SCIENCE NOTES Economic Desalting Of Sea Water Imperative

Press, Volume XCIX, Issue 29227, 10 June 1960, Page 22

SCIENCE NOTES Economic Desalting Of Sea Water Imperative

[By RITCHIE CALDER]

“Man will have no hope of survival unless he can take the salt out of sea-water,” said Dr. H. Heimann, of the Israel Institute of Technology, at the U.N.E.S.C.O. Symposium on Arid Zone Problems held in Paris.

That can be done now—at a price, but, since Dr. Everett D. Howe, of the University of California, pointed out that the best method was still 10 times too costly for irrigation, it is not an immediate solution.

Scientific methods for desalinating either sea water or brackish water are many. By using plastic membranes and passing electric currents through the water, the salts can be deposited and the water freshened. Or resins (on the principle of the domestic water-softeners) can be used. Water can be distilled by solar energy but not in sufficient quantities. Or it can be frozen and the ice-crystals will have rejected the brine and can be melted into fresh water.

One of the developments of the latter process reported from Israel involves pre-cooling the sea-water and injecting it into a vacuum chamber. The ice forms on a series of screens, stacked vertically. It is remelted in a continuous system.

As Dr. Howe pointed out, it may be economic to produce water in this way for drinking or, if water is indispensable to the production of oil or gold, it may pay industrially, but if it is to be used for agriculture it must be cheaper than it is by any present or foreseeable method. Not all the 200 scientists gathered from 33 countries shared Dr. Heimann’s Cassandra-like view, but all of them obviously recognised that water is or should be as great a preoccupation as food—since we cannot have food without water—and not just in the deserts of popular imagination.

One of the grimmest warnings came from the United States, and from one of the most prosperous parts. Dr. Lima B. Leopold, of the United States Geological Survey, said that the semi-arid West was “overspending” its water-capital at an alarming rate. It was taking out of the ground-water reserves was

a thousand times as much as the rains were putting back. The area had developed irrigated agriculture but, in addition to that, there had been a rapid industrial expansion. The aircraft industry haj moved in, because the warmth and clear skies were particularly suitable for the development of airfields, training bases and manufacturing. Other industries had similarly expanded. The water needs of industry began to loom large.

The population increased. The equable climate of the semi-arid south-west promoted the growth of cities, not only for general living but for recreation. In the desert fringes of the urban centres, homes were built in large numbers where no water was available. They developed their own wells and began drawing on water which was stored thousands of years ago and which is not replenished today. i Dr. Leopold warned countries [setting out to develop their arid or semi-arid regions not to repeat the mistakes of the United States. They should treat their subterranean water as a savingsbank from which to draw only when there were drought periods and only when the planned use of water had recognised that such droughts would occur, so that land-use would be within the water-budget. This warning was reinforced by Dr. Georges Drouhin, director of hydraulics in Algeria, when he discussed what he called “captive nappes.” These are natural underground reservoirs which extend for vast distances under the North African deserts and which can gush through borings. Until the full extent and knowledge of the amount of replenishment is established, the drawings from those artesian wells must be kept within the amounts which are known to go into the water-lays from the surface.

One of the ways in which water is lost is through trees. Although the revegetation of the desert has always been regarded as a necessary part of recovery, “new thinking” has reservations. Desert trees, like the tamarisk, stretch down their roots to find the underground water-table but, as Dr. Gilbert Whyte, of Chicago University pointed out, some of those trees will take as much water out of the soil as a field of irrigated crops. Mr Youssef Simaika, of the Ministry of Public Works, U.A.R., pointed out that Egypt, almost rainless and mainly dependent on the flow of the Nile, has a population t of 25 million with a cultivated area of only 6,300,000 acres. Increasing that acreage is possible only by water-storage, but that would not reduce poverty. That could only be done by birth-con-trol and by getting a large proportion of the farming population into industry.

Professor M. C. Shelesnyak. of Israel, also warned the conference that all their magnificent efforts and ingenious methods of finding water and cultivating the deserts might help today and tomorrow but not the day after’tomorrow. The world’s population increase would have to be restrained or it would defeat their objects.—(U.N.E.S.C.O.)