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Review of the Desalination and Water Purification Technology Roadmap Executive Summary In order to maintain economic development and minimize future regional and international conflicts, the United States will need sustainable supplies of high-quality fresh water. Solutions to local water scarcity issues will likely require a combination of approaches, including demand management, improved water storage capacity, water quality protection, and advancements in supply-enhancing water treatment technologies. Desalination technologies can create new sources of freshwater from otherwise impaired waters such as seawater or brackish water. However, like nearly all new fresh water sources, desalinated water comes at substantially higher costs than today’s existing water sources, keeping these technologies out of the reach of many communities. The Bureau of Reclamation and Sandia National Laboratories jointly developed the Desalination and Water Purification Technology Roadmap (Roadmap) to serve as a strategic research pathway for desalination and water purification technologies to “contribute significantly to ensuring a safe, sustainable, affordable, and adequate water supply for the United States” (USBR and SNL, 2003). Critical objectives for desalination technology advancement were determined, and research topics were identified in the technology areas of membranes, thermal technology, alternative technologies, concentrate management, and reuse and recycling. 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. The Bureau of Reclamation approached the National Research Council (NRC) in the fall of 2002 to request an independent assessment of the Roadmap (see Box ES-1 for the Statement of Task), and the study was carried out by a committee organized by the NRC’s Water Science and Technology Board between January and December 2003. A summary of the committee’s findings follows. OVERARCHING REVIEW OF THE ROADMAP Supply-enhancing technologies represent just one component in a multi-faceted strategy necessary to address future water needs. Nevertheless, a careful research and development strategy is necessary to facilitate technological advancements and nurture
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Review of the Desalination and Water Purification Technology Roadmap BOX ES-1 Statement of Task for the Committee to Review the Desalination and Water Purification Technology Roadmap An expert panel was organized by the National Research Council to address the following questions: 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? novel ideas that can enhance water supplies and reduce the costs of current technologies. The Roadmap and its underlying process appear to present an appropriate framework for advancing research in several areas of desalination and water purification technology to help address future water needs across the United States, but the Roadmap document lacks an appropriate focus on desalination research and technology needs to meet the identified water supply objectives. Several recommendations are provided to support future planning efforts that develop from the Roadmapping process: The Roadmap should be developed to include clear, understandable logic and scientific basis for each of the critical objectives. The Roadmap should be developed to include analyses of recent technological advancements, descriptions of current limitations of desalination technologies, theoretical limits in ideal processes, and quantifications of baseline desalination values from which future advancements can be measured, which could provide the basis for developing a strategic research agenda for desalination. A subsequent research agenda should be developed that logically builds from the current state of desalination technology toward the critical objectives. TECHNOLOGIES The five technological areas highlighted in the Roadmap represent appropriate priorities for research and development in the field of desalination and membrane-based water purification, but these technological areas and associated research issues receive only limited attention in the Roadmap. Some important cross-cutting research areas were also not adequately addressed within the Roadmap, including energy use and air emissions from energy intensive desalination technologies. For each technology area,
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Review of the Desalination and Water Purification Technology Roadmap this report describes the cost issues and technical opportunities for contributing to desalination and reviews the related projects identified in the Roadmap. Suggested revisions to the research areas itemized in the Roadmap are provided for each of the technology areas, and these suggestions are summarized in Tables 3-1 through 3-6. Membranes The use of membrane processes for desalination has increased markedly in recent years, as desalination costs for reverse osmosis have declined. Considering the recent improvements in membrane-based desalination, substantial further cost savings could be more difficult to achieve, suggesting the need for a carefully developed research agenda targeted to areas that offer the most promise for cost reduction. Some of the objectives in the Roadmap will not be possible with advances in existing membrane technology alone. The membrane research areas identified in the Roadmap cover a significant portion of the important research areas, but the committee has identified other key areas that are overlooked in the Roadmap. Research is needed to develop on-line sensors to determine the integrity of the membranes and to detect pathogens and other biological contaminants. The development of fouling resistant elements and systems, appropriate indicators of fouling, and improved cartridge filter design to reduce replacement rate could lead to reduced operational costs. Large cost savings are also possible through research to reduce the use of pre- and post-treatment chemicals. Further research should explore improved membrane process design configurations and materials to reduce costs, including dual membrane and hybrid membrane designs. The development of tailorable membrane selectivity would facilitate reliable removal of specific contaminants at an acceptable cost in terms of permeability. Among the membrane technology areas identified in the Roadmap and those additional areas suggested by this committee, several have been designated as high priority research topics within this category: Improving membrane permeability. Improving or developing new methods for reducing energy use or recovering energy. Improving pretreatment and posttreatment methods to reduce consumption of chemicals. Developing less expensive materials to replace current corrosion-resistant alloys used for high pressure piping in seawater reverse osmosis systems. Developing new membranes that will enable controlled selective rejection of contaminants. Improving methods of integrity verification. Developing membranes with more fouling resistant surfaces.
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Review of the Desalination and Water Purification Technology Roadmap Thermal While thermal desalination is not expected to displace membrane-based desalination in the United States, thermal technologies have substantial potential and should be more seriously considered, especially when combined with other industrial applications, such as electric power generating facilities (termed cogeneration), to utilize waste heat and improve flexibility and economics. Overall, thermal desalination research intended to reduce desalination costs should focus on energy efficiency and on material or design research that could influence capital costs. The thermal technology research topics identified in the Roadmap are generally appropriate but could be expanded and, in some cases, revised. The use of alternative energy sources, particularly waste heat sources, is a potential area for future research which could result in improved desalination economics and broader application of thermal desalination. The use of innovative cooling systems may reduce the water intake requirements and allow operation at higher concentration factors. Research to evaluate or refine nonmetallic or polymeric heat transfer materials could significantly reduce capital costs, and improvement in the efficiency of heat transfer surfaces could also reduce operating costs. Research that identifies corrosion mitigation techniques or develops innovative materials of construction that resist corrosion could improve plant economics for thermal desalination plants. Because energy is expensive in the United States and comes with significant environmental impacts, the highest priority research topics focus on examining ways to harness wasted energy for the benefit of water production, including evaluating opportunities for cogeneration of water and power and developing alternative energy sources, including improved use of industrial waste heat. Alternative Technologies The Roadmap’s long-term objectives for desalination cost reductions (50-80 percent by 2020) will not likely be achieved through incremental improvements in existing technologies. Such dramatic cost reductions will require novel technologies, perhaps based on entirely different desalination processes or powered by entirely new energy sources. Specific areas that could benefit from alternative technologies for cost reduction include energy, capital costs, and brine disposal. Because there are many ideas in varying states of development, it is impossible to list all the possibilities, let alone prioritize them. Although the list of alternative desalination research topics contained in the Roadmap is highly speculative in nature, it contains reasonable examples of the types of research that could be considered in a call for proposals. A research funding program to include alternative desalination technologies also would need to be open to consider new, unforeseen research areas, and all proposals should be subjected to a rigorous review process.
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Review of the Desalination and Water Purification Technology Roadmap Reuse/Recycling Aside from the desalination of seawater or brackish aquifers, one potential solution to the nation’s water supply problem is to utilize increasingly impaired waters, such as municipal wastewaters, by applying desalination treatment technologies for contaminant removal. The starting source water qualities and the product water quality objectives for desalination are different from those of water purification by reuse/recycling, and these differences influence the research needs. The committee offers many suggestions to expand upon the research proposed for reuse and recycling in the Roadmap. More complete identification of the contaminants present in treated wastewaters and lower analytical detection limits for contaminants are needed so that potential associations with observed health effects can be discerned. To inform the development of analytical surrogates, an improved understanding of structure-activity relationships between organic molecules and reverse osmosis membrane materials are needed. On-line contaminant monitoring tools, including tools to measure the integrity of membrane systems in real time, are also important research areas. With additional research and development to support cost reductions, membrane bioreactors could provide a higher level of treatment at comparable costs of traditional treatment, thus contributing to better public health protection in reuse applications. Several applied research efforts are proposed that could improve the applicability of water reuse and recycling. A feasibility study should be conducted on the topic of decentralization of water recycling facilities, examining regulatory monitoring and permitting issues. The water reuse industry should also review both successful and unsuccessful reuse projects and apply the lessons learned to future reuse efforts. Among the reuse and recycling research topics identified in the Roadmap and those additional topics recommended by this committee, the following topics have been identified as high priorities: Developing improved techniques for identification and quantification of chemical contaminants. Examining the feasibility of decentralized treatment. Enhancing membrane bioreactor technology. Conducting a risk comparison between various water reuse schemes and potable water counterparts. Developing a set of chemical and microbiological surrogates for indirect potable reuse and developing a better understanding of the relationship between rejected solutes and the membrane. Developing more sensitive on-line membrane integrity monitoring systems. Concentrate Management Concentrate is a residual that needs to be handled in a manner that minimizes environmental impacts and protects human health. Coastal desalination plants are often able to safely dispose of saline concentrate into the ocean or estuaries at relatively modest costs. However, concentrate management can be a very large portion of the cost at inland
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Review of the Desalination and Water Purification Technology Roadmap desalination facilities, and this cost greatly reduces the economic feasibility of desalination technology at inland locations. Reducing the costs of concentrate handling would make many sources of water, especially brackish groundwater, available for use. The committee recommends that several concentrate management research topics be added to those proposed in the Roadmap. Innovative methods are needed for dealing with silica and potentially toxic contaminants, such as arsenic and selenium. Research should explore the fate of these contaminants and the concentration at which deleterious impacts occur in concentrate management applications. Due to limits in salt concentration tolerated in the root zone and the possibility of leachate degrading ground or surface waters, crop irrigation may not be a viable option in most cases, although research is needed to further examine the limits of this disposal option. Research to evaluate methods of improving the efficiencies of near-zero liquid discharge (and possibly zero liquid discharge) could increase their areas of applicability. Cost reductions could also be gained if further research aimed to improve beneficial and sustainable reuse of desalination concentrate. For example, designs should be developed for the management of commercially valued salt solids. Additional geochemical and hydrologic research is needed for further advancement of subsurface concentrate storage. The following high-priority research topics have been identified from those included in the Roadmap and the additional topics suggested by the committee: Reducing concentrate volume. Management/removal of toxic compounds such as arsenic. Improving systems for beneficial and sustainable concentrate reuse, including underground storage and management of concentrates with a total dissolved solids (TDS) level of less than 10,000 mg/L and management of commercially valued salts. Cross-Cutting Technologies One major research area—energy—emerged in this review of the Roadmap, which has the potential to contribute broadly to all aspects of desalination, regardless of the technology chosen. The Roadmap does not look at the broader context of energy costs, such as the contribution of fossil fuels to greenhouse gases or the effect of a large-scale desalination on the cost of energy, which could have a substantial influence on wider implementation of desalination. Research is needed to further examine these broad issues, including research on renewable energy sources, energy conservation, methods to reduce energy emissions, and life-cycle analyses for desalination and water reuse. IMPLEMENTATION The Roadmap does not provide an implementation strategy, and current funding levels within the federal government for non-military application of desalination are insufficient to fund research efforts that would trigger a step change in performance and cost reduction for desalination technologies. Much remains to be done to build on the efforts to date and turn these preliminary research ideas into a program for strategic
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Review of the Desalination and Water Purification Technology Roadmap research investments in the area of desalination technologies. In order to achieve the objectives of the Roadmap, the program will need adequate funding for research, involvement of talented researchers worldwide through a broadly distributed request for proposals, rigorous independent peer review of proposals, strategic awarding of research funding, and effective communication of the research findings to the desalination community. Several recommendations are provided with regard to a future implementation process: The Bureau of Reclamation should work collaboratively with desalination experts from different sectors to develop a strategic research agenda and to estimate the resources needed to place the nation in a likely position to reach the long-term objectives set forth in the Roadmap. Requests for proposals should be announced as widely as possible to scientists and engineers in government, academia, and private industry, and unsolicited proposals should also be considered in areas of innovative technologies. Proposals should be selected through a rigorous independent peer review process, utilizing a rotating panel of independent expert reviewers. The Bureau of Reclamation should encourage and lead the publication and communication of research activities and results through various media, including a central website on the activities and progress of the Roadmap. The general public should be informed about the benefits, affordability, and environmental considerations of desalination.
Representative terms from entire chapter: