resource to the point of having restrictions being placed on production. These restrictions are in response to the potential impact of over-pumping water wells, water quality, springflow, and endangered species. At current permitted pumping, even with all curtailments allowed by statutory authority and current rules, the BSEACD cannot meet Desired Future Conditions during an ongoing drought of record. Within the boundaries of the BSEACD, there exist opportunities for groundwater production in the brackish portion of the Edwards and Trinity aquifers. This paper presents the economic feasibility of undertaking a brackish groundwater desalination project in the saline portion of the Edwards aquifer and also considers technical and regulatory obstacles. It is based upon a model that incorporates prevailing market and hydrogeologic conditions within Central Texas and the BSEACD, such as total dissolved solids content, brackish well depth, concentrate well depth, capital and operational costs of desalination facilities, electricity demands and costs, and water costs into its calculation. Results from this study indicate a reverse osmosis desalination project between the modeled range of 1.25 MGD to 12.5 MGD would be economically feasible. At 2.76 MGD the water would cost $748 per acre foot ($2.30 per 1,000 gal) to produce and gradually decreases in cost as the size of the facility increases due to economics of scale. At approximately 10 MGD of desired daily product generation the optimal price of $648 per acre-foot ($1.99 per 1,000 gal) is reached. While a desalination project within the BSEACD may be economically feasible, there are technical and regulatory obstacles that must be overcome before such project can take commence.Item Fundamental water and ion transport characterization of sulfonated polysulfone desalination materials(2014-08) Cook, Joseph Reuben; Freeman, B. D. (Benny D.)Sulfonated polysulfones BisAS and BPS were fabricated into dense polymer films, and their water and ion transport properties were systematically characterized. Fundamental NaCl and water transport properties were correlated with polymer chemistry, and water and NaCl permeability were found to increase with degree of sulfonation due to the increasing polymer water content. The BisAS backbone structure was found to result in greater water uptake, increasing water and salt permeability, though the polysulfones show evidence of sensitivity to the thermal casting process as well. Additionally, water and ion permeability and sorption values were determined for select polymers when exposed to a feed consisting of mixtures of monovalent and divalent cation salts. The divalent cations were found to sorb into the polymer much more favorably than the monovalent sodium, similarly to charged materials found in the literature. The sodium permeability of sulfonated polysulfones was found to increase in the presence of divalent cations by ratios of 2 to 5 times more than when exposed to an equivalent increase in feed charge concentration of monovalent cations. It has been hypothesized the more strongly charged divalent cations are neutralizing the sulfonate charges and suppressing Donnan exclusionary effects that reduce salt transport in charged polymers.Item Improving recovery in reverse osmosis desalination of inland brackish groundwaters via electrodialysis(2010-08) Walker, William Shane, 1981-; Lawler, Desmond F.; Freeman, Benny D.; Katz, Lynn E.; Kinney, Kerry A.; Liljestrand, Howard M.As freshwater resources are limited and stressed, and as the cost of conventional drinking water treatment continues to increase, interest in the development of non-traditional water resources such as desalination and water reuse increases. Reverse osmosis (RO) is the predominant technology employed in inland brackish groundwater desalination in the United States, but the potential for membrane fouling and scaling generally limits the system recovery. The general hypothesis of this research is that electrodialysis (ED) technology can be employed to minimize the volume of concentrate waste from RO treatment of brackish water (BW) and thereby improve the environmental and economic feasibility of inland brackish water desalination. The objective of this research was to investigate the performance sensitivity and limitations of ED for treating BWRO concentrate waste through careful experimental and mathematical analysis of selected electrical, hydraulic, and chemical ED variables. Experimental evaluation was performed using a laboratory-scale batch-recycle ED system in which the effects of electrical, hydraulic, and chemical variations were observed. The ED stack voltage showed the greatest control over the rate of ionic separation, and the specific energy invested in the separation was approximately proportional to the applied voltage and equivalent concentration separated. An increase in the superficial velocity showed marginal improvements in the rate of separation by decreasing the thickness of the membrane diffusion boundary layers. A small decrease in the nominal recovery was observed because of water transport by osmosis and electroosmosis. Successive concentration of the concentrate by multiple ED stages demonstrated that the recovery of BWRO concentrate could significantly improve the overall recovery of inland BWRO systems. A mathematical model for the steady-state performance of an ED stack was developed to simulate the treatment of BWRO concentrates by accounting for variation of supersaturated multicomponent solution properties. A time-dependent model was developed that incorporated the steady-state ED model to simulate the batch-recycle experimentation. Comparison of the electrical losses revealed that the electrical resistance of the ion exchange membranes becomes more significant with increasing solution salinity. Also, a simple economic model demonstrated that ED could feasibly be employed, especially for zero-liquid discharge.Item Ionic separation in electrodialysis : analyses of boundary layer, cationic partitioning, and overlimiting current(2010-08) Kim, Younggy; Lawler, Desmond F.; Liljestrand, Howard M.; Katz, Lynn E.; Meyers, Jeremy P.; Sepehrnoori, KamyElectrodialysis performance strongly depends on the boundary layer near ion exchange membranes. The thickness of the boundary layer has not been clearly evaluated due to its substantial fluctuation around the spacer geometry. In this study, the boundary layer thickness was defined with three statistical parameters: the mean, standard deviation, and correlation coefficient between the two boundary layers facing across the spacer. The relationship between the current and potential under conditions of the competitive transport between mono- and di-valent cations was used to estimate the statistical parameters. An uncertainty model was developed for the steady-state ionic transport in a two-dimensional cell pair. Faster ionic separations were achieved with smaller means, greater standard deviations, and more positive correlation coefficients. With the increasing flow velocity from 1.06 to 4.24 cm/s in the bench-scale electrodialyzer, the best fit values for the mean thickness reduced from 40 to less than 10 μm, and the standard deviation was in the same order of magnitude as the mean. For the partitioning of mono- and di-valent cations, a CMV membrane was examined in various KCl and CaCl₂ mixtures. The equivalent fraction correlation and separation factor responded sensitively to the composition of the mixture; however, the selectivity coefficient was consistent over the range of aqueous-phase ionic contents between 5 and 100 mN and the range of equivalent fractions of each cation between 0.2 and 0.8. It was shown that small analytic errors in measuring the concentration of the mono-valent cation are amplified when estimating the selectivity coefficient. To minimize the effects of such error propagation, a novel method employing the least square fitting was proposed to determine the selectivity coefficient. Each of thermodynamic factors, such as the aqueous- and membrane-phase activity coefficients, water activity, and standard state, was found to affect the magnitude of the selectivity coefficient. The overlimiting current, occurring beyond the electroneutral limit, has not been clearly explained because of the difficulty in solving the singularly perturbed Nernst-Planck-Poisson equations. The steady-state Nernst-Planck-Poisson equations were converted into the Painlevé equation of the second kind (P[subscript II] equation). The converted model domain is explicitly divided into the space charge and electroneutral regions. Given this property, two mathematical formulae were proposed for the limiting current and the width of the space charge region. The Airy solution of the P[subscript II] equation described the ionic transport in the space charge region. By using a hybrid numerical scheme including the fixed point iteration and Newton Raphson methods, the P[subscript II] equation was successfully solved for the ionic transport in the space charge and electroneutral regions as well as their transition zone. Above the limiting current, the sum of the ionic charge in the aqueous-phase electric double layer and in the space charge region remains stationary. Thus, growth of the space charge region involves shrinkage of the aqueous-phase electric double layer. Based on this observation, a repetitive mechanism of expansion and shrinkage of the aqueous-phase electric double layer was suggested to explain additional current above the limiting current.Item Polyamide desalination membrane characterization and surface modification to enhance fouling resistance(2010-05) Van Wagner, Elizabeth Marie; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R.; Bonnecaze, Roger T.; Lawler, Desmond F.; Mickols, William E.The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling.Item The potential of desalination as an alternative water supply in the United States(2009-05) Naini, Anjali Nina; Butler, Kent S.Many parts of the United States are facing water shortages. Planners have to ensure that there will be an adequate water supply to meet the needs of the growing population. Though many places encourage water conservation, and some even enforce water restrictions, this is not always enough to make up for the shortages. Thus, alternative water sources need to be considered in some cases. The states of Texas and Florida both face uncertainties with their future water supply. To meet the needs of their current and future populations, both states have recently been using desalination at a large scale to supplement their water supplies. This report examines the desalination facilities in El Paso, Texas and Tampa Bay, Florida to determine if desalination is a feasible water supply and to explore the consequences of pursuing the development of this water resource.Item Preparation and characterization of disulfonated polysulfone films and polyamide thin film composite membranes for desalination(2011-12) Xie, Wei, 1982-; Freeman, B. D. (Benny D.); Paul, Donald R.; Sanchez, Isaac C.; Bielawski, Christopher W.; McGrath, James E.The current reverse osmosis desalination membrane market is dominated by aromatic polyamide thin film composite (TFC) membranes. However, these polyamide membranes suffer from poor resistance to continual exposure to oxidizing agents such as chlorine in desalination applications. To overcome these problems, we have synthesized and characterized a new generation of materials, disulfonated poly(arylene ether sulfone) (BPS) random copolymer, for desalination membranes. A key technical feature of these new materials is their high tolerance to chlorine in feed water and their excellent reproducibility in synthesis. In this study, water and sodium chloride solubility, diffusivity and permeability in BPS copolymers were measured for both acid and salt form samples at sulfonation levels from 20 to 40 mol percent. The hydrophilicity of these materials, based on water uptake, increased significantly as sulfonation level increased. The water and salt diffusivity and permeability were correlated with water uptake, consistent with expectations from free volume theory. In addition, a tradeoff was observed between water/salt solubility, diffusivity, and permeability selectivity and water solubility, diffusivity and permeability, respectively. The influence of cation form and degree of sulfonation on free volume, as probed via positron annihilation lifetime spectroscopy (PALS), was determined in BPS random copolymers in both the dry and hydrated states. PALS-based free volume data for hydrated polymers were correlated with water and salt transport properties. The influence of processing history on transport properties of BPS films was also studied. Potassium form BPS films having a 32 mol% sulfonation level were acidified using solid state and solution routes. Additionally, several films were subjected to various thermal treatments in the solid state. The influence of acidification, thermal treatment, and counter-ion form on transport properties was investigated. Finally, the influence of synthesis methods of polyamide TFC membranes from m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization on transport properties is reported. Then, a disulfonated diamine monomer (S-BAPS) was used instead of MPD to prepare TFC membranes. The resulting membranes exhibited reduced chlorine tolerance than those prepared from MPD. However, introduction of S-BAPS to the MPD/TMC polymerization system increased the fouling resistance of the resulting polyamide TFC membranes.Item Sythhesis and Optimization of Hybrid Membrane Desalination Networks with Value Extraction(2014-02-04) AlNouss, Ahmed MMembrane desalination technology has become a valuable advanced water treatment process to purify difficult water sources for potable use. Reverse Osmosis (RO) and Nanofiltration (NF) processes are commonly used desalination technologies. Studies of hybrid RO-NF membrane desalination systems have shown promising benefits of lower power usage, higher overall obtainability, and better water quality. Under the proposed title, a systematic network synthesis approach is to be developed to evaluate the performance of a hybrid membrane desalination plant consisting of NF and RO processes in order to achieve an optimal design network for a given water capacity with ideal operating conditions. This work is done using a superstructure optimization, while taking into account desired process conditions and constraints that are associated with the hybrid RO-NF system. The superstructure captures all the structural and operational options that enable the extraction of a global optimal design, giving a better visualization of the hybrid design network. The optimization problem is formulated while accounting for all the design decisions that are supported by superstructure representation, based on numbers and types of units, flow rates, and pressures.An economic objective function is utilized so as to provide an efficient and desirable configuration capturing all the significant capital and operating costs, such as intake, pre and post treatment, along with the revenue from the value extraction. Optimized designs for hybrid RO-NF desalination plant were illustrated using a case study of sea water desalination with around 35 parts per thousand (ppt) of salinity. The solutions show increased the overall recovery with the addition of an NF membrane into the design.Item The Development of a Synthesis Approach for Optimal Design of Seawater Reverse Osmosis Desalination Networks(2012-10-19) Alnouri, SablaThis work introduces a systematic seawater reverse osmosis (SWRO) membrane network synthesis approach, based on the coordinated use of process superstructure representations and global optimization. The approach makes use of superstructure formulations that are capable of extracting a globally optimal design as a performance target, by taking into consideration desired process conditions and constraints that are typically associated with reverse osmosis systems. Thermodynamic insights are employed to develop lean network representations so that any underperforming solutions can be eliminated a priori. This essentially results in considerable improvement of the overall search speed, compared to previously reported attempts. In addition, the approach enables the extraction of structurally different design alternatives. In doing so, distinct membrane network design classes were established by partitioning the search space, based on network size and connectivity. As a result, corresponding lean superstructures were then systematically generated, which capture all structural and operational variants within each design class. The overall purpose is thus to enable the extraction of multiple distinct optimal designs, through global optimization. This mainly helps provide design engineers with a better understanding of the design space and trade-offs between performance and complexity. The approach is illustrated by means of a numerical example, and the results obtained were compared to previously related work. As anticipated, the proposed approach consistently delivered the globally optimal solutions, as well as alternative efficient design candidates attributed to different design classes, with reduced CPU times. This work further capitalizes on the developed representation, by accounting for detailed water quality information, within the SWRO desalination network optimization problem. The superstructures were modified to incorporate models that capture the performance of common membrane elements, as predicted by commercially available simulator tools, e.g. ROSA (Dow) and IMSDesign (Hydranautics). These models allow tracing of individual components throughout the system. Design decisions that are supported by superstructure optimization include network size and connectivity, flow rates, pressures, and post treatment requirements. Moreover, a detailed economic assessment capturing all the significant capital and operating costs associated in SWRO processes, including intake, pre and post treatment has also been accounted for. These modifications were then illustrated using a case study involving four seawater qualities, with salinities ranging from 35 to 45 ppt. The results highlight the dependency of optimal designs on the feed water quality involved, as well as on specified permeate requirements.Item Water and salt transport structure/property relationships in polymer membranes for desalination and power generation applications(2012-12) Geise, Geoffrey Matthew; Paul, Donald R.; Freeman, B. D. (Benny D.)Providing sustainable supplies of water and energy is a critical global challenge. Polymer membranes dominate desalination and could be crucial to power generation applications, which include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED). Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies. Water and salt transport structure/property relationships provide the fundamental framework for optimizing polymer materials for membrane applications. The water and salt transport and free volume properties of a series of sulfonated styrenic pentablock copolymers were characterized. The polymers' water uptake and water permeability increase with degree of sulfonation, and the block molecular weights could be used to tune water uptake, permeability, and selectivity properties. The presence of fixed charge groups, i.e., sulfonate groups, on the polymer backbone influence the material's salt transport properties. Specifically, the salt permeability increases strongly with increasing salt concentration, and this increase is a result of increases in both salt sorption and diffusivity with salt concentration. The data for the sulfonated polymers, including a sulfonated polysulfone random copolymer, are compared to those for an uncharged polymer to determine the influence of polymer charge on salt transport properties. The sulfonated styrenic pentablock copolymer permeability data are compared to literature data using the water permeability and water/salt selectivity tradeoff relationship. Fundamental transport property comparisons can be made using this relationship. The effect of osmotic de-swelling on the polymers and the transport properties of composite membranes made from sulfonated styrenic pentablock copolymers are also discussed. The sulfonated styrenic pentablock copolymers were exposed to multi-valent ions to determine their effect on the polymer's salt transport properties. Magnesium chloride permeability depends less on upstream salt concentration than sodium chloride permeability, presumably due to stronger association between the sulfonate groups and magnesium compared to sodium ions. Triethylaluminum was used to neutralize the polymer's sulfonic acid functionality and presumably cross-link the polymer. The mechanical, transport, and free volume properties of these aluminum neutralized polymers were studied.