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Desalination technology and potential application in Greece
P. Karachaliou, Desalination technology and potential application in Greece, Postgraduate Thesis, 109 pages, National Technical University of Athens, 2010.
With the term "desalination" we usually characterize any activity of abstraction of salts from a saline substance and from saline waters. Consequently, the desalination is a method of recuperation of potable water from marine water, brackish rivers and lakes. In our days, 13600 of desalination units function worldwide. About 11% of them were installed during the last years (before 2000). 38% of these stand in the Persian Gulf and the 17% in the USA. The more widespread methods are the multiple stage flashing (MSF) and the reverse osmosis (RO), while each one of these produces the 43% of the world product. The method of reverse osmosis provides reliability in all the breadth of sizes of production (from few litres until hundreds cubic metres per day), due inter alia to its relatively compact and easy manufacturing, compared to other methods. On a cost basis of manufacture of selected units in different countries the last 15 years, the cost of desalination with reverse osmosis is shaped diachronically by 1,50 Euros in 2001 up to 0,20 Euros in 2005. During the last years the desalination of marine water is developed with very fast rythms, which indicates that in the future it will constitute one from the main sources of water feeder. Today it is appreciated that in all the world function many units of desalination, that produce over 50 millions m3/day of potable water. The desalination in Greece is not widely used, even though it could constitute a viable solution for the problem of water shortage in the islands of the Aegean Sea and mainly in the very arid islands of Cyclades, where the cost of transported water is very high,. 2 Considering the plenty of sunlight and the intense presence of winds in the Greek islands, Greek and foreigner scientists were led to the designing and the creation of the first in the world navigable unit of desalination, which uses for its operation only renewable sources of energy: the wind for the mainly operation of "navigable factory", and complementarily the sun for the electrification of its operational and remote control systems. This first unit that was named Hydriada, a name taken from the Greek mythology, had a cost of 2,8 millions €, however, the cost for the next corresponding ones is estimated not exceeding the 700.000 €. So much the designing what the results from the operation of the desalination platform have gained the impressions in national but also in international level. The main desalination units in Cyprus are the ones in Dekelia and in Larnaka. Indubitably the contribution of desalination in the confrontation of the water problem in Cyprus is big. Nevertheless the units of desalination appear to be an expensive, energy consuming and environmentally overloading solution for the water problem, contrary to the policy of the most optimal management of the existing resources. The big desalination installations usually use conventional forms of energy, which present important cost fluctuations, which, in their turn, also influence of course the cost of produced water. It is necessary for the desalinated water to be consumed near its region of production, because its long distance transportation away from its production place increases the cost prohibitorily. Consequently the required energy for the installation’s operation should be disposed within the range of the wider region of the desalination unit. The desalination units bring forward two categories of environmental repercussions: the ones derived from the use of energy and the ones derived from the brine rejection. The Renewable Sources of Energy (RSE) have relatively low cost, in as far as they emanate from free of charge raw material 3 but are not always offered for their use in the desalination units. Naturally they do not pollute the environment and are accessible, however they have not even found wider application in small desalination units. The solution of desalination is a good choice from the technical-financial point of view, especially in cases of water need and hence survival. Relative studies on specific islander locations have shown that it is a viable and profitable investment for anyone willing to attempt its concretisation, municipal or community enterprise, even the State. At this very point we should mark that the cost of desalination units depends on the unit capacity but also their combination with RSE. Besides, the systems of energy recuperation in the desalination and storage of energy in aeolian systems, raise considerably the cost of work and hence the price of water, therefore reverses its profits. The problem for the generalised use of desalination methods seems to be not so much economic, provided that the cost of produced water is not necessarily prohibitory, but the existance of repercussions from the desalination units. Despite the fact that the desalination method could constitute a solution in the problem of lack of water, it is not by itself free from repercussions. The condensate of the dense brine returns into the sea, so that the water salinity is increased in enough distance from the point of expense and the marine ecosystem is influenced. Consequently a very careful study is required, depending on the region, in the place of the brine rejection point. Moreover, the drawn water is pre-chlorinated in order to protect the membranes, the cost of which is particularly high. Accordingly the rinsing of the membranes spills into the sea together with the brine condensate, overloading farther the marine ecosystem. 4 The countries that use the desalination are trying to resolve the urgent problems that result from the lack of water, balancing between them and the various repercussions caused by the desalination. The desalination is a method that can offer satisfactory quality and quantity of potable water, independent from the climate of region, and must be sought as a solution. However it is impossible to cover all the needs of water supply, and it should function additionally in a wider policy of completed management of water resources, and in no case should replace the efforts for collection of rain water, the restriction of escapes from the network of water supply, and the choice of suitable cultures in the rural production that is not water consuming, so as to achieve the highest saving of water.
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