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<p>One of the main problems our actual society faces is the shortage of water. Despite the great effort made by authorities and researchers, multiple countries with poor economic resources are experiencing serious difficulties derivative of water scarcity. Desalination provides a feasible solution for inland and coastal areas. Through literature and reviewed articles analysis the reader will meet the actual issues regarding designing a desalination plant, and more over with reverse osmosis (RO) processes, which are the main arguments of this work. One of the big deals is the environmental concern when handling the concentrate disposal. Another important point about desalination processes is the increasingly interest in coupling the units with renewable energy sources (RES). The results point out that regardless of the efforts made until today, additional achievement is required in fields such as membrane’s structure materials for RO method, concentrate disposal systems, governmental water policies review and update, and greater distinction researches between brackish water and seawater RO desalination processes. Taking into consideration the previous outcomes it is finally concluded that some particular steps must be accomplished when beginning a desalination plant design.</p>

One of the main problems our actual society faces is the shortage of water. Despite the great effort made by authorities and researchers, multiple countries with poor economic resources are experiencing serious difficulties derivative of water scarcity. Desalination provides a feasible solution for inland and coastal areas. Through literature and reviewed articles analysis the reader will meet the actual issues regarding designing a desalination plant, and more over with reverse osmosis (RO) processes, which are the main arguments of this work. One of the big deals is the environmental concern when handling the concentrate disposal. Another important point about desalination processes is the increasingly interest in coupling the units with renewable energy sources (RES). The results point out that regardless of the efforts made until today, additional achievement is required in fields such as membrane’s structure materials for RO method, concentrate disposal systems, governmental water policies review and update, and greater distinction researches between brackish water and seawater RO desalination processes. Taking into consideration the previous outcomes it is finally concluded that some particular steps must be accomplished when beginning a desalination plant design.

A survey performed over existing two pilot-scale and two full-scale RO desalination facilities to study the current status of boron rejection showed a highest rejection 85% leading to permeate boron concentration of 0.52 mg/L, and recent studies predicted a cost increase due to incorporation of boron reduction systems. Mathematical models were developed to study the process performance and related cost implications. The deterministic process model was verified with pilot-scale experiment performed using a single spiral wound module and was later modified to represent the full-scale design options available to meet the required water quality criteria. Then the selected full-scale design options were simulated to predict their performance in terms of recovery and boron rejection. For cost analysis, to account for uncertainty probability models were developed for stochastic inputs to the cost estimation model and were used with operating parameters from the full-scale simulations to determine the expected total cost of water produced. Later, a sensitivity analysis was performed to observe the effect of change in uncertainty of inputs. Further, the applications of the deterministic process model are suggested.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 83-86). Also available via the Internet.

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available online.

The optimization of a reverse osmosis (RO) system includes optimization of the design of the individual membrane modules, the system structure and the operating conditions of the system. Most previous studies considered either the optimal design of individual modules only or optimization of system structure and operating conditions for fixed module dimensions. This thesis developed a method to simultaneously optimize the module dimensions, system structure and operating conditions. The method comprised rules for generating a general superstructure for an RO system given the number of modules along with rules for generating technically and mathematically feasible sub-structures. The superstructure was based on maximum connectivity between unit operations. A connectivity matrix was used to represent the superstructure. The matrix was useful for checking sub-structure's feasibility and deriving a model for the sub-structure's optimization, comprising the minimum number of variables and constraints which minimized computational time and increased accuracy. For optimization, a nonlinear objective function of the annualized profit of the RO system was formulated, consisting of the revenue obtained from permeate sales, capital costs of the unit operations and operating costs for the system. It was found that RO system optimization is a nonconvex optimization problem. The most effective optimization procedure involved a combination of evolutionary computation, which was good for locating the global optimum, and a gradient-based method, which was superior in finding the exact optimum. Small population size, adaptive mutation rate and steady state replacement were the most efficient parameter settings for the evolutionary computation. Optimal design of two-stage RO systems with and without energy recovery, bypass and recycle streams was studied. Dimensions of predicted optimal modules approached those of current commercial modules but with much shorter feed channels. The mathematical optimum also had higher operating pressures. The optimum system structure was a series arrangement with different module dimensions in each stage. A sensitivity analysis showed that trends in the optimal design were similar when unit costs changed. An investigation of the scalability of the method for a three-stage RO system revealed several weaknesses. These are probably surmountable with the addition of more RO system specific knowledge.

Clean water is critical to the safety, security and survivability of humankind. Nearly 41% of the Earth's population lives in water-stressed areas, and water scarcity will be exacerbated by an increasing population. Over 96% of the total water is saline and only 0.8% is accessible fresh water. Thus, saltwater desalination has emerged as the key to tackle the problem of water scarcity. Our current work deals with the membrane process of reverse osmosis. Sulfonated polysulfones are a potential alternative to state-of-the-art thin film polyamides. Synthesized by step growth polymerization, polysulfone membranes have smooth surfaces and they are more chemically resistant relative to polyamides. Previously studied sulfonated polysulfone membranes were synthesized by direct copolymerization of pre-disulfonated comonomer and the sulfonate ions were placed on adjacent rings of bisphenol moiety. This study focuses on placing the sulfonate ions differently along the polysulfone backbone on isolated rings of hydroquinone moiety, and on adjacent rings of biphenol moiety- and its effect on the transport and hydrated mechanical properties of the membranes. Selective post sulfonation of poly(arylene ether sulfone) in mild conditions was also found to be an effective way to strategically place the sulfonate ions along the backbone of the polymer chain without the need to synthesize a new monomer. Hydroquinone based, amine terminated oligomers were synthesized with block molecular weights of 5000 and 10,000 g/mol. They were post-sulfonated and crosslinked at their termini with epoxy reagents. Such crosslinked and linear membranes had sulfonate ions on isolated rings of hydroquinone moiety. Synthesis and kinetics of controlled post-sulfonation of poly(arylene ether sulfones) that contained biphenol units were also reported. The sulfonation reaction proceeded only on the biphenol rings. The linear membranes had sulfonate ions on adjacent rings of biphenol moieties. The tensile measurements were performed on the membranes under fully hydrated conditions. All membranes remained glassy at values of water uptake. It was found that elastic moduli and yield strengths in the hydroquinone- based linear and crosslinked membranes increased with decrease in water uptakes in the membranes. The effect of plasticization of water superseded the effect of block length and degree of sulfonation in the membranes. The highest elastic modulus of 1420 MPa at lowest water uptake of 18% was observed in cross linked membrane with 50% repeat units being sulfonated (50% repeat units contain hydroquinone)and target molecular weight of 5000 g/mol. However, the hydroquinone membranes broke at low strains of < 20%. The hydrated mechanical properties could be improved by replacing the hydroquinone with biphenol moieties. The biphenol based post-sulfonated membrane showed high elastic modulus that was comparable to the hydroquinone-based counterparts at similar values of water uptake. The biphenol based membrane broke at higher strains of >80%. The post-sulfonated membranes- hydroquinone-based linear and crosslinked membranes and biphenol-based linear membranes had better transport properties than the previously studied sulfonated polysulfones that were synthesized by disulfonated comonomers.The post sulfonated hydroquinone-based membranes did not show a compromise in the rejection of monovalent ions in the presence of divalent ions in mixed feed water. The superior properties of the post-sulfonated membranes can potentially be attributed to the kinked backbone that potentially increased the free volume in the membranes and the sulfonate ions were spaced apart to potentially reduce their chelation with calcium (divalent) ions in mixed feed water. Interestingly, the biphenol based post-sulfonated membranes also did not have any compromise in the rejection of monovalent ions in the presence of divalent ions. This was potentially because the sulfonate ions were spaced far apart on the non-planar biphenol rings. / PHD / According to the World Economic Forum, the water crisis has remained one of the top five global risks that has had a huge impact on the society. The world population has tripled in the twentieth century. Close to 2 billion people live in water scarce regions, 1.2 billion people lack access to safe drinking water, 2.6 billion have little or no access to sanitation and countless die due to diseases transmitted through unsafe water. Industrialization and climate change have worsened the water crisis. Furthermore, in today’s economies food, energy and water are inherently linked. Thus, a water crisis can have a cascading effect on availability of food and energy. To obtain an adequate and sustainable supply of water, it is important to improve already existing methods and develop new and inexpensive technologies for water purification. According to the U.S. geological survey over 96% of the earth’s water is saline. Thus, salt water desalination has emerged as the key to tackle the problem of scarcity of potable water. Reverse osmosis is a membrane-based process for water desalination wherein the membrane allows water to pass through while rejecting salts. The membranes are composed of long chain molecules called polymers. The current state of the art polymeric membrane made of polyamides show high rejection of salts with fast permeation of water. However, these membranes can be degraded by the chlorinated disinfectants added to the feed water. An alternative polymeric material, sulfonated polysulfone, can potentially be applied for reverse osmosis as these polymers are resistant to the chlorinated species. These membranes are composed of a polysulfone with sulfonate ions present randomly on the chain. This study investigates the effect of the position of the ions on the polymer chain. It is found that the membranes ability to reject salt from water can be improved by strategically placing the charged species on the polymer chain.

Sulfonated poly(arylene ether sulfone)s are a class of engineering thermoplastics well-known for their mechanical properties and chemical/oxidative stability. The research in this dissertation focuses on modifying the structure of sulfonated poly(arylene ether sulfone)s to improve membrane performance. Blends of a 20% disulfonated poly(arylene ether sulfone) (BPS20) with poly(ethylene glycol) (PEG) were investigated with the objective of promoting water flux across a reverse osmosis membrane. It was considered desirable to investigate poly(arylene ether sulfone)s with a hydroquinone unit that could be controllably post-sulfonated without degradation, providing a polymer with controlled sulfonation through controlling hydroquinone content. It also avoided the disadvantages noted previously in polymers with post-sulfonated biphenol units. Initial experiments focused on determining sulfonation conditions to confirm quantitative sulfonation of the hydroquinone without side reactions or degradation. A polymer with 29 mole % hydroquinone-containing units was used to study the rate of sulfonation. Successful post-sulfonation was confirmed and reaction conditions were applied to a series of polymers with varying hydroquinone comonomer contents. These polymers were sulfonated, characterized and evaluated for transport properties. Of interest was the high sodium rejection in the presence of calcium, which in the directly copolymerized disulfonated materials is compromised. The post-sulfonated poly(arylene ether sulfone)s showed no compromise in sodium rejection in a mixed-feed of sodium chloride and calcium chloride. In the membrane electrolysis of water, Nafion's high permeability to hydrogen, particularly above about 80 C, results in back-diffusion of hydrogen across the membrane. This reduces efficiency, product purity, and long-term electrode stability. Hydrophilic-hydrophobic multiblock copolymers based on disulfonated and non-sulfonated poly(arylene ether sulfone) oligomers feature a lower gas permeability. Various multiblock compositions and casting conditions were investigated and transport properties were characterized. A multiblock poly(arylene ether sulfone) showed a significant improvement in performance over Nafion at 95°C. Multiblock hydrophilic-hydrophobic poly(arylene ether sulfone)s have been extensively investigated as alternatives for proton exchange membrane fuel cells. One concern with these materials is the complicated multi-step synthesis and processing of oligomers, followed by coupling to produce a multiblock copolymer. An streamlined synthetic process was successful for synthesizing membranes with comparable morphologies and performance to a multiblock synthesized via the traditional method. / Ph. D.

Brackish waters are now considered valuable alternative water resources. Reverse osmosis (RO) membranes are the most promising candidate for drinking water production through desalination. Low recovery (the fraction of influent water that becomes product water) prevents widespread application of RO inland because of the high cost of waste disposal. The recovery of a brackish RO system is limited by sparingly soluble salts that become supersaturated and precipitate on the membrane surface. Precipitation is controlled through pH adjustment and antiscalant addition; however, at high salt supersaturation, antiscalant control is overcome and precipitation occurs. To further increase RO recovery and avoid precipitation, a three-stage process treated the waste stream (concentrate) of a brackish water RO system through antiscalant degradation, salt precipitation, and solid/liquid separation. Ozone (O3) and hydrogen peroxide (H2O2) were used to degrade antiscalants, pH elevation and base (NaOH/NaHCO3) addition were used to precipitate sparingly soluble salts, and microfiltration (0.1 μm) was used to separate precipitated solids from the water. Optimal parameters (pH, ozone dose, H2O2/O3 ratio, antiscalant type and concentration, water composition) for antiscalant oxidation were determined. The influence of antiscalant type and concentration and pH was investigated for the precipitation and filtration stages. Results were obtained for particle size distribution, extent of precipitation, particle morphology, and particle composition. The effect of ozonation on precipitation and filtration was evaluated, with a comparison to two-stage treatment consisting of precipitation and filtration. Antiscalant oxidation is controlled by bivalent cation coordination, while pH and ozone dose significantly affect the extent of oxidation. The addition of antiscalant prior to precipitation caused changes to particle size and morphology, and results varied with water composition and antiscalant type and concentration. Ozonation, even for small times such as one minute, prior to precipitation and filtration increased calcium precipitation and decomposed the antiscalant enough to remove the effect of the antiscalant on particle characteristics. During ozonation, antiscalants were not completely oxidized, but the partial oxidation products did not seem to affect precipitation. Ozonation also reduced the fouling of microfiltration membranes used for solid/liquid separation. Results indicated concentrate treatment can significantly increase the overall recovery of an RO system. / text