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Review of the Desalination and Water Purification Technology Roadmap 1 Introduction Access to freshwater is an increasingly important national and international issue. In order to maintain economic development and minimize future regional and international conflicts, the United States will need to develop sustainable supplies of high-quality freshwater for drinking and other uses. This will require innovative water management, increased application of water conservation, and novel technologies that can “create” fresh water from nontraditional sources. Desalination technologies can create new sources of fresh water from otherwise impaired waters such as seawater or brackish water, but current financial and energy costs keep these technologies out of the reach of many communities. As a result, the U.S. Bureau of Reclamation and Sandia National Laboratories have developed a research plan to improve desalination technologies, which may lead to more cost effective water treatment so that desalination technologies can better contribute to the water supply needs in the United States. This chapter presents an overview of current water supply needs both nationally and internationally and describes the potential contribution of desalination technologies in that context. Desalination technologies and the historic role of U.S. federal agencies and other public and private organizations in desalination research and development are discussed. The chapter also describes the origins and development of the Desalination and Water Purification Technology Roadmap (Roadmap) and summarizes the study charge and activities that led to this report reviewing the Roadmap. WATER AVAILABILITY Less than three percent of the world’s water has a salinity content that can be considered safe for human consumption. According to the World Health Organization (WHO, 1984), total dissolved solids (TDS) should be less than 1,000 mg/L in drinking water based on taste considerations, and the EPA has set a secondary standard for TDS in drinking water of 500 mg/L (EPA, 2002). By comparison, seawater has an average TDS of about 35,000 mg/L (see Table 1-1). Thus, the vast majority of the earth’s readily available water is too saline for potable use, and yet much of the world’s fresh water is trapped in polar icecaps or is located far underground. It is estimated that less than one-
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Review of the Desalination and Water Purification Technology Roadmap TABLE 1-1 Classification of source water, according to quantity of dissolved solids. Water source Total dissolved solids (milligrams per liter) Potable water <1,000 Mildly brackish waters 1,000 to 5,000 Moderately brackish waters 5,000 to 15,000 Heavily brackish waters 15,000 to 35,000 Average sea water 35,000 Note: Some seas and evaporative lakes can show wide variability in TDS; for example, the Arabian Gulf has an average TDS of 48,000 mg/L and Mono Lake, CA has a TDS of 100,000 mg/L. SOURCE: USBR, 2003a; Pankratz and Tonner, 2003; NRC, 1987. half of one percent of the world’s water is easily accessible and has acceptable salinity levels. According to Envisioning the Agenda for Water Resources Research in the Twenty-First Century (NRC, 2001b), both in the United States and worldwide, “the principal water problem in the early twenty-first century will be one of inadequate and uncertain supplies….” Finite quantities of developed water supplies exist, and growing demand has outstripped supply in many regions of the world, including parts of the United States (see Figures 1-1 and 1-2). Traditional solutions to water scarcity have focused on developing additional supplies (e.g., drilling wells, building dams to store water that would otherwise become irretrievable). However, even when options are available for developing new supplies or transferring water from other areas where supplies are more plentiful, water development can be extremely expensive (AMTA, 2001a). Awareness has also grown over the past few decades about the negative environmental consequences of expanding water development, such as stream degradation and aquifer depletion (Gleick, 2003). Water availability includes issues of both water quantity and quality. After all, just as drought conditions can reduce the amount of water available, reductions in water quality can diminish the available water supply for its intended use. Properly designed water treatment can transform otherwise non-usable water to usable water, thereby increasing the amount of available water. Nevertheless, as increasingly degraded waters are utilized as drinking water sources, caution is required to ensure that the treated water is safe for the general public and sensitive subpopulations to drink, considering the large number of potential contaminants that are not subject to detection by routine water quality monitoring (NRC, 1998; NRC, 2001a). Although water supply issues in the United States are primarily local or regional in nature, the wide distribution of anticipated water shortages has elevated concern to a national level. Water management needs to be considered in a broader context since some approaches that will improve local water availability may impact the quality or quantity of water for downstream users and for the environment. For example, water transfers can increase availability on a local level by decreasing availability elsewhere where water may presently be more plentiful and of a lower economic value. Solutions to local water scarcity issues will likely require a combination of approaches, including demand management (e.g., water trading, conservation), improved water storage capacity such as aquifer storage and recovery (NRC, 2001c; NRC, 2002a), water quality protection, and
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Review of the Desalination and Water Purification Technology Roadmap FIGURE 1-1 Estimated water availability worldwide. SOURCE: Adapted from United States Filter Corporation, 1998 (with permission). FIGURE 1-2 Projected worldwide water scarcity through 2020. SOURCE: Adapted from United States Filter Corporation, 1998 (with permission).
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Review of the Desalination and Water Purification Technology Roadmap advancements in supply-enhancing water treatment technologies (e.g., membrane filtration for desalination or water purification). Desalination technologies offer the potential to add significantly to freshwater supplies although these supplies currently are associated with substantial energy and financial costs. DESALINATION In simple terms, desalination is the process of removing dissolved solids—primarily dissolved salts and other inorganic species—from water (see Box 1-1). Desalination occurs naturally in the hydrologic cycle as water evaporates from oceans and lakes to form clouds and precipitation, leaving dissolved solids behind. Historical records, including descriptions by Aristotle and Hippocrates who described its use in the fourth century B.C., show that humankind has long used basic desalination processes to create drinking water (Koelzer, 1972). Desalination technologies and their application have grown substantially over the last fifty years. As of 1953, there were approximately 225 land-based desalination plants worldwide, with a total capacity of about 27 million gallons per day (mgd) (Evans, 1969). Advances in desalination technologies during the 1960s, including the development of reverse osmosis, led to significant reductions in the cost of desalination processes, BOX 1-1 Desalination and Water Purification Terminology The term desalination means different things to different people. By definition, desalination refers to the process of removing dissolved solids—primarily dissolved salts and other minerals—from water. The terms desalting and desalinization are frequently used interchangeably with desalination, although these terms have additional, alternate meanings. Desalting is used in food, pharmaceutical, and oil industries to describe the removal of salts from a product containing other valuable materials. The term desalinization also describes the removal of salts from soil, typically by leaching. For clarity, the term desalination is used throughout this report. Many persons associate the term specifically with the treatment of seawater or brackish groundwater and are unfamiliar with the application of desalination technology to treat effluent in wastewater reclamation and reuse projects. Wastewater reclamation refers to the treatment of wastewater to water quality conditions that will allow its beneficial reuse. Modern wastewater treatment plants typically reclaim biologically treated wastewater through a final sand filtration step. These reclaimed wastewaters can then be reused for agricultural and landscape irrigation, or for industrial cooling purposes. Water recycling describes the reclamation of wastewater for on-site reuse by the same user. In contrast, the final sand filtration step may be replaced with a desalination technology such as reverse osmosis (preceded by a pretreatment step such as microfiltration or ultrafiltration) to produce much higher quality product water. Sufficient removal of dissolved solids through such a desalination process can result in repurified water that usually exceeds drinking water quality standards (also called potable reuse). Direct potable water reuse involves the immediate addition of repurified wastewater into the water distribution system. With indirect potable reuse, treated water is added to a source water storage area so that it receives additional treatment prior to consumption and provides added protection through mixing, dilution, and time for biological process to further purify the water (NRC, 1998).
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Review of the Desalination and Water Purification Technology Roadmap enabling its broader use. By 2002, there were more than 15,000 desalination plants that had a capacity of 0.026 mgd (100 m3/d) or larger (Wangnick, 2002). Worldwide, the combined capacity of these plants has been estimated to be 8,560 mgd, although the actual production may be less since some of these plants do not operate at full capacity. Desalination plants operate in approximately 125 countries, with seawater desalination plants contributing 59 percent of the total worldwide desalination capacity (Figure 1-3) (Wangnick, 2002). Although some arid regions depend heavily on desalination for their water supply, as of 1999, desalination plants contributed less than 0.2 percent to the world’s water use (Gleick, 2000). More than 1,200 desalination plants operate in the United States, which has 16 percent of the world’s total desalination capacity (Figure 1-4). These U.S. plants primarily desalinate brackish groundwater or purify water for industrial use (AMTA, 2001b). Many different desalination technologies exist to separate dissolved salts from water, and the choice of technology used depends on a number of site-specific factors, including source water quality, the intended use of the water produced, plant size, capital costs, energy costs, and the potential for energy reuse. Thermal technologies heat seawater or brackish water to form water vapor, which is then condensed into fresh water. Membranes can be used to selectively allow or prohibit the passage of ions, enabling the desalination of water (see Chapter 3 for more detail on common desalination technologies). Although thermal technologies dominated from the 1950s until only recently, membrane processes now approximately equal thermal processes in global desalination capacity (Figure 1-5). The U.S. government contributed significantly to the advances in desalination technology and implementation through considerable desalination research funding, beginning with the Saline Water Conversion Act (66 Stat. No. 328) of 1952. The Office of Saline Water was established in 1955, followed by the Office of Water Research and Technology (OWRT) in 1974. Over their history, these offices spent more than $1.4 billion (in 2003 dollars) for desalination research (USBR, 2003b), supporting work that FIGURE 1-3 Charts showing portions of total desalination capacity and total number of desalination plant installations worldwide by source water. SOURCE: Wangnick, 2002.
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Review of the Desalination and Water Purification Technology Roadmap FIGURE 1-4 Chart showing fraction of the worldwide capacity of desalination plants by region. SOURCE: Wangnick, 2002. FIGURE 1-5 Chart showing total capacity of desalination plants worldwide by type of technology used. SOURCE: Wangnick, 2002.
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Review of the Desalination and Water Purification Technology Roadmap comprises the foundation of much of today’s desalination technology, including the development of reverse osmosis. In 1982, the OWRT was abolished, and the funding for water resources research was cut sharply. Although approximately $1 million per year was appropriated for the Bureau of Reclamation’s Advanced Water Treatment Program, little federal support existed for desalination research for the next fourteen years until the passage of the Water Desalination Act of 1996 (Public Law Number 104-298). The Water Desalination Act authorized $5 million/year over six years for desalination research funding and an additional $25 million over six years for demonstration and development projects (Mielke, 1999). From 1996 until fiscal year 2003, a total of $14.15 million has been appropriated under the Water Desalination Act (Kevin Price, written communication, USBR, 2003). The Bureau of Reclamation developed the Desalination and Water Purification Research & Development Program to provide funding grants and cost-sharing agreements to support desalination research and development. With modest investments in research and development from both government and industry, the costs of desalinating seawater with reverse osmosis technology have been coming down, although in most regions desalinated water remains more expensive than water from existing freshwater sources (Figure 1-6; Table 1-2). This decline in costs is attributable to the economies of scale being realized with most new plants and other technological advances. It is, however, very difficult to generalize about costs since they depend so importantly on variables that are peculiar to each site. Desalination costs include capital costs and operation costs, which can vary significantly across various locations and according to source water type (e.g., seawater, brackish water), desired FIGURE 1-6 Recent cost reductions for seawater reverse osmosis production. The price represents the cost per 1000 gallons of water produced, and does not account for additional costs to the consumer, such as distribution (see Table 1-2). The water costs have been corrected for inflation. SOURCE: Lisa Henthorne, Aqua Resources International, personal communication, 2003.
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Review of the Desalination and Water Purification Technology Roadmap TABLE 1-2 Water costs to consumer, including treatment and delivery, for existing traditional supplies and desalinated water. Supply Type Water cost to consumer $ per 1000 gallons Existing traditional supply $0.90-2.50 New Desalted Water: Brackish $1.50-3.00 Seawater $3.00-8.00 Combined supply: 50% traditional supply and 50% brackish water $1.20-$2.75 90% traditional supply and 10% seawater $1.10-$3.05 NOTE: Cost is typical for urban coastal community in the United States, but inland desalination costs may be higher. Note that these costs will be higher than contract water costs shown in Figure 1-6, since consumer costs include fees for distribution to the customer and administrative expenses. SOURCE: AMTA, 2001a. product water quality, and plant capacity. Regulatory issues, concentrate disposal options, and local energy costs also contribute to the overall price of desalinated water. Increased application of desalination technologies will depend upon advancements in concentrate disposal and energy efficiency (see Chapter 3), which contribute substantially to the cost-effectiveness and environmental impacts of desalination. Future penalties on emissions that adversely affect the environment could eventually add to desalination costs. It should also be recognized that new fresh water sources come at substantially higher costs than today’s existing sources, since much of the easily developed fresh surface and groundwater sources in the United States are already being utilized. When these waters are returned to their normal water courses, their water quality is less than that of the original source, as contaminants have been added through normal human activities. Water quality and economics have always been inseparable variables in water supply development. In the past, high quality source waters required minimal treatment and minimal cost to deliver as sources of domestic supply, but as these high quality source waters become scarcer, additional resources will be needed to maintain or restore water quality. While setting an objective to reduce the cost of water in future desalination and water purification projects is admirable, the true cost of water needs to be ascertained for each situation. DESALINATION TECHNOLOGY ROADMAP Since its creation in 1902, the Bureau of Reclamation has been a leader in water resources management and the provision of fresh water, including irrigation water, throughout the arid western states. In 2001, Congress directed the Bureau of Reclamation, in cooperation with Sandia National Laboratories, to evaluate the potential for developing an inland desalination research center in the Tularosa Basin of New Mexico (U.S. Congress Committee on Appropriations, 2001). Because irrigation of agricultural lands can contribute to increased salinity in ground and surface waters, the
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Review of the Desalination and Water Purification Technology Roadmap advancement of inland desalination research is consistent with the agency’s traditional role. The central role of the proposed Tularosa Basin facility would be to evaluate and improve the design and application of desalination technologies for inland brackish waters and would include research initiatives on concentrate management and renewable energy for inland applications (SNL, 2002). In the 2002 Energy and Water Development Appropriation Bill, Congress also suggested that a “technology progress plan” be prepared that could be used to develop the desalination research and development program at the Tularosa Basin facility. Thus, a technology roadmapping activity (the Desalination and Water Purification Technology Roadmap)2 was initiated by the Bureau of Reclamation and Sandia National Laboratories in January 2002. An Executive Committee and a Working Group (collectively known as the Roadmapping Team) comprised of representatives from government, industry, academia, and private and non-profit sectors, including water utilities, were formed to help develop a desalination technology progress plan with a national scope beyond the inland desalination focus of the Tularosa Basin facility. A large number of researchers and managers participated in the roadmapping activity during 2002 through a series of collaborative workshops organized and conducted by Sandia National Laboratories to identify future programmatic and technical objectives for desalination. The Roadmap report (USBR and SNL, 2003) was released in February 2003 and is a product of the Executive Committee. A technology roadmap identifies future needs for technology development, provides a structure for organizing technology programs and technology needs forecasting, and attempts to improve communication between the research and development community and end users. The Desalination and Water Purification Technology Roadmap considers itself a “critical technology roadmap” that is intended to serve as a strategic pathway for future desalination and water purification research. As described in the Roadmap, “Critical Technology Roadmaps must be responsive to the needs of the nation; must clearly indicate how science and technology can improve the nation’s ability to meet its needs; and must describe an aggressive vision for the future of the technology itself” (USBR and SNL, 2003). The Desalination and Water Purification Technology Roadmap report is structured around several national-level water needs that comprise a vision statement for the activity. These needs are to: provide safe water, ensure the sustainability of the nation’s water supply, keep water affordable, and ensure adequate supplies. From these needs (USBR and SNL, 2003), critical objectives were identified that provide metrics that can be used to gauge progress and success in both near- and long-term time horizons (Table 1-3). For example, one long-term critical objective for the national need to “keep water affordable” is to reduce desalination operating costs by 50-80 percent between 2003 and 2020. Near-term objectives were developed based on feasible improvements to current technologies, but reaching the mid- or long-term objectives will 2 The Desalination and Water Purification Technology Roadmap was also called the Desalination Technology Progress Plan and the Desalination Research Roadmap in previous versions of the document and related correspondence.
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Review of the Desalination and Water Purification Technology Roadmap TABLE 1-3 Near-term and long-term critical objectives, as presented in the Roadmap. NATIONAL NEEDS Near-term Critical Objectives (2008) Mid/long term Critical Objectives (2010/2020) Provide Safe Water Develop on-demand removal technologies Remove 60% of synthetics Microbial removal at 4–6 orders of magnitude (today’s removal is 2-3 orders) Remove endocrine disruptors, MTBE, nitrosamines, perchlorate Develop true indicators (not just SDI and turbidity) Surface water and land disposal: Develop science-related concentrate specific regulations related to dispersion modeling of mixing zones and ion imbalance Subsurface injection: Large scale regional characterization of US subsurface injection capability Add all other concentrate specific regulations, refined geographically and addressing cumulative issues. Demonstrate isolation with hydrologic model of receiving formation and formation scale of subsurface injection capability of US Ensure adequate supplies/ensure sustainability Decrease cost of reclaimed waters by 20% Beneficial use: 5% of concentrate Reduce reject to 15% for non-surface water applications Maintain stability of reclaimed waters over time Decrease cost of reclaimed waters by 50% (Stretch target – 80%) Beneficial use: 15% of concentrate Reduce reject to 5% for non-surface water applications Keep water affordable Reduce capital cost by 20% Increase energy efficiency by 20% Reduce operating costs by 20% Reduce cost of ZLD by 20% Reduce capital cost by 50% (Stretch target – 80%) Increase energy efficiency by 50% (Stretch target – 80%) Reduce operating costs by 50% (Stretch target – 80%) Reduce cost of ZLD by 50% (Stretch target – 80%) Source: USBR and SNL, 2003. require revolutionary technological advancements. After developing a series of critical objectives relevant to each of the needs, relevant technological areas and research projects were identified. The five technological areas considered in the Roadmap include membranes, thermal technology, alternative desalination technologies, concentrate management, and reuse and recycling. Case studies are developed to describe how future desalination technologies can help address water supply needs across the nation in coastal cities, inland urban and rural areas, the Mid-Atlantic States, and oil, gas, and coal basin communities. The Roadmap also explores two scenarios of investment in research and development for desalination and the effects on the advancement of desalination technologies. Lastly, the Roadmap identifies several broad strategic actions that will be necessary to enhance water supplies through technological advancements in desalination. The Roadmap will be used within the Bureau of Reclamation as a planning tool to facilitate science and technology investment decisions and as a management tool to help structure the selection of desalination research, development, and demonstration projects. Proponents hope that the Roadmap also will be used by other organizations funding or conducting desalination research (including government, educational and non-profit organizations, and the private sector) to help ensure that research is coordinated and complementary.
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Review of the Desalination and Water Purification Technology Roadmap CHARGE TO THE COMMITTEE The Bureau of Reclamation approached the National Academies3 in the fall of 2002 to request an independent assessment of the Roadmap. To carry out this study, a committee was formed in early 2003, overseen by the National Research Council’s (NRC) Water Science and Technology Board. This report summarizes the findings of the Committee to Review the Desalination and Water Purification Technology Roadmap and addresses the following questions, which comprise the committee’s Statement of Task: Does the Desalination and Water Purification Technology Roadmap present an appropriate and effective course to help address future freshwater needs in the United States? Can further investments advance the implementation of desalination by significantly reducing its cost and otherwise addressing issues associated with its increased use? Does the Roadmap correctly identify the key technical and scientific issues that must be resolved so that desalination can be made more cost-effective? Are there any missing research areas from the Roadmap that should be included? What should be the general priorities for investments? What are the best roles for federal agencies, national laboratories, other research institutions, utilities, and the private sector to help implement the Desalination and Water Purification Technology Roadmap? An interim letter report released in June 2003 (NRC, 2003; see Appendix A) provided an initial assessment of the Roadmap, addressing question #1 of the Statement of Task. This report provides a summary of the findings in NRC (2003) and addresses the remaining questions of the Statement of Task. The committee’s conclusions and recommendations are based on a review of the Desalination and Water Purification Technology Roadmap and relevant technical literature, information gathered at two committee meetings, and the collective expertise of the committee members. The committee’s first meeting included presentations from the Bureau of Reclamation, Sandia National Laboratories, members of the Roadmapping Team, and other experts in desalination research. These presentations were intended to brief the committee on the Roadmap’s development, expected uses, and follow-up activities; help frame the issues; and inform the committee of activities of other federal, state, and local entities engaged in desalination and water purification research and development. Following this introduction, Chapter 2 provides a general assessment of the Roadmap and summarizes the findings in NRC (2003). The major technology areas for desalination are described in Chapter 3 along with the opportunities for cost reductions by further research in these areas. An additional cross-cutting technology area is also presented. The research topics proposed in the Roadmap are evaluated and general priorities are presented for each technology area. Chapter 4 presents suggestions for implementing the Roadmap. 3 The National Academies consists of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council is the advisory arm of the National Academies.
Representative terms from entire chapter: