existing ro plant in yanbu.pdf

A 13.3 MGD seawater RO desalination plant for YanbuIndustrial City

Akili D. Khawaji*,a, Ibrahim K. Kutubkhanaha, Jong-Mihn Wieb

aRoyal Commission for Jubail & Yanbu, P.O. Box 30031, Yanbu Al-Sinaiyah, Saudi Arabia ADK,Tel: 966 4 321 6100; Fax: 966 4 396 0292; email: [email protected] IKK, Tel: 966 4 321 6500;

Fax: 966 4 396 3000; email: [email protected] Arabian Parsons Limited, P.O. Box 30167, Yanbu Al-Sinaiyah, Saudi Arabia

Tel: 966 4 321 6039; Fax: 966 4 396 0503; email: [email protected]

Received 29 January 2006; accepted 12 February 2006

Abstract

This paper presents the major design criteria and features for the 13.3 million gallons per day (MGD)

seawater reverse osmosis (RO) desalination plant that is currently under construction in Madinat Yanbu

Al-Sinaiyah, Yanbu Industrial City, in the Kingdom of Saudi Arabia. The seawater RO plant is made up of

six trains of about 2.2 MGD capacity each. The plant consists of five major systems: seawater supply, seawater

pretreatment, high pressure pumping, RO modules, and permeate posttreatment. The paper also discusses

technical issues and parameters associated with the plant design, and advances made in the seawater reverse

osmosis desalination technology.

Keywords: Seawater reverse osmosis desalination; Plant design; Seawater supply; Pretreatment; Reverse osmosis

module; Permeate posttreatment; Yanbu Industrial City

1. Introduction

The Royal Commission for Jubail andYanbu (RC) is the Saudi government entityentrusted with the mission and responsibility

planning, developing, operating, and

managing the two modern, large world-classindustrial cities in the Kingdom of SaudiArabia. There is one at Madinat Al-JubailAl-Sinaiyah (Jubail Industrial City) on theGulf and one at Madinat Yanbu Al-Sinaiyah

Desalination 203 (2007) 176–188

*Corresponding author.

Presented at EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperationbetween Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European

Desalination Society and the University of Montpellier II, Montpellier, France, 21-25 May 2006

doi:10.1016/j.desal.2006.02.018

_\ 0011-9164/07/$– See front matter � 2007 Published by Elsevier B.V.

of

(MYAS, Yanbu Industrial City) on the RedSea. MYAS is located on the coastline about320 km northwest of Jeddah. Until 2002 theRC Yanbu had operated and maintained themajor utility infrastructure facilities includingthe power, desalination and seawater coolingcomplex, in order to support the MYAScommunity and industries. Because of thearid desert area, MYAS depends on seawaterdesalination for its entire fresh water supply.The 25.3 million gallons per day (MGD)(95,760 m3/day) seawater desalination plantconsists of six 9120 m3/day (2.4 MGD) andthree 13,680 m3/day (3.6 MGD) multi-stageflash (MSF) distillation units.

Because of the projected growth of theMYAS community and industries, additionalseawater desalination units are required tomeet future water demand. The existing desa-lination plant operation with the MSF pro-cess has been very reliable. Out of the twomajor seawater desalination processes for theproduction of fresh water from the sea inlarge quantities, the reverse osmosis (RO)process has gained some popularity andacceptance in recent years due to its simpli-city, improved membrane performance andcost effectiveness for certain sites [1,2].

The major world large seawater RO desa-lination plants include 45 MGD Fujairahplant in UAE [3], 36 MGD Singapore plant[4], 33.1 MGD Point Lisas plant in Trinidad[5], 25 MGD Tampa Bay plant in USA [6],14.9 MGD Marbella plant in Spain [7], 13.2MGD Fukuoka plant in Japan [8], 12 MGDAddur plant in Bahrain [9], and 10.6 MGDOkinawa plant in Japan [10].

In the Kingdom of Saudi Arabia there is alarge number of RO desalination plants ofvarious sizes for both brackish water and sea-water [11]. There are large seawater RO desa-lination plants and several smaller size ROplants (0.6–1.2 MGD) in operation on theGulf and the Red Sea [12]. The large seawater

RO plants built and operated by the SalineWater Conversion Corporation (SWCC)include two 15 MGD Jeddah plants [13–15],24 MGD Jubail plant [16,17] and 33.8 MGDMadina-Yanbu plant [18]. These plants provethe RO process to be very successful indesalination of Saudi Arabian seawaters.

The RC Yanbu has had experience inoperating and maintaining a 1.3 MGD sea-water RO desalination plant that wasinstalled in 1981 [19]. This plant was one ofthe first major RO plants adopted in theworld for desalination of seawater. Theplant was built as a construction supportfacility to supply potable water to MYASuntil the permanent MSF desalination plantwas installed and fully operational. The ROplant consisted of five trains with a produc-tion capacity of 1000 m3/day (0.26 MGD)permeate for each train. The plant was oper-ated for about three years during the initialconstruction period for the Yanbu IndustrialCity development.

In light of the above, a technical and eco-nomic evaluation of the two desalination pro-cesses for MYAS had been carried out todetermine the feasibility of utilizing the ROtechnology for future desalination units [20].On the basis of the evaluation results, a deci-sion was made to construct a new large sea-water RO desalination plant. The RC hasbeen installing a seawater RO desalinationplant for Marafiq Company which suppliesutilities to MYAS. Marafiq Company wasformed in 2002 by privatizing all the RC’sutility facilities. The RO plant consists of six8400 m3/day (2.22 MGD) trains with atotal production capacity of 50,400 m3/day(13.3 MGPD) permeate. The plant isexpected to be commissioned in the thirdquarter of 2006.

This paper presents the major designcriteria and features for the 13.3 MGPDseawater RO desalination plant along with

A.D. Khawaji et al. / Desalination 203 (2007) 176–188 177

technical issues and parameters associatedwith the plant design.

2. Plant design

The 13.3 MGD seawater RO plant is madeup of six trains of about 2.2 MGD capacityeach. Major design considerations ofseawater RO plants include flux, conversionor recovery ratio, permeate salinity, mem-brane life, power consumption, and feedwatersalinity and temperature, etc. The plant con-sists of five major components: a seawatersupply system, a feedwater pretreatment sys-tem, high pressure pumping, RO modules,and a permeate post-treatment system. Theplant is equipped with a distributed controlsystem (DCS) using the-state-of-the-art com-puterized technology.

Flow rates for the seawater RO plant areshown in Fig. 1. Major plant design featuresare presented in Table 1.

The major systems of the RO plant aredescribed below.

2.1. Seawater supply system

Raw seawater is drawn from the existingseawater open intake channel. The intakesystem also supplies seawater to MarafiqCompany’s MSF seawater desalination andsteam turbine power plants, and MYASindustries for cooling purpose. The seawaterflows into the existing pumphouse throughtrash racks and traveling screens to removedebris. The seawater is treated by injectingsodium hypochlorite to remove algae and

bacteria and to prevent microorganismgrowth. Sodium hypochlorite is generated onsite by electrolysis. Residual chlorine after theinjection of sodium hypochlorite varies from0.5 to 0.7 ppm.

The design flow rate of seawater for theRO plant is 5,804 m3/hr. Seasonal variationsof the seawater temperature from 22 to 33 �Coccurring at the site were considered in thedesign. The salinity of seawater is 46,400 ppmof dissolved salts with a chloride concentra-tion of 23,500 ppm. Its pH varies from 8.1 to8.3 and turbidity is in the range of 0.5–1NTU. A typical seawater analysis has beenconsidered the basis of the design for the rawseawater, and it is presented in Table 2.

2.2. Pretreatment system

The pretreatment for the raw seawater,feedwater includes chemicals injection andfiltration to remove particulate matter andto minimize biological fouling and scaling.The filtration is a preliminary polishing stepthat provides a protection to the high pres-sure pumps and the RO membranesemployed in the RO process. In order toreduce the amount of suspended solids andcolloids in the feedwater, the in-line coagula-tion, flocculation and filtration steps areemployed.

An inorganic coagulant, ferric chlorideand organic polyelectrolyte are added to floc-culate colloidal and fine particles in the feed-water. The flocculant addition enhances theperformance of the dual media filters (DMF).

Pretreatment system

RO Modules

Raw Seawater

TreatedFiltered

Feedwater

Reject Brine 21

Product Water2,100

Service Water

5,769

260 3,388

5,509

46,400 ppm TDS

81,316 ppm TDS

pH - 8.2

pH - 6.5

pH - 5 500 ppm TDS

Permeate

Fig. 1. Flow balance on the RO plant

(flow rate in m3/hr).

178 A.D. Khawaji et al. / Desalination 203 (2007) 176–188

Two injection points are located in the feed-water header. A static mixer is installeddownstream of the injection to insure theproper mixing.

Sulfuric acid is injected to the upstream ofthe DMF filters to reduce pH of the feed-water, which enhances the coagulation pro-cess and prevents the formation of calciumcarbonate scale. Bicarbonate ions in seawaterare converted to carbon dioxide by the acid-ification. In addition, low pH helps to avoidhydrolysis of cellulose triacetate (CTA) ROmembranes selected for the plant. An addi-tional acid injection point is downstream ofthe DMF filters. Sulfuric acid is also added tothe neutralization basin for the purpose ofneutralizing industrial wastewater.

The chlorinated and flocculated feedwateris filtered to obtain a silt density index (SDI)value less than 4 after passing through theDMF filters. Fourteen DMF filters (includingone for backwash operation and one for astandby mode) are installed with layers ofproperly graded filter media, anthracite andsand, and gravel for media support. Table 3shows the media depth and particle size for themedia materials. The depth of the filter per-mits the media bed to expand more than 25%during the backwash modes. The flow in thefilters is in the range of 6.4–6.9 m3/m2hr whenone DMF filter is out of service for backwash.

The DMF system provides a backwashcycle. All filters are backwashed by the auto-matic backwash sequence using pneumatically

Table 1

Plant design features

Plant capacity (m3/day) 50,400 [13.3 MGD] @ 22�C seawater temperatureNumber of trains 6Permeate total dissolved solids (TDS) (mg/l) 500Permeate chloride as Cl� (mg/l) 250Seawater TDS (mg/l) 46,400Seawater conductivity @ 25�C (umhos/cm) 57,000–64,000Seawater temperature (�C) 22–33Seawater pH 8.1–8.3Residual chlorine @ RO plant intake as Cl2 (ppm) 0.1–0.25Permeate recovery ratio (%) 38.5Pretreatment recovery rate (%) 95RO pump pressure (kg/cm2g) 64–76Pretreatment methods Filtration and chemicals injectionDMF filter effluent silt density index (SDI) 4RO membrane Cellulose triacetate (CTA) double element

hollow fine fiber (HFF)Total number of membrane elements 1824Number of membrane modules per train 152Number of membrane elements per module 2Arrangement of permeators Horizontal position in parallelMembrane life 5 years with 12% annual replacementPower consumption (kWH/m3) 5.2Chlorination method IntermittentpH of pretreated filtered seawater 6.5Permeate pH 5


operated butterfly valves. Air scouringblowers are used to provide air to penetratethe filter bed just before backwashing. Theair-scouring velocity is 54 m/hr. The back-wash frequency is once every 24 hr with back-wash duration ranging from 15 to 40 min,depending on the seawater quality. The back-wash water rate is 34 m3/hr/m2 using filteredpretreated seawater.

Because of a seasonal variation during thetransition period of summer and winter, theSDI index of seawater can be higher than anormal value. Such a high SDI seawater can

lead to a shutdown of the plant. If the sea-water shows a high SDI index, the pH of theseawater is reduced by increasing sulfuric aciddosing, and the ferric chloride dosing isincreased to improve coagulation of the sus-pended solids. With an increase in the fre-quency of backwashing, the addition of anonionic polyelectrolyte at a rate of 1.4 ppmcan also enhance filtration.

The effluent from the DMF filters is trans-ferred to a filtered water basin and passesthrough cartridge filters to remove suspendedsolids larger than 10 �m. Eight cartridge fil-ters (including one for a standby mode) areinstalled as an additional protection devicefor polishing the feedwater and to serve asbackup of any abnormal operation of theDMF filters. The typical SDI value of thecartridge filter outlet is below 4 which fulfillsthe RO membrane requirement. An antisca-lant is added to the acidified feedwater toinhibit scaling of calcium sulfate, barium

Table 2

Design conditions of raw seawater

Total dissolved solids (TDS) (ppm) 41,300–46,400Conductivity @ 25�C (umhos/cm) 57,000–64,000Turbidity, NTU 0.5–1Total suspended solids (TSS) (ppm) 1pH @ 25�C 8.1–8.3Residual chlorine as Cl2 (ppm) 0.5–0.7Total alkalinity as CaCO3 (ppm) 120–130Bicarbonate alkalinity as CaCO3 (ppm) 85–95Chloride as Cl� (ppm) 21,600–23,500Sulfate as SO¼4 (ppm) 3000–3200Fluoride as F� (ppm) 1.5Nitrate as NO�3 (ppm) <0.1Phosphate as HPO�3

4 (ppm) <0.1Sodium as Naþ (ppm) 11,700–12,500Potassium as Kþ (ppm) 425–650Calcium as Caþþ (ppm) 490–560Magnesium as Mgþþ (ppm) 1500–1600Total iron as Feþþ and Feþþþ (ppm) 0.01Silica as SiO2 (ppm) 0.5Ammonia as NH4

þ (ppm) 0.2Total dissolved oxygen as O2 (ppm) 3.5–5

Table 3

DMF media depth and size

Media Depth (mm) Media size (mm)

Gravel 200 2–4Sand 400 0.4–0.8Anthracite 600 0.8–1.6


sulfate, strontium sulfate, and calcium fluor-ide. Sodium bisulfite (SBS) is injected to theupstream of the suction head of the highpressure feed pumps to avoid oxidation ofthe RO membranes due to residual chlorinein the pretreated feedwater. This dechlorina-tion process by SBS maintains non-oxidationcondition in the RO feedwater.

CTA has the advantage of being resistantto moderate level of chlorine, which isnormally injected for disinfection in the pre-treatment of the raw seawater [21]. Anotherpopular RO membrane material, polyamideis rapidly degraded by oxidizers and can onlybe used if the pretreatment includes a stepremoving oxidizing materials from the sea-water to the RO units [21]. As the CTAmembranes have certain tolerance for chlor-ine, this characteristics is utilized to preventbiological growth on membranes and theintermittent chlorine injection (ICI) asopposed to the continuous chlorine injection(CCI) is adopted. On the ICI mode ofoperation the feedwater is normally chlori-nated by sodium hypochlorite at 0.5 ppmfor one hour a day. The ICI method alsoprevents membrane degradation by oxidationunder the coexistence of chlorine and heavymetals such as Fe, Cu, Co, Ni, Cr and Pb[22]. It has been reported that the heavymetals act as catalysts for the oxidationreaction although CTA is known to be chlor-ine-resistant [22]. The time of the ICI isadjusted in accordance with the residualchlorine level. For this purpose two chlorineinjection points, upstream and downstream ofthe cartridge filters, are provided. The ICImethod has been established and has beenfound to be very effective to prevent biologi-cal fouling and the oxidation reaction in theseawater RO process [23–25].

The chemical dosages for the RO plant areshown in Table 4.

2.3. High pressure pumping system

Six multistage high pressure centrifugal,horizontal pumps of stainless steel construc-tion are used to pump the filtered feedwaterinto six RO trains at a rate of 5509 m3/hr(918 m3/hr each pump). Each pump has adischarge capacity of 964 m3/hr and gener-ates 733 m of total delivery head. As the sea-water temperature increases, the pressurerequired to force feedwater through the ROmembranes decreases. Seawater RO train sizeis normally dictated by the size of the highpressure stainless steel pump available. Thispump size employed for the plant is consid-ered to be one of the largest high pressurestainless pumps for seawater RO application.Each high pressure pump is coupled to asingle hydraulic turbine for energy recovery.The energy recovery turbine (ERT) type is thePelton wheel configuration. This device istypically applied as an add-on package inthe form of a shaft assist mechanism [26].Each turbine is designed to handle560–593 m3/hr at 640–696 m water column,respectively. Energy recovery from the con-centrated brine is accomplished to reduce asubstantial power consumption. The recoveryof energy from RO systems has been a major

Table 4

Chemical dosages

Chemical Dosage, ppm/m3 permeate

H2SO4 (98%) 170FeCl3 5.2NaHSO3 15.2NaOH 67Ca(OH)2 45.7NaOCl 1.4a

Organicpolyelectrolyte

1.4

Antiscalant 2.6

aAs Cl2 for posttreatment, pretreatment and flushing.


factor in the reduction of the desalinatedwater production cost [26].

2.4. RO module system

The pressurized feedwater is fed to six ROtrains in parallel. Each RO train has a capa-city of 350 m3/hr (2.22 MGD) and its designpressure is 64–76 kg/cm2g. In this system38.5% of the filtered seawater, 350 m3/hr isrecovered as permeate. An operating pressureof 64 kg/cm2g is sufficient on new membranesand the pressure increases gradually. Cellu-lose triacetate (CTA) in a hollow fine fiber(HFF) configuration that was proven to bereliable, was selected for the semipermeablemembranes. The membranes restrict thepassage of salts while permitting water topass through. The RO process is of the singlestage configuration since the permeate after aproper treatment is supplied as potable water.Each RO train has 152 HFF membrane mod-ules, and each RO module contains two ROmembrane elements. The plant is installedwith 1824 CTA HFF membrane elements.Salt rejection by the CTA membrane isapproximately 99.4%. The permeate pro-duced by the RO process passes through thepermeate basin and then to the product basin.The remaining 61.5% of the filtered seawater,concentrated brine returns to the ERT tur-bine and then discharged to the brine basinfor further disposal by means of pumps to theexisting seawater return header. The brinebasin also takes backwash water from theDMF filters and other small streams. TheTDS content of the permeate is low initially,and then the TDS levels increase gradually.The RO trains are provided with samplingpanels for permeate.

Chemical cleaning restores the performanceof the membranes. Chemical cleaning of theRO membranes is conducted to remove dirtcollected on the membranes and takes place

after a considerable period of operation(usually 6 months). The cleaning is implemen-ted by recirculating a cleaning solution at highspeed through the membranes. The cleaningsolution is selected on the basis of the type offouling on the membranes. It normally uses a2% citric acid solution at pH 4. The pH of thesolution is adjusted by adding an ammoniasolution. The chemical cleaning system forremoval of fouling materials is connected tothe RO modules. Therefore, the membraneelements are not taken out during cleaning.The frequency of the chemical cleaningdepends on the quality of the feedwater tothe RO trains and performance of the plant.The frequency is determined by differentialpressure across the RO modules, permeateflow, and conductivity of permeate.

2.5. Permeate system

The permeate contains dissolved salts upto 500 mg/l depending upon the membraneoperating time. The water quality of the typi-cal permeate is shown in Table 5. The perme-ate, desalinated water is post-treated andpassivated by the addition of hydrated limethat is supplied from the lime system. Thisincreases hardness and alkalinity, raises pH,and reduces the tendency of the water toleach calcium from any concrete or materials

Table 5

Permeate quality

Composition Concentration (ppm)

TDS <500CI� <250SO4= 15HCO�3 3Naþ 135Kþ 6Caþþ 3Mg þþ 6pH 5


used in the water distribution system [27].The pH of the product water is adjusted tosuch a level that a slightly positive SaturationIndex (SI) is obtained. The permeate is disin-fected by injection of sodium hypochlorite.The product water meets the World HealthOrganization guidelines for drinking water.The lime handling system consists of a limesilo, a transfer conveyor, and a slurry pre-paration and dosing system. The productwater, treated permeate is stored in the pro-duct water storage tanks. The product wateris then pumped to the pump station fordistribution.

2.6. Plant control system

A distributed control system (DCS) usingthe state-of-the-art computerized controltechnology is provided to control and moni-tor the RO plant. The plant is fully operatedfrom the control room. The DCS system pro-vides the total monitoring function for theentire RO plant and sequential and modulat-ing control for the main process as well as theremote manual operation from the operationstation. The plant performance data areanalyzed with the DCS on a routine basis.The DCS system checks and collects processparameters, takes data from the sensors, andsends them to the computers and from thecomputers to the operation station screen.The DCS system is always in communicationwith the status of the plant through digitaland analog inputs. There are two redundantcomputers communicated to the DCS via acommunication interface. There are severalparts on the computer menu in accordancewith the control, monitoring and alarmingprogram pack that can be selected by anoperator. Those include set points processparameters, alarm monitoring, flow diagramsof plant systems and status, and trend gra-phics of each process parameters. The critical

monitoring parameters are flows and pres-sures of feedwater, permeate and brine, pH,conductivity, temperature, pressure drop,recovery ratio, and equipment conditions.

2.7. Power supply system

Voltage is reduced to 13.8 kV by an ROtransformer, followed by further voltage step-down in the plant transformers for in-plantelectric power use. The plant needs a nominalpower supply of about 15 MVA whichincludes non-process uses such as lighting,air conditioning, etc. The power consumptionfor permeate production is about 5.2 kWH/m3 of permeate.

2.8. Auxiliary systems

The auxiliary systems for the RO plantinclude an instrument and plant air system, acooling water system, a chemical waste disposalsystem, a chemical laboratory, a membranestorage area, a skid-mounted membrane testunit, a heating, ventilation and air conditioning(HVAC) system, and fire hydrants and delugefor the transformer system.

2.9. Environmental

In the seawater RO operation the majorenvironmental concerns are pH and chlorinelevel of the concentrated brine discharged tothe sea. The MYAS Environmental Regula-tions and Standards dictate the RO plantbrine discharge. The pH of concentratedbrine generated from the RO reject and thebackwash stream from the DMF filters is inthe range of 6.8–7. These pHs comply withthe MYAS Environmental Standards. ThepH levels can be adjusted by the addition ofcaustic soda, if required.

Due to the adoption of the ICI chlorina-tion method, the brine reject is virtually freeof residual chlorine for 23 h per day and the


residual chlorine level is about 0.2 ppmfor one hour per day. During the DMFbackwash periods of 15–40 min per day, thebackwash streams have a chlorine content of0.2–0.3 ppm. Based on this, the averagechlorine content in the brine disposal isabout 0.02 ppm. During 14 times per day ofbackwash operation the maximum chlorinecontent in the brine reject is 0.19 ppm. Inthe event that the backwash and ICI chlori-nation (one hour) occur simultaneously, thechlorine content in the brine reject increasesup to 0.24 ppm for an 8 min period.

RO membrane cleaning operation requiresthe use of a weak acid or base, depending on thecleaning agent used. The effluent from the ROmembrane cleaning is neutralized in thechemical cleaning tank by adding caustic sodaprior to discharge to the brine basin. The indus-trial wastewater from the RO plant is sent to aneutralization basin where either caustic sodaor sulfuric acid is added. The neutralized waste-water is discharged to Marafiq Company’sIndustrial Wastewater Treatment Plant.

3. Concluding remarks

The RC Yanbu has had experience inoperating and maintaining a 1.3 MGD sea-water RO desalination plant that wasinstalled in 1981 [19]. This plant was one ofthe first major RO plants adopted in theworld for desalination of seawater. Theplant was built as a construction supportfacility to supply potable water to MYASuntil the permanent MSF desalination plantwas installed and fully operational. The ROplant consisted of five trains with a produc-tion capacity of 1000 m3/day (0.26 MGD)permeate for each train. Raw seawater fromthe wells close to the Red Sea was supplied tothe plant and a polyamide membrane wasinstalled for the plant. The plant was oper-ated for about 3 years during the initial

construction period for the Yanbu IndustrialCity development. The 13.3 MGD new ROplant design is based on the most up-to-dateseawater RO technology, together with theexperience gained from the old small plant.The commissioning of the new plant has beenscheduled for the third quarter of 2006, andthe plant is anticipated to achieve theexpected performance as designed.

In the last two decades significantadvances have been made in the seawaterRO technology which are reflected in thereduction of both capital and operationcosts. Primarily two developments havehelped to reduce the water production costof seawater RO plants: the development ofmembranes that can operate efficiently withlonger duration, and the use of energy recov-ery devices [28–31]. The membrane improve-ments typically include better resistance tocompression, longer life, higher recovery,improved flux, and less salt passage. Theenergy recovery devices are connected to theconcentrated brine stream as it leaves the ROpressure vessel. The devices are mechanicaland generally consist of turbines or pumpsof some type that can convert a pressuredrop to rotating energy. Although the MSFdesalination technology will continue to dom-inate large seawater desalination plants, thesignificant growth of the RO desalinationtechnology is expected.

There has been a gradual increase in theRO train size reaching 11,355 m3/day [32]benefiting from the economy of scale,although it is still far off from a MSF unitsize of 68,130 m3/day [32,33]. The currentpermeate recovery rate in an RO plant inthe Middle East countries, a region whereabout two thirds of the desalination waterof the world are produced, is approximately35%. Recently much higher recovery rate,60% has been obtained elsewhere on thePacific Ocean water [8,34]. A higher recovery


rate resulting in reduction in the feed sea-water consumption lowers both plant capitalcost and operating cost.

The RO plant energy consumption isapproximately 6–8 kWh/m3 without energyrecovery. Installing an energy recovery devicereduces the energy consumption to 4–5 kWh/m3 [35]. It has been reported [26] that the unitenergy consumption can be reduced to as lowas 2 kWh/m3. This achievement is dramaticand possible due to the innovation in theenergy recovery device.

The major problem faced by RO plants inthe Middle East and elsewhere is in the pre-treatment area [36–38]. The conventional fil-tration methods are inadequate in certainareas. The seasonal organic blooms, high bio-logical activity, and the turbidity have causedproblems with some plants [32]. Biofoulingcalls for frequent chemical cleaning of themembrane and loss of production. In somecases it is not easy to maintain the requiredfiltrate silt density index (SDI) levels through-out the year. Therefore, a proper pretreat-ment is extremely important to achievesuccessful operation of a seawater RO plant.

One method of reducing the desalinatedwater production cost is to employ a hybridsystem that consists of two or more desalina-tion processes [39–45]. The Fujairah powerand desalination complex in UAE has a capa-city of 620 MW of electricity and 454,200 m3/day of desalinated water. This world largesthybrid desalination plant is designed to pro-duce 283,875 m3/day by MSF and170,325 m3/day by RO [3,46]. A hybrid sys-tem consisting of Power, MSF, and ROplants offers significant advantages, includingthe use of a common seawater intake system,blending of the product water from MSF andRO, reduction of excess power or power towater ratio, and optimization of RO feed-water using MSF heat rejection coolingwater [45–48].

The nanofiltration (NF) membrane pre-treatment in conjunction with the conven-tional filtration system, was successfullyapplied in a pilot plant and later in an oper-ating plant with excellent results [49–53]. Thispromising process prevented membrane foul-ing by the removal of turbidity and bacteria,and a 40% production increase can beachieved in the operating plant [52]. TheSWCC’s extensive development work on theuse of the NF technology demonstrates thetechnical and economic feasibility of introdu-cing NF in conjunction with RO. The inno-vative use of the NF technology offers severalbenefits and advantages which include theprevention of fouling and scaling, a pressurereduction for RO, an increase in productionand recovery, and cost reduction in waterproduction [49–53].

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