[sustainability science and engineering] sustainable water for the future: water recycling versus...

CHAPTER22Global Desalination SituationSabine Lattemann1,�, Maria D. Kennedy2,Jan C. Schippers2 and Gary Amy2

1Institute for Chemistry and Biology of the Marine Environment (ICBM),University of Oldenburg, Oldenburg, Germany2UNESCO – IHE Institute for Water Education, Delft, The Netherlands

Contents

1. Introduction 72. Historical Development 83. Global Installed Desalination Capacity 11

3.1. Projected Growth of the Desalination Market 113.2. Global capacity by source water type 113.3. Global capacity by process 113.4. Global capacity by use type 123.5. Global capacity by plant size 143.6. Costs and energy demand of desalination processes 14

4. Regional Desalination Situation 174.1. The Gulf region 194.2. The Red Sea 194.3. The Mediterranean Sea 194.4. Other regions 23

5. Environmental Concerns of Seawater Desalination 245.1. Intakes 265.2. Discharges 265.3. Energy demand 315.4. Impact mitigation measures 34

6. Summary and Conclusion 35References 38

1. INTRODUCTION

Seawater and brackish groundwater have become the most importantsources of drinking water in a few arid countries of the Middle East, such asKuwait or the United Arab Emirates, which depend heavily ondesalination. Many industrialized and developing regions, however, have

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Sustainability Science and Engineering, Volume 2 ISSN 1871-2711, DOI 10.1016/S1871-2711(09)00202-5r 2010 Elsevier B.V. All rights reserved.

7

recently also started to use desalination as a way to supplement and diversifytheir water supply options. Until a few years ago, desalination plants werelimited to the water-scarce but oil-rich countries of the Middle East andNorth Africa, and to some tropical and subtropical islands. Today,desalinated water has become a commodity for many countries in orderto satisfy their growing demand for water.

For the ‘‘pioneering’’ countries, the driving factors were often a lack ofsurface and groundwater resources, coupled with sufficient natural orfinancial resources to engage in energy-intensive and costly desalinationprojects. For the newly emerging desalination markets, driving factors aremore diverse, including economic and demographic growth, prolongeddroughts, climate change, or declining conventional water resources interms of quality and quantity due to overuse, pollution, or salinization.Moreover, as conventional water production costs have been rising in manyparts of the world and the costs of desalination – particularly seawaterdesalination – have been declining over the years, desalination also becomeseconomically more attractive and competitive (Fig. 1).

This chapter gives a short account of the historical development ofdesalination technologies, an overview on the presently installed worldwidedesalination capacity, distinguishing between different raw water sources,processes and use types. It furthermore discusses regional and future trends,driving factors such as cost and energy demand, as well as concerns, such asthe environmental impacts of the discharges into the sea.

2. HISTORICAL DEVELOPMENT

The extraction of salt from salty water by means of natural evaporation hasbeen practiced for a long time, dating from the time when salt, not water,was the precious commodity [1]. Advanced technologies that mimic naturalprocesses such as evaporation or osmosis in order to extract the water haveonly been developed in modern times. Basic desalting processes were firstused on naval ships in the 17th to 19th centuries. The island of Curac-ao inthe Netherlands Antilles was the first location to make a majorcommitment to desalination in 1928, followed by a major seawaterdesalination plant built in what is now Saudi Arabia in 1938 [1,2].

A major step in the development of desalination technologies cameduring World War II in order to supply water to military establishments inarid areas. After the war, the potential of desalination was recognized andmore research work was continued in various countries. The Americangovernment, through creation and funding of the Office of Saline Water

8 Sabine Lattemann et al.

(OSW) in the early 1950s and its successor organization, the Office ofWater Research and Technology (OWRT) in 1974, helped to providemuch of the basic research and development of the different desaltingtechnologies [2,3].

Many of the early projects focused on thermal processes. Significantwork was completed on construction materials, heat transfer surfaces, andcorrosion, which was instrumental in assisting the design and constructionof the first large distillation systems in the Middle East [2]. The multieffect

Figure 1 Water resource cost trends in the desalination market in US$ per cubicmeter. Top: Total installed capacity and water price development. Bottom:Differentiated between water source type. Adapted from Ref. [6].

Global Desalination Situation 9

distillation (MED) process has been used in industry for a long time,traditionally for the production of sugar and salt. Some of the earlydistillation plants also used the MED process; however, the multistage flash(MSF) process that was developed in the 1950s continually displaced theMED process due to a higher resistance against scaling. A revived interest inMED can be observed since the 1980s due to a lower operatingtemperature and energy demand of the process [3].

During the late 1950s, the first asymmetric membrane for desalinationwas developed by Loeb and Sourirajan, which consisted of cellulose acetatepolymer [4]. The electrodialysis (ED) process, which was commerciallyintroduced in the early 1960s, moves salts selectively through a membranedriven by an electrical potential. It was the first cost-effective way to desaltbrackish water and spurred a considerable interest in using desaltingtechnologies for municipal water supply, especially in the United States. EDis exclusively applied to low brackish and fresh water desalination, since theenergy consumption for seawater treatment would be far too high. Othermilestones included the commercialization of reverse osmosis (RO), apressure-driven membrane process, in the early 1970s [3], followed by thedevelopment of a more robust composite aromatic polyamide spiral woundmembrane in the 1980s [4].

Although a wide variety of membrane materials and moduleconfigurations have been developed over the years, including hollow finefibers from cellulosic or noncellulosic materials, composite aromaticpolyamide membranes in spiral wound configuration are almost exclusivelyused in modern RO plants today. While cellulose acetate seawatermembranes had a specific permeate flux of 0.5 L/(m2 h bar) and a saltrejection of 98.8% in the 1970s, the latest polyamide seawater membraneshave a specific flux of more than 1.2 L/(m2 h bar) and a salt rejection of99.8%. The improvement in specific flux translates into a significantreduction of the specific energy demand of the RO process [4]. Anothersignificant power and cost reduction stems from the development of energyrecovery devices, which result in a total energy demand of 3–4 kWh/m3 ofpermeate water using state-of-the-art technology.

To conclude, it took about 50 years to evolve from the first land-baseddistillations plants into a fully developed industry in the 1980s. By the1990s, the use of desalting technologies for municipal water supplies hadbecome commonplace [3]. Today, municipalities are the main end users ofdesalinated water and the market continues to grow exponentially, with adoubling of the installed capacity expected from 2006 to 2015. RO hasemerged as the most important desalination process today (Section 3, [5,6]).In 1969, the world’s largest RO system in operation was a 380 m3/day


brackish water plant in Dallas, Texas [7]. Today, the largest seawater ROplant produces 330,000 m3 of water per day, the equivalent of 132Olympic-size swimming pools, using 27,000 membrane elements with anactive surface area of about 99 ha (or 200 football fields), which need to bereplaced every 3–7 years. Currently, the membrane market is estimated tohave current sales in excess of US$ 500 million per year, and an annualmarket growth at about 16% annually [7].

3. GLOBAL INSTALLED DESALINATION CAPACITY

The worldwide installed desalination capacity is increasing at a rapid pace.The latest figures from the 20th International Desalination Association(IDA) Worldwide Desalting Plant Inventory [5] indicate that theproduction capacity of all desalination plants worldwide was around 44.1million cubic meters per day (Mm3/day) by the end of 2006. This figureincludes all facilities listed in the inventory that treat seawater, brackishwater, river water, wastewater, brine, and pure water, which are either inconstruction, online, or presumed online.

3.1 Projected Growth of the Desalination MarketThe worldwide installed capacity grew at a compound average rate of 12% ayear over the past 5 years, and the rate of capacity growth is expected toincrease even further. Based upon country-by-country analysis involvingdesalination projects and official data on water supply and demand fromagencies around the world, it is projected that the installed capacity willpresumably reach 64 Mm3/day by 2010 and 98 Mm3/day by 2015 (Fig. 2) [6].

3.2 Global capacity by source water typeMuch of the expected growth of the desalination market will take place in theseawater sector, although brackish water and wastewater desalination processeswill presumably become more important in the future. Only 5% of the totalvolume of 44.1 Mm3/day presently comes from wastewater sources, 19% isproduced from brackish water sources, and 63% from seawater sources(primary data from Ref. [5]). Desalination of seawater is hence the dominantdesalination process and accounts for a worldwide water production of27.9 Mm3/day (Fig. 3, top). For illustration, this is a volume comparable to theaverage discharge of the Seine River at Paris (average flow of 28.3 Mm3/day).

3.3 Global capacity by processAll source water types included, RO is the prevalent desalination process. Itaccounts for slightly more than half (51% or 22.4 Mm3/day) of the globalcapacity (Fig. 3, second row). Forty percent or 17.7 Mm3/day of the global


production of desalinated water comes from distillation plants, eitherusing the MSF or the MED process, with relative market shares of 32%(14 Mm3/day) and 8% (3.7 Mm3/day), respectively. Other minor desalina-tion processes include the membrane-based nanofiltration (NF) and EDprocess with about 4% market share each (2 and 1.6 Mm3/day, respectively).

The picture changes if one distinguishes between the different sourcewater types. Thermal desalination processes account for 61% (17.2 Mm3/day)of the production in all desalination plants that use seawater as raw watersource, of which 50% is produced in MSF plants. Only 35% of the watercomes from RO seawater desalination plants. On the contrary, RO accountsfor 84% (6.9 Mm3/day) and 79% (1.7 Mm3/day) of the production inbrackish water and in wastewater applications, respectively, whereasdistillation processes play a negligible role in brackish water (o2%,0.1 Mm3/day) and a minor role (13%, 0.3 Mm3/day) in wastewaterdesalination (primary data from Ref. [5]).

3.4 Global capacity by use typeAll source water types included, desalinated water is mainly used formunicipal and industrial purposes: 70% (31 Mm3/day) of the globallydesalinated water is used by municipalities and 21% (9 Mm3/day) byindustries (Fig. 3, third row). Other end users include the power generationindustry (4%), irrigation (2%), military (1%), and tourism (1%).

Again, the picture is different if one distinguishes between the differentsource water types. Municipalities are also the main end users of desalinated

Figure 2 Projected growth of the desalination market (including seawater, brackishwater, river water, wastewater, brine, and pure water desalination processes). Theinstalled capacity was 44.1 Mm3/day in 2007 [5] and is expected to more than doubleby 2015. At that time, 38 Mm3/day will presumably be installed in the Gulf region and59 Mm3/day in the rest of the world [6].


Figure 3 Global desalination capacities (in Mm3/day and %) by source water type(top row), by process and source water type (second row), by use type and sourcewater type (third row). Data analysis based on primary data from Ref. [5].Abbreviations: RO, reverse osmosis; MSF, multistage flash distillation; MED, multieffectdistillation; NF, nanofiltration; ED, electrodialysis; XLZ50,000 m3/dayWLZ10,000 m3/dayWMZ1,000 m3/dayWS (see plate 1 in color plate section at the end of this book).


sea and brackish water and account for 83% (23.2 Mm3/day) and 61%(5 Mm3/day) of the production, respectively, and 20% of the production ofrepurified wastewater. As one moves from seawater to brackish water andwastewater, the share of municipal use decreases, while the share of industrialuse increases. The latter accounts for 12% of the production from seawater,23% of the production from brackish water sources, and is the primary userof repurified wastewater: 39% (0.8 Mm3/day) is used for industrial purposesplus an additional 12% is used by the power industry. Irrigation is only thesecond most important use of repurified waste water with a share of 27%(0.6 Mm3/day) after industrial use (39% of the wastewater) (primary datafrom Ref. [5]).

3.5 Global capacity by plant sizeForty-nine percent of the desalinated water is produced by very large facilitieswith production capacities of 50,000 m3/day or more (‘‘XL-sized’’ plants,Fig. 3, last row). The share of production in very large facilities is even higherin the seawater sector, where 66% (18.2 Mm3/day) of the water is produced inonly 122 industrial-sized plants. On the other end of the scale, about 1660small seawater desalination facilities with production capacities of less than1000 m3/day account for only 2% (0.6 Mm3/day) of the production. Theplant size distribution is a bit more homogeneous in the brackish (BW) andwastewater (WW) sectors, where 24% (BW) and 27% (WW) of the water isproduced in XL-sized plants, where large plants account for 34% (BW) and36% (WW) of the production, medium plants for 33% (BW) and 32% (WW)of the production, and small plants for 9% (BW) and 5% (WW) of theproduction, respectively (primary data from Ref. [5]).

To conclude, most of the desalinated water today is produced inindustrial-sized facilities. These include the large thermal distillation plants inthe Middle East with production capacities up to 1.6 Mm3/day. Outside theMiddle East region, seawater reverse osmosis (SWRO) is the dominantprocess that finds application. Majority of the SWRO plants (59%) are small(o1000 m3/day) and account for only 5% of the worldwide production of9.4 Mm3/day, while 2% or 42 large facilities (Z50,000 m3/day) account foralmost (45%) half the worldwide production. The largest RO plant currentlyproduces 330,000 m3/day and a few RO projects up to 500,000 m3/day arebeing planned.

3.6 Costs and energy demand of desalination processesThe rising costs of conventional water production (Fig. 1) that are observedin some parts of the world are caused by increasing technical expenditure


and costs for treating water from conventional sources and for transportingwater over long distances. The water production costs have risen –depending on the country, supply, demand, and technology – to US$1–1.5 m�3. At the same time, the cost of drinking water from desalinationhas been decreasing, in some places even below the cost of conventionalwater production. The causes included improved design and technology,especially of RO processes, the adaptation of facilities to local demand, orthe use of cheapest energy sources [8].

The average investment cost required for engineering, procuring, andconstructing a MSF distillation plant is US$ 1235 per cubic meter and dayinstalled capacity. The capital costs for MED and SWRO plants are lower,with an average of US$ 916 and US$ 641 per cubic meter and day installedcapacity, respectively. The average production costs of desalinated seawaterare in the range of US$ 0.45–0.60 m–3 (Fig. 4) [6]. This includes thereplacement of parts and membranes, chemicals for pretreatment of theintake water, plant cleaning and posttreatment of the product water, laborcosts, and – as the most important cost factor – energy demand. With

Figure 4 Relative operation costs in US$ of the main desalination processes. Adaptedfrom Ref. [6].


current energy prices on the increase, desalination may again become amore costly water supply option in the future.

The amount of energy needed for water production is process-dependant: MSF plants, having a maximum operating temperature of120 1C, require about 250–330 MJ/m3 of thermal and 3.5 kWh of electricalenergy for the production of 1 m3 of water. MED plants, which operate attemperatures below 70 1C, require 145–390 MJ/m3 of thermal and1.5 kWh of electrical energy per cubic meter of water. Seawater ROrequires less energy than distillation processes. The energy demand ofSWRO plants depends on the process design and equipment used(Table 1). The use of low-energy membrane elements, variable frequencypumps, and pressure exchangers can significantly reduce the specific energydemand of a plant. While older plants without energy saving equipmentmay still require about 5 kWh/m3, modern plants usually achieve a totalenergy demand of 3–4 kWh/m3. For example, the Spanish NationalHydrological Plan assumes a total energy value of 4 kWh/m3 under theassumption that plants are equipped with state-of-the-art technologies [9].The Affordable Desalination Collaboration operated a demonstration plantin California over 2 years using state-of-the-art, off-the-shelf technologyand set a world record in specific energy consumption of 1.58 kWh/m3

with a low-energy membrane operated at 42% recovery, but at the expenseof permeate water quality. The energy demand therefore also depends onthe required permeate water quality. For example, employing a second ROpass for boron removal will increase the energy demand. The specific

Table 1 Energy data of RO, MSF, and MED

Reverseosmosis (RO)

Multistageflash (MSF)

Multieffectdistillation (MED)

Operatingtemperature[2,8]

Below 45 1C Below 120 1C Below 70 1C

Main energysource [8]

Electricalenergy

Steam (heat) Steam (heat)

Thermal energydemand [8]

None 250–330 kJ/kg

145–390 kJ/kg

Electrical energydemand [2]

2.5–7 kWh/m3 3–5 kWh/m3 1.5–2.5 kWh/m3


energy demand for SWRO plants usually increases with recovery, but thetotal energy demand decreases with the recovery rate as less feedwater mustbe pumped and treated to obtain the same volume of permeate at a higherrecovery. Therefore, it is important to analyze the desalination process as awhole, and not just the SWRO-specific energy demand. At the mostaffordable point for a 190,000 m3/day plant, total treatment energy in therange of 2.75–2.98 kWh/m3 was demonstrated [10].

4. REGIONAL DESALINATION SITUATION

Forty-eight percent (21.0 Mm3/day) of the global desalination productiontakes place in the Middle East, mainly in the Gulf country states(19.3 Mm3/day). Nineteen percent of the desalinated water is producedin the Americas (8.2 Mm3/day), 14% in the Asia-Pacific region (6.2 Mm3/day), 14% (6.0 Mm3/day) in Europe, and 6% in Africa (2.8 Mm3/day,Fig. 5, primary data from Ref. [5]).

Except for one region, seawater desalination is the prevalent process.Sixty-one percent (17.1 Mm3/day) of the global seawater desalinationcapacity is located in only six GCC countries, including Saudi Arabia,the United Arab Emirates, Kuwait, Bahrain, Qatar, and Oman. Another11% (2.9 Mm3/day) of the global seawater desalination capacity is locatedin Southern Europe and 7% (2.0 Mm3/day) in North Africa. Threeenclosed sea areas therefore account for the lion’s share of the globalseawater desalination capacity – the Gulf, the Red Sea, and theMediterranean Sea.

North America is the only region where brackish water desalination isthe dominating process. The production capacity is 3.0 Mm3/day, whichrepresents more than one-third (36%) of the global brackish waterdesalination capacity. Twenty-one percent of the production from brackishwater sources takes place in the GCC states (1.7 Mm3/day) and 13%(1.1 Mm3/day) in Southern Europe.

Wastewater purification is also primarily practiced in North America (22%or 0.49 Mm3/day), closely followed by East Asia (21% or 0.46 Mm3/day)and the GCC country states (19% or 0.42 Mm3/day). Each of these threeregions accounts for roughly one-fifth of the global wastewater treatmentcapacity, followed by Japan, Korea, and Taiwan (12%) and Southern Europe(10%).

In the following, emphasis will be given to the Gulf, the Red Sea, andthe Mediterranean Sea and the installed seawater desalination capacity inthese sea regions.


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4.1 The Gulf regionIn terms of sea areas, the largest number of seawater desalination plants can befound in the Gulf with a total desalination capacity of approximately12.1 Mm3/day – or a little less than half (44%)1 of the worldwide dailyproduction (Fig. 6). The main producer in the Gulf (and worldwide) isSaudi Arabia with 25% of the worldwide seawater desalination capacity, ofwhich 11% are located on the Gulf shore and 12% on the Red Sea coast(2% unaccounted for), followed by the United Arab Emirates (23%) andKuwait (6%).

Thermal desalination processes dominate in the Gulf region (about 94%of all production), as water and electricity are often generated by largecogeneration plants that use low value steam and electricity from powerplants as a heat source for desalination. Most of the water (81%) in the Gulfis produced by the MSF distillation process. Minor processes are MEDdistillation and RO, which account for 13% and 6% of the production,respectively (primary data from Ref. [5]).

4.2 The Red SeaIn the Red Sea region, desalination plants have a combined productioncapacity of 3.6 Mm3/day (13% of the worldwide capacity, Fig. 7). Similar tothe Gulf, most of the water is produced by large cogeneration plants,mainly on the Saudi Arabian coast in the locations of Yanbu, Rabigh,Jeddah, Assir, and Shoaiba, where the world’s largest desalination complexwith a capacity of 1.6 Mm3/day is located. Saudi Arabia accounts for morethan 92% of the desalinated water production from the Red Sea, with2.6 Mm3/day (78%) produced by thermal plants. Egypt, the second largestproducer of desalinated water in the region, accounts for only 7% of theproduction from the Red Sea, with 90% (0.2 Mm3/day) coming fromsmaller RO plants on the Sinai Peninsula and in the tourist resorts along theRed Sea coast.

4.3 The Mediterranean SeaIn the Mediterranean, the total water production from seawater is about4.0 Mm3/day (14% of the worldwide capacity, Fig. 8). Spain, with about8% of the worldwide desalination capacity, is the largest producer ofdesalinated water in the region with an installed capacity of 2.2 Mm3/day.About 65% (1.4 Mm3/day) of the Spanish capacities are located on the

1The figure of 44% includes only those plants located on the shores of the Gulf. In contrast to the figure of61%,which is given for the GCC states above, the figure of 44% does not include plants in Oman and on theRed Sea coast of Saudi Arabia, but it does include plants in Iran.


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Mediterranean coast and the Balearic Islands, and 25% on the CanaryIslands. The Spanish A.G.U.A. program2 will further augment water supplyon the Mediterranean coast by increasing the desalination capacity to over2.7 Mm3/day until 2010. While thermal processes are dominating in theGulf and Red Sea, 70% of the Mediterranean and 99% of the Spanish

Figure 7 Cumulative MSF, MED, and RO capacities in the Red Sea in cubic meters perday by site location (dots) and by country (triangles). The map shows all sites with aninstalled capacity Z1000 m3/day and displays sites with a capacity Z100,000 m3/dayby name and capacity. The map was first published in Ref. [17,28] and updated usingraw data from Ref. [5] (see plate 4 in color plate section at the end of this book).

2The program ‘‘Actuaciones para la Gestion y la Utilizacion del Agua’’ was introduced by the Spanishgovernment in 2004 following the decision not to divert the Ebro river to Southern Spain. The package ofmeasures includes desalination but also water saving and efficiency of use and water reuse.


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production on the Mediterranean coast is produced by the process ofSWRO.

Larger numbers of distillation plants are only found along the coasts ofLibya and Algeria in North Africa, and also in Italy. However, new plants inthese countries are also often SWRO plants. A tremendous expansion ofcapacities is currently taking place in Algeria, North Africa’s fastest growingdesalination market, where the first large SWRO plant (200,000 m3/day)was opened in February 2008 [11]. It is the first in a series of other projectswith capacities between 50,000 and 500,000 m3/day, which will increasethe country’s desalination capacity to 4 Mm3/day by 2020 [2].

On the Mediterranean coast of Israel, two large SWRO are currently inoperation, the Ashkelon plant with a capacity of 330,000 m3/day – theworld’s largest SWRO project to date – and the Palmachin plant(83,000 m3/day). Desalination presently accounts for approximately 8% ofIsrael’s water supply. According to original plans, this would have beenincreased to more than 30% (1.8 Mm3/day) by 2020 [12]. In 2008,however, the Israeli government approved a new, even more ambitiousemergency program to address the country’s growing water shortage,which will raise the target for desalinated water production to 1.6 Mm3/dayby 2013 and to 2.1 Mm3/day by 2020, which may also reach 2.7 Mm3/daydepending on water demand and other alternatives [13]. Several largeSWRO desalination plants with capacities up to 274,000 m3/day arecurrently being planned along Israel’s Mediterranean coast [14]. Further-more, it is planned to sharply increase the use of the country’s brackishwater resources, from presently around 16,500 m3/day to somewherebetween 220,000 and 274,000 m3/day [15]. Other measures include morewater efficient practices, fixed water quotas, greater enforcement of waterrestrictions, and upgrading wastewater treatment capacities in order toincrease recycling of wastewater from 75% at present to 95% in 5 years [13].

4.4 Other regionsWhile seawater desalination is already a well-established technology in theabove-mentioned sea regions, the era of large-scale desalination projects isabout to start in other parts of the world, such as California, Australia, orChina, just to name a few.

In California, a potential for 15–20 new desalination projects is expecteduntil 2030 with a combined production of 1.7 Mm3/day (Fig. 9). The twomost advanced and largest projects are the 200,000 m3/day facilities inCarlsbad and Huntington Beach, which will presumably start operation in2009 [5].


In Australia (Fig. 10), the first large SWRO plant with a capacity of144,000 m3/day became operational in Perth in 2006. Another projectcurrently under construction is the Sydney plant with an initial capacity of250,000 m3/day, which can, if necessary, be expanded to 500,000 m3/day.Further projects include the Melbourne, Brisbane, and South EastQueensland plants, with projected capacities up to 400,000 m3/day each,and projects in Adelaide, the Upper Spencer Gulf, and a second plant nearPerth, with capacities between 120,000 and 140,000 m3/day each.

A third impressive example is China. The country is expected todramatically expand its desalination capacity and might establish itself asanother important market in the near future. In order to alleviate expectedsevere water shortages, China’s desalination capacity may be increased 100-fold by 2020 – i.e. from presently around 366,000 m3/d to 36 Mm3/d.Besides desalination of seawater, wastewater treatment is a serious optionunder consideration [2].

5. ENVIRONMENTAL CONCERNS OF SEAWATERDESALINATION

The desalination industry has undergone many gradual changes sinceits beginnings in the early 1960s. Today, the trend is towards large,

Figure 9 Seawater desalination projects in California (green: in operation orconstruction, blue: in planning). Adapted from Ref. [25].


industrial-sized facilities with production capacities in the range of100,000 m3/day or more. The implementation of large desalinationfacilities is no longer limited to a few water-scarce but oil-rich countriesof the Middle East. Desalinated water has become a commodity thatamends and diversifies conventional water supplies in many parts of theworld. Due to the growing desalination activity in many sea regions andthe growing number of large facilities, concerns over potentiallynegative impacts of the technology on the environment are beingraised. The main environmental concerns of desalination activity revolvearound the emissions of greenhouse gases and air pollutants, the concentrateand chemical discharges into the sea, the use of large quantities of seawaterfor cooling purposes and as feedwater, causing the impingement andentrainment of marine organisms, and construction-related impacts on thecoastal and near-shore habitats. A brief overview of the main concerns isgiven in the following sections. More details can be found in recentliterature surveys (e.g., [16–18]).

Figure 10 Seawater desalination projects in Australia (green: in operation orconstruction, blue: in planning). Based on Refs. [14,26].


5.1 IntakesSeawater desalination plants can receive feedwater from different sources,but open seawater intakes are the most common intake option. The use ofopen intakes may result in losses of aquatic organisms when these collidewith intake screens (impingement) or are drawn into the plant with thesource water (entrainment). The construction of the intake structure causesan initial disturbance of the seabed, which may result in the resuspension ofsediments, nutrients, or pollutants that may affect water quality. Afterinstallation, the structures can affect water exchange and sediment transport,act as artificial reefs, or may interfere with shipping routes or other maritimeuses. Alternatives are beachwell intakes and infiltration galleries, which areplaced below the seabed.

5.2 DischargesAll seawater desalination processes produce large quantities of a saline wastestream (the concentrate), which may be increased in temperature (thermalplants), contain residues of pretreatment and cleaning chemicals, theirreaction (by-)products, and heavy metals due to corrosion (Table 2).

Chemical pretreatment and cleaning is a necessity in most desalinationplants, which typically includes the treatment against biofouling, scaling,foaming, and corrosion in thermal plants, and against biofouling, suspendedsolids, and scale deposits in membrane plants. The chemical residues and by-products are typically washed into the sea along with the concentrate. Theconcentrate of distillation plants is increased in temperature and salinity andtypically contains residual chlorine and chlorination by-products, antiscalant,and antifoaming agents and certain heavy metals such as copper or nickel.The concentrate of SWRO plants is increased in salinity and typically alsocontains antiscalants, but residual chlorine is removed by dechlorination withsodium bisulfite to protect the RO membranes from oxidation. Theconcentrate of SWRO plants does not contain antifoam agents or significantlevels of metals from corrosion, but it is often used to dilute otherintermittent waste streams such as high-turbidity backwash waters frommedia filters that contain natural solids and coagulants several times per dayor chemical cleaning solutions several times per years. To conclude, thedischarge is a mix of these different pollutants, which may have potentiallysynergistic effects on marine life, such as for example the synergistic effect ofchlorine residues and increased temperature which is well documented [19].The discharge volume depends on the process recovery rate and the size ofthe facility. Also, the composition and concentration of residual pollutantsfrom the pretreatment process is process- and plant-specific.


Tab

le2

Efflu

ent

prop

ertie

sof

RO,M

SF,a

ndM

EDdi

still

atio

npl

ants

,ass

umin

gco

nven

tiona

lpr

oces

sde

sign

[16,

27]

Phys

ical

para

met

ers

Rev

erse

osm

osis

(RO

)aM

ulti

stag

efl

ash

(MS

F)b

Mul

tief

fect

dist

illat

ion

(MED

)b

Salin

ity(S

)(d

epen

ding

onam

bien

tsa

linity

and

reco

very

rate

)

�SW

RO

:65

–85

g/L

�B

WR

O:

1–25

g/L

�C

oolin

gw

ater

:am

bien

tsa

linity

(e.g

.,40

g/L)

�B

rine

:60

–70

g/L

�C

ombi

ned:

45–5

0g/

L

�C

oolin

gw

ater

:am

bien

tsa

linity

�B

rine

:60

–70

g/L

�C

ombi

ned:

50–6

0g/

L

Tem

pera

ture

(T)

�If

subs

urfa

cein

take

sus

ed:m

aybe

belo

wam

bien

tT

due

toa

low

erT

ofth

eso

urce

wat

er�

Ifop

enin

take

sus

ed:

clos

eto

ambi

ent

�If

wat

eris

rece

ived

from

cool

ing

wat

erdi

scha

rges

ofpo

wer

plan

ts:

may

beab

ove

ambi

ent

�B

rine

:3–

51C

abov

eam

bien

t�

Coo

ling

wat

er:

8–12

1C

abov

eam

bien

t�

Com

bine

d:B

5–10

1C

abov

eam

bien

t

�B

rine

:5–

251C

abov

eam

bien

t�

Coo

ling

wat

er:

8–12

1C

abov

eam

bien

t,up

to20

1C

poss

ible

�C

ombi

ned:

B10

–201C

abov

eam

bien

t

Plu

me

dens

ity(r

)�

Low

erth

anam

bien

t(n

egat

ivel

ybu

oyan

tpl

ume)

�P

lum

eca

nbe

posit

ivel

y,ne

utra

lly,

orne

gativ

ely

buoy

ant

depe

ndin

gon

the

proc

ess

desig

nan

dm

ixin

gw

ithco

olin

gw

ater

befo

redi

scha

rge,

typi

cally

posit

ivel

ybu

oyan

t

Diss

olve

dox

ygen

(DO

)�

Ifsu

bsur

face

inta

kes

used

:may

bebe

low

ambi

ent

DO

due

toa

low

erD

Oof

the

sour

cew

ater

�If

open

inta

kes

used

and

ifox

ygen

scav

enge

rsfo

rde

chlo

rina

tion

are

not

over

dose

d:cl

ose

toam

bien

t

�B

rine

:be

low

ambi

ent

beca

use

ofde

aera

tion

and

use

ofox

ygen

scav

enge

rs�

Coo

ling

wat

er:

clos

eto

ambi

ent

(min

oref

fect

son

DO

beca

use

ofch

ange

sin

tem

pera

ture

)�

Com

bine

d:m

ixin

gof

brin

ew

ithco

olin

gw

ater

incr

ease

sth

eD

Oco

nten

tof

the

com

bine

def

fluen

tcl

ose

toam

bien

t;tu

rbul

ent

mix

ing

allo

ws

oxyg

enta

ke-u

pfr

omai

r


Ch

emic

alpa

ram

eter

sR

ever

seos

mos

is(R

O)a

Mul

tist

age

flas

h(M

SF)

bM

ulti

effe

ctdi

still

atio

n(M

ED)b

Bio

foul

ing

cont

rol

addi

tives

and

by-p

rodu

cts

Oxi

dant

s

�M

ainl

ych

lori

ne�

Chl

orin

edi

oxid

eus

edin

som

epl

ants

�T

ypic

ally

dosa

geof

1–2

ppm

toth

efe

edw

ater

inal

lpl

ants

oper

atin

gon

open

seaw

ater

�O

xida

nts

typi

cally

rem

oved

topr

even

tm

embr

ane

dam

age,

usin

gso

dium

bisu

lfite

(tw

oto

four

times

high

erdo

sage

than

oxid

izin

gag

ent

dose

)

�D

ischa

rge

leve

lis

abou

t10

–25%

ofdo

sage

due

toch

lori

nede

man

dof

the

seaw

ater

�B

oth

the

brin

ean

dth

eco

olin

gw

ater

cont

ain

resid

ual

chlo

rine

�C

hlor

ine

typi

cally

not

rem

oved

bya

dech

lori

natio

nst

epin

side

the

plan

t

Hal

ogen

ated

orga

nic

by-p

rodu

cts

such

astr

ihal

omet

hane

s(T

HM

s)

�U

seof

chlo

rine

diox

ide

redu

ces

the

risk

ofby

-pro

duct

form

atio

n

�M

ayfo

rmdu

ring

chlo

rina

tion,

but

leve

lsar

eas

sum

edto

belo

wdu

eto

dech

lori

natio

n

�C

hlor

inat

ion

ofse

awat

erre

sults

inva

ryin

gco

mpo

sitio

nan

dco

ncen

trat

ions

ofha

loge

nate

d(c

hlor

inat

edan

dbr

omin

ated

)or

gani

cby

prod

ucts

,m

ainl

yT

HM

ssu

chas

brom

ofor

m

Rem

oval

oftu

rbid

ity(s

uspe

nded

solid

s)

Coa

gula

nts

�D

osag

e1–

30m

g/L

�O

ften

iron

(III

)sa

lts

�If

filte

rba

ckw

ash

isdi

scha

rged

tosu

rfac

ew

ater

s:m

ayca

use

turb

idity

and

sedi

men

tatio

nin

the

disc

harg

esit

ean

dir

onsa

ltsm

ayca

use

efflu

ent

colo

ratio

n(r

edbr

ines

)

�T

reat

men

tno

tap

plie

d�

Tre

atm

ent

not

appl

ied

Coa

gula

ntai

ds(e

.g.,

poly

acry

lam

ide)

�D

osag

e0.

1–5I

mg/

L�

e.g.

poly

acry

lam

ide

Tab

le2

(Con

tinue

d)28 Sabine Lattemann et al.

Scal

eco

ntro

lad

ditiv

es(u

sed

inal

lde

salin

atio

npr

oces

ses,

can

bea

blen

dof

seve

ral

diffe

rent

antis

cala

nts

inco

mbi

natio

nw

ithac

idtre

atm

ent)

Pol

ymer

ican

tisca

lant

s(e

.g.,

poly

mal

eic

acid

s)an

dph

osph

onat

es�

Dos

age:

1–2

ppm

�M

ainl

yus

edin

RO

�A

ntisc

alan

ton

lypr

esen

tin

the

brin

e,bu

tno

tin

the

cool

ing

wat

er

�D

osag

e/di

scha

rge

conc

entr

atio

nbe

low

toxi

cle

vels

toin

vert

ebra

tean

dfis

hsp

ecie

s;so

me

prod

ucts

are

clas

sified

asbe

ing

harm

ful

toal

gae,

pres

umab

lydu

eto

anu

trie

ntin

hibi

tion

effe

ct�

Slow

degr

adat

ion

(som

epr

oduc

tscl

assifi

edas

‘inhe

rent

ly’

biod

egra

dabl

e)w

ithpr

esum

ably

incr

ease

dre

siden

cetim

esin

surf

ace

wat

ers

Pho

spha

tes

�D

osag

e:2

ppm

�St

illus

edat

alim

ited

scal

e�

Not

stab

leat

high

tem

pera

ture

(ble

nds

ofpo

lym

eric

antis

cala

nts

and

phos

phon

ates

pref

erre

d)

�M

ayca

use

eutr

ophi

catio

nne

arou

tlets

,as

easil

yhy

drol

yzed

toor

thop

hosp

hate

,a

maj

ornu

trie

ntfo

rpr

imar

ypr

oduc

ers

Aci

d(H

2SO

4)

�D

osag

e:30

–10

0pp

m

�Lo

wer

sth

epH

from

arou

nd8.

3(n

atur

alpH

ofse

awat

er)

topH

6–7

�E

ffect

ive

agai

nst

calc

ium

carb

onat

esc

ales

but

not

agai

nst

sulfa

tesc

ale,

ther

efor

em

ore

effe

ctiv

ein

seaw

ater

RO

and

ME

Dpr

oces

ses

whe

reca

lciu

mca

rbon

ate

isth

em

ain

scal

efo

rmin

gsp

ecie

s�

The

acid

ityis

quic

kly

cons

umed

byth

ena

tura

lal

kalin

ityof

seaw

ater

,so

that

the

pHqu

ickl

yre

turn

sto

norm

al

Foa

mco

ntro

lad

ditiv

es

Ant

ifoam

ing

agen

ts(e

.g.,

poly

glyc

ol)

�T

reat

men

tno

tap

plie

d�

Typ

ical

lylo

wdo

sage

(0.1

ppm

)be

low

harm

ful

leve

ls�

Use

din

all

dist

illat

ion

proc

esse

s,bu

tpr

imar

ilyin

MSF

�A

ntifo

amon

lypr

esen

tin

the

brin

e,bu

tno

tin

the

cool

ing

wat

er

Cor

rosio

n

Hea

vym

etal

s�

Met

allic

equi

pmen

tm

ade

from

corr

osio

n-re

sista

ntst

ainl

ess

stee

l�

Con

cent

rate

may

cont

ain

low

leve

lsof

iron

,ch

rom

ium

,

�M

etal

liceq

uipm

ent

mad

efr

omca

rbon

stee

l,st

ainl

ess

stee

l,co

pper

nick

elal

loys

�M

etal

liceq

uipm

ent

mad

efr

omca

rbon

and

stai

nles

sst

eel,

alum

inum

and

alum

inum

bras

s,tit

aniu

m,

orco

pper

nick

elal

loys


nick

el,

mol

ybde

num

iflo

w-

qual

ityst

eel

isus

ed�

Con

cent

rate

may

cont

ain

iron

and

copp

er,

copp

erle

vels

can

bean

envi

ronm

enta

lco

ncer

n

�Lo

wer

corr

osio

nra

tes

than

inM

SF�

No

data

onbr

ine

cont

amin

atio

nav

aila

ble

Cor

rosio

npr

even

tion

�N

otne

cess

ary

besid

esch

oice

ofm

ater

ials

�A

sth

efe

edw

ater

isde

aera

ted,

the

brin

eis

also

deae

rate

dbe

fore

mix

ing

with

cool

ing

wat

er,

whi

chis

not

deae

rate

d�

InM

SF,

the

feed

wat

er(b

utno

tth

eco

olin

gw

ater

)m

ayal

sobe

trea

ted

with

oxyg

ensc

aven

gers

(e.g

.,so

dium

bisu

lfite

),w

hich

may

also

rem

ove

resid

ual

chlo

rine

Cle

anin

gso

lutio

ns(o

nly

pres

ent

ifcle

anin

gso

lutio

nsar

edi

scha

rged

tosu

rface

wat

ers)

Cle

anin

gch

emic

als

(use

din

term

itten

tly)

Alk

alin

e(p

H11

–12)

orac

idic

(pH

2–3)

solu

tions

with

addi

tives

,e.

g.:

–D

eter

gent

s(e

.g.,

dode

cylsu

lfate

)–

Com

plex

ing

agen

ts(e

.g.,

ED

TA

)–

Oxi

dant

s(e

.g.,

sodi

umpe

rbor

ate)

–B

ioci

des

(e.g

.,fo

rmal

dehy

de)

Aci

dic

(low

pH)

was

hing

solu

tion

whi

chm

ayco

ntai

ning

corr

osio

nin

hibi

tors

such

asbe

nzot

riaz

ole

deri

vate

s

aN

ous

eof

cool

ing

wat

erin

the

proc

ess,

but

RO

plan

tsm

ayre

ceiv

eth

eir

inta

kew

ater

from

cool

ing

wat

erdi

scha

rges

.b

Ass

umin

gth

atth

etw

ow

aste

stre

ams

from

the

desa

linat

ion

proc

ess

are

com

bine

d,th

atis,

the

brin

eis

dilu

ted

with

maj

oram

ount

sof

cool

ing

wat

erfr

omth

ede

salin

atio

npr

oces

s;fu

rthe

rdi

lutio

nw

ithco

olin

gw

ater

from

pow

erpl

ants

may

occu

rbu

tis

not

cons

ider

edhe

re.

Tab

le2

(Con

tinue

d)

Ch

emic

alpa

ram

eter

sR

ever

seos

mos

is(R

O)a

Mul

tist

age

flas

h(M

SF)

bM

ulti

effe

ctdi

still

atio

n(M

ED)b


Negative effects on the marine environment can occur especially whenwastewater discharges and pollutant loads coincide with sensitiveecosystems. The impacts of a desalination plant on the marine environmentdepend on both the physical and chemical properties of the reject streamsand the hydrographical and biological features of the receiving environ-ment. The concentrate of SWRO plants is negatively buoyant due tohigher than ambient salinity values, with the potential of plume sinking andseafloor spreading. The concentrate of distillation plants can be negatively,positively, or neutrally buoyant, depending on the salinity and temperaturevalues and the amount of cooling water co-discharge, which results fromthe desalination process itself and co-located power plants. It is most likelypositively buoyant due to large cooling water flows with a higher thanambient temperature. The concentrate of SWRO and distillation plantstherefore affects different realms in the marine environment. Seafloorspreading may negatively affect benthic ecosystems such as seagrassmeadows or macroalgae stands and associated benthic species such as seaurchins or shrimps, whereas neutrally or positively buoyant plumes spreadin the water column and could affect nektonic species such as fish, turtles,or mammals. As these are mobile species, they can be assumed to avoid thedischarge site, which could result in a loss of habitat, such as foraging,resting or reproduction areas, for the affected species. Enclosed and shallowsites with abundant marine life can generally be assumed to be moresensitive to desalination plant discharges than exposed, high-energy, open-sea locations [20], which are more capable to dilute and disperse thedischarges. Environmental baseline studies thus provide important informa-tion for project planning and site selection, while monitoring duringconstruction and operation is useful for compliance and effect monitoring.Although the number of publications discussing the potential for negativeenvironmental impacts of effluents from desalination facilities has beensteadily increasing over the last years, a surprising paucity of usefulexperimental data, either from laboratory tests or from field monitoring stillexists. Therefore, a considerable amount of uncertainty still exists about theenvironmental impacts of desalination [2].

5.3 Energy demandDesalination of seawater consumes significant amounts of energy (Table 1),either directly in the form of steam (distillation processes) or indirectlythrough electricity use from the electricity grid. Energy supply is consequentlyan important factor in the planning of new facilities. The main environmentalconcern associated with energy demand, both directly and indirectly, is the


emission of air pollutants. Air quality may be affected by emissions ofgreenhouse gases (mainly CO2), acid rain gases (NOx, SOx), fine particulatematter (PM), and other air pollutants that are produced when fossil fuels areused for electricity/steam generation. The production of greenhouse gases isrelevant in the context of national and international efforts to limit theseemissions to minimize the impacts of climate change. Significant local impactsmay further occur if emissions conflict with applicable air quality standards ormanagement plans, contribute substantially to other existing or projected airemissions (cumulative impacts) in the vicinity and expose the residentpopulation to increased pollutant concentrations [18]. Concerns may also arisedue to more indirect impacts, such as the cooling water requirements ofpower plants or the increasing risk for accidents associated with the transportof fuels. When existing power plant capacities are increased or new plantsconstructed in order to provide additional electricity for desalination, theseindirect impacts will likely be intensified.

As the treatment and distribution of water from conventional sourcesand by conventional processes also requires energy, it is necessary toconsider both the total energy increase caused by desalination processes andthe relative increase compared to other water supply options.

Reference values are often used to put the energy demand ofdesalination into perspective, which may influence how we perceive andevaluate the significance of energy demand and associated environmentalimpacts, for instance by comparing it to energy demand on a local, regional,or national level or to other energy consumers. Some examples [21]:� On the Canary Islands, desalination accounts for 14% of all energy

demands [22].� The SWRO plant of Carboneras (capacity of 120,000 m3/day) on the

Mediterranean coast of Spain consumes about one-third of theprovince’s electrical energy [23].� The Spanish Agua program shall increase desalination capacity on the

Mediterranean coast of Spain from 1.1 Mm3/day (2005) to over2.7 Mm3/day (2010). This will require additional 11 GWh/day ofelectricity assuming an energy demand of 4 kWh/m3 of desalinatedwater as foreseen in the Spanish National Hydrological Plan [9] and willcause a 1.4% increase over 2005 national electricity generation levels(805 GWh/d or 294 TWh in 2005 [24]). It would result in additionalCO2 emissions of 5475 tons/day, which represents a 0.6 % increase innational CO2 emissions compared to pre-2005 levels of 326 million tonsCO2 in 2004.� For California, it is estimated that the currently proposed desalination

plants with a total capacity of 1.7 Mm3/day would increase the water-related energy use by 5% over 2001 levels assuming an average energy use


of 3.4 kWh/m3 [1]. The total water-related energy use was 48,012 GWhin 2001, representing 19% of the total energy use in California [25].In another source [26], an average energy use of 2.9 kWh/m3 is assumedto produce the 1.7 Mm3/day by desalination in 2030, which is realistic asfurther energy savings are to be expected in the future. Desalinationwould thus increase the water related-energy use by 1800 GWh/year orabout 4% over 2001 levels.� The Sydney desalination plant with an initial capacity of 250,000 m3/day

is expected to result in a 1.2% increase of New South Wales’ electricitydemand if upgraded to a capacity of 500,000 m3/day [27]. ThePerth SWRO plant in Western Australia is responsible for about 0.67%of the energy demand in the region (at peak power consumption of3574 MW in summer), compared to 30% as used for air-conditioning inPerth [28].� In Kuwait, co-generation plants produce 443 Mm3 of desalinated water

(90% of the national water supply) and 42,257 GWh of electricity peryear, using 462 million GJ of energy, which is 54% of the national fueluse. About 10% of the national fuel use and the national emissions arethus attributed to the production of desalinated water and 43% toelectricity generation. As the plants use mainly heavy oil (78%) and crudeoil (20%), air pollution from cogeneration plants is significant andamounts to 7 million tons of CO2, 0.13 tons of SO2, and 0.02 tons ofNOX per year for water production, and 30 million tons CO2, 0.54 tonsSO2 and 0.06 NOX per year for electricity production. 62% of the totalfuel energy (290 M-GJ) are rejected to the atmosphere (46 M-GJ) and tothe sea (243 M-GJ) as cooling water. 60% of the cooling water dischargesare attributed to the power plants and 40% to the MSF plants [29].To conclude, desalination can be a significant energy consumer in some

parts of the world, which depend heavily on desalinated water. As seen inthe aforementioned examples, desalination accounts for 14% of the energydemand on the Canary Islands or for 10% of the national fuel use inKuwait. On the mainland of Spain, however, desalination accounts for onlyabout 1.4% of national electricity generation, and this value would even belower if the energy use of desalination would be compared to the totalSpanish energy demand taking emissions for example from transportationor heating into account. The value of 1.4% is similar in magnitude to thereference values given for Sydney (0.6% of the regional electricity demandfor a single 250,000 m3/day facility) and Perth (0.67% of the regional peakenergy demand for a single 140,000 m3/day facility). Taking these lattervalues into consideration, energy use seems to be a minor energy consumeron a regional or national level in industrialized regions. However,environmental impact assessments may still find energy use to be asignificant factor, which may entail some form of impact mitigation. For


example, the projects in Sydney and Perth compensate the electricitydemand by renewable energy projects.

5.4 Impact mitigation measuresA widely recognized and accepted approach for investigating, evaluating,and mitigating impacts of development projects on the environment is theenvironmental impact assessment (EIA). To date, only a handful of EIAstudies have been carried out for desalination plants and made publiclyavailable. In some cases, the investigations are carried out under immensetime constraints. For instance, only 4 months were set aside for an EIAstudy for a 200,000 m3/day SWRO plant in Algeria [21]. This shows thatenvironmental concerns can be of secondary importance when a readysupply of freshwater is urgently needed. The opposite is also true:comprehensive environmental studies are currently being carried out forthe large SWRO projects in Australia, and environmental concerns are themajor hurdle in the permitting process of new projects in California, wherethe planning and permitting process of the first large plant took more than10 years.

A central element of all EIA studies is the comparison of alternatives,such as alternative project sites or technologies in order to identify theoption with the least environmental footprint. Especially the selection of asuitable project site for a new desalination project can be a very effectiveway of minimizing and preventing impacts on the environment.Furthermore, several technical options can be implemented to mitigatethe environmental effects of the waste discharges. For example, advanceddiffuser systems can achieve a maximum dilution with a minimum salinityincrease of one unit above background levels in the sea. Negative impactsfrom chemicals can be minimized by treatment before discharge, bysubstitution of hazardous substances, and by implementing alternativenonchemical treatment options. For instance, backwash waters frompretreatment filters can be dewatered and deposited on land, or membranecleaning solutions can be treated on-site in special treatment facilities ordischarged to a sanitary sewer system [16].

The use of alternative pretreatment methods may be considered wherefeasible. Prefiltration with ultrafiltration (UF) or microfiltration (MF)membranes may reduce the need for chemical pretreatment. The UF/MFmembranes usually require chemically enhanced backwash and periodiccleaning. The process is therefore not entirely ‘‘chemical-free,’’ but anadvantage of intermittent cleaning over continuous pretreatment is thatwastewaters are produced in smaller volumes and can be treated effectively.


A nonchemical treatment option is irradiation of the intake water with UV-light at 200–300 nm wavelengths for disinfection. A major advantage ofUV-light is that storage, handling, and disposal of toxic chemicals areavoided; however, UV-irradiation has not been found to be an effectivepretreatment for large desalination plants to date.

Air pollutant emissions can be minimized by increasing the energyefficiency of the desalination process. For instance, use of energy recoverydevices allow for a reduction of the specific energy demand in seawater ROplants to 2–3 kWh/m3, which may be decreased further in the future.Furthermore, air emissions can be controlled at the source – the powerplant – as emissions depend on the fuel source (e.g., gas, coal), thetechnology and efficiency of the power plant, as well as on any exhaustpurification equipment installed (e.g., scrubbers capturing sulfur emissions).When electricity is taken from the electricity grid, the composition of theenergy mix must furthermore be taken into account when estimating theindirect air emissions of a single desalination project.

Finally, the potential for renewable energy use (solar, wind, geothermal,biomass) may be investigated to minimize impacts on air quality andclimate. This may be in the form of desalination systems directly driven byrenewable energy, or as an indirect compensation measures such as theinstallation and use of renewable energy in other localities or for otheractivities. For instance, the large SWRO projects in Perth and Sydney,Australia, compensate for their energy demand through wind farm projects.

6. SUMMARY AND CONCLUSION

In a nutshell, 63% of the worldwide (44.1 Mm3/day) desalination capacityis produced from seawater sources. Of this water, 61% is produced bythermal processes. The MSF distillation process is almost exclusively usedfor the desalination of seawater in the Gulf countries. The RO process isthe second most important process for treating seawater on a global scale,but it is the first choice in many industrialized and developing countries thatare now starting to consider seawater desalination. Eighty-three percent ofthe treated seawater is for municipal use. Sixty-six percent of the seawaterdesalination capacity is attributed to industrial scale facilities, withproduction capacities in single MSF distillation plants up to 1.6 Mm3/day,while proposed capacities for single SWRO plants approach 500,000 m3/day. Seventy-nine percent of the global seawater desalination capacity islocated in the Middle East, North Africa, and Southern Europe, with 71%being located in the Gulf, the Red Sea, and the Mediterranean Sea. The


enclosed nature of these sea areas makes them especially susceptible to anyform of pollution, and desalination plants have been classified as a maincontributor to land-based pollution in the Gulf and Red Sea [22,23].

Only 19% of the global desalination capacity is presently produced frombrackish water sources and 5% from wastewater sources, with 84% of thebrackish water and 79% of the wastewater being treated by RO. This shareincreases to 98% and 85%, respectively, if one includes the othermembrane-based processes, that is, NF and ED, as well.

Although brackish water and wastewater treatments offer a great futurepotential, desalination of seawater will remain the dominant process forsome time. This is mainly because Saudi Arabia and the United ArabEmirates will continue to be the largest desalination markets in theforeseeable future, where seawater desalination plays a prominent role.MSF distillation will therefore continue to be the main desalination process,but will presumably lose further market shares to MED and RO. Whilethermal cogeneration facilities predominate in the oil-rich countries of theMiddle East, which produce both electricity and water, RO is usually thepreferred process where cheap fossil energy or waste heat is not available,due to its lower energy demand. Consequently, most countries outside theMiddle East choose RO for seawater desalination.

As the need for desalination accelerates in many parts of the world, theproblem spreads from water scarcity to energy use and airborne emissions[9,24], and from overused polluted freshwater bodies to the marineenvironment. Due to the environmental concerns associated with thedesalination of seawater, this option should therefore only be consideredafter other alternatives have been tapped to the full potential, such as watersaving and water reuse. Examples such as Spain or Israel (cf. Section 4.3),however, show that desalination developments are often only one aspect ofa whole package of water management measures, and not necessarily thefirst and only choice to satisfy the ever-growing demand for water and toreduce the burdens of drought. To negate the need for desalination incountries such as Israel or Spain would also mean that societies in the Northwould have to make concessions, as much of what we eat and wear isgrown in sunny but water-scarce regions.

The question is not if desalination will provide the ultimate solution tothe world’s water problems. In the end, decisions about desalinationdevelopments revolve around complex evaluations of local circumstancesand needs, economics, financing, environmental and social impacts, andavailable alternatives [1]. The question is rather which mitigation measuresare necessary to reduce the environmental burden of desalination to


acceptable levels. Many useful ideas have been put forward in recentliterature to minimize the environmental footprint of desalination. The bestproject design, however, can only be identified in project- and site-specificstudies. A catalogue of best available techniques (BAT) and bestenvironmental practices (BEP) may be useful in guiding practitioners,consultants, and decision makers in their choices when undertaking newdesalination projects. Furthermore, there is need for ongoing research anddemonstration projects to gain experience, knowledge, and trust in newenvironmentally friendly technologies, as well as political incentivesthrough policies or financial support to implement state-of-the-arttechnologies. Some of these measures will increase the price of desalinatedwater production; however, technological advances will most likely resultin a lower energy consumption and production cost of desalinated water inthe future. Sustainable desalination is not a utopia, but requires acommitment to providing water at a reasonable price, which includes notonly the construction and operating costs, but also the costs to mitigateenvironmental impacts, including the costs for environmental studies,advanced technology, or compensation measures.

In the end, some advantages of wastewater desalination over seawaterdesalination should be highlighted. Water reuse is practiced in many parts ofthe world, but the use of desalination technologies in water reuse has beenlimited so far. The world’s largest desalination facility treating waste waterwith an output capacity of 310,000 m3/day is located in Sulaibiya, Kuwait.It uses ultrafiltration followed by reverse osmosis to treat secondary effluentwaste water. The main advantage of treating waste water is that it is cheaperand the energy demand is lower than for seawater RO. An expansion ofwaste water desalination is therefore expected in the future. Second, mostof the waste is already where it is most needed, that is, near urban areas.Even if the decision is made not to use the purified wastewater for directpotable use (though from a technical point of view, the product can complywith WHO standards), it can be used for industrial use or landscapingactivities in urban areas. And third, wastewater and some of itscontaminants, including nutrients, metals, or micropollutants such aspharmaceutical and personal care products, are still a burden for manyrivers, estuaries, and coastal seas. Purifying and reusing wastewater does notonly produce a new source of water supply, but can eliminate a wasteproduct if the waste stream from the desalination process, which is about15% of the original waste water volume, is treated instead of discharged.Zero liquid discharge (ZLD) technologies could be used for this purpose.While some media vilify reclaimed wastewater by negative headlines,


public education programs using terms such as ‘‘new’’ or ‘‘purified’’ watercan help to establish a positive attitude.

REFERENCES

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[8] K. Wangnick, IDA Worldwide Desalting Plant Inventory Report No. 18, WangnickConsulting, Germany, 2004.

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