Seawater desalination


Sea – salt = hope
Drinking water is scarce in many countries. Seawater desalination is complex and energy-intensive. Now the amazingly simple invention of a BMW designer promises a remedy.

How does technical progress work? Sometimes this is the case: an authority gives inventors an almost impossible task and lures them with a reward. Singapore is a rich but small country. The area is not sufficient to supply water to the five million inhabitants; clean water is partly imported from Malaysia. The removal of salt from sea water is an obvious alternative. But the conventional plants for this, which are common in the oil states of the Middle East in particular, consume enormous amounts of fossil energy because they heat and vaporize the salt water. Per cubic metre of water they need about ten kilowatt hours (kWh), the energy content of one litre of heating oil. Saudi Arabia alone produces four million cubic meters of fresh water per day, four billion liters.

A more economical technique is reverse osmosis, in which the sea water is pressed at high pressure through semipermeable membranes that retain the salt. But the minimum energy consumption of modern plants is still about three kilowatt hours per cubic meter. The vision of the “Singapore Challenge” was a desalination technology that requires only 1.5 kilowatt hours. This is quite close to the theoretically conceivable minimum value: a minimum amount of energy is always required to extract seawater from the salt in the form of electrically charged ions. 36 teams took part in the competition: universities, small companies, large corporations. In the end, the race was won by a concept from Siemens AG. It doesn’t quite meet the desired value, but with 1.7 kWh per cubic meter of desalinated water it comes very close to it – thanks to the combination of two technologies that manage completely without heat and high pressure.

This is how low-energy desalination works
Figuratively speaking, the process can be compared to a magnet that pulls the salt ions out of the water. For this purpose, an electric field is generated in the salt water basin, in which ingeniously arranged membranes are located. The first step is electrodialysis. The positively charged sodium ions and the negatively charged chloride ions migrate through the membrane landscape and collect in chambers. The salt concentration then rises there; in the residual water it drops in the multi-stage process from 3.5 percent to a value at which electrodialysis becomes inefficient. For this reason, a process that has proven its worth in the production of ultrapure water in the pharmaceutical and computer industries now follows: the more expensive but more efficient “continuous electrodeionization”, in which an “ion exchange resin” between the membranes accelerates ion migration and reduces the residual salt load of the former seawater to the 0.05 percent required for drinking water.

Siemens received four million Singapore dollars (around two million euros) in 2008 to build a pilot plant in Singapore with the concept (which at the time only worked on a laboratory scale). Since 2010, 50 cubic meters of water per day have been desalinated in the plant. In 2014, the first commercial-scale plant is scheduled to be built in Singapore: more than 1,000 cubic meters per day. The demand is immense. With the world’s population growing, a water emergency is inevitable. Today, 300 million people are already dependent on water from desalination plants. 16,000 plants have been installed worldwide, most of them in the Middle East, followed by the USA and the Mediterranean region. “This will develop dramatically upwards,” says Rüdiger Knauf, development manager of the Water Division at Siemens.

Economical technology is good, but even it cannot compete with the elegance that is standard in nature: solar energy evaporates seawater, salt remains in the ocean – and fresh water rains from the clouds. A decisive step would be to use renewable energy sources such as the sun in industrial plants as well. This is not yet planned in Singapore. A solar-powered seawater desalination plant based on the principle of reverse osmosis is currently under construction in Saudi Arabia with the help of IBM. Novel photovoltaic modules and membrane materials are being tested here. But problems remain: In all large-scale plants, extremely saline wastewater is produced, which is returned to the sea and damages the organisms there. And: The systems are so expensive that poor countries cannot afford them. This is where the inventor of the “Watercone” comes in. Stephan Augustin, 44, is a full-time industrial designer at BMW and loves “ethical challenges” beyond his job.

low-tech desalination
During a Fuerteventura vacation in 1997, he sat on the beach and considered whether there might not be a very simple way to obtain drinking water from sea water plus sun. In small quantities. Without electricity. Without membranes. In a portable vessel. Decentralized. Affordable. It took several years for Augustin to come up with the Watercone prototype in his spare time: the bottom is a flat black plastic bowl 80 centimeters in diameter. Above it there is a transparent lid in the shape of a cone with a collecting channel at the bottom and a closure at the tip. Sea water is poured into the bowl. The sun causes it to evaporate; the water vapour condenses on the cone and runs off into the channel. After a sunny day it is full, now all you have to do is turn the appliance over, open the cap and fill the fresh water into bottles, cups or canisters: one to one and a half litres, the daily drinking water requirement of a child.

A three-month field trial conducted in 2004 in a fishing village in Yemen showed that the fish were not being caught: The low-tech principle works. Augustin won design and environmental prizes, and in 2008 Kofi Annan presented him with the “Energy Globe”. Nevertheless, only about 5000 cones have been sold. The previous price, 50 US dollars, is quite high because of the special plastic and the manufacturing process; on top of that, the material did not last for five years as expected. An optimised model is in the works and will soon be launched on the market – cheaper and made of more suitable plastic.

Technical progress can also function in this way: A person sits on the beach, has an inspiration, experiments, tests, rejects, improves – until the idea is ready to assert itself.

Source: Hanne Tügel – – Werkstatt Zukunft

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