The Future of Seawater Desalination: Energy, Technology, and the Environment
05 Aug 2011-Science (American Association for the Advancement of Science)-Vol. 333, Iss: 6043, pp 712-717
TL;DR: The possible reductions in energy demand by state-of-the-art seawater Desalination technologies, the potential role of advanced materials and innovative technologies in improving performance, and the sustainability of desalination as a technological solution to global water shortages are reviewed.
Abstract: In recent years, numerous large-scale seawater desalination plants have been built in water-stressed countries to augment available water resources, and construction of new desalination plants is expected to increase in the near future. Despite major advancements in desalination technologies, seawater desalination is still more energy intensive compared to conventional technologies for the treatment of fresh water. There are also concerns about the potential environmental impacts of large-scale seawater desalination plants. Here, we review the possible reductions in energy demand by state-of-the-art seawater desalination technologies, the potential role of advanced materials and innovative technologies in improving performance, and the sustainability of desalination as a technological solution to global water shortages.
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TL;DR: This work investigates permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions, which reveal that the GO membrane can attract a high concentration of small ions into the membrane, which may explain the fast ion transport.
Abstract: Graphene-based materials can have well-defined nanometer pores and can exhibit low frictional water flow inside them, making their properties of interest for filtration and separation. We investigate permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions. The laminates are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves, blocking all solutes with hydrated radii larger than 4.5 angstroms. Smaller ions permeate through the membranes at rates thousands of times faster than what is expected for simple diffusion. We believe that this behavior is caused by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The anomalously fast permeation is attributed to a capillary-like high pressure acting on ions inside graphene capillaries.
2,055 citations
TL;DR: In this article, molecular-level design approaches for membrane materials, focusing on how these materials address the urgent requirements of water treatment applications, are reviewed for water scarcity and the pollution of aquatic environments.
Abstract: Membranes have an increasingly important role in alleviating water scarcity and the pollution of aquatic environments. Promising molecular-level design approaches are reviewed for membrane materials, focusing on how these materials address the urgent requirements of water treatment applications.
1,900 citations
TL;DR: The results indicate that the water permeability of this material is several orders of magnitude higher than conventional reverse osmosis membranes, and that nanoporous graphene may have a valuable role to play for water purification.
Abstract: We show that nanometer-scale pores in single-layer freestanding graphene can effectively filter NaCl salt from water. Using classical molecular dynamics, we report the desalination performance of such membranes as a function of pore size, chemical functionalization, and applied pressure. Our results indicate that the membrane’s ability to prevent the salt passage depends critically on pore diameter with adequately sized pores allowing for water flow while blocking ions. Further, an investigation into the role of chemical functional groups bonded to the edges of graphene pores suggests that commonly occurring hydroxyl groups can roughly double the water flux thanks to their hydrophilic character. The increase in water flux comes at the expense of less consistent salt rejection performance, which we attribute to the ability of hydroxyl functional groups to substitute for water molecules in the hydration shell of the ions. Overall, our results indicate that the water permeability of this material is several ...
1,852 citations
TL;DR: The permeability/selectivity trade-off is discussed, similarities and differences between synthetic and biological membranes are highlighted, challenges for existing membranes are described, and fruitful areas of future research are identified.
Abstract: BACKGROUND Synthetic membranes are used for desalination, dialysis, sterile filtration, food processing, dehydration of air and other industrial, medical, and environmental applications due to low energy requirements, compact design, and mechanical simplicity. New applications are emerging from the water-energy nexus, shale gas extraction, and environmental needs such as carbon capture. All membranes exhibit a trade-off between permeability—i.e., how fast molecules pass through a membrane material—and selectivity—i.e., to what extent the desired molecules are separated from the rest. However, biological membranes such as aquaporins and ion channels are both highly permeable and highly selective. Separation based on size difference is common, but there are other ways to either block one component or enhance transport of another through a membrane. Based on increasing molecular understanding of both biological and synthetic membranes, key design criteria for new membranes have emerged: (i) properly sized free-volume elements (or pores), (ii) narrow free-volume element (or pore size) distribution, (iii) a thin active layer, and (iv) highly tuned interactions between permeants of interest and the membrane. Here, we discuss the permeability/selectivity trade-off, highlight similarities and differences between synthetic and biological membranes, describe challenges for existing membranes, and identify fruitful areas of future research. ADVANCES Many organic, inorganic, and hybrid materials have emerged as potential membranes. In addition to polymers, used for most membranes today, materials such as carbon molecular sieves, ceramics, zeolites, various nanomaterials (e.g., graphene, graphene oxide, and metal organic frameworks), and their mixtures with polymers have been explored. Simultaneously, global challenges such as climate change and rapid population growth stimulate the search for efficient water purification and energy-generation technologies, many of which are membrane-based. Additional driving forces include wastewater reuse from shale gas extraction and improvement of chemical and petrochemical separation processes by increasing the use of light hydrocarbons for chemicals manufacturing. OUTLOOK Opportunities for advancing membranes include (i) more mechanically, chemically, and thermally robust materials; (ii) judiciously higher permeability and selectivity for applications where such improvements matter; and (iii) more emphasis on fundamental structure/property/processing relations. There is a pressing need for membranes with improved selectivity, rather than membranes with improved permeability, especially for water purification. Modeling at all length scales is needed to develop a coherent molecular understanding of membrane properties, provide insight for future materials design, and clarify the fundamental basis for trade-off behavior. Basic molecular-level understanding of thermodynamic and diffusion properties of water and ions in charged membranes for desalination and energy applications such as fuel cells is largely incomplete. Fundamental understanding of membrane structure optimization to control transport of minor species (e.g., trace-organic contaminants in desalination membranes, neutral compounds in charged membranes, and heavy hydrocarbons in membranes for natural gas separation) is needed. Laboratory evaluation of membranes is often conducted with highly idealized mixtures, so separation performance in real applications with complex mixtures is poorly understood. Lack of systematic understanding of methodologies to scale promising membranes from the few square centimeters needed for laboratory studies to the thousands of square meters needed for large applications stymies membrane deployment. Nevertheless, opportunities for membranes in both existing and emerging applications, together with an expanding set of membrane materials, hold great promise for membranes to effectively address separations needs.
1,794 citations
TL;DR: Recent development in nanotechnology for water and wastewater treatment is reviewed, covering candidate nanomaterials, properties and mechanisms that enable the applications, advantages and limitations as compared to existing processes, and barriers and research needs for commercialization.
1,744 citations
Cites background from "The Future of Seawater Desalination..."
...This strategy may greatly improve the energy efficiency for treatment of waters with low osmosis pressure, but it may have limited advantage in seawater RO, whose energy consumption is already close to the thermodynamic limit (Elimelech and Phillip, 2011)....
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References
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TL;DR: Some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water are highlighted.
Abstract: One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water and sanitation. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water-rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. Here we highlight some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water.
6,967 citations
TL;DR: Gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores enable fundamental studies of mass transport in confined environments, as well as more energy-efficient nanoscale filtration.
Abstract: We report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. The measured gas flow exceeds predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations. The gas and water permeabilities of these nanotube-based membranes are several orders of magnitude higher than those of commercial polycarbonate membranes, despite having pore sizes an order of magnitude smaller. These membranes enable fundamental studies of mass transport in confined environments, as well as more energy-efficient nanoscale filtration.
2,637 citations
TL;DR: Mixed-charge materials have been shown to be equivalent to zwitterionic materials in resisting nonspecific protein adsorption when they are uniformly mixed at the molecular scale.
Abstract: In recent years, zwitterionic materials such as poly(carboxybetaine) (pCB) and poly(sulfobetaine) (pSB) have been applied to a broad range of biomedical and engineering materials. Due to electrostatically induced hydration, surfaces coated with zwitterionic groups are highly resistant to nonspecific protein adsorption, bacterial adhesion, and biofilm formation. Among zwitterionic materials, pCB is unique due to its abundant functional groups for the convenient immobilization of biomolecules. pCB can also be prepared in a hydrolyzable form as cationic pCB esters, which can kill bacteria or condense DNA. The hydrolysis of cationic pCB esters into nonfouling zwitterionic groups will lead to the release of killed microbes or the irreversible unpackaging of DNA. Furthermore, mixed-charge materials have been shown to be equivalent to zwitterionic materials in resisting nonspecific protein adsorption when they are uniformly mixed at the molecular scale.
1,715 citations
TL;DR: The most commonly used desalination technologies are reverse osmosis (RO) and thermal processes such as multi-stage flash (MSF) and multi-effect distillation (MED) as mentioned in this paper.
1,708 citations
TL;DR: In this paper, the authors used surface plasmon resonance spectroscopy and self-assembled monolayers (SAMs) to determine the characteristics of functional groups that give surfaces the ability to resist the nonspecific adsorption of proteins from solution.
Abstract: This paper describes the use of surface plasmon resonance (SPR) spectroscopy and self-assembled monolayers (SAMs) to determine the characteristics of functional groups that give surfaces the ability to resist the nonspecific adsorption of proteins from solution. Mixed SAMs presenting different functional groups were prepared for screening using a synthetic protocol based on the reaction of organic amines with a SAM terminated by interchain carboxylic anhydride groups. Surfaces that presented derivatives of oligo(sarcosine), N-acetylpiperazine, and permethylated sorbitol groups were particularly effective in resisting the adsorption of proteins. Incorporation of these groups into single-component SAMs resulted in surfaces that are comparable to (but slightly less good than) single-component SAMs that present oligo(ethylene glycol) in their ability to resist the adsorption of proteins. In the group of surfaces examined, those that resisted the adsorption of proteins had the following properties: they were ...
1,678 citations