MEMBRANE AND THERMAL DESALINATION TECHNOLOGIES AND VIVENDI WATER'S ROLE IN LARGE-SCALE DESALINATION FOR ISRAEL

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1 MEMBRANE AND THERMAL DESALINATION TECHNOLOGIES AND VIVENDI WATER'S ROLE IN LARGE-SCALE DESALINATION FOR ISRAEL Marie Marguerite Bourbigot (Director Technical Development & Innovation) and Tom Pankratz (Director Corporate Projects) Vivendi Water, 52 rue d Anjou Paris Cedex 08, FRANCE Desalination technology has been available for decades. However, until recently, economic considerations have limited its widespread use to areas of extreme water scarcity. Recent technological developments have reduced capital and operating costs to the point that desalination is now a viable alternative in many regions, and particularly in water-short countries throughout the Middle East and North Africa region, including the areas relying upon the Jordan River watershed. Thermal desalination has historically been the more commonly used process to desalinate water. Membrane technologies, such as reverse osmosis, are relatively young compared to thermal technologies but have grown in use until presently the market is approximately equally shared between the two types of technologies. The desalination market is growing rapidly, and is expected to double its size over the next 20 years, to over 40 million m 3 /day of installed capacity. This increase in the market is anticipated to be valued at more than $70 billion. It is understood that Israel alone may have approximately 275,000 m 3 /day of desalination capacity planned for development in the next five years. This paper will consider both thermal and membrane desalination technologies and will review recent cost and performance improvements, and strategies for further improvements, in order to provide the reader with a thorough understanding of the various technological options presently available for desalination. Building on this information, we will also outline Vivendi Water's strengths and qualifications towards meeting the needs of large-scale desalination in the State of Israel, and outline the benefits of privatized supplies in relation to Vivendi Water's performance in this global competition of providing privatized water supplies. 59

2 As Israel journeys into the arena of large-scale desalination (presently preparing tenders for a 50 million m 3 per year [137,000 m 3 /day] plant), it is critical that all involved parties fully understand the options available for desalination, and the expertise and full capabilities of the offerers so as to ensure success of the project. Thermal Technologies The thermal technologies employed for landbased seawater desalination systems >750 m 3 /day are the multistage flash evaporation (MSF) process and the multiple effect distillation (MED) process. Thermal desalination technologies are frequently used in applications where low grade heat from power plant turbines can be used to provide heat for the thermal desalination plant, thereby significantly reducing the energy cost for the thermal desalination plant. Vivendi Water s expertise and capability in thermal technologies is available through its SIDEM Group (France). Multistage flash (MSF) desalination systems have been commercially available since the early 1960's. Until recently, MSF was the only process used on large (i.e. >9,000 m 3 /day) landbased seawater desalination systems. In an MSF plant, a stream of heated brine flows though a vessel containing up to 40 chambers, or stages, each operating at a slightly lower pressure than the previous one. As 60

3 brine enters each stage, a portion of it "flashes" into steam and is then condensed to produce a pure distillate. The concentrated brine remaining at the end of the process is rejected as blowdown. Most large MSF plants are of the "brine recirculation" type where a portion of the remaining brine is mixed with feedwater and recirculated through the system. Brine recirculation reduces the quantity of seawater required for the production of fresh water significantly over "once through" systems. MSF operating temperatures range from 100 to 110 C (212 to 230 F), and they produce 6.0 to 11.0 kilograms of distillate per kilogram of steam applied. While offering large MSF units, SIDEM has continued to develop its multiple effect distillation (MED) technology to take advantage of the process' inherent operating and economic advantages. In the MED process, distillation takes place in a series of chambers, or effects, operating at progressively lower pressures. As seawater is sprayed in a thin film over a heat exchanger tube bundle, steam flowing through the tubes is condensed into pure product water. The seawater film on the outside of the tube boils as it absorbs heat from the steam and its vapour is introduced into the tubes in the next effect. The process is repeated through the plant and the product water is collected and extracted. 61

4 Vapours produced in this process contain brine droplets which are removed as the vapour passes through mist eliminators installed in each effect. A portion of the vapour produced in the last effect is entrained in a ejectocompressor. The ejectocompressor utilises the pressure of the supply steam to recycle the heat remaining in the last effect steam. By boosting this steam pressure, it can be used as heating steam in the first effect. MED systems operate at lower temperatures (63-80 C / F) than MSF systems, reducing operational problems with scaling and corrosion. Seawater intake water requirements can potentially be 50% that of a similarly sized MSF, significantly reducing pumping power requirements. Realization of MED's process advantages is evident when comparing its growth rate against that of MSF's recent installed capacity. For the 1995 to 1997 period, MSF installed capacity grew by only 2.7 %, while MED grew by 16.8%. The size of individual MED units has increased significantly in the last ten years. SIDEM has recently been awarded an order for two, five-effect MED units, each rated at 22,700 m3/day with a top temperature of 63 C and an 8.0 GOR (Gain Output Ratio - ratio of mass flow of product to steam input). Very large MED units such as these have an approximate capital equipment cost 15-20% lower than a comparable MSF plant. As the size of an overall desalination system increases, so does its dependence on the reliability of individual units to meet production requirements. It is important that these large units be designed and constructed to insure maximum availability. For example, materials of construction such as type 316L stainless steel vessels and a combination of titanium/aluminum bronze tubes are recommended as a minimum. Through SIDEM, Vivendi Water continues its innovative developments in making MED a cost-effective and O&M dependable technology for application throughout the world. Recent installments in the Caribbean and new orders in the Middle East are demonstrating the clear advantages of MED in the thermal family of technologies. Membrane Technologies Reverse osmosis (RO) membrane technology is a more recent development than the thermal processes previously described and RO systems now represent the fastest growing segment of 62

5 the desalination market. This rapid growth is due to the inherent lower capital cost of membrane technologies over thermal technologies, and the improved productivity and recent cost reductions for use of membrane technologies, combined with the growing global need for desalinated water not necessarily tied to power generation. RO uses pressure as the driving force to separate the saline feed water into a product stream and a concentrate stream, with the majority of the dissolved solids remaining in the concentrate stream. Although the membranes are sensitive to fouling, and product water quality is not as high as most thermal processes, RO is an ideal choice for many seawater and brackish water desalination applications. With the growth in the membrane market, a series of other membrane types have been developed and expanded into the water treatment applications. These include: nanofiltration (NF) - used predominantly for membrane softening and sulfate removal ultrafiltration (UF) - used for color, odor, some volatile organics, and suspended solids removal microfiltration (MF) - used for turbidity reduction, and removal of suspended and biological solids An additional impetus for growth of RO in the desalination market is recent technological developments that have increased RO system applicability and performance. Some of these advances include: Salt rejection improvements from 98.6 to 99.8% Flux increases of 86% Improved chlorine tolerance Greater fouling resistant reducing cleaning costs, improves availability Improvements in durability and longevity One of the historic challenges for membrane facilities which utilize warm seawater as their feed source, such as that being considered presently by Israel, is the issue of sufficient pretreatment to minimize and control fouling of the membranes. An area of very exciting 63

6 development in water treatment is the integration of the different membrane types, as presented above, in order to customize the overall treatment approach to the specific needs of the application. For example, utilizing MF or UF as pretreatment for RO in both seawater desalination and water reuse applications, is being found to be highly effective (Adham, 1999; Alawadhi, 1999; Mills, 1999; Won, 1999). Vivendi Water's Memcor Group has installed a 37,850 m 3 /day MF system in Scottsdale, Arizona to pretreat secondary effluent prior to RO desalination. This is the first phase of a project with a planned MF capacity of 155,185 m 3 /day. A similar Memcor MF system at California's West Basin Municipal Utility District in California microfilters 11,355 m 3 /day of secondary effluent prior to RO desalination. The high quality filtrate produced by the Memcor microfiltration systems reduces RO fouling, thereby reducing membrane cleaning requirements, and providing significant improvements in RO productivity and membrane life. This existing expertise and product line within the Vivendi Water family provides significant advantages over other potential desalination suppliers. An important consideration when planning very large desalination plants is the inherent modularity of RO systems. The complexity of the design and operation of a large scale RO plant is not significantly different than that of a smaller plant. In fact, economies of scale contribute to a reduction in unit costs of production. There is no theoretical or design size limit for RO systems. Vivendi Water has demonstrated capability in building and operating large-scale membrane plants. A cursory search of existing RO membrane plants in the Worldwide Desalting Plants Inventory shows at least 11 plants of a similar scale of size to those plants presently being considered by Israel. 64

7 One of the newest large-scale membrane plants just constructed and now operational is the 140,000 m 3 /day Mery sur Oise nanofiltration (NF) plant, located outside Paris, France. This plant was designed, and is operated by Vivendi Water. Though this plant is not intended for desalination, it utilizes custom-made NF membranes for disinfection and specific contaminant removal, and has many common design features to an NF or RO plant for desalination. Hybrid and Dual Purpose Plants It is difficult, if not impossible to make a generalized statement that one thermal or membrane process is better than another without conducting an in-depth study for a specific application, evaluating both technical and economic factors. Even when such a study is conducted - especially for a very large installation - the reviewers often consider a large thermal plant a more conservative choice than one relying solely on membranes. This is due to the fact that MSF and MED are well-proven and have a greater tolerance for variable feedwater conditions and maloperation. Changes in the cost and 65

8 frequency of membrane replacement could dramatically affect the economics and security of a water supply during the life of a plant. An option being considered on an increasingly frequent basis is a Hybrid Plant that uses both thermal and membrane processes. This alternative improves the overall process efficiency by allowing operation at an increased membrane flux rate when using the warm cooling water effluent stream from the MSF/MED as RO feedwater. Hybrid systems provide flexibility by using two different forms of energy; electricity for RO and steam for MSF/MED, and eliminates the dependence on a single technology. Dual Purpose Plants use steam to drive both an electric generator (via a steam turbine) and provide thermal energy to evaporate seawater as part of the desalination process. From an energy perspective, a Dual Purpose Plant is an excellent combination. Some of the electric power can be used to operate a membrane plant and the balance sold to a local power company. The exhaust heat from the gas turbine, or steam from a steam turbine, is used to provide heat to operate a thermal desalination plant. During maximum water demand conditions, the membrane plant would be operated at maximum capacity. When water requirements subside, membrane plant water production would be reduced and more electrical power would be sold to the electric power company, while the thermal desalination plant continues to operate at rated capacity. Such an arrangement provides maximum flexibility to meet fluctuating demands. Privatization As the capital and operating costs of seawater desalination, wastewater and water treatment plants continues to rise, many governmental entities are turning to public-private partnerships where a growing number of tasks are delegated to a private enterprise. These partnerships may range from a plant operation and maintenance service contract, to a build-operatetransfer (BOT) contract, to a long term concession, or even a privately owned and operated plant. Under a build-own operate (BOO) and design-build-own-operate (DBOO) contract arrangements, a private party provides the capital to design, build and operate the treatment plant for a fixed period of time, often fifteen to thirty years. The cost of the facility is then recovered by selling the water on a unit basis, with an off-take agreement between the parties. 66

9 The advantages of the various water supply privatization models to the State of Israel are considerable. The technical and economic risks to the public are minimized, and it allows for long-term financing of the capital cost of the plant, thereby minimizing the immediate financial burden of the community. Vivendi Water is the leader in providing privatized water supply services to communities and industry under any of the various contractual arrangements. This flexibility is coupled with our access to the full array of technologies and capabilities through the Vivendi Water family of companies. A few examples where Vivendi Water is providing privatized municipal water services include : Lyon, France : 180,000 m 3 /day Lyon Surface Water Treatment Plant (DBO) Paris, France : 800,000 m 3 /day Choisy-le-Roi Surface Water Treatment Plant (DBO) Puerto Rico Aqueduct & Sewer Authority : 130 plants providing 1.2 m 3 /day (O&M) Hawaii, USA : 45,420 m 3 /day Honouliuli Water Reclamation/Reuse Plant (DBOO) Sydney, Australia : 2 plants providing 370,000 m 3 /day Water Treatment Plants (BOOT) Bogota, Colombia : 900 m 3 /day Water Plant (BOT) Conclusion Desalination technology has become significantly more cost-effective, dependable and efficient over the last decade. The State of Israel, as it moves forward with large-scale seawater desalination, must choose a water supplier to provide desalination capacity with the proven technical and management capability to ensure this water is dependably and economically supplied over the life of the contract. Vivendi Water offers a full range of technical, product, and privatized management experience. We are the largest supplier of desalination systems in the world with approximately 9% of the world's installed desalination capacity, and we presently provide the water supply to over 100 million people in more than 100 countries. Through the capabilities and experience residing in the Vivendi Water companies OTV, SIDEM, Metito, Enerserve, Bekox, and Memcor, we are available to provide the State of Israel long-term, large-scale, 67

10 seawater desalination capacity, cost-effectively, and dependably, and at a guaranteed price over the life of the contract. References Adham, S., p. Galiardo, S. Trussel, D. Smith, K. Gramith, and R. Trussell, "Water Repurification with Integrated membrane Systems", International Desalination Association 1999 Congress, San Diego, CA, Alawadhi, A., A. Hedha, and B. Hallmans, "Rehabilitation of Ad Dur RO Desalination Plant, Bahrain", International Desalination Association 1999 Congress, San Diego, CA, Mills, W.R., T. Dawes, G. Leslie, T. Snow, and J. Kennedy, "Advances in membrane Technology to Provide Cost Effective Water in the 21st Century", International Desalination Association 1999 Congress, San Diego, CA, Wangnick, K., "1998 IDA Worldwide Desalting Plants Inventory, Report No. 15", Wangnick Consulting GMBH, June, 1998, and database, Won, W., and P. Shields, "Comparative Life Cycle Costs for Operation of Full Scale Conventional Pretreatment/RO and MF/RO Systems", AWWA Membrane Conference, Long Beach, CA,