More drinking water from seawater Special polymers prolong the life of desalination plants It happens just before the water boils: The salts dissolved in the water precipitate as carbonate and hydroxide. The dreaded limescale forms - a conspicuous feature of immersion heaters or the heating elements of a washing machine, for example. It is no different in a thermal desalination plant. The seawater is heated up, and drinking water is recovered from the steam. What is left is a concentrated salt solution that is pumped back into the sea. Only scale inhibitors can prevent a hard crust of limescale forming on the evaporators during this process. In addition to this thermal technique for recovering drinking water, there is a second method that involves desalinating the seawater with the help of a membrane that is only partially permeable. But this “reverse osmosis” technique faces similar problems. The lion’s share of water - approximately two-thirds of that available worldwide - is used in agriculture for irrigation. In dry regions, this figure can be as high as 90 percent. One-third of the world’s food production is already dependent on irrigation, and this figure continues to rise. Yet the countries involved, both the Mediterranean countries and, for example, the Persian Gulf states, actually have abundant water - namely, seawater. However, because of its salt content, seawater can be used neither as drinking water nor for agriculture. With the help of huge dams, river water is therefore collected in reservoirs. Where this proves impossible, authorities are increasingly falling back on a completely different option: desalination of seawater. In Italy alone, there are now more than 130 desalination plants in operation; in Spain there are over 200. Worldwide, there are more than 12,000 such plants, approximately half of which operate using the vaporization principle, also known as the “thermal process.” Altogether, they produce 26 million cubic meters of drinking water per day. Almost one-third of this amount is accounted for by the Persian Gulf region, where per capita water consumption of 700 to 1,000 liters daily is not uncommon. This includes the water used for drinking, for irrigating fields and gardens, and for pools and golf courses. By way of comparison: Water consumption in German households is 130 liters per person, according to the National Gas and Water Industry Association. In southern California it is 3,100 liters, and in the Sahel, per capita consumption is only 30 liters. As the number of inhabitants and tourists increases, water shortages will become more acute. Furthermore, over half of the water that does exist is lost as a result of faulty irrigation systems. The importance of potable water recovery is therefore growing. But the desalination of seawater consumes a large amount of energy. Research therefore focuses on making the desalination plants more efficient. Improving the process itself is one of the approaches being pursued, and that’s also a goal of the researchers at BASF. To this end, they have developed scale inhibitors that suppress deposits and extend the service life of desalination plants. In thermal desalination plants, seawater is heated and fresh drinking water is recovered from the steam. What is left is a concentrated salt solution that is piped back into the sea. In a process similar to that which occurs in a kettle that scales up with time, this desalination method produces crystals that accumulate in the plant and dramatically reduce its efficiency. Every two to three months, considerable efforts must then be made to clean it. “The scale inhibitors lengthen these intervals to about one-and-a-half years,” says Karl-Heinz Büchner, who oversees the development of such products at BASF’s Performance Polymers division and provides customers with technical support. “And when scale does form, it’s never more than a thin, soft deposit that can easily be removed during regular operation, so the useful life of the plant increases.” http://www.corporate.basf.com/en/stories/wipo/meerwasser/story.htm?id=BvNrS94Rxbcp3Vp