Water desalination systems

Figure for Prob. 13.12. Solar Water Desalinization System. 

K.B. Franca, H.M. Laborde, and H. Neff, Solar Powered Water Desalination Systems,... 

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 two water desalination applications described above represent the majority of the market for electrodialysis separation systems. A small application exists in softening water, and recently a market has grown in the food industry to desalt whey and to remove tannic acid from wine and citric acid from fruit juice. A number of other applications exist in wastewater treatment, particularly regeneration of waste acids used in metal pickling operations and removal of heavy metals from electroplating rinse waters [11]. These applications rely on the ability of electrodialysis membranes to separate electrolytes from nonelectrolytes and to separate multivalent from univalent ions. 

In this chapter, some important examples of integrated membrane systems will be presented starting from the most well-known application of membrane technology, that is, water desalination. 

Although RO water desalination is today considered as the most cost-effective solution [4], key factors for further improvements in membrane-based desalination systems are enhancement of water-recovery factor, cost reduction, improvement of water quality, new brine-disposal strategies. All these issues can be addressed by an integrated approach. 

Integrated Membrane Processes for Water Desalination 266 Integrated Membrane Process for Wastewater Treatment 271 Integrated Membrane System for Fruit-Juices Industry 274 Integrated Membrane Processes in Chemical Production 276 Conclusions 281 References 281... 

Glueckstern P. and Priel M. (1998) Advanced concept of large desalination system for Israel. International Water Services Association Conference, Membranes in drinking and Industrial water production, Amsterdam, Holland, September, 1998. 

Apart from the features of the membranes to be used for the needs of waste management technology, there is one more question to cope with pretreatment engineering. Even in the case of a relatively simple system for water desalination, pretreatment becomes a key problem. In engineering practice, specifically when wastewater is dealt with, the membrane systems to be used are as intricate as are the solutions, the mixtures and their combinations (along with the colloid particles included in them) which have to be treated. 

Persistent interest in studying the clathrate systems is largely caused by the great diversity of areas of their practical application. They can be used in efficient fine purification of substances, in isomer separation [95,96], in the development of energy-saving water desalination technologies, etc. In recent... 

When a membrane-based desalination process is used, seawater is first collected and pumped to the water-treatment plant. Sodium hypochlorite is injected periodically after the intake pumps to prevent biological growth within the water-treatment system. Suspended solids are retained by sand filters or MF. The filtered water is then acidified. 

Molinari, R., Argurio, P., Poeiro, T., Caruso, A. (2006). Stagnant sandwich and supported liquid membrane systems for removal of pharmaceuticals in water. Desalination, 199, 529-31. 

More specifically, these systems, whether operated in the conventional mode or as rotary units have been successfully utilized in applications such as the recovery of protein and lactose from cheese whey, separation of fermentation products, concentration of fluids foods and juices, manually operable sea water desalinators, recovery of starch from potato processing fluids, and processlng/separatlon of pharmaceutical and chemical mixtures. 

Later, our system proved to work successfully also for desalination of water, but the development through the pharmaceutical to the food and dairy industries and pulp and paper industry did give a great deal of experience which has been extremely valuable for our design of water desalination plants as constructed today. 

The use of LLC-based membrane systems is still in its infancy. Promising early results indicate that research in this field will be expanded. The applications outlined here are just a few where functional LLC materials might be implemented. More challenging separation materials, such as water desalination membranes, selective proton-conducting membranes for fuel cells, catalytic membranes, chromatography, and chiral separation media are perhaps future candidates for new LLC membrane materials. 

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