Ghaffour - Desalination and Water Reuse
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Ghaffour - Desalination and Water Reuse Ghaffour - Desalination and Water Reuse Document Transcript

  • DESALINATION AND WATER REUSEAS AFFORDABLE SOLUTION FOR WATER SUPPLY IN WANA COUNTRIES Dr. Noreddine Ghaffour, Principal Research Scientist, Water Desalination & Reuse Center, King Abdullah University of Science and Technology (KAUST), Saudi Arabia1. IntroductionThe WANA region except Turkey has minimal rainfall and limited aquifers.It is the driest regionin the world with renewable water resources less than the critical level of 1000 m 3 per inhabitantper year, as defined by the World Health Organization (WHO).Most of the countries in the region are or, with population growth and economic development,will be dependent on desalination of sea/brackish water to cater their actual and future needs forpotable water. Because of the scarcity of natural fresh water and the reduced cost of desalination,waste water processing for reuse, which uses much the same technology as desalination, is orcould be another source of water for WANA region population. These, and other factors,combine to create a dire need for water with good quality as a reliable source for the future.In many countries where desalination was unthinkable, it is now adopted as feasible andeconomical option for potable water supply.The measures taken to supply water to the regionshould not be for short term. They should utilize a technology that can be relied upon for manyyears and can ensure a guaranteed water supply independent of climatic conditions that prevail inthe area. Desalination and water reuse fit this requirement. It has been established practice inseveral countries such as GCC states, Algeria and Libya that their future water demand is to bemet by desalination. On the other hand, it is becoming the only viable and economic solution forcountries such as Jordan, Israel, and Palestine to embark on desalination. North African countriesvary in their demand for desalination from needs to supply water to sea resorts such as in Egyptand Tunisia, to provide an alternative to major water transport schemes such as Egypt in its Sinaidevelopment, and Morocco for supply to its southern region. Whereas Syria and Lebanon maynot see the need for desalination, Syria with thousands of illegally drilled wells abstracting itsaquifers still has to consider desalination in its interior far from rivers and sea. Yemen, on theother hand, the worst water depressed country in the world, has the additional demise of beingforced to a combination of desalination and major transport schemes. Iraq is likely to undergosevere water treatment requirements equivalent to desalination, and will also need solutionsinvolving desalination in its southern territories [1].Desalination processes have experienced many developments in the past thirty years. Thesedevelopments have led to the reduction in desalinated water cost to a level that has madedesalination a viable option for potable water supply.It is now technically and economicallyfeasible to generate large volumes of water of suitable purity through the desalination ofseawater, brackish water, and water reuse.The region has out of necessity become a world leader in water desalination. Desalination fills asignificant portion of the shortfall in water supply in the region. GCC countries are among thehighest producers of desalinated water in the world and produce about half the world’sdesalinated water. However, some environmental impacts are associated with desalination,including entrapment of aquatic creatures in plants intakes, discharge of hot brine and theproduction of CO2. 1
  • 2. Desalination status and capacityMany regions in the water stressed countries are augmenting their water supplies withdesalinated water to meet the needs of the continuous growth of population and industrial,tourism and agriculture developments. Although desalination has been considered among thenon-conventional water resources, it can no longer be considered as a marginal resource becausesome countries such as Qatar and Kuwait rely 100% on desalinated water for domestic andindustrial use, whereas Saudi Arabia reliance is nearly 60% [1].Desalination, along with water reuse, water harvesting have been classified as non-conventionalwater resources. This classification can easily raise controversy in countries that have been usingdesalination substantially for more than 50 years. Generations of water professionals in thosecountries have long forgotten that this resource is non-conventional.Desalination has become the main source of potable water in all the GCC States where demandhas multiplied from 1.5 bi m3/yr in 1980 to 6 bi m3/yr in 2000. It is expected that by 2015 anadditional 5 bi m3/yr is to be provided through desalination. This need for desalinated water is nolonger associated only with the GCC. Almost all countries of the region are now consideringdesalination. This growth is driven by chronic water shortages due to persisting droughts,increasing populations, increasing per capita water demand and growth of industrialization. Onthe other hand, this growth is also enhanced by the decrease in the costs, due mainly totechnology improvements and competition, associated with the production of desalinated waterwhere prices have fallen from around US$ 4 /m3 to less than US$ 1/m3 and even reached belowUS$0.5/m3 for some specific large scale projects.Presently, the total desalination capacity is around 60 million m3/d and will reach aroundhundred millions m3/d by 2015 [2,3]. 64.6% of the total capacity is produced by membraneprocesses and 34% by thermal processes. 62.4% of the feed water is from seawater and 20%from brackish water and the remaining is from surface water and wastewater (Figure 1a)[1].Over 66% of the desalinated water is used for municipalities and 23.5% for industry (Figure1b). These figures are susceptible for quick changes as desalination market is growing very fastwith an annual growth rate of about 55%.Figure 1: Installed capacity by feed water type and by user type [2].In non-GCC countries, most of which are new to the desalination industry and had to consider itto augment their water supply, either nationally or at the local level in some parts of thecountries. For example, Iraq has two major rivers passing through, but some of the locations inthe south exhibit water shortages that have to be met by desalination. 2
  • 3. Desalination development potential and financeDesalination has a great development potential on a global scale. This is attributed to the factthat, out of 71 large cities that do not have local access to new freshwater source, 42 are coastal[4]. Out of the entire world population, 2,400 million inhabitants representing 39% live at adistance of less than 100 km from the sea [4] including most of the large cities in WANA region.Other than the fact that desalination may be the only option for some countries, there are drivingforces behind its development potential, making it more favorable than conventional resources.Being independent of climatic conditions, rainfall and so on, a primary force is its identificationas a secure source of supply.4. Desalination technologiesDesalination is a separation process that produces two streams, fresh water and saline solution(brine). Saline water is classified as either brackish water or seawater, depending on the salinity.Two main commercial desalination technologies have gained acceptable recognition throughoutthe world, namely those based on thermal or on membrane processes.Thermal processes, except freezing, mimic the natural process of producing rain, where salinewater is heated, producing water vapor that is in turn condensed to form fresh water, thusproducing fresh water by distillation. These processes include Multi-Stage Flash (MSF), Multi-Effect Distillation (MED), and Vapor Compression (VC) Distillation. In all these processes,condensing steam is used to supply the latent heat needed to vaporize the water. Thermalprocesses, due to their high-energy requirements, are normally used for seawater desalination,and in duel power and water production plants (co-generation).Membrane processes include Reverse Osmosis (RO) and Electrodialysis (ED). WhereasED/EDReversal is suitable for brackish water, RO can be used for both brackish and seawater.Nanofiltration (NF), known as a softener membrane, could also be used to desalinate partly saltywaters and for hazard materials removal. For example, in Senegal, groundwater supply containshigh concentration of fluoride which leads to many teeth and bones diseases (Figure 2). NF wasused to reduce the fluoride concentration in water to a level of acceptabledrinking water standardas recommended by WHO (< 1.5 mg/L).Figure 2: Case study of dental (a) and bones (b) fluorosis [5]: 3
  • (a) Dental Flurosis (F-> 2 mg/L), 10 years of exposure to 4 mg/L F-, Senegal. (b) OsseousFluorosis (F-> 4 mg/L), 15 years of exposure to 6-10mg/L F-, Senegal.5. Water reuseAnother prominent role to the desalination industry is becoming evident. Wastewater treatmentfor reuse and desalination have membranes as the common denominator. Initially they were usedin the pretreatment for better operations of RO plants. This has opened a wide world ofopportunities. Ultrafiltration (UF) technology appears in the form of filter backwash, in thetertiary treatment after secondary treatment of wastewater and in what is known as single-stagemembrane bioreactor (MBR) process. Extensive use of these technologies will be seen in thenear future. MBR competes with conventional secondary wastewater treatment while UF offerscost-effective options for many tertiary treatment applications. The use of RO after the secondaryand tertiary treatments offers a drinkable water quality as it is the case for New-Water inSingapore and similarly in Namibia as well as the largest wastewater treatment plant in Kuwait(Sulaibia plant). So far the product water is used for other purposes or injected into the aquifer inmany countries (ASR: Aquifer Storage and Recovery) as it’s not easily accepted by humans fordrinking or even for other purposes especially in Muslim countries.6. CostsAlthough desalination is not a cheap option for the provision of potable water, the cost ofdesalination plants, particularly RO plants, is decreasing. Membrane prices have dropped at arate of around 10 percent yearly for the past 20 years. Prices of thermal processes are also fallingdue to increasing competition. Also, since technological developments affect a reduction in thecost of equipment, the overall relative plant costs are expected to decline. This trend has madedesalination, once a costly alternative to the provision of potable water, a viable solution andeconomically competitive with other options of water supply.Figure 3 gives the cost trends for different raw waters treated by RO. It shows that the cost ofdesalination and water reuse is reduced to a level to compete with traditional water supplyoptions. 7 Marginal water 6 withdrawal 5 Cost $/m3 Freshwater treatment 4 3 Reuse 2 1 Desalination 0 1990 2000 2010 2020 YearFigure 3: Water resource cost trends [4].Table 1 gathered the main parameters related to cost as its main criterion for the selection ofsuitable desalination technologies though that the total water cost depends on many parameters 4
  • mainly desalination process, plant size, geographical location and site specific characteristics,raw water quality, intake arrangement, requested product water quality, reject discharge type,energy, materials, chemicals and other consumablesprice, financing details and amortizationperiod, operation and maintenance.Table 1: energy consumption and water cost of large scale commercial desalination processes[6]. Process Thermal Electrical Total Capital cost Unit Typical energy energy energy US$/m3/day water single train kWh/m3 kWh/m3 kWh/m3 cost capacity US$/m3 m3/d MSF 12 - 7.5 3.5 – 2.5 15.5 – 10 1500 – 1000 1 - 0.8 5,000-70,00 0 MED 7-4 2 – 1.5 9 – 5.5 1200 – 900 0.8–0.6 – 500 12,000 SWRO - 6–3 6–3 1000 – 800 0.5-0.8 25,000 – 1 BWRO - 2.5 – 0.5 2.5 – 0.5 800 > 0.3–0.1 25,000 – 17. ConclusionThis chapter reviewed current desalinationand water reuse issues, and attempted to provide acomprehensive look at these technologies from an integrated perspective that targets decisionmakers to adopt these technologies to cater the actual and future water needs in the region.Desalination is no longer a marginal water resource. It is now adopted as a reliable and economicsolution for water shortage in countries where desalination was unthinkable. Water reuse alsooffers potable water quality and hence is part of the integrated water resource management.8. References1. World Bank water report, 2006.2. WDR/GWI, IDA Desalination Yearbook and market profile, 2009-2010.3. T. Pankratz, MEDRC workshop on Membrane Technology Used in Desalination and Wastewater Treatment for Reuse, Muscat, Oman, March 2008.4. K. Quteishat, Desalination and water affordability, SITeau International Conference, Casablanca, Morocco, January 2009.5. M. Pontie, H. Dach, P. Jaouen, C. Diawara, J. Leparc, M. Hafsi, N. Ghaffour, “Intensification of brackish water desalination using NF membranes: Case studies in Morocco and Senegal”, 3rd Oxford Water and Membranes Research Event, The University of Oxford, UK, 2010.6. K.V. Reddy and N. Ghaffour, Overview of the cost of desalinated water and costing methodologies, Desalination 205 (2007) 340-353. 5