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Desalination: A National Perspective
Summary
Efforts to identify new, untapped sources of supply have dominated water policy for the past century. There has been an exponential increase in desalination capacity both globally and nationally since 1960, fueled in part by this growing concern for local water scarcity and made possible to a great extent by a major federal investment for desalination research and development in the late 1950s to the early 1980s. Traditional sources of supply are increasingly expensive, unavailable, or controversial, but desalination technology offers the potential to substantially reduce water scarcity by converting the almost inexhaustible supply of seawater and the apparently vast quantities of brackish groundwater into new sources of freshwater. Although total water use in the United States has remained steady over recent decades, interest in brackish water and seawater desalination will likely continue, particularly in water-scarce regions, in localities experiencing rapid population growth, or where users are able and willing to pay for a high-quality, reliable new supply.
Historically, the high cost and energy requirements of desalination had confined its use to places where energy is inexpensive and freshwater scarce. Recent advances in technology, especially improvements in membranes, have made desalination a realistic water supply option. The cost of desalinating seawater in the United States is now competitive with other alternatives in some locations and for some high-valued uses, and there is considerable interest in hastening the time when costs of desalination are routinely competitive with the costs of alternatives.
With support from the U.S. Bureau of Reclamation and the U.S. Environmental Protection Agency, the National Research Council convened the Committee on Advancing Desalination Technology to assess the state of the art in relevant desalination technologies and factors such as cost and implementation challenges. The committee also was asked to describe reasonable long-term goals for advancing desalination technology and to provide recommendations for action and research. Finally, the committee was asked to estimate the funding necessary to support the
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Desalination: A National Perspective
Summary
Efforts to identify new, untapped sources of supply have dominated water policy for the past century. There has been an exponential increase in desalination capacity both globally and nationally since 1960, fueled in part by this growing concern for local water scarcity and made possible to a great extent by a major federal investment for desalination research and development in the late 1950s to the early 1980s. Traditional sources of supply are increasingly expensive, unavailable, or controversial, but desalination technology offers the potential to substantially reduce water scarcity by converting the almost inexhaustible supply of seawater and the apparently vast quantities of brackish groundwater into new sources of freshwater. Although total water use in the United States has remained steady over recent decades, interest in brackish water and seawater desalination will likely continue, particularly in water-scarce regions, in localities experiencing rapid population growth, or where users are able and willing to pay for a high-quality, reliable new supply.
Historically, the high cost and energy requirements of desalination had confined its use to places where energy is inexpensive and freshwater scarce. Recent advances in technology, especially improvements in membranes, have made desalination a realistic water supply option. The cost of desalinating seawater in the United States is now competitive with other alternatives in some locations and for some high-valued uses, and there is considerable interest in hastening the time when costs of desalination are routinely competitive with the costs of alternatives.
With support from the U.S. Bureau of Reclamation and the U.S. Environmental Protection Agency, the National Research Council convened the Committee on Advancing Desalination Technology to assess the state of the art in relevant desalination technologies and factors such as cost and implementation challenges. The committee also was asked to describe reasonable long-term goals for advancing desalination technology and to provide recommendations for action and research. Finally, the committee was asked to estimate the funding necessary to support the
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proposed research agenda and to identify appropriate roles for governmental and nongovernmental entities. This report builds on a 2004 National Research Council report that provided a scientific assessment of the Bureau of Reclamation’s and Sandia National Laboratories’ Desalination and Water Purification Technology Roadmap, or Roadmap, which was intended to serve as a strategic pathway for future desalination and water purification research (USBR and Sandia National Laboratories, 2003).
WATER FOR THE FUTURE: THE ROLE OF DESALINATION
When considering future water supplies, it is important to recognize that past patterns of water use will not always be a reliable indicator of future demand. In particular, the assumption that water demands will inevitably parallel population and economic growth no longer appears to be correct. Nevertheless, water scarcity in some regions of the United States will certainly intensify over the coming decades, and no one option or set of options is likely to be sufficient to manage this intensifying scarcity. Desalination, using both brackish and seawater sources, is likely to have a niche in the future water management portfolio of the United States.
The committee was specifically asked to address the potential for seawater and brackish water desalination to help meet anticipated water supply needs in the United States. The committee concluded that the potential for desalination cannot be definitively determined because it depends on a host of complicated and locally variable economic, social, environmental, and political factors. In the complete absence of these factors, the theoretical potential for desalination is effectively unlimited. Large quantities of inland brackish groundwater appear to be available for development; in coastal areas, ocean resources are essentially infinite in comparison to human demands. But, as with most resource questions, the theoretical potential and the practical potential are far different. All water management and planning takes place in the context of economic, social, environmental, and political factors, and these factors are far more important than technological desalination process constraints in limiting the potential for desalination to help meet anticipated water supply needs. As a result, this report addresses key technological issues that may lend themselves to focused research and development efforts, but the report also addresses nontechnical questions that may ultimately prove to be more limiting.
The costs of producing desalinated water—the cost of removing salts to create freshwater—is no longer the primary barrier to implementing
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desalination technology, because there have been significant reductions in desalination production costs. Meanwhile, the costs of other alternatives for augmenting water supplies have continued to rise, often making desalination more attractive in a relative sense. A continuation of these trends would likely make desalination costs more attractive and less of a constraint in the future. Nevertheless, concentrate management costs vary widely, depending on local regulations and site-specific conditions, and have generally increased in recent decades. Where low-cost concentrate management alternatives are not available, the financial costs of desalination can be prohibitive. There is also considerable uncertainty about the environmental impacts of desalination and, consequently, concern over its potential effects. Possible environmental impacts of desalination are impingement and entrainment of organisms when seawater is taken in, ecological impacts from disposing of salt concentrates, and increased greenhouse gas emissions from increased energy use, among other concerns. Although limited studies to date suggest that the environmental impacts may be less detrimental than many other types of water supply, site-specific information necessary to make detailed conclusions on environmental impacts is typically lacking.
A strategic desalination research and development effort can help make desalination a more attractive water supply option for communities facing water shortages and can enable desalination technology to serve a larger role in addressing the nation’s water demands. The two main goals of this research and development effort should be (1) to understand the environmental impacts of desalination and develop approaches to minimize these impacts relative to other water supply alternatives, and (2) to develop approaches to lower the financial costs of desalination so that it is an attractive option relative to other alternatives in locations where traditional sources of water are inadequate. Success of the proposed research agenda will depend on coordinated federal leadership and participation by state and local governments, nongovernmental organizations, and the private sector.
CURRENT INVESTMENT IN DESALINATION RESEARCH AND DEVELOPMENT
Based on the committee’s survey of federal investment in desalination research and development together with estimates and analyses of state, nongovernmental organizations, and private-sector funding, the committee reached several conclusions (see also Chapter 2) that underscore the need for the development of a national strategic research agenda for desalination:
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There is no integrated and strategic direction to the federal desalination research and development efforts. Desalination research and development efforts are funded through at least nine federal agencies and laboratories, each with their own research objectives and priorities. The majority of federal desalination research and development funding also comes from congressional earmarks, which limits the ability to develop a steady research program. Federal funding for desalination research declined from approximately $24 million per year in fiscal years (FYs) 2005 and 2006 to $10 million in FY 2007 (a decline of nearly 60 percent), largely due to an absence of earmarks in FY 2007.
Some states, especially California, have also made sizeable recent investments in desalination research and development. The majority of this funding is being directed toward site- or region-specific problems, with heavy emphasis on pilot and demonstration projects.
The private sector appears to fund the majority of desalination research, with total annual spending estimated to be more than twice that of all other surveyed sources of such funding. Based on the judgment of individuals working in the industry, the private sector allocates a smaller fraction of its research portfolio to high-risk desalination research than the federal government. Given the large research investment, however, private-sector funding for high-risk activities is estimated to be roughly equivalent to federal funding for high-risk research.
STATE OF DESALINATION TECHNOLOGY
The state of desalination technology, including intakes, pretreatment, desalination processes, post-treatment, and concentrate management, is outlined in Chapter 4. Industry has made great strides in reducing energy use for desalination with the commercialization of high-efficiency energy recovery devices and improvements in membrane technology. Reverse osmosis (RO) technology is relatively mature, and current energy use is within a factor of 2 of the theoretical thermodynamic minimum value for separating solutes from water. Thus, RO is the standard by which novel desalination technologies should be assessed when specific energy use is the main consideration. Meanwhile, opportunities exist to further reduce cost and energy use of current technologies by small but economically significant amounts:
In RO desalination, the costs and energy requirements of water production can be further reduced by mitigating fouling through pretreatment; developing high-permeability, fouling-resistant, high-rejection, oxidant-resistant membranes; and optimizing membrane
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module and membrane system design. Operating the RO process at lower hydraulic pressure while maintaining high throughput is the key to reducing the specific energy for membrane-based desalination. To fully utilize the capacity of high-permeability RO membranes and to accommodate even more permeable RO membranes in the future, it is imperative to reduce fouling and concentration polarization effects and to develop new module configurations and system designs to avoid or overcome thermodynamic restriction. Fouling can be reduced by a more robust pretreatment and by the development of fouling-resistant membranes. Practical and economic constraints, however, are likely to inhibit RO energy use from decreasing more than approximately 15 percent below the values of the best current technology. This level of improvement would still be valuable for reducing cost and energy use, but greater returns on investment than this should not be expected.
Seawater desalination using thermal processes can be cost effective when waste heat is utilized effectively. Location of low-grade and/or waste heat resources near large water consumers may reduce the cost of heat energy and offset the higher specific-energy requirements of thermal desalination when compared to RO. Hybrid membrane–thermal desalination approaches offer additional operational flexibility and opportunities for water production cost savings for facilities co-located with power plants.
Few, if any, cost-effective environmentally sustainable concentrate management options exist for inland desalination facilities. Several methods are currently available for concentrate management, and each method has its own set of site-specific costs, benefits, regulatory requirements, environmental impacts, and limitations. Low- to moderate-cost inland disposal options can be limited by the salinity of the concentrate and by location and climate factors. Only evaporation ponds and high-recovery/thermal evaporation systems are zero-liquid discharge solutions, but high costs limit their consideration for most municipal applications.
ENVIRONMENTAL IMPACTS
Knowledge of the potential environmental impacts of desalination processes is essential to water supply planners when they consider desalination among many water supply alternatives. All components of the water use cycle should be considered, including source water impacts, the likely greenhouse gas emissions from the energy requirements of the desalination process, potential impacts from concentrate management approaches, and environmental health considerations in the product wa-
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ter. Ideally, these considerations should be compared against equally rigorous environmental impact analyses of water supply alternatives, so that decisions can be made based on comparisons of the full economic costs and benefits, including environmental and social costs and benefits, among the various water supply alternatives.
There is a considerable amount of uncertainty about the environmental impacts of desalination and, consequently, concern over its potential effects. Therefore, the following research is recommended:
Site-specific assessments of the impacts of source water withdrawals and concentrate management should be conducted and the results synthesized in a national assessment of potential impacts. The ecological effects of concentrate discharge into the ocean appear to vary widely and depend on the site-specific environment, the organisms examined, the amount of dilution of the concentrate, and the use of diffuser technology. The ecological impacts of surface water intakes have been well studied for power plants but not for desalination plants, and these impacts will likely vary from place to place. General information on potential impacts from groundwater withdrawal and injection are available from decades of hydrogeologic studies for other purposes, but site-specific analyses are necessary to understand the impacts from a proposed facility. Once a number of rigorous site-specific studies are conducted, this information should be synthesized, using other existing data, to develop an overarching assessment of the possible range of impacts from desalination in the United States.
Monitoring and assessment protocols should be developed for evaluating the potential ecological impacts of surface water concentrate discharge. Adequate site-specific studies on potential biological or ecological effects are necessary prior to the development of desalination facilities, and planners would benefit from clear guidance on appropriate monitoring and assessment protocols. Specific recommendations are provided in Chapter 5.
Longer-term, laboratory-based assays on the sublethal effects of concentrate discharge should be conducted to understand the range of environmental impacts from desalination plants. Except for a few short-term lethality studies that do not give insight into long-term effects, little research has been done on the impacts of concentrate discharges on organisms in receiving waters. Longer-term laboratory-based biological assays should evaluate impacts of concentrate on development, growth, and reproduction using a variety of different organisms, including those native to areas where desalination plants are proposed. These results can be utilized in a risk assessment framework.
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Water quality guidance, based on an analysis of the human health effects of boron in drinking water and considering other sources of exposure, is needed to support decisions for desalination process design. There are concerns about boron in product water from seawater desalination because the boron levels after single-pass RO commonly exceed current WHO health guidelines and the EPA health reference level. A range of water quality levels (0.5 to 1.4 mg/L) have been proposed as protective of public health based on different assumptions in the calculations. The EPA has decided not to develop a maximum contaminant level for boron because of its lack of occurrence in most groundwater and surface water and has encouraged affected states to issue guidance or regulations as appropriate. Therefore, most U.S. utilities lack clear guidance on what boron levels in drinking water are suitably protective of public health. Boron can be removed through treatment optimization, but that treatment could aversely affect the cost of seawater desalination.
Further research and applications of technology should be carried out on how to mitigate environmental impacts of desalination and reduce potential risks relative to other water supply alternatives. For example, intake and outfall structures could be designed to minimize impingement and entrainment and to encourage improved dispersion of the concentrate in coastal discharges. Research could also explore beneficial reuse of the desalination by-products and develop technologies that reduce the volume of this discharge.
Desalination efforts do not need to be halted until this research is done and uncertainties are removed, but research investments should be made to help reduce potential risks.
COSTS AND BENEFITS OF DESALINATION
Historically, the relatively high financial costs of water production via desalination have constrained the use of desalination technologies in all but a few very specific circumstances. As discussed earlier, the financial cost picture has changed in a number of important ways. There have been significant reductions in membrane costs and improvements in the energy efficiency of the desalination process. Perhaps more significant, the costs of other alternatives for augmenting water supplies have continued to rise, making desalination production costs more attractive in a relative sense. The trend of cost reduction may be abetted through a program of strategically directed research aimed at achieving potentially large cost reductions. Nevertheless, the costs of concentrate management
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are potentially large and vary from site to site. Such costs have the potential to offset reductions in water production costs. The following conclusions about the cost and benefits of desalination are based on the discussion and analyses in Chapter 6:
Substantial reductions in the financial cost of producing desalinated water will require substantial reductions in either energy costs or capital costs. Energy and capital costs are the two largest components of financial cost for both thermal and membrane seawater desalination processes. Future trends in energy costs also will be important inasmuch as significant increases in energy prices could offset or more than offset cost reductions in other areas and make desalination technologies less attractive. Cost savings are possible if novel technologies or configurations are developed that optimize the use of alternative energy sources, including low-grade or waste energy.
For brackish water desalination, the costs of concentrate management can vary enormously from project to project and may rival energy and capital costs as the largest single component of cost. The high cost of environmentally sustainable concentrate management at some inland locations ultimately offsets the cost advantage that can be obtained from utilizing feed waters with lower salinity.
Conservation and transfers from low- to high-valued uses will usually be less costly than supply augmentation schemes, including desalination. In many circumstances, there remain methods of demand management that can make significant additional quantities of water available at less cost than desalination. Similarly, market-like transfers of water can also offer relatively low-cost ways of acquiring additional supplies of water. Conservation and efficiency improvements that reduce the total demand for water often come with associated benefits, such as reduced energy costs.
There are small but significant efficiencies that can be made in membrane technologies that will reduce the energy needed to desalinate water and, therefore, offer potentially important process cost reductions. Development of membranes that operate effectively at lower pressures could lead to 5 to 10 percent reductions in total costs of the desalination process associated with a 15 percent decrease in energy use. In contrast, extending membrane life beyond the current 5-year design life is likely to have a small impact on desalination costs because membranes account for a minimal proportion of total costs. Prevention of catastrophic failure through robust pretreatment is important because membrane failure within the first year of operation can cause an annual cost increase of more than 25 percent.
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To make the true costs of desalination transparent, the economic costs should be accounted for and reported accurately. Failure to price water accurately can lead to inefficient use and overuse. Average cost pricing understates the cost of desalinated water to the consumer, and the supplier should take care in reporting the true and accurate economic costs publicly.
A STRATEGIC DESALINATION RESEARCH AGENDA
Over the past 50 years the state of desalination technology has advanced substantially. Even so, concerns about potential environmental impacts continue to limit the application of desalination technology in the United States, and desalination remains a higher-cost alternative for water supply in many communities. In order for desalination to become a more attractive water supply option for communities facing water shortages, two overarching long-term research goals need to be met:
Understand the environmental impacts of desalination and develop approaches to minimize these impacts relative to other water supply alternatives, and
Develop approaches to lower the financial costs of desalination so that it is an attractive option relative to other alternatives in locations where traditional sources of water are inadequate.
Although the environmental impacts of coastal desalination may be less than that of other water supply alternatives, the uncertainty about potential site-specific impacts and their mitigation for both coastal and inland operations are large barriers to the application of desalination in the United States. This uncertainty leads to stakeholder disagreements and a lengthy and costly planning and permitting process. Without rigorous scientific research to identify specific potential environmental impacts (or a lack of impacts), planners cannot assess the feasibility of desalination at a site or determine what additional mitigation steps are needed.
At present, desalination costs are already low enough to make desalination an attractive option for some communities when the benefits of desalination are considered, such as providing a drought-resistant supply and providing a means to diversify a large community’s water supply portfolio. However, the costs of desalination, like the costs of water supply alternatives, are locally variable and are influenced by factors such as site conditions and concentrate management options. In addition, increasing awareness of potential environmental impacts is raising the costs of
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permitting and intake and outfall configurations in the United States. Meanwhile, the future costs of energy are uncertain.
A strategic research agenda in support of these two overarching goals is described in Chapter 8 (see Box S-1). This research agenda is broadly conceived and includes research that could be appropriately funded and conducted in either the public or the private sector. Several recommendations for implementing the proposed research agenda follow:
A coordinated, strategic plan should be developed to ensure that future federal investments in desalination are integrated and prioritized and address the two major goals identified in this report. The strategic application of federal funding for desalination research can advance the implementation of desalination technologies in areas where traditional sources of water are inadequate. Responsibility for developing the plan should rest with the Office of Science and Technology Policy (OSTP). Initial federal appropriations on the order of recent spending on desalination research (total appropriations of about $25 million annually) should be sufficient to make good progress toward these goals, when complemented by ongoing nonfederal and private-sector desalination research, if the funding is directed toward the proposed research topics recommended in this report. Reallocation of current federal spending will be necessary to address currently underfunded topics. If current federal research and development funding is not reallocated, new appropriations will be necessary. However, support for the research agenda stated here should not come at the expense of other high-priority water resources research topics. Five years into the implementation of this plan, the OSTP should evaluate the status of the plan, whether goals have been met, and the need for further funding.
Environmental research should be emphasized up front when implementing the research agenda. Uncertainties regarding environmental impacts and ways to mitigate these impacts are some of the largest hurdles to implementation of desalination in the United States, and research in these areas has the greatest potential for enabling desalination to help meet future water needs in communities facing water shortages. Priority areas of environmental research are discussed in Chapters 5 and 8.
Research funding in support of reducing the costs of desalination should be directed strategically toward research topics that are likely to make improvements against benchmarks set by the best current technologies for desalination. Because the private sector is already making impressive strides toward reducing the process costs of desalination, the federal research funding should emphasize long-term,
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BOX S-1
Priority Research Areas
The committee has identified priority research areas to help make desalination a competitive option among water supply alternatives for communities facing water shortages. These research areas, which are described in more detail in Chapter 8, are summarized here. The highest priority topics are shown in bold. Some of this research may be most appropriately supported by the private sector. The research topics for which the federal government should have an interest—where the benefits are widespread and where no private-sector entities are willing to make the investments and assume the risk—are marked with asterisks.
GOAL 1. Understand the environmental impacts of desalination and develop approaches to minimize these impacts relative to other water supply alternatives
Assess environmental impacts of desalination intake and concentrate management approaches**
Conduct field studies to assess environmental impacts of seawater intakes**
Conduct field studies to assess environmental impacts of brackish groundwater development**
Develop protocols and conduct field studies to assess the impacts of concentrate management approaches in inland and coastal settings**
Develop laboratory protocols for long-term toxicity testing of whole effluent to assess long-term impacts of concentrate on aquatic life**
Assess the environmental fate and bioaccumulation potential of desalination-related contaminants**
Develop improved intake methods at coastal facilities to minimize impingement of larger organisms and entrainment of smaller ones**
Assess the quantity and distribution of brackish water resources nationwide**
Analyze the human health impacts of boron, considering other sources of boron exposure, to expedite water-quality guidance for desalination process design**
GOAL 2. Develop approaches to lower the financial costs of desalination so that it is an attractive option relative to other alternatives in locations where traditional sources of water are inadequate
Improve pretreatment for membrane desalination
Develop more robust, cost-effective pretreatment processes
Reduce chemical requirements for pretreatment
Improve membrane system performance
Develop high-permeability, fouling-resistant, high-rejection, oxidant-resistant membranes
Optimize membrane system design
Develop lower-cost, corrosion-resistant materials of construction
Develop ion-selective processes for brackish water
Develop hybrid desalination processes to increase recovery
Improve existing desalination approaches to reduce primary energy use
Develop improved energy recovery technologies and techniques for desalination
Research configurations and applications for desalination to utilize waste heat**
Understand the impact of energy pricing on desalination technology over time**
Investigate approaches for integrating renewable energy with desalination**
Develop novel approaches and/or processes to desalinate water in a way that reduces primary energy use**
GOAL 1 and 2 Cross Cuts.
Develop cost-effective approaches for concentrate management that minimize potential environmental impacts**
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high-risk research that may not be attempted by the private sector and that is in the public interest. Investigator-driven research should be permitted throughout the proposal process.
Research cannot address all barriers to increased application of desalination technology in regions facing water scarcity concerns; thus, practical desalination implementation issues that pertain to water providers are discussed in Chapter 7. Recommendations in Chapter 7 include building trust and educating the public on desalination project planning, anticipating the sometimes cumbersome regulatory and permitting process, and utilizing pilot testing to optimize the process design.
PROSPECTS FOR DESALINATION
The potential for desalination to meet anticipated water demands in the United States is constrained not by the source water resources or the capabilities of current technology, but by a variety of financial, social, and environmental factors. Substantial uncertainty remains about the environmental impacts of desalination, and resolving these uncertainties and developing methods to mitigate the impacts is the highest priority for future research. Research and development also are needed to continue current trends in reducing the process costs of desalination and developing cost-effective, environmentally sustainable approaches for concentrate management. Implementing the proposed research agenda will require federal leadership and a coordinated, strategic plan among multiple agencies. In addition, the success of the research agenda will depend on participation by federal, state, local agencies, nongovernmental entities, and the private sector.
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