Water desalination technologies utilizingconventional and renewable energy sources

Mahmoud Shatat and Saffa B Riffat

Institute of Sustainable Energy Technology University of Nottingham Nottingham NG72RD UK

Corresponding author

enxms9nottinghamacuk

AbstractWater is one of the earthrsquos most abundant resources covering about three-quarters of the planetrsquossurface Yet there is an acute shortage of potable water in many countries especially in Africa and theMiddle East region The reason for this apparent contradiction is of course that 975 of the earthrsquoswater is salt water in the oceans and only 25 is fresh water in ground water lakes and rivers and thissupplies most human and animal needs Tackling the water scarcity problem must involve better andmore economic ways of desalinating seawater This article presents a comprehensive review of waterdesalination systems whether operated by conventional energy or renewable energy to convert salinewater into fresh water These systems comprise the thermal phase change and membrane processes inaddition to some alternative processes Thermal processes include the multistage flash multiple effectsboiling and vapour compression cogeneration and solar distillation while the membrane processesinclude reverse osmosis electrodialysis and membrane distillation It also covers the integration intodesalination systems of potential renewable energy resources including solar energy wind andgeothermal energy Such systems are increasingly attractive in the Middle East and Africa areassuffering from shortages of fresh water but where solar energy is plentiful and where operational andmaintenance costs are low The advantages and disadvantages including the economic andenvironmental aspects of these desalination systems are presented

Keywords desalination thermal process membrane process renewable energy

Received 3 January 2012 revised 17 February 2012 accepted 23 February 2012

1 INTRODUCTION

Water is essential for life Many countries around the world es-pecially developing countries and countries in the Middle Eastregion suffer from a shortage of fresh water The UnitedNations (UN) Environment Programme stated that one-thirdof the worldrsquos population lives in countries with insufficientfreshwater to support the population [1] Consequently drink-ing water of acceptable quality has become a scarce commod-ity The total global water reserves are 14 billion km3 ofwhich around 975 is in the oceans and the remaining 25is fresh water present in the atmosphere ice mountains andground water Of the total only 0014 is directly availablefor human beings and other organisms [2] Thus tremendousefforts are now required to make available new water resourcesin order to reduce the water deficit in countries which haveshortages [3] According to World Health Organization(WHO) guidelines the permissible limit of salinity in drinkingwater is 500 ppm and for special cases up to 1000 ppm [4]Most of the water available on the earth has a salinity up to

10 000 ppm and seawater normally has salinity in the range of35 000ndash45 000 ppm in the form of total dissolved salts [5]Desalination is a process in which saline water is separated intotwo parts one that has a low concentration of dissolved saltswhich is called fresh water and the other which has a muchhigher concentration of dissolved salts than the original feedwater which is usually referred to as brine concentrate [6] Thedesalination of seawater has become one of the most importantcommercial processes to provide fresh water for many commu-nities and industrial sectors which play a crucial role in socio-economic development in a number of developing countriesespecially in Africa and some countries in the Middle Eastregion which suffer from a scarcity of fresh water There is ex-tensive RampD activity especially in the field of renewable energytechnologies to find new and feasible methods to producedrinking water [7 8] Currently there are more than 7500 de-salination plants in operation worldwide producing severalbillion gallons of water per day Fifty-seven per cent are in theMiddle East [9] where large-scale conventional heat and powerplants are among the regionrsquos most important commercial

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processes they play a crucial role in providing fresh water formany communal and industrial sectors especially in areas witha high density of population However since they are operatedwith fossil fuel they are becoming very expensive to run andthe environmental pollution they produce is increasinglyrecognized as very harmful to the globe Moreover such plantsare not economically viable in remote areas even near a coastwhere seawater is abundant Many such areas often also experi-ence a shortage of fossil fuels and an inadequate electricitysupply The development of compact small-scale systems forwater desalination is imperative for the population in suchareas [7 8] Thermal solar energy water desalination is knownto be a viable method of producing fresh water from salinewater [10] in remote locations conventional basin solar stillswith a relatively large footprint are an example of such simpletechnology And using a clean natural energy resource in waterdesalination processes will significantly reduce the pollutionthat causes global warming This article aims to present areview of the published literature on the various desalinationtechnologies and their advantages and disadvantages in add-ition to their economics

2 OVERVIEW OF DESALINATIONPROCESSES

Various desalination processes have been developed some ofwhich are currently under research and development Themost widely applied and commercially proven technologies canbe divided into two types phase change thermal processes andmembrane processes and as shown in Figure 1 both

encompass a number of different processes In addition thereare the alternative technologies of freezing and ion exchangewhich are not widely used All are operated by either a conven-tional energy or renewable energy to produce fresh water

21 Thermal desalination processesThermal desalination often called distillation is one of themost ancient ways of treating seawater and brackish water toconvert them into potable water It is based on the principlesof boiling or evaporation and condensation Water is heateduntil it reaches the evaporation state The salt is left behindwhile the vapour is condensed to produce fresh water [11] Inmodern times the required thermal energy is produced insteam generators waste heat boilers or by the extraction ofback-pressure steam from turbines in power stations [12] Themost common thermal desalination processes are

dagger multi-stage flash distillation (MSF)dagger Multiple-effect distillation (MED)dagger vapour-compression evaporation (VC)dagger cogenerationdagger solar water desalination

211 Multi-stage flash distillationWater distillation in a vessel operating at a reduced pressureand thus providing a lower boiling point for water has beenused for well over a century In the 1950s Weirs of Cathcart inScotland used this concept to invent the MSF process and ithad significant development and wide application throughout

Figure 1 Classification of water desalination technologies

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the 1960s due to both to its economical scale and its ability tooperate on low-grade steam [13] MSF is currently producingaround 64 of the total world production of desalinatedwater Most of the MSF plants are located in the Arab regionAlthough the MSF process is the most reliable source for theproduction of fresh water from seawater it is considered as anenergy intensive process which requires both thermal andmechanical energy [14]

In the MSF process illustrated in Figure 2 feed water(saline water) is heated in a vessel called the brine heater untilit reaches a temperature below the saturation boiling tempera-ture The heated seawater flows through a series of vessels insequence where the lower ambient pressure causes the water toboil rapidly and vaporize This sudden introduction of heatedwater into the reduced-pressure chamber is referred to as thelsquoflashing effectrsquo [15] because the water almost flashes intosteam

A small percentage of this water is converted into watervapour the percentage is mainly dependent on the pressureinside the stage since boiling continues until the water coolsand vaporization stops The vapour steam generated by flash-ing is converted to fresh water by being condensed on thetubes of heat exchangers (condenser) that run through eachstage The incoming feed water going to the brine heater coolsthe tubes This in turn heats up the feed water and increasesthe thermal efficiency by reducing the amount of thermalenergy required in the brine heater to raise the temperature ofthe seawater

An MSF unit that used a series of stages set at increasinglylower atmospheric pressures was developed so that the feedwater which was passed from one stage to another was boiledrepeatedly without adding more heat Typically an MSF plantcontains between 15 and 25 stages [6] Distillation processesproduce 50 of the worldwide desalination capacity and84 of this is produced by MSF technology Most MSF plantshave been built in the Middle East where energy resourceshave been plentiful and inexpensive [16]

Advantages and disadvantages of MSF

dagger MSF plants are relatively simple to construct and operate[15]

dagger They have no moving parts other than conventionalpumps and incorporate only a small amount of connectiontubing [15]

dagger The quality of water effluent contains 2ndash10 ppm dissolvedsolids a high level of purification Therefore it isre-mineralized in the post-treatment process [17]

dagger The quality of the feed water is not as important as it is inthe reverse osmosis (RO) system technology [6]

dagger Operating plants at higher temperatures (over 1158C)improves their efficiency but causes scaling problems wherethe salts such as calcium sulphate precipitate on the tubessurfaces and create thermal and mechanical problems liketube clogging [6]

dagger It is considered as an energy intensive process whichrequires both thermal and mechanical energy but it can beovercome by the cogeneration system [14]

dagger Adding more stages improves the efficiency and increaseswater production but it increases the capital cost and oper-ational complexity [6]

212 Multi-effect distillationThe MED process is the oldest large-scale distillation methodused for seawater desalination At present 35 of theworldrsquos desalted water is produced by MED plants [18] Highdistilled water quality high unit capacity and high heat effi-ciency are its most obvious characteristics [18 19] In additionMED has traditionally been used in the industrial distillationsector for the evaporation of juice from sugarcane in the pro-duction of sugar and in the production of salt using the evap-orative process The MED process like MSF takes place in aseries of vessels or evaporators called effects and it also usesthe principle of evaporation and condensation by reducing the

Figure 2 Multi-stage flashing processmdashMSF [8]

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ambient pressure in the various effects This process permitsthe seawater feed to undergo multiple boiling without supply-ing additional heat after the first effect The seawater enters thefirst effect and is raised to the boiling point after being pre-heated in tubes The seawater is sprayed onto the surface of theevaporator tubes to promote rapid evaporation The evapor-ator tubes are heated by externally supplied steam normallyfrom a dual-purpose power plant The steam is condensed onthe opposite side of the tubes and the steam condensate isrecycled to the power plant for its boiler feed water as shownin Figure 3

The MED plantrsquos steam economy is proportional to thenumber of effects The total number of effects is limited by thetotal temperature range available and the minimum allowabletemperature difference between one effect and the next effectOnly a portion of the seawater applied to the tubes in the firsteffect is evaporated The remaining feed water is fed to thesecond effect where it is again applied to a tube bundle Thesetubes are in turn heated by the vapours created in the firsteffect This vapour is condensed to form the fresh waterproduct while giving up heat to evaporate a portion of theremaining seawater feed in the next effect

The process of evaporation and condensation is repeatedfrom effect to effect each at a successively lower pressure andtemperature This continues for typically 4ndash21 effects and aperformance ratio between 10 and 18 is found in large plants[20]

Advantages and disadvantages of MED The MED process isdesigned to operate at lower temperatures of 708C (1588F)This minimizes tube corrosion and the potential of scale for-mation around the tube surfaces [6]

dagger The quality of the feed water is not as important as in theRO system technology Hence the pre-treatment and oper-ational costs of MED are low

dagger The power consumption of MED is lower than that of theMSF plant [15]

dagger The performance efficiency in MED plants is higher thanthat in MSF plants therefore the MED process is more effi-cient than the MSF process in terms of heat transfer andfresh water production cost [21]

213 Vapour-compression evaporationThe vapour compression distillation process is used in combin-ation with other process like MED and single-effect vapourcompression In this process the heat for evaporating the sea-water comes from the compression of vapour VC plants takeadvantage of the principle of reducing the boiling point tem-perature by reducing the pressure Two devices a mechanicalcompressor (mechanical vapour compression) and a steam jet(thermal vapour compression) are used to condense the watervapour to produce sufficient heat to evaporate incoming sea-water as illustrated in Figure 4

The mechanical compressor is usually electrically or diesel-driven VC units have been built in a variety of configurationsto promote the exchange of heat to evaporate the seawater Thecompressor creates a vacuum in the evaporator and then com-presses the vapour taken from the evaporator and condenses itinside a tube bundle Seawater is sprayed on the outside of theheated tube bundle where it boils and partially evaporates pro-ducing more vapour With the steam-jet type of VC distillationunit called a thermo compressor a venturi orifice at the steamjet creates and extracts water vapour from the evaporator cre-ating a lower ambient pressure The extracted water vapour iscompressed by the steam jet This mixture is condensed on thetube walls to provide the thermal energy (heat of condensa-tion) to evaporate the seawater being applied on the other sideof the tube walls in the evaporator

Advantages and disadvantages of VC

dagger The simplicity and reliability of plant operation make it at-tractive unit for small-scale desalination units They areusually built up to a capacity of 3000 m3day and are often

Figure 3 Multi-effect distillation plant [30]

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used for resorts industries and drilling sites where freshwater is not readily available [6]

dagger The low operating temperature of VC distillation makes it asimple and efficient process in terms of power requirement

dagger The low operating temperatures (below 708C) reduces thepotential for scale formation and tube corrosion

214 Cogeneration system for power and water desalinationIt is possible to use energy in a dual use or cogenerationsystems in which the energy sources can perform several differ-ent functions such as electric power generation and water de-salination Most of the desalinated potable water and electricityin the Arabian Gulf countries and North Africa are producedby cogeneration plants associated with multi-stage flash desal-ination units operating on seawater [6] Although other distil-lation processes such as thermal vapour compression and MEDare starting to find their way into the market the MSF processis still considered as the workhorse of the desalination industryThis process has proven its reliability and flexibility over almost50 years of plant design and operation For large desalinationcapacity the MSF process can be considered as the only candi-date commercially However on the cogeneration plant sidethe situation is different in that several alternatives are com-mercially available to provide the required electrical power andsteam for desalination [22] In cogeneration plants the electri-city is produced with high-pressure steam to operate the tur-bines the steam produced by boilers at temperatures up to5408C As this steam expands in turbines its temperature andenergy level are reduced As previously stated distillationplants need steam with temperatures lower than 1208C andthis can be obtained easily at the end of the turbine after muchof its energy has been utilized in electric power generationThis steam is used in the desalination process and the

condensate from the steam is then returned to the boiler to bereheated again for use in the turbine The main advantage ofthis system is that it uses much less fuel than each plant oper-ating separately and energy costs are a crucial factor in any de-salination process In contrast one of the disadvantages is thepermanent coupling between the desalination plant and thepower plant which can create a problem in water productionwhen the demand for electricity is reduced or when theturbine or generator is down for repair The size of the desalin-ation plant can be efficiently integrated with a power cogener-ation plant so that the ratio of desalted water to powerproduction is consistent with water and power requirements ofthe community it serves Cogeneration plants have alsoreduced power costs Meanwhile other types of cogenerationplants have achieved lower costs by benefiting from heat recov-ery systems on gas turbines heat pumps and other industrialprocesses such as burning solid wastes in an incinerator [7]

22 Membrane processesSynthetic membranes were first introduced in separation pro-cesses in the 1960s but they began to play an increasinglycrucial role in water desalination in the 1980s Originallymembrane applications were limited to municipal water treat-ment such as microfiltration and desalination but with the de-velopment of new membrane types uses have expanded tocover not only the water industry but also high return pro-cesses such as chemical separations enzyme concentration andbeverage purification This technology uses a relatively perme-able membrane to move either water or salt to induce twozones of differing concentrations to produce fresh water Theseprocesses are also useful in municipal water treatment RO andelectrodialysis (ED) are replacing phase change desalting tech-nologies for supplying water to coastal and island communitiesall over the world RO in particular is becoming an

Figure 4 Vapour-compression evaporation [6]

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economical alternative to the traditional water softening pro-cesses [23] Membrane technology includes several processesbut the principal difference between them lies in the size of theentities ions molecules and suspended particles that areretained or allowed to pass through the membranes Typicalseparation processes are nano-filtration ultra-filtration micro-filtration and filtration used in the pre-treatment stages of de-salination to remove large particles bacteria ions and forwater softening [15] Figure 5 shows the effective range ofmembrane processes and applications

This section looks at the following process

dagger reverse osmosisdagger electrodialysisdagger membrane distillation (MD)

221 Reverse osmosisThe RO process is relatively new in comparison to other tech-nologies and was introduced as a successful commercializedtechnology in water desalination in the early 1970s RO is amembrane separation process in which the water from a

pressurized saline solution is separated from the solutes (thedissolved material) by flowing through a membrane withoutthe need for heating or phase change The major energyrequired is for pressurizing the feed water [6] It can also bedescribed as a process of forcing a solvent from a region ofhigh solute concentration through a membrane to a regionof low solute concentration by applying a pressure in excess ofthe osmotic pressure as shown in Figure 6 Thus water flowsin the reverse direction to the natural flow across the mem-brane leaving the dissolved salts behind with an increase insalt concentration [24]

A typical large saline water RO plant consists of five majorcomponents a saline water supply system a feed water pre-treatment system high-pressure pumping RO modules (mem-brane separation) and post-treatment system [25] In the recentyears the largest RO desalination plants have been built in theMiddle East and particularly in Saudi Arabia A plant inJeddah produces 15 million gallon per day (MGD) while theAl Jubail and Yanbu RO plants have capacities of 24 and338 MGD respectively [25 26]

Seawater supply system An open intake channel supplies theplant with raw seawater which is pumped through trash racksand travelling screens to remove debris [27]

Pre-treatment Pre-treatment is very important in the ROprocess because it protects membrane surfaces from foulingand also provides protection to the high-pressure pumps andthe RO section of the plant The nature of the pre-treatmentdepends largely on the feed water characteristics the mem-brane type and configuration the recovery ratio and therequired product water quality In this stage the seawater istreated against debris particles and suspended solids by amultimedia gravity filter that removes particles larger than10 mm The water is biologically disinfected by injecting

Figure 5 Effective range of membrane processes and applications [23]

Figure 6 Osmosis and RO processes [66]

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chemicals like sodium hypochlorite to remove algae and bac-teria and to prevent microorganism growth Also added areferric chloride as a flocculant and sulphuric acid to adjust pHand control scale formation [25]

High-pressure pumping The high-pressure pump supplies theappropriate pressure needed to enable the water to passthrough the membrane where the semi-permeable membranerestricts the passage of dissolved salts while permitting water topass through Then the concentrated brine water is dischargedinto the sea This pressure ranges from 15 to 25 bar for brack-ish water and from 54 to 80 bar for sea water [6 20]

RO modules (membrane separation) The membrane must bestrong enough to withstand the drop of the entire pressureacross it A relatively small amount of salts passes through themembrane and appears in the permeate [6] In principle ROmembranes should be semi-permeable possessing a highdegree of water permeability but presenting an impenetrablebarrier to salts A membrane should have a large surface areato allow maximum flow There are membranes available whichare suitable for pump operation up to 84 kgcm2 dischargepressure This pressure ranges from 54 to 80 bars for seawaterdepending on its salt content Most RO applications requiretwo or more modules arranged to operate in series [28] asshown in Figure 7

RO membranes are made in a variety of configurations Twoof the most commercially successful membranes are spiralwound and hollow fine fibre (HFF) and both of these are usedto desalt brackish water and seawater [29]

Spiral wound membrane This type of membrane element ismost commonly manufactured as a flat sheet of either a cellu-lose diacetate and triacetate blend or a thin film compositeusually made from polyamide polysulphone or polyurea poly-mers The configuration is illustrated in Figure 8 [30]

HFF membrane HFF is a U-shaped fibre bundle housed ina pressure vessel The membrane materials are based on cellu-lose triacetate and polyamide and its arrangement allows thehighest specific surface area of all the module configurationsresulting in compact plants Figure 9 illustrates the HFF forma-tion [30]

Post-treatment The post-treatment generally stabilizes thewater and might include pH adjustment by adding lime tomeet the potable water specifications and the removal of dis-solved gases such as hydrogen sulphide and carbon dioxide[20]

Advantages and disadvantages of RO process

dagger Material corrosion problems are significantly less comparedwith MSF and MED processes due to the ambient tempera-ture conditions

dagger Polymeric materials are utilized as much as possible ratherthan the use of metal alloys [20]

dagger Two developments have also helped to reduce the operatingcost of RO plants during the past decadedagger The development of operational membranes with high

durability and lower pricesdagger The use of energy recovery devices that are connected to

the concentrated stream as it leaves the pressure vessel

Figure 7 Cross-section of a pressure vessel with three membrane elements [6]

Figure 8 Cutaway view of a spiral wound membrane element [30]

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The concentrated brine loses only 1ndash4 bar relative tothe applied pressure from the high-pressure pump Thedevices are mechanical and generally consist of turbinesor pumps that can convert a pressure difference into ro-tating energy that can be used to reduce energy costs

dagger RO units sold for residential water filtration require verylarge quantities of water since they recover only 5ndash15 ofthe feed water that enters the filter In seawater systems forevery 5 gallons of usable water 40ndash90 gallons of water aresent to the wastewater system [6]

dagger Membrane scaling caused by the precipitation of salts is acommon problem in the RO process but it is less than in MSF

dagger Membranes are liable to be fouled (plugged) by large parti-cles but this can be avoided by pre-filtering the feed waterthrough a 5ndash10 mm cartage micro-filter Biological foulingcan be caused by the formation of micro-organism coloniesand by entrapping dead and live organisms Colloidalfouling is caused by the settlement on membrane surfaces ofcolloids from an accumulation of aluminium silicate andclays and from soap detergents and organic materials [15]

222 ElectrodialysisED was commercially introduced in the early 1960s about10 years before RO It provided a cost-effective way to desaltbrackish water and spurred considerable interest in the wholefield of using desalting technologies to produce potable waterfor municipal use [6] It also has many other applications inthe environmental and biochemical industries as well as in theproduction of table salt [15 31]

ED is an electrochemical separation process that employs elec-trically charged ion exchange membranes with an electrical poten-tial difference as a driving force It depends on the fact that mostsalts dissolved in water are ionic being either positively (cationic)or negatively (anionic) charged and they migrate towards electro-des with an opposite electric charge Membranes can be con-structed to permit the selective passage of either cations or anionsA schematic diagram of the process is illustrated in Figure 10

Advantages and disadvantages of ED

dagger It has the capability of high recovery in terms of more freshwater product and less brine [6]

dagger ED is feasible for brackish water with a salinity of 6 gl ofdissolved solids but not suitable for water with dissolvedsolids of 04 gl

dagger The desalination of water with concentrations of dissolvedsolids higher than 30 gl like seawater is possible but it isnot economically viable [32]

dagger The major energy requirement is the direct current to separ-ate the ionic substances in the membrane

dagger Energy usage is proportional to the salts removeddagger It can treat feed water with a higher level of suspended

solids than ROdagger Chemical usage for pre-treatment is low [6]

223 Membrane distillationMD was first studied at the end of 1960s [33] but developedcommercially on a small scale in the 1980s [15] This technol-ogy is a thermally driven membrane-based process combinesthe use of distillation and membranes and is essentially anevaporation process It takes advantage of the temperature dif-ference between a supply solution coming in contact with thesurface on one side of the readily selected micro-porousmembrane and the space on the other side of the membraneas shown in Figure 11 This temperature difference results in avapour pressure difference leading to the transfer of the pro-duced vapour through the membrane to the condensationsurface The overall process is based on the use of hydrophobicmembranes permeable by vapour only thus excluding transi-tion of liquid phase and potential dissolved particles [34]After the vapour passes through the membrane it is condensedon a cooler surface to produce fresh water In the liquid formthe fresh water cannot pass back through the membrane so itis collected as the fresh water product [6] Although MD hasnot achieved great commercial success at the beginning whilethe most recent research and development proved a promising

Figure 9 Hollow fine fiber membrane module [30]

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success for small-scale MD desalination systems combinedwith solar energy

Advantages and disadvantages of MD

dagger The main advantages are its simplicity and the low operat-ing temperature rise it requires to operate These facilitateand make utilizing the waste heat as a preferable energysource possible such as by coupling the MD units withsolar energy sources which is attractive [6 15]

dagger It requires a lower operating pressure than pressure-drivenmembrane processes and reduced vapour space comparedwith conventional distillation [35]

dagger MD requires more space than other membrane processeshowever the recent RampD will reduce the size [6]

dagger Energy consumption is approximately the same as that ofMSF and MED plants [6 15]

dagger The MD process requires that the feed water should be freeof organic pollutants this explains the limited use of thismethod [15]

23 Alternative processesA number of other processes have been used in water desalin-ation but none has achieved as high a productive performanceor reached the same level of commercial success as the MSF

Figure 10 Movement of ions in the ED processmdashadapted from [6]

Figure 11 Schematic diagram of the MD system [34]

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ED and RO processes They may prove valuable under specialcircumstances or after further research and development

231 FreezingExtensive commercial research was done during the 1950s and1960s to improve the performance of the freezing process Thebasic principles of freezing desalination are simple During theprocess of freezing dissolved salts are excluded during the for-mation of ice crystals Seawater can be desalinated by coolingthe water to form crystals under controlled conditions Beforethe entire mass of water has been frozen the mixture is usuallywashed and rinsed to remove the salts in the remaining wateror adhering to the ice crystals The ice is then melted toproduce fresh water [6] The main heat transfer processes thatis freezing and melting are regenerative resulting in very high-energy efficiency [36] A small number of plants have beenbuilt over the past 40 years but the process has not been acommercial success in the production of fresh water for muni-cipal purposes The most recent significant example of desalt-ing by freezing was an experimental solar-powered unitconstructed in Saudi Arabia in the late 1980s but that planthas been disassembled At present freezing technology prob-ably has better applications in the treatment of industrialwastes than in the production of municipal drinking water[6 20]

Advantages and disadvantages

dagger The advantages include a lower theoretical energy require-ment minimal potential for corrosion and little scaling orsalt precipitation

dagger It can produce very pure potable water and it has specialadvantages to produce water for irrigation [36]

dagger The disadvantage is that it involves handling ice and watermixtures that are mechanically complicated to move andprocess [6]

232 Ion exchange solvent processIn the last 50 years ion exchange membranes have been movedfrom a laboratory tool to industrial products with a significanttechnical and commercial impact Today ion exchange mem-branes are receiving considerable attention and are successfullyapplied in the desalination of sea and brackish water and intreating industrial effluents They are efficient tools for theconcentration or separation of food and pharmaceutical pro-ducts containing ionic species as well as in the manufacture ofbasic chemical products [37] Ion exchangers are organic or in-organic solids that are capable of exchanging one type ofcation (or anion) immobilized in the solid for another type ofcation (or anion) in solution For example Nathorn ions in solu-tion can be replaced with Hthorn by a cation exchanger and Cl2

can subsequently be replaced with OH2 by an anion exchangerresulting in the complete lsquodemineralizationrsquo of a NaCl solutionThe process can be reversed by regenerating the cation

exchanger with an acid and the anion exchanger with a baseIn practice ion exchange is a useful process for completely de-mineralizing water in applications where high purity isrequired as in high-pressure boilers Unfortunately it is notsuited to treat and desalinate brackish or sea water simplybecause its costs are prohibitive [38 39]

3 RENEWABLE ENERGY WATERDESALINATION

The potential use of renewable energy as a clean friendlysource of energy to operate small-scale desalination units inremote communities has received increasing attention in recentyears [40] The coupling of renewable energy sources and desal-ination such as solar wind and geothermal energy with desal-ination systems holds great promise for tackling water shortageand is a potential for viable solution of climate change andwater scarcity [41]

An effective integration of these technologies will allowcountries to address water shortage problems with a domesticenergy source that does not produce air pollution or contributeto the global problem of climate change due to lower conven-tional energy consumption and lower gas emissionsMeanwhile the cost of desalination and renewable energysystems are steadily decreasing while fossil fuel prices arerising and its supplies are depleting The desalination unitspowered by renewable energy systems are uniquely suited toprovide water and electricity in remote areas where water andelectricity infrastructures are currently lacking [42] The rapidincrease in demand for energy is making the world focus onalternative sustainable sources In 2008 10 of the generatedelectricity worldwide was produced by renewable energysources (hydropower biomass biofuels wind geothermal andsolar) A recent assessment conducted by the US Energy infor-mation administration forecasts that by 2035 consumption ofrenewable energy will be 14 of total world energy con-sumption which shows strongest growth in global electric gen-erating capacity as illustrated in Figure 12 [43]

The majority of desalination systems that use a renewableenergy source can be divided into three categories wind solar[photovoltaics (PVs) or solar collectors] and those that usegeothermal energy These renewable energy sources can becoupled with thermal distillation or membrane desalinationsystems as shown in Figure 13 to produce water In some cases[34 44] these systems are connected with a conventionalsource of energy (eg local electricity grid) in order to minim-ize the variations in the level of energy production and conse-quently water production [45] When renewable energy sourcesare used to operate the RO plants the cost was found to dra-matically increase (1032 $m3) due to high cost of desalinationunit capital cost [46]

It has become obvious that the solar energy is themost widely used among other renewable energies as illustrated

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in Figure 14 For the relative distribution betweendesalination processes using renewable energy sources seeQuteishat et al [47]

31 Solar-powered water desalination311 Introduction to solar energyThe sun was adored by many ancient civilizations as a powerfulGod and solar energy is the oldest energy source used byhuman beings The first known practical application was indrying for food preservation Scientists have long looked atsolar radiation as a source of energy trying to convert it into auseful form for direct utilization Archimedes the Greek math-ematician and philosopher (287ndash212 BC) used the sunrsquosreflected heat to burn the Roman fleet in the Bay of Syracuse[32] During the eighteenth century the French naturalistBoufon experimented with various solar energy devices whichhe called lsquohot mirrors burning at long distancersquo [48] Mostforms of energy are solar in origin Oil coal natural gas andwood were originally produced by photosynthetic processes[49] Even wind and tide energy have a solar origin since they

are caused by differences in temperature in various regions ofthe earth The great advantages of solar energy compared withother forms of energy are that it is clean sustainable and canbe used without any environmental pollution Solar energy isused to heat and cool buildings to heat water for domesticand industrial uses to heat swimming pools to power refrig-erators to operate engines and pumps to desalinate water fordrinking purposes to generate electricity in chemistry applica-tions and for many more functions The decision about whichsource of energy to use should be made on the basis of eco-nomic environmental and safety considerations Because of itsdesirable environmental and safety advantages it is widelybelieved that where possible solar energy should be utilizedinstead of energy derived from fossil fuels even when the costsinvolved are slightly higher [50] This section focuses on thedesalination of saline water by using solar energy

312 Water desalination using solar powerSolar water desalination has a long history The first documen-ted use of solar stills was in the sixteenth century and in 1872the Swedish engineer Carlos Wilson built a large-scale solarstill to supply a mining community in Chile with drinkingwater [51] Solar desalination using humidification and dehu-midification is a promising technique for producing freshwater especially in remote and sunny regions It has the poten-tial to make a significant contribution to providing humanswith fresh water using a renewable free and environmentallyfriendly energy source [52] Solar energy can be used toconvert saline water into fresh water with simple low cost andeconomical technology and thus it is suitable for small com-munities rural areas and areas where the income level is verylow [53] Recent developments have demonstrated that solar-powered desalination processes are better than the alternativesincluding ED RO and freezing for fresh water provision inremote rural areas [54] Solar-powered desalination processesare generally divided into two categories direct and indirectsystems

Direct systems The direct systems are those where the heatgaining and desalination processes take place naturally in the

Figure 13 Combinations of renewable energy resources with water

desalination technologies

Figure 12 World renewable electricity generation forecast [43]

Figure 14 Renewable energy sources for desalination

Water desalination technologies

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same device The basin solar still represents its simplest appli-cation the still working as a trap for solar radiation that passesthrough a transparent cover

Solar still Solar still distillation represents a natural hydro-logic cycle on a small scale The basic design of a solar stillwhich is similar to a greenhouse is shown in Figure 15 Solarenergy enters the device through a sloping transparent glass orplastic panel and heats a basin of salt water The basin is gener-ally black to absorb energy more efficiently The heated waterevaporates and then condenses on the cooler glass panels Thecondensed droplets run down the panels and are collected foruse as fresh water Experience proves that 1 m2 of groundwill produce 3ndash4 lday of freshwater Because of this low pro-duction it is important to minimize capital costs by using veryinexpensive construction materials Efforts have been made byvarious researchers to increase the efficiency of solar stills bychanging the design by using additional effects such as multi-stage evacuated stills and by adding wicking material etc andthese modifications have increased production per unit area[6] In the simple solar still shown in Figure 15 the latent heat

of condensation is dissipated to the environment However thelatent heat of condensation can be used to preheat the feedwater and this obviously leads to an improvement in the stillefficiency

Advantages and disadvantages of the solar still Solar stilltechnology requires a large area for solar collection so it is notviable for large-scale production especially near a city whereland is scarce and expensive The comparative installation coststend to be considerably higher than those for other systemsThey are also vulnerable to damage by weather Labour costsare likely to be high for routine maintenance to prevent scaleformation and to repair vapour leaks and damage to the stillrsquosglass [6 38] However they can be economically viable forsmall-scale production for households and small communitiesespecially where solar energy and low cost labour are abundant[6 53]

Indirect systems In these systems the plant is separated intotwo subsystems a solar collector and a desalination unit Thesolar collector can be a flat plate evacuated tube or solar con-centrator and it can be coupled with any of the distillation unittypes described previously which use the evaporation and con-densation principle such as MSF VOC MED and MD forpossible combinations of thermal desalination with solarenergy Systems that use PV devices tend to generate electricityto operate RO and ED desalination processes [38] Figure 16shows the worldwide use of the various desalination technolo-gies using solar power sources [55]

Factors for the selection of solar collectors There are manyfactors that influence the selection of solar collectors for desal-ination processes The flat plate and evacuated tube solar col-lectors are appropriate for low-temperature processes whichuse heat to evaporate the saline water often utilizing low-pressure conditions created with vacuum pumps Evacuatedtube collectors ensure some energy even on cloudy days andtheir efficiency at high-operating temperatures or low insola-tion is significantly better than that of flat-plate collectorsCylindrical tracking collectors can be more efficient than evac-uated tube collectors but they have almost no output oncloudy days and collect only a small fraction of the diffuse ra-diation Parabolic concentrating collectors require very accuratetwo-axis tracking mechanisms but they can produce tempera-tures of more than 1208C which is higher than the tempera-ture needed for solar desalination [56] The selection of themost appropriate solar desalination technology is affected bymany factors including plant size feed water salinity remote-ness availability of grid electricity technical infrastructure andthe type of solar technology available

There are several possible combinations of desalination andsolar energy technologies that could have more promisingwater production in terms of economic and technologicalfeasibility than others Some combinations are better suited forlarge-size plants whereas some others are better suited forsmall-scale applications Prior to any process selection thewater resources should be investigated Brackish water is the

Figure 15 Solar still unit [38]

Figure 16 Water desalination technologies coupled with solar power sources

installed worldwide [44]

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most economical as its salinity is normally much lower (10000 ppm) and the energy requirement would be lower asexplained earlier in the literature

Solar still coupled with solar collectors In order to increasestill productivity many researchers have experimented withcoupling a single still or multi-effect stills with solar collectorsas shown in Figures 17 and 18 respectively Coupling morethan one solar still with such solar collector panels producesan increase in efficiency through utilizing the latent heat ofcondensation in each effect to deliver heat to the next stage

Solar humidification and dehumidification Potable watermay be obtained from saline water through a humidificationndashdehumidification cycle In this process saline water is evapo-rated by thermal energy and the subsequent condensation ofthe generated humid air usually at atmospheric pressure pro-duces freshwater [57] Air has the capability to hold large quan-tities of water vapour and its vapour carrying capabilityincreases with temperature [58] Many studies on desalinationusing humidificationndashdehumidification have been conductedwith a variety of fabricated devices [59] The principle of this

desalination process is based on the evaporation of water andthe condensation of steam from humid air The humid airflows in a clockwise circuit driven by natural convectionbetween the condenser and the evaporator as shown inFigure 19 In this example the evaporator and condenser arelocated in the same thermally insulated box Seawater is heatedin the evaporator and distributed slowly as it trickles down-wards The air moves in a countercurrent flow to the brinethrough the evaporator and becomes saturated with humidityPartial evaporation cools the brine that is left in the evaporationunit and it now has a higher salt concentration while the satu-rated air condenses on a flat-plate heat exchanger

The distillate runs down the plates and trickles into a col-lecting basin The heat of condensation is mainly transferred tothe cold seawater flowing upwards inside the flat-plate heat ex-changer Thus the temperature of the brine in the condenserrises from 408C to 758C In the next step the brine is heatedto the evaporator inlet temperature which is between 80 and908C The salt content of the brine as well as the condenserinlet temperature can be increased by a partial reflux from theevaporator outlet to the brine storage tank [60] Then distillatecan be collected in a vessel and the brine goes also to salinewater tank to recover a portion of the heat

Water desalination powered by solar PV Solar PV systemsfor generating electricity have become more popular due to therecent introduction by governments of Feed in Tariffs systemwhich enable their owners to sell some or all of the electricitythey generate thus reducing the payback period and increasingthe attractiveness of this technology [61] Solar PV systems dir-ectly convert sunlight into electricity by using solar cells madefrom silicon or other semiconductor materials Usually anumber of solar cells are connected together to form a PVmodule which supplies the power required by the needed

Figure 17 Schematic diagram of a single solar still coupled with a solar

collector [2]

Figure 18 Schematic diagram of multi-effect solar still coupled with a solar collector [80]

Water desalination technologies

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load In addition to the PV module power-adapting equip-ment (eg charge controller inverters and energy storageequipment) such as batteries might be required to supplyenergy to a desalination plant Charge controllers are used forthe protection of the battery from overcharging Inverters areused to convert the direct current from the PV modules systemto alternating current to the loads The rapid development ofPV technology and the dramatic recent decrease in the PV cellprices in the market have made several desalination technolo-gies more affordable especially for remote and poor areas indeveloping countries Currently (November 2011) the lowestretail price for a multicrystalline silicon PV module is $131(pound085) per watt from a US retailer or $128 (pound083) per wattfrom an Asian retailer However at this price of the cost of thePV module represents only 40 of the total cost of a solar PVsystem The total current cost including the necessary poweradapting equipment is shown in Table 1 [62]

The PV generator can be connected either with RO or EDwater desalination technology as described previously [63]Figure 20 shows the assembly of an RO desalination plantcoupled with a PV generator with multi-PV modules toproduce electricity a charge controller to protect the batteryblock from deep discharge and overcharge a set of batteryblocks to stabilize the energy input to the RO unit and to com-pensate for solar radiation variations and an RO unit to desal-inate the water

4 ECONOMICS AND PERFORMANCE OFDESALINATION PROCESSES

Phase change water desalination processes which use conven-tional sources of fuel and energy and which usually have largeproduction capacities are more expensive than membraneplants because of the large quantities of fuel required to vapor-ize salt water Membrane methods are also more economicalfor brackish water desalination [45] A detailed cost compari-son is illustrated in the next section

41 Economics of thermal desalination processesThermal process desalination plants are mostly operated byfossil fuel which jeopardizes a high cost of desalination perunit cost In the case of multi-effect distillation (MED) thecost for large systems with a daily production from 91 000 to320 000 m3 ranges between 052 and 101 $m3 These costsrefer to examples of plants built between 1999 and 2009 withthe most recent having lower costs and the older installationsbeing the most expensive [45] For medium-sized systemswith a daily production from 12 000 to 55 000 m3 the costranges between 095 and 15 $m3 For small systems with adaily capacity around 100 m3 the cost varies between 250 and10 $m3 For the MSF method the cost can vary between 052and 175 $m3 for systems with a daily production of 23 000 to528 000 m3 The cost is reduced when MSF is coupled withelectric power generation in a cogeneration plant

Figure 19 Schematic diagram of the distillation systemmdashadapted from [60]

Table 1 PV solar system elements and cost adapted from [62]

SN Solar PV system elements Prices

in US$

Prices in

GBP pound

1 PV Module per Wp 128 083

2 Inverter per Wp 0714 0462

3 Battery per Wp 0213 0138

Subtotal 2207 143

4 Charge controller 10 of total system cost 022 0143

Total 2427 1573

Figure 20 Schematic diagram of RO desalination unit coupled with a PV

generator

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VC is used mainly for small systems with production ofaround 1000 m3day and a cost that ranges between and 201and 266 US$m3 [64 65] Table 2 shows the water unit cost forvarious thermal desalination processes

42 Economics of water desalination usingmembrane processesThe cost of membrane desalination technology has steadilydecreased from its commercial introduction in 1970s untiltoday despite rising energy prices Recent developments inmembrane materials pumping and energy recovery systems

have dramatically reduced the energy consumption in RO de-salination processes as shown in Figures 21 and 22 respectively[66 67]

The cost of water desalination in membrane processes variesaccording to the type and composition of the feed waterLarge-scale RO plants can use brackish water containing totaldissolved solids (TDS) of from 2000 to 10 000 ppm [68] butas TDS concentrations increase the unit cost of the desalinatedwater also increases as shown in Figure 22 [69] The cost ofbrackish water desalination in the Middle East with a TDS con-centration of 2300 ppm is 026 $m3

while in Florida forbrackish water with a TDS of 5000 ppm it is 027 $m3 [70]In small-scale RO units the costs are greater For example thecost of a desalination unit of 1000 m3day ranges from 078 to123 $m3 [71 72] or even 133 $m3 [73] For the desalinationof seawater the RO method has been used more and more inrecent years as the cost of membranes has fallen but it is stillslightly costly [74] For instance the estimated water produc-tion cost for the worldrsquos largest RO seawater desalination plantat Ashkelon in Israel with a capacity of 320 000 m3day is052US$m3 [75] and costs at an RO plant with a capacity of94 600 m3day in Tampa Bay in USA was reported to be at$056m3 [76] Table 3 shows typical costs for RO desalinationof brackish water and seawater [45]

43 Summary of water desalination economicsTo sum up the desalination systems can be operated by theuse of conventional and renewable energy sources and the vastmajority of desalination plants over the world are currentlyoperated by fossil fuel instead of renewable energy due to tech-nical and economical barriers From the literature it has beenconcluded that the cost of water produced from desalinationsystems using a conventional source of energy is much lowerthan those powered by renewable energy sources Generallywater desalination prices have been decreased over the recentyears due to technical improvements and research advance-ments in technologies In conventional systems the cost forseawater desalination ranges from 035 Eurom3 to more than

Figure 21 Development of achievable energy consumption in RO

desalination processes

Table 2 Cost of desalinated water in thermal processes

Desalination process Capacity of desalination

plant (m3day)

Desalination cost

per m3 (US$)

Multi-effect distillation MED 100 25ndash10

12 000ndash55 000 095ndash195

91 000 052ndash101

Multi-stage flash MSF 23 000ndash528 000 052ndash175

Vapour compression 1000ndash1200 201ndash266

Figure 22 Energy requirement for RO desalination (Sea and Brackish Water Feed)

Water desalination technologies

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27 Eurom3 while for brackish water desalination the cost isalmost half When renewable energy sources are used the costis much higher and in some cases can reach even 1032 Eurom3due to most expensive energy supply systems However thiscost is counter balanced by the environmental benefits Table 4summarizes the cost of fresh water when the desalinationsystem is powered by conventional and renewableenergy sources

RO methods which become dominant in the desalinationof brackish and seawater have the lowest cost mainly due tomuch lower energy consumption and the recent technologicaladvances that have been achieved in membranes and energy re-covery systems Therefore the potential of coupling solarenergy sources with desalination systems are cost promisingespecially in the Middle East and areas of plentiful sun avail-ability Table 5 illustrates the performance and cost of varioussolar desalination plants

5 HEALTH AND ENVIRONMENTALASPECTS

The number of desalination plants worldwide is growingrapidly and as the need for fresh water supplies grows moreacute desalination technologies improve and unit costs arereduced Desalination processes should aim to be environmen-tally sustainable Most drinking water applications use WHOdrinking water guidelines as water quality specificationslsquoWHO Guidelines for Drinking-water Qualityrsquo cover a broadspectrum of contaminants including inorganic and syntheticorganic chemicals disinfection by-products microbial

indicators and radionuclides and are aimed at typical drinkingwater sources and technologies Currently WHO says thatexisting guidelines may not fully cover the unique factors thatcan be encountered during the intake production and distri-bution of desalinated water Hence it imposes stringent guide-lines not only for drinking water quality but also forenvironmental protection issues This is in order to assist withthe optimization of both proposed and existing desalination fa-cilities and to ensure that nations and consumers will be ableto enjoy the benefits of the expanded access to desalinatedwater with the assurance of quality safety and environmentalprotection [77] Obviously the intake and pre-treatment ofseawater as well as the discharge of the concentrate reject waterproduced have to be adapted to the specific conditions at thesite of each desalination plant Hence it is necessary to con-sider and evaluate the criteria that help to select the best avail-able technology and the optimal solution for the intake andoutfall system at each plant These environmental aspects arejust as important as the commercial details and must be con-sidered in the design and construction phases and during plantoperation Important elements regarding the environmentalimpact requirements that should be considered for differentoptions are [77 78]

dagger Concentrate discharge standards and locationsdagger Wastewater discharge standardsdagger Air pollution control requirementsdagger Noise control standardsdagger Land usedagger Public services and utilitiesdagger Aesthetics light and glare

6 CONCLUSIONS AND OUTLOOK

The desalination of brackish water and seawater is proving tobe a reliable source of fresh water and is contributing to tack-ling the worldrsquos water shortage problems This article has

Table 4 Type of energy supplied and water production cost [45]

Type of feed water Type of energy Water cost (Eurom3)

Brackish water Conventional fuel 021ndash106

Photovoltaic cells 45ndash1032

Geothermal 2

Sea water Conventional fuel 035ndash270

Wind energy 10ndash50

Photovoltaic cells 314ndash90

Solar collectors 35ndash80

Table 3 Cost of desalinated water in membrane (RO) plants

Type of feed water Capacity of desalination

plant (m3day)

Desalination cost

per m3 (US$)

Brackish water 20 563ndash129

20ndash1200 078ndash133

40 000ndash46 000 026ndash054

Seawater 100 15ndash1875

250ndash1000 125ndash393

15 000ndash60 000 048ndash162

100 000ndash320 000 045ndash066

Table 5 Performance and cost of various solar desalination plantsadapted from [45 81]

Technology Feed water type Specific energy

consumption

(kWhm3)

Recovery

ratio ()

Water cost

(US$m3)

MSF Seawater brackish

water

81ndash144 (thermal) 06ndash6 1ndash5

MED Seawater brackish

water

50ndash194 (thermal) 6ndash38 2ndash9

MD Seawater brackish

water

100ndash600

(thermal)

3ndash5 13ndash18

RO Seawater brackish

water

12ndash19 (electric) 10ndash51 3ndash27

ED Brackish water 06ndash1 (electric) 25ndash50 3ndash16

M Shatat and SB Riffat

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reviewed a number of thermal and membrane water desalin-ation processes developed during recent decades The advan-tages and disadvantages including economic for eachdesalination technology have also been covered In recent yearsthere have been considerable developments in membrane desal-ination processes especially in terms of the design of mem-brane module energy recovery and pre-treatment methodswhich have made it cost competitive with thermal processesThe use of renewable energies for desalination becomes a rea-sonable and technically mature alternative to the emerging andstressing energy situation and a sustainable solution for waterscarcity Currently coupling desalination plants with cleanenvironment-friendly energy resources is a pressing issue dueto the dramatic increase in fossil fuel prices and the harmfulimpacts of burning fossil fuels such as environmental pollu-tion and climate change

The scarcity of drinking water limits the socio-economic de-velopment in many areas where solar resources are abundantHence the use of solar energy for water desalination in coun-tries in Africa and the Middle East region which have plenty ofsolar energy is a promising issue for meeting water demandand would definitely contribute both towards solving waterscarcity problems and reducing carbon dioxide emissions bymeans of an environmentally friendly process

Collective research and development programmes involvingall the stakeholdersmdashgovernments industries universities andresearch institutionsmdashare required to improve and develop sea-water desalination technologies to make them affordableworldwide and especially in countries lacking conventionalforms of energy and suffering shortages of water Accordinglyvarious water desalination systems require extensive researchand analysis for evaluating their potentials of developmentapplications and performance The most mature technologiesof renewable energy application in desalination are wind andPV-driven membrane processes and direct and indirect solardistillation The connection of RO membrane technologywould be considered the most cost-competitive solar desalin-ation technologies approaching conventional desalinationwater costs Hence the linkage of photovoltaic cells and mem-brane water desalination processes could be also considered thesecond most competitive alternative for brackish water desalin-ation because of low water cost as presented in El-Nashar [79]in addition to the current rapid decrease in PV modules pricesin the market However solar distillation may be advantageousfor seawater desalination as solar-MED is recommended forlarge-scale solar desalination other renewable energy resourceshave to be taken into account such as wind and geothermalenergy which could be suitable for different desalination pro-cesses at viable costs Moreover the coupling of renewableenergy and desalination systems has to be optimized andfurther technical research development of renewable energyaugmented desalination technologies that require little main-tenance and waste heat source are recommended which areuniquely suited to provide fresh water in remote areas wherewater and electricity infrastructure are currently lacking

REFERENCES

[1] United Nations Environment Programme httpwwwuneporgthemes

freshwaterhtml (10 April 2008)

[2] Al-Kharabsheh S Theoretical and experimental analysis of water desalin-

ation system using low grade solar heat PhD dissertation University of

Florida 2003

[3] Colombo D De Gerloni M Reali M An energy-efficient submarine desal-

ination plant Desalination 1999122171ndash6

[4] WHOEU drinking water standards comparative table Water treatment amp

Air purification and other supporting information httpwwwlenntech

comWHO-EU-water-standardshtml (26 October 2007)

[5] Tiwari GN Singh HN Tripathi R Present status of solar distillation Solar

Energy 200375367ndash73

[6] Buros OK The ABCs of Desalting 2nd edn ASIN B0006S2DHY

International Desalination Association 2000 30

[7] Buros OK The ABCs of Desalting International Desalination Association

1999 31

[8] Gleick PH (ed) The Worldrsquos Water The Biennial Report of Fresh Water

Resources 1998ndash1999 Island Press 1998

[9] WDI Water Desalination International Introduction Published by WDI

httpwwwaterdesalinationcomintroductionhtm (21 April 2008)

[10] Al-Kharabsheh S Yogi Goswami D Analysis of an innovative water

desalination system using low-grade solar heat Desalination

2003156323ndash32

[11] Winter T Pannell J McCann Mc The Economics of Desalination and Its

Potential Application in Australia University of Western Australia 2005

[12] Raluy RG Serra L Uche J et al Life-cycle assessment of desalination tech-

nologies integrated with energy production systems Desalination

2004167445ndash58

[13] Multi Stage Flash Halcrow Water Services httpwwwhwsdesalination

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[14] Hamed O Mustafa GM BaMardouf K et al Prospects of improving

energy consumption of the multi-stage flash distillation process In

Proceedings of the Fourth Annual Workshop on Water Conservation in

Dhahran the Kingdom of Saudi Arabia 2001

[15] Water Desalination Technologies in the ESCWA Member Countries

UN-ESSWA ASIN EESCWATECH20013 United Nations 2001 172

[16] Introduction to desalination technologies httpwwwtexaswatertamu

edureadingsdesalIntrotoDesalpdf (2 October 2007)

[17] Khawaji AD Wie J-M Potabilization of desalinated water at Madinat

Yanbu Al-Sinaiyah Desalination 199498135ndash46

[18] Wangnick K IDA worldwide desalting plants inventory report No 16

Produced by Wangnick Consulting for the International Desalination

Association 2000

[19] Al-Shammiri M Safar M Multi-effect distillation plants state of the art

Desalination 199912645ndash59

[20] Khawaji AD Kutubkhanah IK Wie J-M Advances in seawater desalination

technologies Desalination 200822147ndash69

[21] Darwish MA El-Dessouky H The heat recovery thermal vapour-

compression desalting system a comparison with other thermal desalin-

ation processes Appl Thermal Eng 199616523ndash37

[22] El-Nashar AM Cogeneration for power and desalinationmdashstate of the art

review Desalination 20011347ndash28

[23] The Desalting and Water Treatment Membrane Manual A Guide to

Membranes for Municipal Water Treatment Water Treatment Technology

Program Report No 1 September 1993 published by the United States

Department of the Interior Bureau of Reclamation Denver Office

Research and Laboratory Services Division Applied Sciences Branch

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(R-93-15) httpwwwusbrgovpmtswaterpublicationsreportpdfs

report001pdf (15 March 2008)

[24] Ayyash Y Imai H Yamada T et al Performance of reverse osmosis mem-

brane in Jeddah Phase I plant Desalination 199496215ndash24

[25] Khawaji AD Kutubkhanah IK Wie J-M A 133 MGD seawater RO

desalination plant for Yanbu Industrial City Desalination 2007203

176ndash88

[26] AL Mobayed AA Balaji S Successful Operation of Pretreatment in

Al-Jubail SWRO Plant Paper presented at IDA World Congress on

Desalination amp Water Reuse Conference 11ndash16 September 2005 pp 12

[27] Al-Sheikh AHH Seawater reverse osmosis pretreatment with an emphasis

on the Jeddah Plant operation experience Desalination 1997110183ndash92

[28] Kayyal M Study on Wastewater Treatment and Water Desalination

Technologies for ESCWA Countries United Nations 2000

[29] Bou-Hamad S Abdel-Jawad M Al-Tabtabaei M et al Comparative per-

formance analysis of two seawater reverse osmosis plants twin hollow fine

fiber and spiral wound membranes Desalination 199812095ndash106

[30] El-Dessouky H Ettouny H Study on Water Desalination Technologies

Prepared for ESCWA United Nations 2001

[31] Strathmann H Winston WS Sirkar KK Membrane Handbook

ISBN-0-442-23747-2 Van Nostrand Reinhold 1992 246ndash54

[32] Kalogirou SA Seawater desalination using renewable energy sources Prog

Energy Combust Sci 200531242ndash81

[33] Findley ME Vaporization through porous membranes Ind Eng Chem

Process Des Dev 1967 6 226

[34] Mathioulakis E Belessiotis V Delyannis E Desalination by using alterna-

tive energy review and state-of-the-art Desalination 2007203346ndash65

[35] Tomaszewska M Membrane distillationmdashexamples of applications in

technology and environmental protection Polish J Environ Stud

2000927ndash36

[36] Rice W Chau DSC Freeze desalination using hydraulic refrigerant com-

pressors Desalination 1997109157ndash64

[37] Xu T Ion exchange membranes State of their development and perspec-

tive J Membrane Sci 20052631ndash29

[38] Miller J Review of Water Resources and Desalination Technologies Materials

Chemistry Department Sandia National Laboratories 2003 httpwww

prodsandiagovcgi-bintechlibaccess-controlpl2003030800pdf (3

March 2008)

[39] Introduction to Desalination Technologies in Australia 2002 httpwww

environmentgovauwaterpublicationsurbandesalination-summaryhtml

(13 April 2008)

[40] Werner M Schafer AI Social aspects of a solar-powered desalination unit

for remote Australian communities Desalination 2007203375ndash93

[41] Renewable desalination market analysis in Oceania South Africa

Middle East amp North Africa 2010 wwwaquamarinepowercom

(November 2011)

[42] Mahmoudi H Abdellah O Ghaffour N Capacity building strategies and

policy for desalination using renewable energies in Algeria Renew Sustain

Energy Rev 2008 in press

[43] US Energy information administration International Energy Outlook

2010mdashhighlights httpwwweiadoegov (26 November 2011)

[44] Ali MT Fath HES Armstrong PR A comprehensive techno-economical

review of indirect solar desalination Renew Sustain Energy Rev

2011154187ndash99

[45] Karagiannis IC Soldatos PG Water desalination cost literature review and

assessment Desalination 2008223448ndash56

[46] Tzen E Renewable energy sources for desalination Paper presented at

Workshop on Desalination Units Powered by RES Athens 2006

[47] Quteishat K Abu Arabi M Promotion of solar desalination in the MENA

region report Middle East Desalination Research Centre 2004

[48] Delyannis E Historic background of desalination and renewable energies

Sol Energy 200375357ndash66

[49] Kreith F Kreider JF Principles of Solar Engineering McGraw-Hill 1978

[50] Kalogirou SA Solar thermal collectors and applications Prog Energy

Combust Sci 200430231ndash95

[51] Intermediate Technology Development Group Solar Distillation Technical

Brief The Schumacher Centre for Technology amp Development http

wwwitdgorgdocstechnical_information_service (8 October 2007)

[52] Fath HES Ghazy A Solar desalination using humidificationndashdehumidifi-

cation technology Desalination 2002142119ndash33

[53] Ali Samee M Mirza UK Majeed T et al Design and performance of a

simple single basin solar still Renew Sustain Energy Rev 200711543ndash9

[54] Abdel-Rehim ZS Lasheen A Improving the performance of solar desalin-

ation systems Renew Energy 2005301955ndash71

[55] Kaushal A Varun Solar stills a review Renew Sustain Energy Rev

201014446ndash53

[56] Hamed OA Eisa EI Abdalla WE Overview of solar desalination

Desalination 199393563ndash79

[57] The Encyclopedia of Desalination and Water Resources (DESWARE) http

wwwdeswarenet (8 October 2007)

[58] Parekh S Farid MM Selman J et al Solar desalination with a humidifica-

tionndashdehumidification techniquemdasha comprehensive technical review

Desalination 2004160167ndash86

[59] Orfi J Galanis N Laplante M Air humidificationndashdehumidification for a

water desalination system using solar energy Desalination 2007203

471ndash81

[60] Muller-Holst H Engelhardt M Scholkopf W Small-scale thermal seawater

desalination simulation and optimization of system design Desalination

1999122255ndash62

[61] Renewable energy solutions httpwwwenvikocomtechnologysolar-pv

(29 November 2011)

[62] Solar energy markets and growth httpwwwsolarbuzzcomfacts-and-Fig

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[63] Mahmoud MM Ibrik IH Techno-economic feasibility of energy supply of

remote villages in Palestine by PV-systems diesel generators and electric

grid Renew Sustain Energy Rev 200610128ndash38

[64] Voivontas D Misirlis K Manoli E et al A tool for the design of desalin-

ation plants powered by renewable energies Desalination 2001133175ndash98

[65] Zejli D Benchrifa R Bennouna A et al Economic analysis of wind-

powered desalination in the south of Morocco Desalination

2004165219ndash30

[66] Fritzmann C Lowenberg J Wintgens T et al State-of-the-art of reverse

osmosis desalination Desalination 20072161ndash76

[67] Stover RL Energy recovery devices for seawater reverse osmosis 2006

Retrieved 4 May 2008 from the World Wide Web httpwww

energyrecoverycomnewsdocumentsERDsforSWROpdf

[68] Delyianni E Belessiotis B Methods and Desalination SystemsmdashPrinciples of

the Desalination Process NCSR lsquoDemokritosrsquo 1995

[69] Liu C Rainwater K Song L Energy analysis and efficiency assessment of

reverse osmosis desalination process Desalination 2011276352ndash8

[70] Avlonitis SA Operational water cost and productivity improvements for

small-size RO desalination plants Desalination 2002142295ndash304

[71] Al-Wazzan Y Safar M Ebrahim S et al Desalting of subsurface water

using spiral-wound reverse osmosis (RO) system technical and economic

assessment Desalination 200214321ndash8

[72] Jaber IS Ahmed MR Technical and economic evaluation of brackish

groundwater desalination by reverse osmosis (RO) process Desalination

2004165209ndash13

[73] Sambrailo D Ivic J Krstulovic A Economic evaluation of the first desalin-

ation plant in Croatia Desalination 2005179339ndash44

M Shatat and SB Riffat

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[74] IDA Desalination Yearbook 2006ndash2007 Water Desalination Report Global

Water Intelligence and International Desalination Association

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Water technology net httpwwwwater-technologynetprojectsIsrael

(21 November 2011)

[76] Wilf M Bartels C Optimization of seawater RO systems design

Desalination 20051731ndash12

[77] Desalination for Safe Water Supply Guidance for the Health and

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2008)

[78] Peters T Pinto D Seawater intake and pre-treatmentbrine dischargemdash

environmental issues Desalination 2008221576ndash84

[79] El-Nashar AM The economic feasibility of small solar MED seawater

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[80] Shatat MIM Mahkamov K Determination of rational design parameters

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[81] Miller JE Review of Water Resources and Desalination Technologies Sandia

National Laboratories 2004 49 pp httpwwwsandiagovwaterdocs

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