Lack of clean fresh water is one of the most pervasive problems afflicting people throughout the world. Efficient desalination of sea and brackish water and safe reuse of wastewater become an insistent need. However, such techniques are energy intensive, and thus, a good control design is needed to increase the process efficiency and maintain water production costs at an acceptable level. This thesis proposes solutions to the above challenges and in particular will be focused on two membranebased water systems: Membrane Distillation (MD) and Membrane Bioreactor (MBR) for wastewater treatment plant (WWPT). The first part of this thesis, Direct Contact Membrane Distillation (DCMD) will study as an example an MD process. MD is an emerging sustainable desalination technique which can be powered by renewable energy. Its main drawback is the low water production rate. However, it can be improved by utilizing advanced control strategies. DCMD is modeled by a set of Differential Algebraic Equations (DAEs). In order to improve its water production, an optimization-based control scheme termed Model Predictive Control (MPC) provides a natural framework to optimally operate DCMD processes due to its unique control advantages. Among these advantages are the flexibility provided in formulating the objective function, the capability to directly handle process constraints, and the ability to work with various classes of nonlinear systems. Motivated by the above considerations, two MPC schemes that can maximize the water production rate of DCMD systems have been developed. The first MPC scheme is formulated to track an optimal set-point while taking input and stability constraints into account. The second MPC scheme, Economic MPC (EMPC), is formulated to maximize the distilled water flux while meeting input, stability and other process operational constraints. The total water production under both control designs is compared to illustrate the effectiveness of the two proposed control paradigms. Simulation results show that the DCMD process produces more distilled water when it is operated by EMPC than when it is operated by MPC. The above control techniques assume the full access to the system states. However, this is not the case for the DCMD plant. To effectively control the closed-loop system, an observer design that can estimate the values of the unmeasurable states is required. Motivated by that, a nonlinear observer design for DCMD is proposed. In addition, the effect of the estimation gain matrix on the differentiation index of the DAE system is investigated. Numerical simulations are presented to illustrate the effectiveness of the proposed observer design. The observer-based MPC and EMPC are also studied in this work. Mathematical modeling of a wastewater treatment system is critical because it enhances the process understanding and can be used for process design and process optimization. Motivated by the above considerations, modeling and optimal control strategies have been developed and applied to the MBR-based wastewater treatment process. The model is an extension of the well-known Benchmark simulation models for wastewater treatment. In addition, model predictive control has been applied to maintain the dissolved oxygen concentration level at the desired value. In addition, a conventional PID controller has also been developed. The simulation results show that the both of controllers can be used for dissolved oxygen concentration control. However, MPC has better performance compared to PID scenario.

Approximately 35% of the population of the Navajo Nation does not have direct access to the electric grid and public water supply. Tribal members haul their potable and livestock water from public water systems that are located great distances from their homes. The Navajo Nation Solar Desalination Research Pilot Demonstration Project is designed to provide residents affordable livestock water. The same technology can later be adopted to provide potable water. The project has deployed an off-grid, prototype water purification unit at a demonstration site north of Leupp, AZ utilizing membrane distillation (MD) technology. A second prototype for the same purposes utilizing nanofiltration (NF) membrane technology has been designed, built, and operated at The University of Arizona. Through experimentation I confirmed information provided the manufacturer of the NF membrane, calculated the production rate to be 636 gallons per day, and calculated the cost of desalinated water to be $0.003 per gallon. Both systems use solar energy to desalinate brackish ground water and the second prototype will later be deployed at the same site for side-by-side comparison. A critical part of the project is the development of technology transfer methods that will help the community take ownership of the project. To accomplish this goal I have written a comprehensive manual that will be given to the Navajo Department of Water Resources. The demonstration site will act as an applied research site for investigation, demonstration, and training related to sustainable water and energy systems designed to address the needs of remote, rural communities in arid and semi-arid regions. The aim is to inform a regional plan for Southwestern Navajo Nation Chapters to address chronic water and energy shortages, demonstrate renewable energy application for water treatment of brackish ground water, evaluate trade-offs in energy and water supplies, and foster community development. The research and demonstration site has been developed by an interdisciplinary and collaborative effort between the Bureau of Reclamation, Apex Applied Technology, Inc., and The University of Arizona.

<p>Current global water scarcity and the spectre of a future critical shortage are driving the need for novel and energy saving water technology approaches. Desalination of seawater and the reuse of treated wastewater effluent, which have historically been viewed as undesirable water sources, are increasingly being explored as sources for reducing water consumption. Although the dominant technologies for taking these water sources to potable quality, energy consumption still makes them unsustainable for widespread application. Membrane distillation (MD) is an innovative water purification method that has shown promise as a technology that can address several of these issues. MD is a membrane process that produces very high quality product water. However, similarly to other thermal desalting processes, MD utilizes heat as the dominant source of energy rather than pressure, and can potentially be used to produce water at higher recoveries (and therefore less waste) than is feasible with existing approaches. Another important advantage of MD is that the water separation occurs at modest temperatures (<90oC), opening the door for the utilization of currently usable waste heat sources. Despite these advantages, MD is primarily a lab scale technology, and key questions concerning process performance, including flux magnitude, energy efficiency, fouling propensity, membrane performance, and long-term system performance must be addressed to fully vet this technology. </p><p>This work is represents an attempt to provide insight into several of these issues. The overarching approach taken throughout this project is the parallel evaluation of ceramic membranes alongside commonly used polymeric (PTFE) membranes. The combined factors of MD being a relatively nascent technology and the fundamental separation mechanism point toward initial real-world applications of MD for the treatment of high concentration water that may necessitate membranes exposure to harsher thermal and chemical environments. The robust and inert nature of ceramics make them ideal candidates for such application, although their hydrophilic surface do allow for direct implementation in MD. The first phase of this work details the evaluation of several candidate surface treatments for modifying ceramic membranes and shows that aluminum oxide ceramic membranes can be successfully modified with perfluorodecyltriethoxysilane to possess the necessary hydrophobicity for MD application. The effectiveness of the surface treatment in modifying the membrane surface chemistry was assessed using a multitude of analytical approaches, which showed that the modified ceramic surface attained high hydrophobicity and thus are suitable for application of the membranes in direct contact membrane distillation (DCMD).</p><p>The next phase of research details the development and verification of a model for DCMD performance. The relative membrane performance was compared, with the polymeric membrane consistently outperforming the modified ceramics, which was attributed to a combination of superior thermal and physical membrane characteristics. Beyond attempting to evaluate the performance differences, this model allows the consideration of various operational scenarios, focusing on membrane flux and energy performance as various membrane and operational parameters change to determine conditions that maximize MD performance as well as provide insight critical to develop MD-specific membranes. </p><p>Finally, membrane performance was evaluated during the treatment water containing various organic foulants as well for the treatment of municipal wastewater. The results showed that the level of fouling was highly dependent on foulant type, with alginate identified as a component that produces severe fouling under all conditions evaluated, and wastewater fouling being relatively minimal. Membrane cleaning solutions were implemented to show that near-complete flux recovery was attainable, and plain deionized water was shown to be as effective as sodium hypochlorite.</p> / Dissertation

Salinity is one of the most critical environmental problems for water scarce countries, / Thesis (Ph.D.Eng.)-University of KwaZulu-Natal, 2006.

No description available.

Gas separations are often required in chemical processes, e.g. air separation, ethylene production, etc. These are often challenging and costly processes because of the low temperature and high pressure needed if vapour-liquid phase separations are involved. This thesis focuses on hybrid membrane-distillation separations as an opportunity to develop more energy-efficient separation processes. In a typical ethylene plant, recovery, the separation and purification of the cracked product are economically important. The focus of this thesis is on the ‘C2splitter’ which separates the desired product, ethylene, from ethane. Cryogenic distillation, which is currently used to separate the binary ethylene-ethane mixture, is extremely expensive in terms of both capital and operating costs, especially because of refrigerated cooling requirements. Hybrid membrane-distillation processes are able to effectively separate low-boiling compounds and close-boiling mixtures and to reduce energy consumption, relative to cryogenic distillation. However, hybrid membrane-distillation processes present challenges for process modelling, design and operation. There are two major challenges associated with the modelling of hybrid processes for low temperature separations: i) the complex interaction between the process and the refrigeration system and ii) the large number of structural options, e.g. conventional column, membrane unit or hybrid membrane-distillation separation, where the distillation column can be integrated with the membrane unit to form a sequential, parallel, ‘top’or ‘bottom’ hybrid scheme. This thesis develops a systematic methodology to design, screen, evaluate and optimise various design alternatives. Schemes are evaluated with respect to energy consumption, i.e. power consumption of process and refrigeration compressors, or energy costs. In the methodology, process options are screened first for feasibility, based on numerous simulations and sensitivity analyses. Then, the feasible options are evaluated in terms of energy consumption and compared to the performance of a conventional distillation column. Finally, economically viable schemes are optimised to identify the most cost-effective heat-integrated structure and operating conditions. The methodology applies models for multi-feed and multi-product distillation columns, the membrane, compressor and refrigeration system; heat recovery opportunities are systematically captured and exploited. For the separation of relatively ideal mixtures, modified shortcut design methods, based on the Fenske-Underwood-Gilliland method are appropriate because they allow fast evaluation without needing detailed specification of column design parameters (i.e. number of stages, feed and side draw stage locations and reflux ratio). The modifications proposed by Suphanit (1999) for simple column design are extended to consider multi-feed and/or multi-product columns. The complex column designs based on the approximate calculations method are validated by comparison with more rigorous simulations using Aspen HYSYS. To design the hybrid system, a reliable and robust membrane model is also needed. To predict the performance of the module model, this work applies and modifies detailed membrane model (Shindo et al., 1985) and approximate method (Naylor and Backer, 1955) to avoid the need for initial estimates of permeate purities and to facilitate convergence. Heat integration opportunities are considered to reduce the energy consumption of the system, considering interactions within the separation process and with the refrigeration system. A matrix-based approach (Farrokhpanah, 2009) is modified to assess opportunities for heat integration. The modified heat recovery model eliminates the need to design the refrigeration cycle and uses a new simple, linear model that correlates the ideal (Carnot) and a more accurately predicted coefficient of performance. This work develops a framework for optimising important degrees of freedom in the hybrid separation system, e.g. permeate pressure, stage cut, side draw molar flow rate and purity, column feed and side draw locations. Heat recovery options between: i) column feeds and products; ii) the membrane feed and products and iii) the associated refrigeration system are considered. A deterministic and a stochastic optimisation algorithm are applied and compared for their efficiency of solving the resulting nonlinear optimisation problem. The new approach is demonstrated for the design and optimisation of heat-integrated sequential and parallel hybrid membrane-distillation flowsheets. Case study results show that hybrid scheme can reduce energy cost by 11%, compared to distillation, and that parallel schemes have around 8% lower energy costs than sequential hybrid schemes. These results suggest hybrid membrane-distillation processes may be competitive with distillation when applied for ethylene-ethane separations, but that further development of suitable membranes may still be needed.

In Gulf Cooperation Council (GCC) countries, a lack of freshwater, poor soil quality, and ambient temperatures unsuitable for cultivation for parts of the year hinders domestic agriculture. The result is a reliance on a fluctuating supply of imported fresh produce which may have high costs and compromised quality. There are agricultural technologies available such as hydroponics and controlled environment agriculture (CEA) that can allow GCC countries to overcome poor soil quality and ambient temperatures unsuitable for cultivation, respectively. Evaporative cooling is the most common form of cooling for CEA and requires a significant amount of water. In water-scarce regions, it is desirable for sea or brackish water to be used for evaporative cooling. Unfortunately, in many coastal desert regions, evaporative cooling does not provide enough cooling due to the high wet-bulb temperature of the ambient air during hot and humid months of the year. A liquid desiccant dehumidification system has been proven to lower the wet-bulb temperature of ambient air in the coastal city of Jeddah, Saudi Arabia to a level that allows for evaporative cooling to meet the needs of heat-sensitive crops. Much of the past research on the regeneration of the liquid desiccant solution has been on configurations that release water vapor back to the atmosphere. Studies have shown that the amount of water captured by the liquid desiccant when used to dehumidify a greenhouse can supply a significant amount of the water needed for irrigation. This thesis studied the regeneration of a magnesium chloride (MgCl2) liquid desiccant solution from approximately 20 to 31wt% by direct contact membrane distillation and explored the possibility of using the recovered water for irrigation. Two microporous hydrophobic PTFE membranes were experimentally tested and modeled when the bulk feed and coolant temperature difference was between 10 and 60°C. In eight experiments, the salt rejection was higher than 99.97% and produced permeate suitable for irrigation with a concentration of MgCl2 less than 94 ppm.

Sustainable desalination technologies are the smart solution for producing fresh water and preserve the environment and energy by using sustainable renewable energy sources. Membrane distillation (MD) is an emerging technology which can be driven by renewable energy. It is an innovative method for desalinating seawater and brackish water with high quality production, and the gratitude is to its interesting potentials. MD includes a transfer of water vapor from a feed solution to a permeate solution through a micro-porous hydrophobic membrane, rejecting other non-volatile constituents present in the influent water. The process is driven by the temperature difference along the membrane boundaries. Different control applications and supervision techniques would improve the performance and the efficiency of the MD process, however controlling the MD process requires comprehensive mathematical model for the distributed heat transfer mechanisms inside the process. Our objective is to propose a dynamic mathematical model that accounts for the time evolution of the involved heat transfer mechanisms in the process, and to be capable of hosting intermittent energy supplies, besides managing the production rate of the process, and optimizing its energy consumption. Therefore, we propose the 2D Advection-Diffusion Equation model to account for the heat diffusion and the heat convection mechanisms inside the process. Furthermore, experimental validations have proved high agreement between model simulations and experiments with less than 5% relative error. Enhancing the MD production is an anticipated goal, therefore, two main control strategies are proposed. Consequently, we propose a nonlinear controller for a semi-discretized version of the dynamic model to achieve an asymptotic tracking for a desired temperature difference. Similarly, an observer-based feedback control is used to track sufficient temperature difference for better productivity. The second control strategy seeks for optimizing the trade-o between the maximum permeate flux production for a given set of inlet temperatures of the feed and the permeate solutions, and the minimum of the energy consumed by the pump ow rates of the feed and the permeate solutions. Accordingly, Extremum Seeking Control is proposed for this optimization, where the pump flow rates of the feed and the permeate solutions are the manipulated control input.

Absorption dehumidification requires regeneration system to regenerate diluted desiccant solutions, which are still highly concentrated. A novel multi-stage vacuum membrane distillation system was applied for separating water out of the highly concentrated solution. The performance of this novel membrane distillation system with high concentration solution is studied, as well as the effect of solution concentration, heating temperature and feed flow rate on concentration increase, permeate flux and specific energy consumption was studied. Feed solutions are LiCl solution (22-30 wt%) and CH3COOK solution (50-60 wt%).Other experimental parameters studied were: heating temperature, 70-80 °C, feed flow rate, 1.2-2.0 l/min. Response surface method is applied for model building, in order to provide a better understanding of the interactions between different parameters. Compared with pure water, high concentration solution has lower vapor pressure, which leads to lower permeate flux. The highest concentration the system can reach is 36.5 wt% for LiCl solution and over 70 wt% for CH3COOK solution, when the heating temperature is 80 °C. Lower concentration and higher heating temperature will result in larger increase in concentration, higher permeate flux and also lower specific energy consumption. But due to the configuration of the system, optimal flow rates can be found under different conditions. Within the testing region, the permeate flux ranges between 0.147-1.802 l/(m2h) for LiCl solution and 0.189-1.263 l/(m2h) for CH3COOK solution. With low concentration, high heating temperature and low feed flow rate, low specific energy consumptions, 0.85 kWh/l and 0.94 kWh/l for LiCl and CH3COOK solutions are observed respectively. With external heating recovery system, this value can be further reduced.

The simultaneous treatment of different produced water streams with the forward osmosis membrane distillation hybrid system (FO-MD) has been suggested recently. This work investigates the need for pretreatment of produced water prior to filtration with FO-MD in order to reduce the level of fouling and scaling in the system. The desalter effluent (DE) stream was selected as FO feed solution, and the water oil separator (WO) stream was used as FO draw solution/MD feed solution, and a significant flux decline was observed in FO and MD within the first 5 hours of operations. SEM and EDX analysis indicated that the formation of scale layer on both membranes was the main reason for the sharp flux decline. Silica was the major contributor to the scaling of the support layer of the FO membrane. While the scaling layer on MD membrane consisted mainly of CaSO4 crystals with some deposition of Silica. Therefore, electrocoagulation (EC) was selected for the pretreatment of produced water to target the removal of Ca, SiO2 and SO4 ions in order to reduce the likelihood of inorganic fouling in FO-MD. The different parameters of EC, namely, the current density, electrolysis time, and initial pH were tested at a wide range of values of 7-70 mA/cm2 , 10-60 minutes, 5-9, respectively. calcium and sulfate ions were not effectively removed at the relatively high applied current density of 70 mA/cm2 , while high removal of silica was achieved even at low applied current densities. The optimum conditions of EC for silica removal were found to be 7 mA/cm2 for the current density and 10 minutes for the electrolysis time which resulted in a 97% removal of silica. it was found that due to pretreatment, the average FO and MD fluxes increased by 49% (9.93 LMH) and 39% (8.55 LMH), respectively. Therefore, even though EC did not show promising results in terms of the removal of calcium and sulfate, efficient silica removal was achieved with minimum energy requirements which suggests that it could have a potential to be integrated with the FO-MD hybrid system for the treatment and reclamation of produced water.