No description available.

No description available.

This thesis investigates the technical problems associated with large-scale stand-alone wind powered desalination employing a short-term energy store, particularly the complexities associated with the intermittent operation of the desalination plant. To achieve this, a non-linear, time domain system model of an existing wind powered desalination plant has been developed using the propriety code Simulink. Two desalination techniques have been considered: reverse osmosis and electrodialysis, due firstly to their relatively low specific energy consumption, and secondly, their efficient coupling to a wind turbine generator. As a way of reducing power mismatch, optimising water production, and above all reducing the switching rates of the desalination units, operation of the reverse osmosis and electrodialysis units under variable power conditions is suggested. Little information is available on plant performance under such conditions. A mathematical model has therefore been developed to ascertain the performance of reverse osmosis and electrodialysis processes under transient power conditions. The model consists of the set of partial differential equations (PDEs) describing the conservation of mass, momentum and chemical species coupled with the appropriate boundary conditions. A numerical solution based on the finite volume method has been employed to solve for the system of PDEs, as no analytical solution is available for the particular set of model equations derived. Sensitivity of plant performance to key design parameters (such as operating pressure and energy storage capacity) and operational strategies is predicted from simulation results. This technology is economically attractive for islands where wind energy density is high and water resources are scarce.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1960. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2007. / Perdue, E. Michael, Committee Chair ; Ingall, Ellery, Committee Member ; Stack, Andrew, Committee Member ; Nenes, Athanasios, Committee Member ; Pfromm, Peter, Committee Member.

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Cyclic electrodialysis is a novel separation process in which a modified membrane stack is operated in a periodic unsteady-state manner. Repeated reversals of polarity could avoid the main problems encountered in conventional electrodialysis; fouling and scale formation on the membranes. In cyclic electrodialysis the standard electrodialysis stack is converted into an adsorption-desorption stack with only one set of flow channels, the other set being replaced by storage compartments. Thesr compartments are in the form of three-layer membranes consisting of an anion and a cation selective membrane enclosing a core of non- selective material. The depleted and enriched products are produced successively in the single set of channels instead of simultaneously in adjacent channels. The process is potentially applicable for commercial desalination of brackish water to make it potable, to remove harmful ions from discharge waters, or to concentrate ionic solutions for recovery of valuable materials. Previously reported experiments with aqueous NaCl solutions in a closed (batch) system showed that a large separation factor could be obtained in cyclic electrodialysis. Batch operation is somewhat analogous to total reflux in distillation. The present work extends the earlier work to potentially more useful operating conditions in which feed is supplied and product removed. A constant-rate model has been developed for the process and used extensively throughout the work as a simple and efficient tool to compare various operating cycles and modes of operation. Scattered articles in the literature on the resistance of an electrodialysis stack have been compiled to develop a stack resistance model. Good agreement was obtained between the model predictions and measured values of resistance. Experimental apparatus is described and the effects of the following eight system parameters are reported: (i) Demineralizing path length (ii) Production rate (iii) Pause time (iv) Applied voltage (v) Initial concentration (vi) No-pause operation (vii) Pure-pause operation (vii) Semi-symmetric operation Large separations were achieved for asymmetrical paused operation with long demineralizing path, long pause time, high applied voltage, low feed concentration and small production rate. Despite the strong trade-off between production rate and separation, a separation factor as high as 50 was obtained at the highest production rate used. This value is higher than that obtained in commercial plants currently in use. The process looks promising and is worth further consideration. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Ocean salinity is a renewable energy source that has not been recognized and could provide an opportunity to capture significant amount of clean energy when it mixes with river water. One of the processes emerging as a sustainable method for capturing energy from seawater is reverse electrodialysis (RED), which generates power via the transport of the positive and negative ions in the water through selective ion exchange membranes (IEMs). RED power generation is relatively close to commercialization, but its application is often limited by system power efficiency in natural water conditions. Although various types of salt ions exist in environmental saline water, most efforts have been focused on sodium chloride as a single ionic source in the water and the effects of other common multivalent ions (e.g., magnesium and sulfate) on power generation remain unexplored. Moreover, the commercial feasibility of RED is highly challenged by the absence of specialized RED membranes. Currently available IEMs are not optimized for RED power conversion systems, but successful operation is highly dependent on the membranes used. Major advances in manufacturing of proper IEMs will be a critical pathway to accelerate large-scale energy conversion by RED. Therefore, this study aimed at advancing our understanding of the RED power system for efficient and stable salinity gradient energy generation. Specifically, it is comprised of three parts. First, a mathematical model is developed for three different monovalent and multivalent ion combinations to determine the effect of different ionic compositions of the feed solution on the power density. Efforts are further made to optimize the RED system with respect to improving power density by investigating the sensitivity of key response parameters such as flow rate ratios and intermembrane distance ratios. Second, novel organic-inorganic nanocomposite cation exchange membranes (CEMs) are synthesized for RED application by introducing functionalized inorganic materials into an organic polymer matrix. The effect of inorganic particle filler loading within the organic polymer matrix on physico- and electrochemical performance is investigated. The results revealed that the increase of functionalized nanoparticle loading controls the effective ion transport in the membrane structure and there exists an optimum amount of nanoparticles (i.e., charged groups), which performs the best in selectively exchanging counter-ions, while excluding co-ionic species. Third, the membrane structure modification is demonstrated to enhance ion transport while maintaining large surface-charged functional groups in the polymer matrix. We have synthesized custom nanocomposite CEMs to tailor porous membrane structures of various thicknesses, aging (evaporation) time, and inorganic nanoparticle loadings. We have further tailored the membrane structure by incorporating different inorganic particle filler sizes. These engineered design approaches are found to be highly effective in obtaining desired physico- and electrochemical properties, which allowed higher ionic current flow throughout the system. Furthermore, for the first time we showed the successful application of tailor-made nanocomposite CEMs in a RED stack and achieved superb power density, which exceeds the power output obtained with the commercially available membranes. In summary, this dissertation has advanced our understanding of salinity gradient energy generation using RED technique. Specifically, computational modeling and simulation study investigates the development and optimization approaches of the RED process for practical application of RED using natural water conditions. Furthermore, the RED membranes developed in this dissertation focuses on fabrication, characterization, and optimization of cation exchange membranes. Overall, the results of this study are anticipated to benefit the future optimization of energy-capturing mechanisms in RED and provide the better pathway for the sustainable salinity gradient power generation.

Nutrient removal is one of the primary goals of wastewater treatment and large amounts of ammonia are present throughout the wastewater treatment process. Conventional ammonia removal technologies are energy intensive and do not result in recoverable forms of the nutrient. Anaerobic dewatering side-streams are the liquid recovered during the biosolids dewatering processes following anaerobic digestion. The dewatering side-streams contain high concentrations of ammonia (~1000 mg/L NH4-N) making them an excellent candidate for resource recovery technologies. In this study electrodialysis (ED) was investigated for ammonia (NH4-N) recovery from anaerobic dewatering side-streams with an emphasis on fouling and scaling control on ion exchange membranes (IEMs). The experimental set-up consisted of 3 bench-scale electrodialyzers operating in parallel. The dewatering side-stream (centrate) was collected directly from centrifuges at a local WWTP and pretreated using a 0.3-mm screen. Electrodialyzer operation over 2.25 hrs achieved 95% NH4-N removal and the ammonia separation rate was slowed down by the concentration gradient between concentrate and diluate streams. A combined 269 hrs of operation during fouling experiments showed that electrodialysis (ED) performance decreased over time due to IEM fouling and thus clean-in-place (CIP) procedures was conducted every 60-120 hrs to restore the ED effectiveness. The two stage CIP procedures consisted of a NaCl Clean (5% NaCl, 2 hrs recirculation) and an Acid Clean (5% v/v HCl, 2 hrs recirculation). The NaCl Clean targeted organic fouling and the Acid Clean removed scales that precipitated on the IEMs. CIP procedures were able to recover 84-90% of the initial separation efficiency, the permanent loss in separation efficiency indicating that a portion of IEM fouling (10-16%) is irreversible. The higher applied voltage condition (7.5 V) showed faster fouling rates compared to low voltage conditions (4.5 V), while the degree of irreversible fouling was independent of the applied voltage. Organic fouling and inorganic scaling were individually quantified during CIP procedures using electrochemical impedance spectroscopy (EIS). While both fouling and scaling contributed significantly to the overall increase in the IEM stack resistance (63% scale formation, 37% organic fouling), inorganic scaling was found to play a more important role in reducing the separation rate in ED. ICP and SEM-EDS analysis identified the scale that formed on the surface of the IEMs as mostly of CaCO3 precipitation with smaller amounts of struvite. This finding indicates that the pretreatment of dewatering side-streams should be more focused on removing divalent cations (Ca2+ and Mg2+), but also still consider organic foulant removal for its treatment in ED. Since organic fouling primarily affects anion exchange membranes (AEMs), the impacts of fouling were investigated on two types of AEMs (AR908, AR204). Fouling experimentation showed minor differences in current density and separation efficiency over 269 hrs of operation, with AR204 AEMs showing signs of worse irreversible fouling. Particle size analysis of centrate suggested that large suspended particles could obstruct electrodialyzer chambers. Screening pretreatment (0.3 mm) effectively removed large particles and mitigated clogging issues without having to increase intermembrane distances. The experimental results suggest that ED is a promising technology for recovering ammonia from nutrient rich wastewaters. ED was able to efficiently achieve high levels of ammonia separation from centrate, while fouling was shown to be manageable using CIPs at reasonable intervals. Overall ED was shown to be an effective way to recover ammonia from dewatering side-streams, but pretreatments targeting scaling and organic fouling could better mitigate performance losses due to fouling and further improve the process. / Thesis / Master of Applied Science (MASc)

Complexities associated with dissolved organic matter (DOM) isolation from seawater have hampered compositional characterization of this key component of global carbon and nutrient cycles. Two techniques, Electrodialysis (ED) and Solid Phase Extraction (SPE), were combined to more effectively isolate DOM from salt-containing waters. Sample recovery was optimized and evaluated on a range of samples including coastal ocean seawater, open ocean seawater, artificial seawater from cultures of marine phytoplankton, and artificial seawater samples containing standard compounds of different molecular sizes and charge. ED was performed with a system optimized for processing 2 to 10 L sample volumes and SPE was performed using Bond Elut PPL exchange resin. With the combination of ED and PPL techniques an average recovery of 76.7 ± 2.6% was obtained for natural coastal seawater. Comparison of C/N ratios and fluorescence excitation emission matrices (EEMs) taken at the beginning and end of the recovery process indicated that the final recovered material was representative of the DOM present in the original samples.