New membrane technology offers cheap drinking water from seawater

The consumption of drinking water is still increasing, while the availability of drinking water decreases. About 1 billion people in the world have no access to enough clean drinking water, while 70% of the Earth is covered with water. Eight Dutch companies and one Belgian company developed a new membrane based technology to convert seawater into drinking water. The so called Memstill technology radically improves the economy and ecology of existing desalination technologies, by being more energy efficient.

Memstill (a contraction of membrane and distillation) is a distillation technique that uses membranes filtration and waste-heat energy from factories. Waste-heat is a cheap energy source that is plentiful in industrial countries. The cold seawater flows through a condenser with non-permeable walls. Then, the water flows through a heat exchanger where the seawater is heated to 80 degrees Celsius (180 degrees Fahrenheit). The temperature rises a few degrees further with the waste-heat from a nearby factory. Thanks to the high vapor pressure of the hot seawater, the clean water evaporates through a membrane, while the dirty, salty seawater is left behind. These membranes are made of teflon and are microporous and hydrophobic.

The technique can be compared with a sport jacket. A sport jacket stops the rain pouring in, but lets your sweat through. In the next step the water vapor condensates, this releases energy that can be used to heat the water at the beginning of the process.

After successful research in the laboratory, the Memstill technology has been tested in Singapore since February. The test facility has a modest capacity of one cubic meter water per hour. The pilot plant uses the waste heat from the Senoko "waste-to-energy plant". A second and third pilot plant will be built on the Dutch North Sea coast next year.

Nine companies developed the Memstill technology. Also Dutch beer brewer Heineken is involved because Memstill offers an energy efficient way to make brackish soil suitable for beer production.

Other techniques to convert seawater into drinking water, like RO, MSF, or MED, use a lot of energy to vaporize the water or push the water through a membrane under high pressure. Memstill uses cheap waste-energy, which cuts down the energy consumption and CO2 emissions. The cost of desalination of one cubic meter water with Memstill could be under $0.50, where other distillation techniques cost about 1 dollar for the same amount of water.

Another great advantage of the Memstill technology is that it is just as efficient on great scale as on small scale. Applications on small scale, like horticulture or the provision of drinking water to remote islands, will be possible. But also Western countries are interested in the cheap distillation technology. For example, Spain could cut down on the expensive transport of water from the north to the dry south, and the brackish coast of Belgium could cheaply produce drinking water from seawater

Sources:
- TNO Press Release (A Dutch Research Center)
- Memstill Official Website

Published 31 March 2006