Desalination seawater

Fuhy aromatic, thermally (up to 250°C) and hydrolyticahy resistant films of PODs have been reali2ed from polyhydra2ides (56). Films of these polymers are useful as seawater desalination membranes. 

The copper-chelating abihty of sahcylaldoxime has been used to remove copper from brine in a seawater desalination plant effluent. A carbon—sorbate bed produced by sorption of the oxime on carbon proved to be extremely effective in the continuous process (99). In another apphcation, the chelating abihty of sahcylaldoxime with iron and copper was used to stabilize bleaching powders containing inorganic peroxide salts (100). 

The first reverse osmosis modules made from cellulose diacetate had a salt rejection of approximately 97—98%. This was enough to produce potable water (ie, water containing less than 500 ppm salt) from brackish water sources, but was not enough to desalinate seawater efficiently. In the 1970s, interfacial composite membranes with salt rejections greater than 99.5% were developed, making seawater desalination possible (29,30) a number of large plants are in operation worldwide. 

The pressure to be used for reverse osmosis depends on the salinity of the feedwater, the type of membrane, and the desired product purity. It ranges from about 1.5 MPa for low feed concentrations or high flux membranes, through 2.5—4 MPa for brackish waters, and to 6—8.4 MPa for seawater desalination. In desalination of brackish or sea water, typical product water fluxes through spiral-wound membranes are about 600—800 kg/m /d at a recovery ratio RR of 15% and an average salt rejection of 99.5%, where... 

The fluxes in hoUow-fiber membranes used in seawater desalination are 20—30-fold smaller, but the overall RO system size does not increase because the hoUow-fiber membranes have a much larger surface area per module unit volume. In use with seawater, their RR is about 12—17.5% and the salt rejection ratio is up to 99.5%. 

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

Xu P, Brissaud F, Salgot M (2003) Facing water shortage in mediterranean tourist. Area seawater desalination or water reuse Wat Sci Tech/Wat Supply 3(3) 63-70... 

Commercial interest in RO began with the first high-flux, high-NaCl-retention Loeb-Sourirajan anisotropic cellulose acetate membrane. Practical application began with the thin film composite (TFC) membrane and implementation for seawater desalination at Jeddah, Saudi Arabia [Muhurji et ak. Desalination, 76, 75 (1975)]. 

Applications RO is primarily used for water purification seawater desalination (35,000 to 50,000 mg/L salt, 5.6 to 10.5 MPa operation), brackish water treatment (5000 to 10,000 mg/L, 1.4 to 4.2 MPa operation), and low-pressure RO (LPRO) (500 mg/L, 0.3 to 1.4 MPa operation). A list of U.S. plants can be found at www2.hawaii.edu, and a 26 Ggal/yr desalination plant is under construction in Ashkelon, Israel. Purified water product is recovered as permeate while the concentrated retentate is discarded as waste. Drinking water specifications of total dissolved solids (TDS) < 500 mg/L are published by the U.S. EPA and of < 1500 mg/L by the WHO [Williams et ak, chap. 24 in Membrane Handbook, Ho and Sirkar (eds.). Van Nostrand, New York, 1992]. Application of RO to drinking water is summarized in Eisenberg and Middlebrooks (Reverse Osmosis Treatment of Drinking Water, Butterworth, Boston, 1986). 

Kupitz, Juergen, 1995, Nuclear energy for seawater desalination updating die record, IAEA Bulletin 37, no. 2 21. 

Cross flow is a better reflection of practical configurations. The well-mixed assumption is only reasonable for low concentrations and low values of 9. As a comparison, seawater desalination involves a feed with a concentration of the order of 35,000 ppm. 

Figure 23.2 shows a schematic representation of a boiler feedwater treatment system. Raw water from a reservoir, river, lake, borehole or a seawater desalination plant is fed to the steam system. However, it needs to be treated before it can be used for steam generation. The treatment required depends both on the quality of the raw water and the requirements of the utility system. The principal problems with raw water are1,2 ... 

Reverse osmosis membrane process, 27 637 Reverse osmosis membrane cleaning citric acid application, 6 647 Reverse-osmosis membranes, 75 811, 825 development of, 75 797 Reverse osmosis models, 27 638-639 Reverse osmosis permeators, 76 19 Reverse osmosis seawater desalination process, 26 85 Reverse osmosis systems blending in, 26 80-81 brackish and nanofiltration, 26 80-83 Reverse osmosis technology... 

The concentrations of seawater and brackish water can vary significantly, and as such there is a difference between the concentrate produced from seawater desalination plants and brackish water desahnation plants. Seawater typically has a level of total dissolved solids (TDS) between 33,000-37,000 mg/L. The average major ion concentration of seawater is shown in Table 2.1 along with water from the Mediterranean Sea, and water from Wonthaggi off the southern coast of Australia. Seawater sahnity increases in areas where water evaporates or freezes, and it decreases due to rain, river runoff, and melting ice. The areas of greatest salinity occur and latitudes of 30° N and S where there are high evaporation rates. 

Curcio, E., Drioli, E. Membranes for Desahnation. In Cipollina, A., Micale, G., Rizzuti, L. (eds.) Seawater Desalination Conventional and Renewable Energy Processes, pp. 41-75. Springer, Heidelberg New York (2009)... 

Lattemann, S., Hopner, T. Environmental impact and impact assessment of seawater desalination. Desalination 220(1-3), 1-15 (2008). 

Discharge to surface water is the most economical form of concentrate management for seawater desalination plants, regardless of the discharge volume. Due to the availability of ocean discharge for seawater desalination plants, the cost of disposal tends to be less costly than for inland desalination. Costs include pumps and pipes. 

Concentrate can be harmful to the environment due to either its higher than normal salinity, or due to pollutants that otherwise would not be present in the receiving body of water. These include chlorine and other biocides, heavy metals, antisealants, coagulants and cleaning chemicals. Of particular concern is the effect of pollutants on delicate ecosystems and endangered or threatened species. However, with appropriate measures in place, the discharge of concentrate to surface water can remain a viable method for seawater desalination plants. 

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). 

Al-Barwani, H., Pumama, A. Simulating brine plumes discharged into the seawaters. Desalination 221(1-3), 608-613 (2008)... 

Voutchkov, N. Seawater desalination costs cut through power plant co-location. Filtr. Sep. 41(7), 24-26 (2004)... 

Permeability Properties of Cellulose Triacetate Hollow-Fiber Membranes for One-Pass Seawater Desalination... 

On the other hand, the development of seawater desalination, which was the original target of RO process, was delayed because of the insufficient performance of membrane under operating conditions of high pressure and high salt concentration. 

For this reason, two pass seawater desalination process have been necessarily employed till quite recently, and the results obtained have been satisfactory to some extent with regard to water quality and practical operation. However, one pass process has advantages over two pass process for simple and compact plant, simple operation, easy maintenance and lower energy consumption. 

We have developed one pass seawater desalination module so called, "Hollosep-High Rejection Type" with excellent salt rejection in 1978. 

Long term experiments of one pass seawater desalination using our module have been carried out at Chigasaki Laboratory of Water Reuse Promotion Center under the supervision of Ministry of International Trade and Industry, Japan (4). A continuous long term test for 12,000 hours was successfully conducted with the m-value of 0.02. Another demonstration plant with an 800 m3/D capacity has also been operating over 3,000 hours at the recovery ratio of using the feed water of F.I. value of about 4. 

Characteristics of the hollow fiber membrane is shown in Table 2. The outer diameter and wall thickness of this hollow fiber membrane is fairly thick compared with those of other hollow fibers for seawater desalination. Salt rejection of hollow fiber membrane is high enough to be applied to one pass seawater desalination. 

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