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Right there, under the ground By Jack Gilron Tags: Israel News The severe water shortage facing Israel this year has reached the point where the government has decided to ban the watering of city gardens with fresh water, and the Agriculture Ministry is warning that thousands of acres of orchards will have to be uprooted in an effort to limit demand. On the supply side, the government has more than doubled the mandate for seawater desalination that was established at the beginning of the decade, to over 700 million cubic meters per year (present production is at 133 million m³/year). In the flurry of all this activity, another alternative has been overlooked as a potential water source (especially in peripheral regions): desalination of brackish groundwater. The 10th conference of the Israel Desalination Society, to be held at Sapir Academic College this coming Monday, will focus on this resource and its potential for promoting regional development - especially in the Negev region. Already in this decade, both the Mekorot national water company and private companies have installed brackish water reverse osmosis (or RO, a process in which water is pushed through a membrane that passes water, but rejects salt) plants, which together yield 37 million m³/year, and there are plans to increase this capacity by 70 percent within the next few years (figures furnished by the Israel Water Authority). Most of these plants produce water for around 50 cents per cubic meter. By comparison, the cost of supplying desalinated seawater to the national water grid now runs 63 to 76 cents per cubic meter. Advertisement Brackish groundwater differs from seawater in three main ways: composition, location and quantity. All three have an impact on its continued role vis-a-vis the national water economy. Whereas seawater has a salinity of around 40,000 milligrams per liter, brackish water's is generally between 1,500 and 5,000 mg/L. Since potable water has salinities in the range of 250-500 mg/L, in both cases desalination is required. This is usually done by RO. Some of that water must be retained to help carry away the leftover salt, in the form of concentrated brine. The energy required by RO rises with the salinity level, so that brackish water demands only 20-40 percent of the energy needed to desalinate seawater. The economic savings will increase as energy costs go up. While seawater is readily accessible to the large population on the coast, getting product water to peripheral inland regions such as the Negev may require pumping over long distances. On the other hand, significant deposits of brackish groundwater underlie many areas of the country. Developing these sources will thus entail double energy savings: more efficient desalination and lower distribution costs. Location has in fact determined placement of the existing brackish water desalination plants: Today, there are significant-sized plants in the southern Arava and western Negev, providing both drinking and irrigation water. In fact, brackish water desalination was first tried in these regions as early as the 1960s and '70s, pioneered by researchers of the Negev Research and Development Authority (which later became part of Ben-Gurion University). This was a key to development of these regions, since it made high-quality water available to residents. Mekorot is also applying the technology to help protect existing parts of the coastal aquifer in the Kiryat Malakhi region. Location also affects the method of disposal of the saline brine that remains after the fresh water is produced. In coastal seawater (and brackish water) installations, this brine can be discharged to the sea. Inland, brine removal is more problematic, and hence raises the cost of water production. Brine removal in evaporation ponds costs up to $2 per cubic meter of brine. This, plus the cost of developing and pumping from the brackish water wells (often 300-600 meters deep in the Negev) makes it imperative to extract as much product water as possible out of the raw feed water. The Ketziot plant has a recovery rate of 87-88 percent. Now, groups of researchers at both Ben-Gurion University and at the Technion - Israel Institute of Technology are developing novel processes that could push recovery levels to 95-98 percent. In terms of quantity, brackish water is limited by the amount available in underground porous geological layers (aquifers), the rate at which it can be pumped out of extraction wells, and the rate at which these aquifers are replenished. As a result, the technology of brackish water desalination is intimately bound up in issues of hydrology. It is also influenced by the political implications of the fact that these brackish aquifers run beneath borders. The supply of seawater, on the other hand, is unlimited. It is inevitable that Israel's water needs will be satisfied from a number of sources (seawater, brackish, recovered municipal wastewater) as well as from conservation. However, brackish water has more potential than is presently being exploited. Its desalination can play a larger role in Negev development and in reducing the water crisis' impact on this region. Greater interaction of academia, government and industry can make this a reality. Dr. Jack Gilron is a senior scientist in the desalination department of the Zuckerberg Institute for Water Research, at Ben-Gurion University of the Negev. Bookmark to del.icio.us   Enough is enough Livni says time will come when Israel tells Gaza militants: Enough! Oxbridge anti-Semitism Report: Oxford students face anti-Semitism charges over 'pretty Jewish girls' party.

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