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Pure water without electricity

July 22, 2002

Many a visitor to Majorca - the island of choice for German and British vacationers - has made the bitter experience: The drinking water in some parts of the island is unbearably salty. Naturally, water treatment plant operators make a concerted effort to lower the salt and lime content of their water to acceptable levels by mixing in fresh water. Yet when the supply of sweet water is insufficient, too often the only alternative is bottled or imported water. A third option - a desalination system - eliminates the inconvenience of having to transport water in bulk. An especially compact device that also works in remote areas without electricity is being introduced by the Fraunhofer Patent Center for German Research PST.

Most modern desalination systems work on the principle of reverse osmosis, as Edelgard Hund explains: "Salt water is fed under pressure into a module and flows over a synthetic membrane. The polymer material allows water to pass through but rejects the passage of salt ions. Desalinated or fully de-ionized water flows out on the other side." As with distillation, this process requires the use of energy. With devices such as those manufactured by UT&S GmbH, however, the pressure necessary to force the salt water through the membrane "against its will" is generated using a water-jet pump.

"Of course, this presumes that enough water with a minimum feed pressure is available," admits Hund. "Unfortunately, this is not always the case, particularly in countries with poorly developed infrastructures." As a result, drinking water currently remains a prospect for the future because it's a question of cost for hotel operators: How much will they have to pay per cubic meter of de-ionized water processed with such a system? Would it be more cost-efficient in the end to opt for the traditional, but ecologically questionable, solution of having water brought in by tanker? Two further applications of the technology are on the horizon. Tests are currently being performed on industrial dishwashers that operate without chemical water softeners. The use of de-ionized water for the final rinse eliminates the need to hand-polish glasses to remove lime spots. The new desalination devices are already being successfully employed in other sectors of industry. In electroplating plants, metallic salt baths must either continually or at regular intervals be renewed . Plant operators require de-ionized water for this process, as the introduction of foreign salts adversely effects the properties of the metallic coatings. As simple as it might seem, "plain" water is not just any water.

Fraunhofer-Gesellschaft