Desalination water

Brackish water desaHnation was the first successful appHcation of RO with the first large-scale plant built in the late 1960s using cellirlose acetate membranes. The first seawater RO (SWRO) was built in 1973 with the advent of high permeabifity polyamide membranes. By 1993, the SWRO total capacity had reached 56,800 tn /d. In 2008, membrane desaHnation constituted 50% of total desaHnation capacity of which 45% was RO and 5% was EDR, and the rest 50% was thermal. However, 80% of aU desaHnation plants were membrane — 90% RO and 10% EDR. Desalination dominates the RO market and breaks down to 51 % desaHnation, 35% industrial and 14% residential/commercial and non-desal water [44]. In 2012, the global desaHnation capacity exceeded 60 M tn /d with more than 60% produced by RO membranes. The global water production by desaHnation in 2016 is projected to be 100 M m /d, twice the rate ofglobal water production by desalination in 2008 [45,46]. 

Seawater RO membrane desaHnation has become a viable process since its inception in 1970 for several reasons  

Integrated membrane system systems deploying MF, UF, NF or some combination of these for RO feed water pre-treatment instead of conventional pre-treatment. For example, it has been shown that hoUow fibre UF membrane systems are more efficient and cost-effective for RO brackish water and seawater plants [3,48,49]. MF/UF are very effective in removing fines and coUoidal particles, oil is effectively removed by UF, and NF is very effective in removing hardness and low molecular weight organics. 

Electrodialysis/electrodialysis reversal (ED/EDR) represents 3% of aU the desalination capacity in the world [48]. It is, however, used mainly for desalinating brackish water. It can achieve 95% water recovery with minimal chemical feed. However, it can only reject ionised matter. Substances such as colloids, silica and boron at pH 8.0 are not removed. A triple-membrane system using UF-EDR-RO has been very effective in producing purified water for power plants [50]. In this integrated system, UF is used for removing suspended solids and macromolecules  

EDR removes bulk of dissolved ions and RO removes the remaining dissolved ions, silica and the smallest organics. 

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Water clarification Water, cooling Water desalination Water dispersions Water drainage Water fastness Water fluoridation... 

Developments and advances in both membrane materials and reverse osmosis modules have increased the range of appHcations to which RO can be apphed. Whereas the RO industry has developed around water desalination (9,53,73,74), RO has become a significant cornerstone in other industries. 

Desalination. A special case of distillation is water desalination. In places where energy is abundant but fresh water is not, eg, the Arabian Peninsula, water may be produced from seawater ia flash evaporators. Low pressure turbiae steam is extracted to provide heat for the evaporators. Coadeased steam is returned to the cycle. Such units may be particularly prone to corrosion by salts. Sizes vary, but a plant scheduled for completion in 1996 had six units and a total capacity of 345,600 m /d. Power generation was expected to be 17,500 MW (36). 

In some places and under certain conditions, freshwater can be obtained more cheaply by desalination of seawater than by transporting water. This is tme when all the costs of extremely large monetary investments in dams, reservoirs, conduits, and pumps to move the water are considered. Before the rapid escalation of fuel costs between 1973 and 1980, the cost of desalination of seawater to adequately supply southern California would have been less than that of transport to the Peripheral Canal. This would have been the case even if there were an unlimited supply of water in the mountains of northern California, a condition that does not appear to exist. It has been shown that before 1973 a seacoast town could have been suppHed with 7-12 x lO" /d of freshwater more cheaply by desalination than by damming and piping water a distance of >160 km km (7). Indeed, the 1987—1992 drought in California has compelled the city of Santa Barbara to constmct a water desalination plant, and a 76,000-m /d plant is plaimed for the western coast of Florida (8). 

Bromley and co-workers (36) have calculated the minimal energy of separation of water from seawater containing 3.45 wt % salt, at 25°C, to be 2.55 kj/(kg fresh water) for the case of 2ero fresh water recovery (infinitesimal concentration change) and 2.91 kj/(kg fresh water) for the case of 25% fresh water recovery. is, however, severalfold smaller than the energy necessary for water desalination ia practice. 

The major water desalination processes that ate currendy in use or in advanced research stages are described herein. Information on detailed modeling can be found in the Hterature cited. The major texts on water desalination written since the 1980s are those by Spiegler and Laird (47), Khan (48), which contains many practical design aspects, Lior (49) on the measurements and control aspects, Heitman (40) on pretreatment and chemistry aspects, and Spiegler and El-Sayed (50), an overview primer. Extensive data sources are provided in References 39 and 51. 

Water Desalination in Developing Countries, U.N. Pubhcation 64 11 B 5-1964, United Nations New York, 1964. 

V. B. Chemo2ubov and co-workers, in Proceedings of the 1 st International Symposium on Water Desalination, Washington, D.C., Oct. 1965, p. 139. CIBA-Geigy Corp., The Application ofBelgardEU and Belgard EUN in Sea Water Evaporators, CIBA-GEIGY pamphlet DB 21. 

N. Lior, ed.. Measurements and Control in Water Desalination, Elsevier, Amsterdam, the Netherlands, 1986. 

Of these special surfaces, only the double-fluted tube has seen extended services. Most of the gain in heat-transfer coefficient is due to the condensing side the flutes tend to collect the condensate and leave the lauds bare [Caruavos, Proc. First Int. Symp. Water Desalination, 2, 205 (1965)]. The coudeusiug-film coefficient (based on the actual outside area, which is 28 percent greater than the nominal area) may be approximated from the equation... 

Lee RW, Glater J, Cohen Y, Martin C, Kovac K, Milobar MN, Bartel DW (2003) Low-pressure RO membrane desalination of agricultural drainage water. Desalination 155(2) 109-120... 

Desalt- entries Water desalination brackish water, 15 834-835, 837... 

Nanofiltration water desalination, energy consumption in, 26 87 Nanogold technology, 12 701 Nanoimprinting, optical, 15 193-195 Nano Indentor, 21 743 Nanoinhibitor design, 10 343 Nanomachines, 24 61-62 Nanomaterials, for sensors, 22 266 NanoMatrix, Inc., collagen nanofiber research, 1 723 Nanomedicine, 10 343... 

Water desalination, 26 51-102 economic aspects of, 26 96 energy requirements for, 26 59-61 freshwater manufacture via, 26 58-61 future prospects for, 26 96-98 membrane desalination processes, 26 73-87... 

Water desalination. See also Distillation processes, Water problem Water desalination processes, 26 59, 61 Water-dominated hydrothermal resources, 12 530-533... 

Fresh water is also in short supply in many areas. Plentiful inexpensive energy allows sea water desalination to provide almost unlimited supplies of fresh water. 

PVA/Poly(ethylene glycol) (PEG) membranes crosslinked by aldehydes and sodium salts were used in water desalination by pervaporation. The desalination of 8 % NaCl solution by... 

Crystallisation by freezing, or freeze crystallisation, is a process in which heat is removed from a solution to form crystals of the solvent rather than of the solute. This is followed by separation of crystals from the concentrated solution, washing the crystals with near-pure solvent, and finally melting the crystals to produce virtually pure solvent. The product of freeze crystallisation can be either the melted crystals, as in water desalination, or the concentrated solution, as in the concentration of fruit juice or coffee extracts. Freeze crystallisation is applicable in principle to a variety of solvents and solutions although, because it is most commonly applied to aqueous systems, the following comments refer exclusively to the freezing of water. 

The concentration of brackish water is far more variable than seawater. Depending on the location, brackish groundwater can have TDS concentrations ranging from several hundred up to several thousand mg/L. Table 2.2 shows the ion concentrations from the feed of three brackish water desalination plants in the Emirate of Abu Dhabi, United Arab Emirates. It can be seen that even three water sources in the same region can have widely variable concentrations of dissolved salts. 

Data from the Al Wagan BWRO desalination plant (Mohamed et al. 2005) has been used to highlight a typical brackish water desalination scenario. The following has been calculated assuming 200 m /day of brackish water is treated at a recovery of 70%. From Eq. 2.1 ... 

Cotravo, J.A. Water Desalination Processes and Associated Health and Environmental Issues. Water Cond. Purif. (January), 13-17 (2005). 

Examples of desalination plants that currently blend their concentrate with treatment plant outfall include the Thames Water Desalination Plant in London (150,000 m /day capacity) and the Barcelona Seawater Desalination Plant (200,000 m /day capacity). 

Schliephake, K., Brown, P., Mason-Jefferies, A., Lockey, K., Farmer, C. Overview of Treatment Processes for the Production of Fit for Purpose Water Desalination and Membrane Technologies, ASIRC Report No. R05-2207. Australian Sustainable Industry Research Centre Ltd., Churchill (2005)... 

NaA Selective layer Polyamide Support PSF NA Thin-film composite fiat sheet Liquid separations (e.g., water desalination) [83]... 

Geong and coworkers reported a new concept for the formation of zeolite/ polymer mixed-matrix reverse osmosis (RO) membranes by interfacial polymerization of mixed-matrix thin films in situ on porous polysulfone (PSF) supports [83]. The mixed-matrix films comprise NaA zeoHte nanoparticles dispersed within 50-200 nm polyamide films. It was found that the surface of the mixed-matrix films was smoother, more hydrophilic and more negatively charged than the surface of the neat polyamide RO membranes. These NaA/polyamide mixed-matrix membranes were tested for a water desalination application. It was demonstrated that the pure water permeability of the mixed-matrix membranes at the highest nanoparticle loadings was nearly doubled over that of the polyamide membranes with equivalent solute rejections. The authors also proved that the micropores of the NaA zeolites played an active role in water permeation and solute rejection. 

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