Costing a Major Desalination Plant for Gaza on the Mediterranean Region

Transcription

1 Costing a Major Desalination Plant for Gaza on the Mediterranean Region Khairy H. Al-Jamal 1 and Monther E. Shoblak 2 1 Senior Operations Officer World Bank Project, 2 Director Palestinian Water Authority Abstract: This paper summarizes appropriate configurations for large scale reverse osmosis (RO) seawater desalination plant on the Mediterranean. As a case study, the discussion will focus on the proposed Gaza plant. Despite of the specificity of the location of Gaza plant, there is great deal of similarity shared with other areas around the Mediterranean that makes the conclusions of this study widely applicable. In particular, the paper will compare different seawater intakes, brine disposal and main process components. The effect of the scale and energy cost on the total cost of desalination will be considered. In order to reach a well informed decision, desalination is discussed in the context of integrated water resource management for Gaza region. 1. Introduction The Mediterranean region in general and the southern cost in particular is characterized by its low rain fall and considered as arid region. The rapid population growth rate and the scarcity of water resources constrain the development of the region beyond the limits. In many places, like Gaza, the shadow price of water is estimated to be higher than the desalination cost. In such cases of weak economy, the financing of desalination scheme is a real burden. However, and once funds are available, the feasibility of desalination projects can be simply justified. This must alarm the private sector involvement and justify the case for the government to pursue economic reforms in order to minimize the risks and attract private investors. In some cases, the current economy can not support the construction of desalination plants. Aids from the donors community should be encouraged. However, the authors believe that in such areas gradual independence should be supported and such countries should at least target the recovery of the operation and maintenance. The history of desalination shows that the cost has dropped dramatically over the last decade and further decrease, but with less rate, is expected to take place for the coming few years. This can be looked at as a great potential for developing countries to be able to recover the renewal cost of their plant. Among other factors that affect the cost of desalination are: the seawater quality and the pretreatment quality, the seawater intake, the plant civil and electromechanical works, post treatment, labor and energy costs. While boreholes intake are favored for their simplicity and easy to control and cleanliness of water, they were not seen to be the most appropriate for the case of Gaza. The appropriateness of any configuration is not absolute and should be determined based on the location geology which influence the yield of a borehole and the hydrology offshore which affects the civil works design and construction. The paper will cover the issues as outlined below: 1. Analysis of the water situation in the region and Gaza in Particular 2. Desalination and integrated water resource management 3. Components of desalination plant and their costing 97

2 Seawater intakes Brine disposal Pretreatment and post treatment High pressure pumps Membrane Dosing units Energy recovery 4. Case studies on Gaza, production cost Economy of scale 5. Energy cost and desalination 6. Conclusions 2. Analysis of the water situation in the region and Gaza in Particular 2.1. Water Resources Profile in Palestine The West Bank is a hilly area, with elevation varying from 400mmsl in the Jordan Valley to 1000mmsl in the hills. The West Bank receives rainfall ranging about 600mm/yr. However, annual rainfall varies from less than 100mm in the East and South to 700 mm in the North and West. The Surface geology of the West Bank is comprised of well fractured and crystallized carbonate rocks, both limestone and dolomite. Various geological formations are generally non-covered and show outcrops at the surface. This holds even for the very deep formations. Outcrops appear at the top of hills as a result of strong holding and faulting. Therefore, it is likely that these hills are the major recharge zones for the West Bank aquifer systems, especially in the non-covered areas. The situation in the Gaza Strip is different. The ground elevation varies from sea level of the Mediterranean to meanly 80mmsl in the East. The rainfall varies form 200 mm in the South to 400mm in the North. The surface geology is comprised of sand and sandstone and clayey sand with potentially high prevention West Bank: The structure of the hydrological system in the West Bank is complex. The axes of the main structural anticlines divide the groundwater to the west, to the east and to the north. Accordingly, the hydrological system related to the West Bank can be divided into three major Aquifer Systems. The common boundary between the systems is outlined along the assumed groundwater divide and along hydrological barriers The aquifer system consists of three multi aquifers, the Western, the Northeastern and the Eastern Aquifer Systems (or basins), while the first two Systems are shared between the West Bank and Israel. The Eastern falls entirely within the West Bank. The Western system and the northeastern system are qualified as trans-boundary, since they cross the Green Line The main formations of the Aquifer system are composed in the anticlinoria backbones of central Palestine. The outcrops of cretaceous Aquifer system are the main exposure. These exposures act as replenishment area to the aquifer systems, from which flow diverges in all directions. Rainfall that infiltrates downward reaches the water table, and the confined portions of the aquifers, where it primarily flows laterally towards the discharge areas. 98

3 The total amounts of natural recharge (replenishment) into the Aquifer System are variable, and dependent on yearly rainfall. Various estimates of the average potentials of the Aquifer system are reported in different sources as shown in Table 1. Fig. 1 shows the present utilization of the mountain aquifer system. Table.1: Average Potential Natural Recharge Quantities of the Aquifer System Aquifer System/ Source Article 40 Assaf et al 1993 North eastern Western Eastern Total Part of the available water in the system is issuing as brackish water as listed: -The Western Basin: 350mcm (40mcm of that are brackish). -The northern eastern basin: 130mcm (70mcm brackish). -The eastern basin: 150mcm (70mcm brackish). It is estimated that some 80-90% of the western and nearly 100% of the Northern system are recharged by precipitation falling within the West Bank area. Historically, the use of the Western Aquifer by the local Palestinian population was limited to part of the flow of springs as well as in the coastal and plain area. Jewish settlers staring in the 1930 s prior to the establishment of the state of Israel initiated intensive exploitation of groundwater, particularly the Western Aquifer System. The Remaining potential of the Western System was developed by Israeli settlement on the West Bank after its occupation following A similar history and use pattern can be drawn up for the Northeastern Aquifer System. The Eastern Aquifer System was until 1967 exclusively development by Palestinian in the West Bank. After 1967, Israeli authorities expanded their control over this system as well and began to develop it, mainly to supply Israeli settlements implanted in the area Gaza Strip: Gaza s water resources are essentially limited to that part of the coastal aquifer that underlies its 360km 2 area (Fig.1). The coastal aquifer is the only aquifer in the Gaza Strip and is composed of Pleistocene marine sand and sandstone, intercalated with clayey layers. The maximum thickness of the different bearing horizons occurs in the northwest along the coast (150m) and decreasing gradually toward the east and southeast along the eastern border of Gaza Strip to less than 10m. The base of coastal aquifer system is formed of impervious clay shade rocks of Neogene s age (Saqiyah formation) with a total thickness ranges between m. Depth to water level of the coastal aquifer varies between few meters in the low land area alone the shoreline and about 70m along the eastern border. The coastal aquifer holds approximately 5x10 9 m 3 of groundwater of different quality. However, only 1.4 x10 9 m 3 of this is freshwater, with chloride content of less than 500mg/l. This fresh groundwater typically occurs in the form of lenses that float on the top of the brackish and/or saline ground water. That means that approximately 70% of the aquifer are brackish or saline water and only 30% are fresh water. 99

4 Israel Egypt Fig. 1: Location map of Gaza Strip. The major source of renewable groundwater in the aquifer is rainfall. Rainfall is sporadic across Gaza and generally varies from 400mm/yr in the North to about 200mm/yr in the south. The total rainfall recharge to the aquifer is estimated to be approximately 45m 3 /yr. The remaining rainwater evaporates or dissipates as run-off during the short periods of heavy rainstorms. The lateral inflow to the aquifer is estimated at between x10 6 m 3 /yr. Some recharge is available from the major surface flow (Wadi Gaza). But because of the extensive extraction from Wadi Gaza in Israel, this recharge is limited to, at its best 1.5-2x10 6 m 3 during the ten or 50 days the Wadi actually flows in a normal year. As a result, the total freshwater recharge at present is limited to approximately x10 6 m 3 /yr Demand Projections in Gaza: Mainly the population growth and socio-economic development control water demand for the different uses. The annual population growth rate in Gaza was recorded at 5.9 and 6.8% between 1980 and 1996, by which time Gaza had a population of 963,000 inhabitants. Based on Palestinian Central Bureau of Statistics census (PCBS) Dec 1997, Gaza population was recorded at 1,020,080. Using a conservative growth rate of about 3.5% and assuming an influx of 50,000 returnees by 2010, the estimated population in 1999 was slightly over 1,100,000 and forecast population of 2,140,000 by This means that population is expected to be double after 20 years (Fig.2). 100

5 Population Fig.2: Population growth projection in Gaza assuming growth rate of 3.5% and an influx of 50,000 returnees until the year 2010 In 1999, it was estimated that a proximately 140x10 6 m 3 /yr of water was pumped from about 3500 wells. Of which, about 90x10 6 m 3 /yr of water uses was used for irrigation and 50x10 6 m 3 /yr were pumped for domestic and industrial from 90 municipal wells. The World Health Organization (WHO) recommends an average of 150 liters per capita per day (l/c/d) as a minimum standard for individual water use. In 1999, it is estimated that 80 l/c/d were actually made available to consumers. On the other hand, only about 13 l/c/d meet WHO quality standards. As social development occurs, the demand for water will increase to meet the average WHO recommendation of 150 l/c/d in future years. These facts make it evident that the Gaza Coastal Aquifer is in extreme danger of becoming unusable for drinking water and irrigation. Over exploitation of the aquifer has resulted in salt water intrusion and continuous decline in groundwater levels has been observed in most of the areas of Gaza Strip since mid-1970s. The ability of the aquifer to sustain life for the increasing population and a basic agriculture industry will be destroyed in twenty years if no action will be taken Domestic and Industrial Water Demand: Population growth, the changing water needs of households and industry and changing demands of agriculture will shape in the future (D&I) water demand. The projected (D&I) demand for the next 20-years is graphically presented in Fig.4. The D&I demand include net demand for domestic, industrial, public customers and livestock water supply. Water losses through transmission pipeline and water distribution system are included. Therefore, D&I demand presents quantity of water at water supply source that should be delivered to the D&I customers. It is clear that the total D&I water needs will reach to about 182mcm by 2020 assuming an overall efficiency of 80% Agricultural Water Demand: Y e a r If the demand for irrigation is calculated on the basis of the food requirements of the growing population, it appears that it will increase from the present usage of about 90 x10 6 m 3 /yr to 185x10 6 m 3 /yr by2020. However that figure is not realistic projection for Gaza, because neither the water nor the land to support an increase in agricultural activity exists. 101

6 Fig.4. illustrates the continuing trend in decreasing the agricultural water demand reflecting the decrease use of both irrigated and rain fed agricultural land area in Gaza. That is occurring as result of the growth of urban areas, which expand onto agricultural land. This encourages farmers to bring what had been marginal land into production. It also means that farmers are turning to more intensive methods of agriculture, which require expensive inputs. In general, there is a trend to select crops of less water needs. It is expected that the agriculture demand will be preserved to about 80x10 6 m 3 /yr Overall Water Demand: Generally, the overall water demand in Gaza Strip is estimated to increase from present of about 145x10 6 m 3 /yr to about 260x10 6 m 3 /yr in 2020, as shown in Fig.3. This includes D&I demand at water supply source and agricultural demand Agri M &I/m cm total 175 Demand (mcm) Years Fig.3: Overall Water Demand in Gaza until the Year Palestinian Water Resources Policy and Integrated Water Resources Management: Water resources must be developed and managed efficiently in order to meet present and future water needs, in an environmentally sustainable way. Wastewater reclamation and reuse, desalination and storm water recharge together with renewable aquifer capacity will provide quantity of the water that would satisfy water demands in the Gaza Strip for the next 20-years. However, comprehensive aquifer protection is necessary to maintain its sustainable capacity. Certain aspects of water demand management and water quality management should be considered to support management of the aquifer at its sustainable capacity. The Palestinian Water Authority (PWA) has considered the following three principal objectives for sustainable water resources management: Provide quantity and quality of water for domestic purpose in compliance with WHO standards. Supply adequate quality and sufficient quantity of water that is required for the planned agricultural production in Gaza Strip. Managing the Gaza Coastal Aquifer at its safe yield and preventing further deterioration of the aquifer water quality. 102

7 Fig. 4: Supply and Demand balance for Gaza as predicted in accordance to the integrated water resource Management for the year

8 Accomplishment of those principal objectives is based on the following fundamental promises: Reclamation of wastewater and maximum use of the reclaimed water for agriculture. Introduction of new water resource(s) into the Gaza Strip water sector as soon as possible to meet the projected water demands. Improve pumped groundwater quality needed for domestic use by desalination facilities. Successful implementation of those issues will be able to maintain water balance and prevent further deterioration of the aquifer. In parallel, clear and precise legislation and strict water sector implementation policies are must for successful implementation. The integrated water resources management plan indicates that the future demand can be met as combination of groundwater, treated wastewater, stormwater, brackish water desalination and seawater desalination at various capacities as shown in Fig Desalination and Integrated Water Resources Management: 3.1. Potential of Brackish Groundwater Desalination: Presently 5mcm/yr of potable water for domestic use is purchased from Mekorot (Israeli water supply company). Purchase of an additional 5x10 6 m 3 /yr has been ratified by Oslo-II agreement and is considered as new water resource that will be introduced to the water supply system for domestic use within the next 2-years after completing the North-South Gaza water carrier. Two beach well seawater RO desalination plants are proposed by PWA and will be constructed and operated within 1-2 years. These two plants are considered also as new water resources that will provide when completed additional 2.25x10 6 m 3 /yr of fresh potable water to the Gaza Strip for drinking. This means, a total of x10 6 m 3 /yr will be available for domestic use during the next 2-years from both Mekorot and beach well desalination plants. The available fresh groundwater resources in the Gaza Coastal Aquifer that can be used for domestic uses and fit with the recommended WHO guidelines in terms of water quality is in the range of 15% of the total aquifer capacity. At the present, most of the domestic municipal water produced is far away from the acceptable level. As mentioned before, the total projected domestic demand will reach to about 182mcm/yr by 2020 considering that the total of about 12.25mcm/yr will be supplied through Mekorot and beach well RO desalination plants. The remaining quantity required will be more or less 170x10 6 m 3 /yr considering the water balance as well as the groundwater yielding capacity, it has been assumed that a total 128x10 6 m 3 /yr can be produced from the groundwater aquifer for domestic by About 20% of total domestic water demand (38x10 6 m 3 /yr) can be produced from the aquifer and mixed directly with about 77x10 6 m 3 /yr of treated or/desalinated groundwater through RO desalination facilities in order to fulfill domestic water compliance with WHO water quality standard. The remaining 64x10 6 m 3 /yr will be supplied from Mekorot and seawater desalination Prospect of Seawater Desalination: In order to maintain the water balance to the positive condition and to fulfill the domestic water demand in terms of quality and quantity, new water resources should be introduced into the Gaza Strip water sector as soon as possible. Those new water resources will relief stress on the aquifer and prevent further deterioration of its water quality. 104

9 With the assumption of efficient comprehensive wastewater management in terms of the reuse of reclaimed wastewater for agriculture and recharge the surplus wastewater into the aquifer, the proposed water balance will be improved relatively and the total water deficit will be of about 54.8x10 6 /yr in 2020 (Fig.6). Many alternatives have been examined to minimize the water deficit and fulfill domestic water demand, but seawater RO desalination has been identified as the most realistic option. Following this concept large scale RO seawater desalination plant with four different production phases is proposed as follow: Phase-1: 60,000 m 3 /d, in operation by 2004 Phase-2: 60,000 m 3 /d, in operation by 2008 Phase-3: 20,000 m 3 /d, in operation by 2014 Phase-4: 10,000 m 3 /d, in operation by 2017 Total desalination capacity will be by about 150,000 m 3 /d (~55x10 6 m 3 /yr) by w ater deficit quantity (x10^6 m^3) Fig.5: Water Balance With Seawater RO Desalination Plant and Efficient Reclaimed Water Reuse. 4. Components of Proposed Gaza RO Desalination Plant: 4.1 Gaza Seawater Desalination Plant's General Concept: In accordance with the Coastal Aquifer Management Program (CAMP) financed by the USAID, it has been identified that the most critical element in bringing the Coastal Aquifer into balance and restoring the viability of the potable water aquifer in Gaza is providing new sources that will offload the seriously depleted groundwater supply. This first step in the overall program will ultimately provide a new supply of potable water that represents up to twenty-five percent (25%) of the municipal and industrial demand. Several alternatives were studied for seawater sources, treatment processes and treatment plant sites to determine the optimum combination of facilities that would meet the objectives of the CAMP. These alternatives were developed from the criteria identified in the Integrated Aquifer Management Program (IAMP) published in May The planning criteria's were refined and finalized for this evaluation through discussions with staff of the Palestinian Water Authority (PWA) and USAID. The first project required to implement this program is construction of one regional desalination facility to be located at the southern end of Gaza Governorate (our case study). Following this concept, a large scale RO seawater desalination plant (Fig.6) will be phased as discussed in section 3.2. y ea r 105

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11 Fig 6: Schematic Diagram of Gaza RO Seawater Desalination Plant Process 107

12 4.2 Gaza Seawater Desalination Plant's Components Description: Seawater intakes: The intake and pipeline to Gaza Seawater Desalination Plant (GSWDP) are sized for the eventual plant product capacity of 150,000m 3 /day in the final phase. Based on a 45% overall recovery, the intake system will have a feed capacity of approximately 330,000 m 3 /day. The plant will take its water supply from a sea intake up to 1 km out into the Mediterranean Sea and will be a submerged, screened intake structure designed to minimize entry of sea life and suspended matters. A pumping station located at the beach will pump raw water to the plant site at the beach highway. Brine disposal will be through an outfall pipe and diffuser approximately 0.6 km into the Sea. The pumping station will be equipped with m 3 /hr vertical centrifugal pumps in a dry well. The pump station will have three constant speed pumps and one variable speed pump. Fig. 7 shows a conceptual layout of the sea intake, pumping station and raw water supply main in relation to the proposed plant site. The pumping station will have emergency generation capacity and be linked to the treatment plant by SCADA system for remote operation. The raw water pipeline will be a medium pressure HDPE pipeline of 1200 mm in diameter. It will be 0.5 km in length from the pumping station to the treatment plant. Fig. 7: Schematic layout of the Seawater Intake for Gaza RO seawater desalination plant 108

13 4.2.2 Pretreatment and post treatment: Pretreatment: Pretreatment of the raw seawater is provided to remove suspended solids that might foul the RO membranes, and to disinfect the raw water for inactivation of microbes. Because the RO membranes used most commonly today are sensitive to oxidation by chlorine, any residual chlorine must be removed prior RO membrane treatment. A pretreated water quality with SDI's (Salt Density Index) below 3 is required to ensure warranty guarantees from the RO vendors. The SDI measurement is a guide to determine the fouling potential of the pretreated water by measuring the volume of pretreated water passing through a 0.45 m filter pad over a 15 minute period. Based on the feed-water analysis provided in Table 2 for the case of GSWDP, the following conventional pretreatment (Fig. 8) was evaluated as the base case design for the purpose of this facility (further details are provided in Table 3): Table.2: Gaza Seawater Desalination Plant's Feed-water Analyses Model No. Test Parameter Result 1 Temperature (field) 15, 26, and 33 C 2 ph (field) Conductivity (at 25 C) 53,250 mmho 4 TDS 35,500 mg/l 5 Calcium 660 mg/l 6 Magnesium 1,447 mg/l 7 Sodium 10,200 mg/l 8 Potassium 510 mg/l 9 Barium 0 mg/l 10 Strontium 0 mg/l 11 Iron 0 mg/l 12 Bicarbonate 160 mg/l 13 Carbonate 10 mg/l 14 Carbon Dioxide 2.2 mg/l 15 Sulfate 2,500 mg/l 16 Chloride 21,500 mg/l 17 Fluoride 0 mg/l 18 Nitrate 0.1 mg/l 19 Silica 10 mg/l 20 Ammonium 1.0 mg/l 21 Turbidity 0 NTU 22 Silt density index (15 min., field) 0 23 Hydrogen sulfide 0 mg/l The raw seawater will be pumped through a venturi meter vault into a chemical mixing structure, where sodium hypo chlorite and polymer will be added. From there, the flow will enter concrete channels for distribution to cluster filters. Waste backwash flows from the filters will be injected into the brine waste pipeline for disposal into the sea. Filtered water will be injected with anti-scalant, acid, and sodium-bisulfate, and then pumped through cartridge filters in the process building for fine particle removal. A stainless 109

14 steel header will deliver the water to each skid in a piping gallery below the process room floor. Table.3: Details of Gaza RO seawater desalination plant Pretreatment Process Pretreatment Item Chloramination Acidification Coagulation Scale Inhibition Dechlorination Filtration Details Used as needed, 2 mg/l Cl 2, 1 mg/l NH 4 OH, 0.5 mg/l NH 2 Cl residual Use 95% H 2 SO 4, dosed at 3.4 mg/l Use FeCl 3 dosed at 5 mg/l Use polymeric inhibitor, dose at 0.5 mg/l Use NaHSO 3 dosed for 0.5 mg/l NH2Cl residual 2-stage, loading of 120 L/min m 2, backwash once/hr, 10 filters total, multimedia of sand, coal, and garnet Cartridge Filtration 5 micron rating, 5.5 m 3 /min design flow, loading of 5 L/min m 2, 16 housings, changed monthly Fig.8: Conceptual Layout of the Pretreatment Process Post Treatment: Post treatment is intended to provide stabilization, disinfection and fluoridation of the product water. Stabilization is required to reduce corrosion of the downstream piping, and disinfection and fluoridation provide health benefits to the consumers. For the case of GSWDP the permeate will be disinfected using Chlorination. Both chloramination and chlorination were considered in the evaluation of the base case design. Chloramination may reduce the potential of disinfection by-product formation and can maintain a longer-term disinfection residual than chlorine, and chloramination also reacts with nitrates to quickly form nitrites. Due to the high level of nitrates in the groundwater that will be blended with the desalinated water in Gaza Regional Water Carrier, chlorination was considered the better disinfection method. For the purposes of cost estimate, fluoridation has not been included as it has yet to be determined by PWA that it is desired. The post-treatment system details are provided in Table (4) 110

15 Post-Treatment Item Chlorination Stabilization Table 4: Post-Treatment System Information Details Dosed at 2mg/l C12 Use lime dosed at 0.5 mg/l for positive LSI Reverse Osmosis Block: In addition to the membranes cleaning equipment, the associated piping, instrumentation and control devices, the RO block is composed of the following components: High pressure pumps, Post-membrane treatment, Energy recovery unit, High pressure pumps: In the case of GSWDP, as illustrated in Fig. 9, the booster pump will boost the water pressure to more than 1200 psi ahead of the reverse osmosis skid, where the HP pumps system consist of five centrifugal pumps with discharge pressure of kpa Post-membrane treatment: A booster pump will boost the water pressure to more than 1200 psi ahead of the reverse osmosis skid. The multi-stage reverse osmosis process will recover 45 percent of the water as potable quality water (permeate). As illustrated in Fig. 9, the first pass consists of 129 high-pressure vessels and 1,032 seawater membranes. The second pass consists of 9 medium-pressure vessels and 72 brackish water membranes. The entire 60,000 m 3 /d first pass system consists of a total of 774 highpressure vessels and 6,192 seawater membranes. The entire 60,000 m 3 /d second pass system consists of a total of 54 medium-pressure vessels and 432 brackish water membranes. The entire 75,000 m 3 /d first pass system consists of a total of 903 high-pressure vessels and 7,224 seawater membranes. The entire 75,000 m 3 /d second pass system consists of a total of 63 medium-pressure vessels and 504 brackish water membranes Energy recovery unit: Energy recovery devices work to retrieve energy in the form of pressure available in the exiting concentrate stream, and to transfer this energy to the feed stream. The product stream has little available pressure once it passes through the membrane, but the concentrate stream pressure has only been reduced through pressure losses in the piping of the RO system. Therefore, significant energy can be recovered from this process stream. The present generation of energy recovery devices has greatly improved efficiency and usefulness in seawater RO facilities. Energy is an increasingly large share of the total likecycle cost of SWRO desalination as membrane prices have dropped in recent years. Increased competitiveness among privatized water suppliers has also created more demand for efficient energy recovery systems. Historically, the Francis turbine and Pelton wheel type energy recovery devices has been utilized to reduce the load on the high pressure feed pump motor. More efficient technologies that have become commercially available more recently include the pressure exchanger and the work exchanger, both of which directly recycle the energy in the high pressure concentrate stream to a low pressure feed stream. The pressure exchange is more suitable for smaller seawater RO plants, while the work exchanger is best suited for medium to-large facilities as for the case of GSWDP. 111

16 In the case of GSWDP, the energy recovery devices at each skid will recover more than 35 percent of the power required to operate the reverse osmosis system. Waste brine, or concentrate, will be collected in a pipe in the gallery to be discharged through an outfall pipeline to the Sea. The RO block details are provided in Table (5)! "#$! %$# "& ' Fig.9: Configuration of the RO GSWDP Table 5: RO Block Information RO System Items Details Seawater elements, 1 st pass Five operating trains operating at 47% recovery, 6 elements per vessel, 5,580 elements, product water quality of 452 mg/l, average flux of 13.5 L/m 2 -hr, producing m 3 /day of product Brackish elements, 2 nd, pass Five operating trains operating at 90% recovery with 66.7% blending ratio, 6 elements per vessel, 1 st stage: 390 elements, 2 nd stage: 210 elements, blended product water quality of 303 mg/l3, average flux of 37.4 L/m 2 -hr, producing 60,000 m 3 /day blended product water Total Vessels 930 seawater vessels and 100 brackish vessels HP pumps Five centrifugal pumps with discharge pressure of 7,000 kpa, with energy recovery, power requirement of approximately 9MW Booster Pumps Five centrifugal pumps with discharge pressure of kpa, power requirement of 0.5 MW Energy Recovery Device Approximately 35% energy recovery, work exchangertype 112

17 4.2.4 Brine Disposal: The residual pressure in the brine waste from the reverse osmosis process will be ample to deliver the waste stream to a sea outfall. The backwash waste from the sand filters will be pumped into this pipeline; where the brine disposal system in our case consists of a wet well to collect all the plant's waste streams and includes submerged pumping, Fig. 10. The plant requires an outfall for disposal of approximately 75,000 m 3 /d of waste brines at ultimate build out of the facility. An 800-mm outfall should be adequate for all brine disposal needs at a velocity of approximately 1.7 m/sec. The specific requirements of the concentrate disposal system are as follows: Locate diffuser offshore approximately 600 m beyond the surf zone in 6 m of water or deeper. (The Gaza Power Plant s brine outfall line is located approximately 400 m from shore. For this study, 600 m was used for cost estimating purposes). Requires current measurements in diffuser area and fathometer survey to determine bottom topography If HDPE is used, it will require concrete collars to overcome the buoyant forces. The joints can be fused on shore or on a barge, and the pipe pulled off the shore or floated into place and sunk. If PCCP with a liner is used, it can be a conventional barge laid process with divers bolting up the joints. Diffuser should be laid toward the northeast Diffuser should be designed as a manifold jet diffuser after modeling Outfall will be trenched into seabed and protected with armor rock Requires permit from Israel (similar to sea intake) Fig.10: Schematic Brine Disposal System for Gaza RO seawater desalination plant. 113

18 5. Costing of Proposed Gaza RO Seawater Desalination Plant: The cost of water production is composed of the capital cost and the operating cost Capital Cost: Table 6 summarizes the costs of the various components of the proposed RO seawater desalination plant for Gaza. These costs were estimated by the consultant Metcalf and Eddy under the Coastal Aquifer Management Program, financed by the USAID for Gaza. The table also illustrates the capital cost per cubic meter of the desalinated water. Table 6: Break down of the capital cost for proposed Gaza RO seawater desalination plant. Installations Category Components Estimated Cost Life time Cost USD Years USD/m 3 Main Installations Row water intake 1,155, Pump station 3,282, Raw water supply main 239, Concentrate outfall 740, Treatment plant 33,928, Contractors Mark up 10% 3,934, Contingency 10% 4,327, Engineering and Admin. 5% 2,380, Subtotal (1) 49,986, Other Installations Finished water storage 4,509, High Service pumps 1,327, Connection to the carrier 1,124, Contractors Mark up 10% 696, Contingency 10% 765, Engineering and Admin. 5% 421, Subtotal (2) 6,960, Total (1+2) 56,946, Operating Cost: Table 7 summarizes the costs of the various operating cost components of the proposed RO seawater desalination plant for Gaza. These costs were estimated by the consultant Metcalf & Eddy under the Coastal Aquifer Management Program, financed by the USAID for Gaza. Table 7: Break down of the operating cost for proposed Gaza RO seawater desalination plant. Cost Item Unit Cost Annual cost Cost USD/ Unit USD USD/m 3 Energy at 3 kwhr/ m ,285, Chemicals 982, Labor 291, Utilities 150, Miscellaneous 100, Total 4,808,

19 5.3. Total cost and sensitivity analysis: From the above discussion the total cost of water produced at the plant entrance is expected to be about US$ 0.45/m 3. Thanks to the reduction in energy consumption. The latest development in the energy recovery devices allows the utilization of the high efficiency pressure exchangers to reduce the total energy consumption from 5.5 kw.hr/m 3 down to 3 kw.hr/m 3. In general the desalination cost is very sensitive to the plant cost, the energy cost and the financing cost. Fig. 11 and Fig. 12 illustrate these relationships. Total Cost ($/m3) % 5% 10% 15% 20% 25% Interest Rate (%) Fig. 11: The Impact of financing the interest rate on the cost of desalination. Total Cost ($/m3) Specific Energy Consumption (kw.hr/m3) Fig.12: The Impact of specific energy consumption on the cost of desalination. 115

20 5.4. Middle Area Desalination Plant and the Economy of Scale: Other experiences have been practiced in Gaza where a small scale beach well seawater desalination plant was constructed in order to produce 600 m 3 /day as a first phase and a final phase to produce 1200 m 3 /day. Due to the high cost of distribution and the high competition of the private venders of desalinated brackish water's, the developer of the plant could not produce more than 100 m 3 /day. This has led to high labor cost 2400$/month. More over the relatively high specific energy consumption of 9kW.hr/m 3 at USD 0.06/kW.hr have increased the operation cost of the middle area desalination plant to a level that made it not acceptable. 6. References 1. Palestinian Central Bureau of Statistics, Palestinian Authority, General Census, Palestinian Water Authority and Palestinian Energy Authority, Water Desalination Plan, Draft Report, Palestinian Water Authority / USAID, Coastal Aquifer Management Program (CAMP), Integrated Management Plan, Gaza, Palestinian Water Authority / USAID, Coastal Aquifer Management Program (CAMP), Gaza Desalination Master Plan, Gaza, Sep Palestinian Water Authority / USAID, Gaza Seawater Desalination Plant Feasibility Study Volume 1" (Aqua Resources International, LLC), Gaza Desalination Master Plan, February