Sustainable Energy Technologies for Seawater Desalination

By Marc A. Rosen and Aida Farsi

Sustainable Energy Technologies for Seawater Desalination provides comprehensive coverage of the use of renewable energy technologies for sustainable freshwater production. Included are design concepts for desalination and sustainable energy technologies based on thermodynamics, heat transfer, mass transfer and economics. Key topics covered include desalination fundamentals and models, desalination assessments using energy and exergy methods, economics of desalination and the optimization of renewable energy-driven desalination systems. Illustrative examples and case studies are incorporated throughout the book to demonstrate how to apply the concepts covered in practical scenarios.

Following a coherent approach, starting from fundamentals and basics and culminating with advanced systems and applications, this book is relevant for advanced undergraduate and graduate students in engineering and non-engineering programs.

• Provides a comprehensive resource on sustainable freshwater production
• Describes how to analyze renewable energy-based desalination using energy and exergy methods and economic assessments, and how to carry out performance optimization
• Incorporates numerous examples and case studies to illustrate practical applications
• Presents the most up-to-date information with recent developments

• Language: English
• Publisher: Academic Press
• Release date: Feb 15, 2022
• ISBN: 9780323999410

Marc A. Rosen

Marc A. Rosen is founding Dean of Engineering and Applied Science at the University of Ontario Institute of Technology in Oshawa, Canada. A Past-President of the Canadian Society for Mechanical Engineering, Dr. Rosen received an Award of Excellence in Research and Technology Development from the Ontario Ministry of Environment and Energy, and is a Fellow of the Engineering Institute of Canada, the American Society of Mechanical Engineers, the Canadian Society for Mechanical Engineering, and the International Energy Foundation. He has worked for Imatra Power Company in Finland, Argonne National Laboratory, and the Institute for Hydrogen Systems, near Toronto.

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Chapter One

Introduction to desalination and sustainable energy

Abstract

Although water is the one of the most abundant substances on the planet, only 0.5% of natural water resources are freshwater. The global need for freshwater is increasing dramatically, while natural readily available freshwater resources, such as rivers, lakes and aquifers, are diminishing. Numerous freshwater supply options have been employed in the past, but they cannot meet the rising freshwater demands in all sectors (municipal, industrial, electrical, irrigation, etc.). Desalination of brackish water and seawater has received a great deal of attention over the years as a viable means of satisfying freshwater demands around the world. Population growth, urbanization, and industrialization appear to be the main drivers in recent years of the need for desalination, as a reliable technique for producing freshwater from a relatively low-quality water resource. This book addresses seawater desalination processes, with a focus on sustainable approaches to providing freshwater.

This chapter describes the status of desalination systems, including the number of desalination plants installed around the world and their freshwater production capacities as well as other important factors such as feed water type, geographical parameters, and desalting technologies. This chapter also provides insights into the historical development of desalination, and the potential for driving desalination systems using sustainable energy resources. Using sustainable energy in seawater desalination systems has the potential to permit continuous freshwater production with low impacts on the environment.

Keywords

Freshwater; desalination; sustainable energy; sustainable freshwater production; environment

1.1 Resources and the need for seawater desalination

Although water is the one of the most abundant substances on the planet, only 0.5% of natural water resources are freshwater. The global need for freshwater is increasing dramatically, while natural readily available freshwater resources, such as rivers, lakes and aquifers, are diminishing. Numerous freshwater supply options have been employed in the past, but they cannot meet the rising freshwater demands in all sectors (municipal, industrial, electrical, irrigation, etc.). Desalination of brackish water and seawater has received a great deal of attention over the years as a viable means of satisfying freshwater demands around the world. Population growth, urbanization, and industrialization appear to be the main drivers in recent years of the need for desalination, as a reliable technique for producing freshwater from a relatively low-quality water resource.

This book addresses seawater desalination processes, with a focus on sustainable approaches to providing freshwater. This chapter, in particular, describes the status of desalination systems, including the number of desalination plants installed around the world and their freshwater production capacities as well as other important factors such as feed water type, geographical parameters, and desalting technologies. This chapter also provides insights into the historical development of desalination, and the potential for driving desalination systems using sustainable energy resources. Using sustainable energy in seawater desalination systems has the potential to permit continuous freshwater production with low impacts on the environment.

Water covers roughly three-fourths of the surface of the earth and constitutes the most abundant substance on the planet (USGS, 2021a). In Table 1.1, water resources are classified based on salinity (total dissolved solids). Only 2.5% of the world’s water is freshwater and brackish water, and these resources are primarily found in lakes and rivers, polar regions, and ground water (USGS, 2021a). Of the 2.5% fresh/brackish water resources, about 70% is frozen in the form of glaciers, snows, and ices (USGS, 2021a). About 29.75% of freshwater and brackish water resources are found underground, usually in deep aquifers, while rivers and lakes contribute only 0.25% of overall freshwater and brackish water resources (USGS, 2021a). Fig. 1.1 shows a breakdown of water resources around the world.

Table 1.1

Data from (WHO, 2008; Kucera, 2019).

Fig. 1.1 Distribution of world’s water resources.

Population growth and industrialization are significantly increasing freshwater demand and this effect is expected to grow in the future. In addition, climate change and its effects are becoming more concerning and accelerating as industrialization and population grow, resulting in worsening droughts in many parts of the world. Pollution of water resources due to the activities of people and civilizations is another reason of freshwater shortages.

The uneven distribution of freshwater resources exacerbates the problem of water scarcity. Some regions such as Scandinavia, northern Russia, northern North America (Canada, Alaska), and central and southern coastal regions of South America have large freshwater resources (NRC, 2004). For example, Canada has 20% of the global freshwater resource (Government of Canada, 2018), yet it has less than 0.5% of total world population (Worldometer, 2021).

Around 70% of global water consumption is used for agriculture, 20% for industry, and 10% for domestic applications (The World Bank 2017).

There are several methods to measure water stress (e.g., the Falkenmark Indicator) with which current and projected future water stress levels can be described. The Falkenmark indicator is one of the widely used indexes for measuring water scarcity in an area. With this method, water scarcity is defined in terms of total water resources that are available to the population of an area. In fact, the water scarcity is measured through the amount of renewable water resources available for each person per year (Falkenmark, 1989). Renewable water supplies are water supplies that are continuously replenished. Renewable water sources include precipitation from the atmosphere (e.g., rain, snow) and water quantities transferred through streams, rivers, and shallow ground water. Note that renewable water resources do not include deep aquifers of water that are formed by precipitates over centuries. If the amount of renewable water for each person in a country is below 1700 m³ per year, that country is experiencing water stress. Also, if the amount of renewable water available for each person is below 1000 m³, the country is experiencing water scarcity and below 500 m³, absolute water scarcity (White, 2012).

Fig. 1.2 shows the global water stress for two years: 2019 and 2030. It is evident that the worldwide water scarcity is expected to increase over this time period. According to UN medium population projections (GRID-Arendal, 2009), 48 countries will encounter water stress by 2025, corresponding to 2.8 billion people (or 35% of the global population of 7.9 billion in 2021) facing water crises. The majority of these countries are in North Africa, south and middle East Asia, and the southern United States. Also, it is predicted that, by 2050, the number of countries facing water stress will reach 54 by 2025, corresponding to 4 billion people (GRID-Arendal, 2009).

Fig. 1.2 Global water stress in 2019 and 2030. Source: ( WRI Aqueduct, 2019) available at https://www.wri.org/applications/aqueduct/water-risk-atlas (accessed on 24 August 2021).

Approaches such as transferring freshwater from the water-rich areas to the water-poor areas, conservation, recycling/reuse of freshwater sources, and freshwater production using desalination can be employed to reduce water scarcities. Among these, desalination is recognized as a viable approach to meet freshwater demand around the world.

In terminology, the word desalination means remove salts from (MWD, 2021); however, desalination is conventionally defined as removing minerals and dissolved solids from water. The purpose of a desalination process is to clean saline water and thereby to provide water with an allowable limit of dissolved solids (around 500 ppm or less based on the World Health Organization (WHO, 2017)). Water can be classified into freshwater, brackish water, and seawater based on its salinity. Total dissolved solids are 500–1000 ppm for freshwater, 100–35000 ppm for brackish water, and 35,000–45,000 ppm for seawater (USGS, 2021b). The salinity of the feed water input to a desalination system varies depending on the feed water source, which can be saline aquifer, seawater, or wastewater.

Fig. 1.3 shows global desalination plants and their capacities and user sectors. It can be seen that the many of the desalination plants are installed in the United States, China, North Africa, the Middle East, and Australia. The majority of desalination facilities are located on coastlines, and desalination plants installed on and around coastlines are typically larger than inland desalination facilities. Most of the desalination plants dedicated to municipal applications are concentrated in the Middle East and North Africa (MENA) region, while most desalination plants for nonmunicipal applications are found in North America, Western Europe, East Asia, and Pacific regions. Fig. 1.4 shows the numbers and capacities of desalination plants, broken down by region. Around half of global freshwater is produced in the MENA region, with Saudi Arabia contributing 15% of global freshwater production, the United Arab Emirates 10%, and Kuwait 3.7%. The East Asia and Pacific regions have the next highest share of global freshwater production, due to large capacities in China (7.5%) and the United States (11.2%). About half of the freshwater production in Western Europe is associated with Spain, which is responsible for 5.7% of global freshwater production capacity. It is noteworthy that most of the desalination facilities are located in countries with relatively high incomes.

Fig. 1.3 Global share of operational desalination plants, with capacities and customer types. Source: ( Jones et al., 2019).

Fig. 1.4 Data on freshwater production facilities worldwide, broken down by geographical area: freshwater production capacity (in million m ³ /day) (outside ring); and number of freshwater production facilities (inside ring). Data from Jones et al. (2019).

The municipal sector is the largest freshwater user, consuming 62.3% of the total freshwater produced by desalination plants, while the industrial sector consumes 30.2% of the produced freshwater (Jones et al., 2019). The electrical and irrigation sectors, respectively, consume 4.8% and 1.8% of the total freshwater production from desalination plants (Jones et al., 2019).

Among desalination technologies, reverse osmosis (RO) systems are the most widely used, accounting for about 69% of installed desalination facilities. The next most common thermal desalination technologies are multistage flash (MSF) and multieffect desalination (MED), contributing 18% and 7%, respectively, of the total number of operational desalination plants around the world (Jones et al., 2019). In general, industrial desalination systems can be categorized as thermal (or phase change) processes such as MSF, MED, and mechanical vapor compression (MVC) and membrane-based (or single phase) process such as RO. Fundamentals and models of industrial desalination technologies are presented and discussed in Chapters 2 and 5.

1.2 History of desalination

In this section, the history is presented of the development and commercialization of currently used desalination systems. The history of desalination technologies is divided into three categories: MSF, MED, and MVC; solar stills and humidification–dehumidification (HDH); and membrane-based desalination systems, including RO and membrane desalination (MD).

1.2.1 History of MSF, MED, and MVC desalination systems

Historically, one of the first practices of desalination was on ships, which carried on to as late as 1800 (El-Dessouky and Ettouney, 2002). Single-stage stills were used in a batch mode to evaporate seawater with heat supplied by cock stoves. In such systems, condensation heat was not recovered. Instead sponges were used to absorb the material that evaporated.

The evaporation process developed further with progress in the sugar industry, leading to stills with enlarged scales and improved performance.

In the early of 20th century, the desalination industry progressed markedly. In Egypt, a six-effect desalination plant was installed, with a freshwater production capacity of 75 m³/day (El-Dessouky and Ettouney, 2002). Then, between 1929 and 1937, freshwater production capacities further increased, corresponding to the advent of the oil industry. Further improvements in and enlargements of desalination systems occurred from 1935 to 1960, a period that saw an annual freshwater production growth rate of 17% (El-Dessouky and Ettouney, 2002).

The historical development of thermal desalination systems in various regions is now described.

In 1957, a four-stage flash desalination plant (i.e., an MSF unit) was constructed by Westinghouse company in Kuwait (Al-Wazzan and Al-Modaf, 2001). At the same time, a patent by Silver led to a significant improvement in the performance of MSF systems, in which the number of stages was about three times the performance ratio (i.e., the ratio of freshwater produced to the steam used as a heat source to drive MSF system) (Al-Wazzan and Al-Modaf, 2001). In the Silver configuration, there was a considerably smaller specific heat transfer area for condensation compared to the Westinghouse configuration. This resulted in a significant reduction in the capital cost of plant, as the condenser tubes, which have a high cost, were substituted by inexpensive partitions in the MSF system.

In 1960, an MSF plant with 19 stages was installed in Shuwaikh, Kuwait. The freshwater production capacity was 4550 m³/day and the performance ratio was 5.7 (Al-Wazzan and Al-Modaf, 2001).

In 1959, the first antiscaling material known as Shuwaikh Mix or SALVAP was tested in a thermal desalination plant in Kuwait (Al-Falah and Al-Shuaib, 2001). Utilization of this polyphosphate-based material increased the operation time from 200–600 h to 8000 h. The operation of a desalination plant using Shuwikh Mix was limited to a top brine temperature (TBT) of 95 °C. Although scale formation was successfully eliminated, the desalination process operation exhibited some problems with performance ratio and productivity.

During 1960–1969, an improved MSF plant with 40 stages was installed in the Channel Islands, with a freshwater production capacity of 6800 m³/day (Al-Falah and Al-Shuaib, 2001). The performance ratio of this plant was enhanced from 10 to 12.5, representing the highest known performance ratio for an MSF desalination system. Furthermore, during this period of time, several developments were achieved such as acid cleaning, improved antiscaling chemical additives, feed deaeration, and cogeneration plant designs for seawater desalination.

In 1970–1979, advances were made in the construction and operation of desalination plants, in prevention and control of corrosion, and in chemical treatment. Furthermore, large desalination plants capacities were constructed in the 1970s in Japan, capable of freshwater production rates of 22,500–25,500 m³/day (El-Dessouky and Ettouney, 2002; Maciver et al., 2005).

In 1980–1989, a polymer-based antiscaling material was introduced which had advantages over polyphosphate-based materials, such as higher TBT operation (around 110 °C), which resulted in a higher freshwater production rate (27,200 m³/day) and performance ratio (about 8.65). Also, primary low-temperature single and multiple effect evaporation desalination processes were introduced in the 1980s. An MVC process is used in the single-effect desalination system, and a thermal vapor compression process in MED. The relatively low-temperature operation of single and MED systems allows for the use of inexpensive aluminum alloys and leads to reduced scaling phenomena during desalination.

Further enhancements and improvements in both MSF desalination and MED systems were made since 1995, in which a plant factor of 90% and continuous plant operation of 2–5 years were attained.

From 1990 to the present, there has been a tendency to shift from MSF desalination systems to MED systems. For instance, from 2001 to 2003, two MED units with a thermal vapor compressor (TVC) replaced an aging MSF system in Japan (Maciver et al., 2005). Each MED unit was able to produce 100 m³/day freshwater, and consisted of four effects, three tubular type preheaters and a tubular condenser within each evaporator. Titanium-pressed plates were used in the evaporators (Fig. 1.5). For each plate, falling-film evaporation occurs on one side and condensation on the other side. The steam enters from the top on the condensation side and condenses while moves down the plate and collected in the distillate headers on the bottom. The feed seawater flows down on the evaporation side of the pressed plate, absorbs the latent heat of condensation of the steam, and partially evaporates. The remaining part of the feed (brine stream) moves down and collects on the bottom. The generated steam is transferred into the next effect where it condenses and releases its latent heat. The plant was placed outdoors but, to prevent any effects due to weather changes between summer and winter, the plant was insulated completely. Fig. 1.6 shows a photograph of the MED plant installed in Japan.

Fig. 1.5 Left: Pressed plate falling film configuration used in the effect of the MED system (modified from Maciver et al. (2005)). Right: Plate pack arrangement in the evaporator of the MED system installed in Japan (from Maciver et al., (2005)).

Fig. 1.6 View of MED desalination plant built in 2003 in Japan. Source: ( Maciver et al., 2005).

Between 1960 and 1980, most of the large capacity thermal desalination systems installed in the Middle East were of the MSF kind. Although MSF desalination plants exhibited large freshwater production capacities, using a TVC in MED desalination plants led to energy efficient and competitive thermal desalination plants. The TVC module in MED plants increases freshwater production capacity, reduces brine temperature, and reduces the amount of steam heat source used to drive the MED unit. MED-TVC desalination plants are thermodynamically efficient owing to their lower operation temperatures and lower pressure drops at high vapor flow rates. In recent decades, issues surrounding fossil fuel resources, their costs, and environmental impacts have led to significant developments in cogeneration plants. But, the capability of MED-TVC plants to be driven by low-cost/low-grade energy or waste heat has often made them more favorable than MSF desalination systems.

1.2.2 History of solar still and HDH desalination systems

The idea of dehumidification of humid air comes from natural/artificial caves where the cool stones act as a dehumidifier to condense the moisture in humid air (Seifert et al., 2013). The solar still can be treated as a predecessor of the HDH desalination process. Solar stills are considered one of the first human-made desalination technologies, dating back to the 19th century. In a conventional solar still, a basin is filled with seawater or brackish water. The basin is commonly painted black to increase solar energy absorption. Fig. 1.7 shows a solar still desalination system. A transparent tilted cover (typically glass or plastic) is used to close the basin and form a greenhouse effect, creating a heat trap. Solar radiation passes through the glass and heats the seawater, vaporizing a part of it. The humid air carrying the produced vapor is condensed on the inner surface of the glass, which has a lower temperature than the seawater in the basin. On the surface of glass, the latent heat of condensation is transferred to the air. The condensed distillate drops and collected. In fact, in solar stills the area close to the surface of the seawater acts as a humidifier and the glass surface acts as a dehumidifier.

Fig. 1.7 Solar still desalination system.

In 1872, a noteworthy solar still was built in Las Salinas, Chile (Delyannis, 2003). The solar still had a cover area of 4700 m² and a freshwater production capacity of 4.9 kg/m² of glass surface area. The plant operated for more than 40 years (Delyannis, 2003; Mahian et al., 2015). As noted earlier, HDH desalination processes originated from solar still desalination systems. The thermal inefficiencies in solar stills, such as those due to natural convection and infrared radiation from the warm brine to the condenser surface, reduce the brine temperature and result in the need for a large solar collector area for producing freshwater. These thermal inefficiencies also lead to a low gained output ratio (GOR), which is defined as the ratio of the latent heat of evaporation of the freshwater produced to the total heat input. As an alternative, using separate components for each thermal process leads to better thermal efficiencies. HDH desalination systems were designed to allow for better flexibility in thermodynamic design of the vaporization and condensation processes. Consequently, main advantages of HDH over solar still desalination are a relatively higher GOR and a lower required area for freshwater production.

During 1962–1965, University of Arizona investigated the technical feasibility of a small pilot plant for a solar multieffect HDH desalination, which was subsequently built in Puerto Peñasco, Mexico (Hodges and Kassander Jr, 1962; Hodges and Thompson, 1966). The solar collectors used in the HDH desalination system were of the double-glazed type, with two plastic covers and a small air gap between them to reduce convection heat loss. The collectors have a surface area of 292 m² and include a basin slightly filled with seawater. Fig. 1.8 shows a flow diagram and view of the constructed solar HDH desalination system in Puerto Peñasco, Mexico. Seawater is heated in the collectors to 65 °C and stored in the storage tank, which enables 24-h operation. Then, the seawater is pumped from the storage to the evaporator of the evaporation/condensation tower located at a height of 13 m. The evaporation/condensation tower comprises two compartments, one for evaporation of seawater (the humidifier) and another containing finned aluminum condensing tubes (the dehumidifier). The heated seawater enters the top of the evaporator and heats and humidifies air rising from below. The saturated air moves from the evaporator to the condenser compartment and the latent heat of condensation preheats the feed seawater entering at 25 °C. The plant was designed to yield 18 m³/day of freshwater in the summer.

Fig. 1.8 Early solar driven humidification–dehumidification desalination plant in Puerto Peñasco, Mexico. From Hodges et al. (1964).

1.2.3 History of membrane-based desalination systems

The initial idea of using membranes in desalination systems was drawn from biological membranes such as skin, lungs, and cell membranes. The elementary separation process is based on the difference in particle size (e.g., separation of fine grains from coarse grains). Furthermore, the membrane-based separation process was developed based on differences in diffusion rates of diverse constituents through the membranes. The concepts of osmosis (solvent passage through a membrane from low to high concentration) and dialysis (solvent passage through a membrane from high to low concentration) were explained by Dutrochet (1995), Graham (1858), and Fick (1995,1855). The concept of using seawater as a source for freshwater was introduced by Hassler (1949,1950), and expanded on subsequently (Hassler and McCutchan, 1960), but his idea was not successful in practice. Nonetheless, other scientists carried on with research following Hassler’s concept, leading to the development of present-day membranes.

Reid and Brenton (1959) introduced early cellulose acetate RO membranes in 1959 at University of Florida. A permeator was developed to measure the semipermeability of RO membranes. The permeator is a container divided into two by a semipermeable membrane (Fig. 1.9). In a permeator, pressure is applied via compressed air to the feed solution. The pressurized feed passes through the membrane and is collected at the bottom of the permeator, and then its constituents are determined. The salt rejection percentage was used as a measure of semipermeability. Although a salt rejection of 98% with 0.10M sodium chloride was obtained at pressures up to 5860.5 kPa, the permeate flux value was very low (around 0.5–4 µL/cm²h) (Reid and Breton, 1959). To address this issue, the cellulose acetate RO membrane was subsequently modified by Loeb and Sourirajan (1963, 1960) to produce practical amounts of permeate while maintaining high-levels of salt rejection.

Fig. 1.9 Apparatus for measuring the semipermeability of imperfect osmotic membranes. Modified from ( Reid and Breton, 1959).

A major breakthrough in membrane technology was achieved when Loeb and Sourirajan (1960,1963) made a cellulose acetate polymer membrane that was homogeneous but physically asymmetric. Fig. 1.10 shows an early RO desalination system developed at the University of California, Los Angeles by Loeb and Sourirajan (1960,1963). In preparation of the casting solution, aqueous magnesium perchlorate was used, which acted as a pore former (or swelling agent). The presence of a swelling agent was found to be necessary, as water molecules could be absorbed into the polymer to form sufficiently large pores for a practical RO desalination process. The first practical RO membranes, which exhibited high salt rejection and permeate flux rates due to the porous structure in a thin surface, resulted from the efforts of Loeb and Sourirajan. In the 1980s, cellulose-based RO MD systems were used for industrial processes. Nonetheless, there were some drawbacks associated with these types of membranes, which fostered research into new types of membranes.

Fig. 1.10 Early reverse osmosis desalination system developed at University of California, Los Angeles by Loeb and Sourirajan (1960, 1963).

In the mid-1960s, two chemical companies, Dow and Dupont, focused on the development of hollow fiber MD modules. Dow focused on cellulose acetate fibers (Mahon, 1966), while Dupont was involved with polyamides. In 1985, Dupont developed a hollow fiber membrane from aromatic polyamide. Note that early studies on aliphatic compounds (Richter et al., 1971) in part led to the development of aromatic polyamide hollow fibers. In1971–1973, aromatic polyaramid hollow fine fibers known as Permasep B-9 and B-10 permeators were introduced by Dupont for brackish water and seawater desalination, respectively (Eckman et al., 1994; Richter et al., 1971). After 20 years, these two permeators were commercialized and became standards for freshwater production with appropriate quality. In1994, a new double bundle permeator known as TWIN was developed and commercialized by Dupont based on optimized bundle design and flow patterns (Eckman et al., 1994). Fig. 1.11 shows the flow pattern of the TWIN permeator. The permeate flow is increased by increasing the length of fiber, while reducing the length of fiber lowers costs and reduces salt passage (Eckman et al., 1994). The high performance of these polyamide membranes encouraged their adoption by industries over cellulose-based membranes.

Fig. 1.11 Tubular membrane filtration module.

In 1961, a tubular membrane configuration was developed for casting membranes inside cylindrical fiberglass tubes (Glater, 1998). The tubular configuration served two functions: a tube surface to support the membrane and a tube wall to serve as a pressure vessel. The membrane is located at the inner side of the tube and the saline water flows inside the tube. Permeate passes across the membrane and reaches the surface of the tube. The tubes are porous to allow permeate transfer from the inside to the outside of the tube. Fig. 1.12 shows a tubular membrane used in RO desalination. Tubular membranes were modified later by Loeb (1966), who used techniques such as solution casting, membrane tube casting, wrapping, applying seals and end fittings and heating of the assembly to fabricate a composite tubular assembly for RO desalination. The methods used by Loeb were previously developed at the University of California, Los Angeles for flat sheet acetate cellulose membranes.

Fig. 1.12 Flow pattern of hollow fiber TWIN permeator developed and commercialized by Dupont in 1994. Based on Eckman et al. (1994).

Around 1975, a spiral wound polyamide thin film composite membrane was introduced (Channabasappa, 1975). Enhancements of this membrane continued until 1989 for higher salt rejection and higher permeate production. Fig. 1.13 shows a simplified schematic of a spiral wound reverse membrane. It consists of number of membrane envelopes attached with a porous spacer wound around permeate collection tube. By 2000, both spiral wound and hollow fiber RO membrane configurations were commercialized and used for large-scale seawater desalination, permitting the production of more than two billion gallons of freshwater per day.

Fig. 1.13 Simplified schematic of a spiral wound reverse osmosis membrane.

Due to the high capital cost of tubular configuration of RO membrane systems, they are used only for specific applications such as industrial waste treatment. Nowadays, most RO desalination plants employ polyamide membranes rather than tubular and spiral wound membranes. This is mainly due to the lower specific energy consumption (i.e., energy use per unit freshwater production) of polyamide membranes compared to other types of membranes. For current RO membranes, the energy consumption typically is 2–5 kWh/m³. Nonetheless, research to develop a better performing, chlorine- and fouling-resistant membrane carries on.

1.3 Review of sustainable energy technologies

Renewable energy can be defined as naturally persistent and repetitive flows of energy that occur in the environment. Renewable energy technologies are devices for harvesting energy from such energy flows. In contrast, nonrenewable energy resources (sometimes referred to as brown energy resources) are finite in extent, usually in static underground stores that can be released by human