Freeze concentration is a thermal separation process that is used to purify aqueous solutions. One application of recent interest is seawater desalination. For freeze concentration to be an effective desalination method, a high ice growth rate and product purity must be achieved with energy usage comparable to that of competing technologies. The purpose of this thesis is to develop a coupled heat and mass transfer model to predict the growth rate and purity of the solid phase for ice grown about a horizontal, immersed tube. By simultaneously solving the heat and mass transfer problems, this model improves upon previous attempts found in the literature. In addition, an experimental apparatus was constructed and a series of ten experiments was run, considering a range of cooling rates, process times, and saltwater concentrations. Average ice growth velocities ranged from 3.1-13.1 mm/h and the observed partition coefficient ranged from 0.42-0.71. The model was calibrated using experimental data, and the coefficients of variation for the fitted model's prediction of ice mass and capture concentration were 15.4% and 7.6% respectively. Based on insights from modeling and experimentation, a series of suggestions are made regarding future modeling and process design. / Master of Science / Freeze concentration is a thermal process that is used to purify a liquid containing dissolved solids. One application of recent interest is seawater desalination. For freeze concentration to effectively purify seawater, a high ice growth rate and product purity must be achieved with energy usage comparable to that of competing technologies. The purpose of this thesis is to develop a coupled heat and mass transfer model to predict the growth rate and purity of the solid phase for ice grown about a horizontal, immersed tube. By simultaneously solving the heat and mass transfer problems, this model improves upon previous attempts found in the literature. In addition, an experimental apparatus was constructed and a series of ten experiments was run, considering a range of cooling rates, process times, and saltwater concentrations. Average ice growth velocities ranged from 3.1-13.1 mm/h and the salinity of the ice ranged from 0.42-0.71% of the original concentration. Based on insights from modeling and experimentation, a series of suggestions are made regarding future modeling and process design.

Yes / Models’ accuracy and reliability are important factors for designers of the humidification-dehumidification (HDH) desalination systems. A model used for designing the system must consider all important parameters in order to maintain high accuracy over the wide range of fluctuating conditions. The empirical models for HDH systems which are mostly available in literature are simple and easy to develop but also have limited predictive accuracy for extreme conditions because of consideration of only a few of many influential parameters. Usage of these models may lead to an expensive redesign at latter stages in development of the real system. Therefore, the aim of this paper is to propose the mechanistic model of the HDH desalination process with an improved prediction accuracy as an alternative to conventional models. This model is developed by coupling the heat and mass transfer equations at the water–air interface into enthalpy equations. Performances of the proposed model and an empirical model from literature are compared against experimental data obtained from the HDH system, which is also designed in this work. Results show the proposed model has relatively low mean square error (0.4) hence more accurate than the empirical model with mean square error of 7. It was also found that, the recovery ratio attained by the system increases substantially with an increase of the feed water temperature, but decreases with an increase of water-to-air flow ratio. Freshwater productivity increases with an increasing packing's specific area while doubling of dehumidifiers’ surface area improves the recovery ratio by 16%.

Water is life for all living organisms on earth, and all human beings need water for every socio-economic activity in their daily lives. However, constant challenges are faced in securing quality water resources due to environmental pollution, a growing demand, and climate changes. To overcome imminent worldwide challenges on water resources, desalination of seawater and saline wastewater became inevitable, and significant efforts have been deployed by the desalination research community to advance the technology. However, there is still a gap to take it to a higher sustainability and compatibility compared to conventional water treatment technologies. Among all efforts, the hybridization of two or more processes stands among the promising solutions for sustainable desalination, which synergizes benefits of multiple technologies. To evaluate the sustainability of hybrid desalination technologies, two different systems, namely; (i) multi-effect distillation – adsorption (MED-AD) and (ii) forward osmosis – membrane distillation (FO-MD), are investigated in this study. The method developed for the analysis of primary energy consumption in complex desalination systems is used to evaluate the performance of the MED-AD pilot facility at King Abdullah University of Science and Technology (KAUST). Results of the MED-AD pilot operation showed an improvement in water production with a higher energy efficiency under the same operating conditions (near the ambient temperature with the solar thermal system). For the FO-MD hybrid system, an investigation is carried out on a novel in-house integrated module and a comparative analysis with the conventional module is provided. An isolation barrier carefully placed in the novel design enhanced the hybrid performance by reducing both concentration and temperature polarization. In addition, the FO-MD hybrid process is evaluated for brine reclamation application in a SWRO-MD-FO system. The sustainability of the proposed system and the potential of a flexible sustainable operation are presented with the experimental study with real seawater and brine from the full-scale desalination plant.

Shortage of drinking water in most parts of the world has been a growing concern in recent times. The situation has been getting worse in underdeveloped and developing countries due to sudden explosion in population growth and the growth in the industries. The natural resources for potable water are limited and unless a feasible solution is obtained in the near future, the ‘concern situation’ may turn into a ‘panic situation’. A possible solution for the shortage in drinking water is to use water from inexhaustible sources such as oceans and seas and make it potable using desalination process. However, the process of desalination is an energy intensive process which the poor countries can not afford. In recent times, the cost of fossil fuels has been skyrocketing. With the crude oil costing more than Rs.5200 (US$120) a barrel as on September 2008, even the rich countries like USA and the countries in the European Union are feeling the pinch of the energy cost. Alternate energy sources such as solar, wind, geo-thermal, hydrogen etc., have become the order of the day. These sources are renewable and are environmental friendly. More than one third of the populations of the world live in coastal areas. These areas get abundant amount of solar energy throughout the year. Utilization of this energy in desalination process would solve drinking water problem to a very great extent. However, construction of centralized desalination plants requires large amount of capital which the poor countries can ill-afford. An alternate solution would be to construct decentralized smaller plants that would require smaller capital to construct and easier to maintain. If the energy requirement is tapped from renewable sources such as solar, then the operational cost also becomes affordable for the poor countries. By taking care of the water requirement of the coastal areas through this process, one may save large amounts of money in transporting potable water from interior areas to the coastal areas. There would be enough water for the people living in the interior areas. The water bed level in the interior areas would gradually increase, thereby reducing the drinking water concerns significantly. In this thesis, a small scale stand alone power generation system for the desalination process is proposed that is suitable to provide clean potable water from sources such as sea water or brackish water. Solar energy is proposed as a source of energy for the proposed desalination system. This source is available in plenty in arid and semi-arid areas. It is free and is also friendlier to the environment. It is proposed to use solar energy in thermal form to obtain energy equivalent of ‘latent heat of vaporization’ for the vaporization process and in electrical form for operating the dc machines and electronic control units that are integral parts of the desalination system. The proposed desalination unit can be built as small as possible even to feed a single household’s requirement and hence can be conceptualized as decentralized units. These units would require considerably less capital to build, and would require minimum maintenance. The desalination process is based on flash evaporation wherein a heated liquid is subjected to a pressure reduction by passing through a throttling device resulting in an initially superheated state. In the proposed desalination process, the traditional flash evaporator is extended to include continuous dynamic pressure modulation to obtain an optimal flow rate for a specified energy input. The cost function or the performance index for optimization is defined as the ratio of flow rate to the energy spent. The optimal flow rate occurs at a specific chamber pressure for a given inlet water temperature. By operating at optimal pressure, significant energy is saved for a specific flow rate. This principle is validated experimentally and the results are presented and discussed in the thesis. This proposed scheme along with hybrid energy input will prove to be an attractive solution for community drinking water problem. A system needs to have a mathematical representation in order to predict the dynamic behavior of the system. This thesis proposes the bond graph method of modeling the physical system wherein the energy flow across the electrical, thermal and the hydraulic domains are included. A system may comprise of several subsystems and the energy flow in each subsystem may be in a different domain. A desalination system is such a system wherein the energy flow in subsystems is in different domains such as electrical, thermal and hydraulics. The bond graph approach is best suited for modeling of such systems where the power/energy flow across domains can be easily and seamlessly integrated. The thesis proposes a fifth order dynamic model of a single stage flash evaporation with pressure modulation using the bond graph approach. The proposed model incorporates the effects of chamber pressure variation, the entropy flow from the chamber due to conduction, convection, radiation and also the thermal dynamics of the water bodies in the evaporation, condensation and collection chambers. The proposed model is simulated in MATLAB/Simulink environment. The simulation results are compared with the experimental results to validate the model. This proposed model can be used for both analysis and synthesis of a desalination system. The desalination system is a complex system wherein multiple energy domains are involved. The thesis presents a systematic process for the design of the desalination system. Design of the desalination system involves design of multi domain subsystems. The design becomes much more complex if the energy source to run the system is solar/ hybrid solar based. The energy budget has to be carefully evaluated considering the worst case conditions for the availability of solar energy. Hence, the information on the quantum of solar energy available at any location is a critical parameter needed for design of the desalination system. A generic method of developing a solar insolation model for a specific region such as the Indian sub-continent is proposed in this thesis along with the validation of the model by comparing measured value with the values that are obtained from the model. As the insolation model is dependent on the water vapor content in the vertical column at the location, the methodology is further applied to develop a model for estimating the precipitated water vapor content in a vertical column for any location. The model is validated by comparing the computed values to the measured values. The thesis further presents the design and selection of the balance of the system. The selection of the balance of the system includes sizing of solar thermal plate collectors such as flat plate for pre-heating and paraboloid for vaporization, solar PV panels for operating pumps, actuator and control units, and battery for backup source for night loads and during ‘no-sun days’, criteria of selecting centrifugal pump for circulating condensation water, vacuum pump for dynamic pressure modulation and selecting linear actuator for Sun tracking of the paraboloid concentrator. A discussion on the electronic circuits used in the control scheme is presented in this thesis. This includes the circuit for maximum power point tracking, circuit for DC-DC conversion, circuit for pressure modulation, circuit for speed control of linear actuator, and finally the circuit for water level limiter. A discussion on the life cycle costing is also presented in this thesis. This is an important parameter that refers to the accumulated worth of all the costs related to building and operating the desalination plant during its life span. It is emphasized that the objective of the design process is to minimize the life cycle cost while meeting other performance requirements. Thus, life cycle costing is an essential part of the design cycle. The design methodology and the approach used to design the desalination system are implemented in the form of a toolbox in the MATLAB environment. The various functions of the toolbox are highlighted by a detailed step by step presentation of the design modules in the thesis. The modules form the components of the design toolbox for designing the proposed desalination system.

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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

This was a study on the history of the Colorado River, the water challenges of the Lower Basin states and the international water laws that govern the United States and Mexico concerning the Colorado river. The main purpose of this study was to determine possible long-term solutions to the growing water needs of the Lower Basin states and how Mexico could help. After discussing some concerns that the Lower Basin states had, research was done on the different types of desalination. This research included the different methods and their processes. MSF, MED, RO and MVC methods are discussed mentioning their different strengths and limitations. Next different possible solutions are discussed. These possible solutions include current practices and their successes. The solution that is discussed in length is water desalination as it offers another method of obtaining water. This part also discusses different ways to power the plant. As Mexico was already going to build nuclear power plants one idea was to build a plant in Mexico and use their power to run a desalination plant. This is one possible solution, to have a desalination plant desalinate water out of the Sea of Cortez in Mexico for the Southwest to use using the Mexico’s nuclear power plant to run the system. The economics of a desalination plant are discussed. The cost of building a plant, cost of desalinating the water, and water transportation costs are examined. After an examination on these different costs are completed it is discussed on who would pay for the desalination plant and who would receive the water. One possibility discussed is that Arizona, California and Nevada all pay an equal share in the cost of building the desalination plant in Mexico. California would then receive the water from the plant and thus would cut back on their consumption from the Colorado River allowing both Arizona and Nevada to increase theirs. A PEST analysis is done at the end of this study. It covers Political, Economical, Socio-cultural and Technological categories associated with this study. It covers different concerns and possible legislations that would need to be amended in order to continue with international desalination.

The aim of this study is to develop a seawater desalination system that uses sea-wave energy as the sole energy source for system operation. This system is composed of a sea-wave energy acquisition system, a reverse-osmosis device, and a proposed mechanism linking the system to function synchronously. The relationships between various system parameters and system characteristics are analyzed. The limitations and constraints of system operations are then suggested. For the purpose of comparison, another system, which indirectly drives the reverse-osmosis system through an additional stage of energy storage, is introduced. To analyze the system dynamic properties, the following steps are implemented. First, a mathematical model than can properly describe the system characteristics is derived. This model is found to be a nonlinear one, which increase the difficulties of system analysis enormously. However, it is also noted through a preliminary examination that the effect of system nonlinearity becomes insignificantly if the system parameters are properly adjusted. Under these parameters, the linearied model is analyzed. The effects of different system parameters on the amount of energy acquisition and desalinated water are investigated. The analysis indicates that the amount of energy acquisition or desalinated water is closely related to both the selected energy acquisition system and the desalination system. For a given energy acquisition system and sea wave condition, an improper system parameter selection of desalination system will either make the whole system operation inefficient or devastate the functioning of acquisition system. This suggests that certain parameters of the desalination system must be adjustable in a real operation. The study also shows that the linearied system can be approximated by a model with two degrees of freedom. This model may offer the convenience for the optimization of system parameters.

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. / text

In spite of abundant water resources, world is suffering from the scarcity of usable water. Seawater Reverse Osmosis (SWRO) desalination technology using polymeric membranes has been recognized as a key solution to water scarcity problem. However, economic sustainability of this advanced technology is adversely impacted by the membrane fouling problem. Fouling of RO membranes is a highly studied phenomenon. However, literature is found to be lacking a detailed study on kinetic and dynamic aspects of SWRO membrane fouling. The factors that impact the fouling dynamics, i.e., pretreatment and water quality were also not adequately studied at full–scale of operation. Our experimental protocol was designed to systematically explore these fouling aspects with the objective to improve the understanding of SWRO membrane fouling mechanisms. An approach with multiple analytical techniques was developed for fouling characterization. In addition to the fouling layer characterization, feed water quality was also analysed to assess its fouling potential. Study of SWRO membrane fouling dynamics and kinetics revealed variations in relative abundance of chemical and microbial constituents of the fouling layer, over operating time. Aromatic substances, most likely humic–like substances, were observed at relatively high abundance in the initial fouling layer, followed by progressive increase in relative abundances of proteins and polysaccharides. Microbial population grown on all membranes was dominated by specific groups/species belonging to different classes of Proteobacteria phylum; however, similar to abiotic foulant, their relative abundance also changed with the biofilm age and with the position of membrane element in RO vessel. Our results demonstrated that source water quality can significantly impact the RO membrane fouling scenarios. Moreover, the major role of chlorination in the SWRO membrane fouling was highlighted. It was found that intermittent mode of chlorination is better than continuous mode of chlorination of seawater, as anti–biofouling strategy. It was also confirmed that significant biofilm development was inevitable even with the use of chlorine to disinfect SWRO membranes. Our findings on the dynamic patterns of SWRO membrane fouling should help in further elaborating research projects focusing on the development of better strategies to minimize this troublesome phenomenon.