Low-Energy Water Filtration  

Technology Review has an article on a new technique for water filtration - a new membrane-free water-purification system uses small amounts of energy - which could be a low-energy alternative to desalination in some areas.

Most water-filtration technologies require a lot of energy to push water through membranes that eventually become fouled and need to be replaced. Both factors make water filtration costly for most applications.

Now researchers at Palo Alto Research Center (PARC) have been able to overcome those challenges by incorporating scientific insights from the physics of toner particle movements into a low-energy water-filtration device that doesn't use membranes.

That's all good news for the looming specter of filtering brackish drinking water that threatens much of the developing world and even some water-stressed areas in developed countries. In the past, however, the economics have been the stumbling block for creating affordable water-treatment systems. The United Nations estimates that over the next eight years, some 900 million people will need a safe supply of drinking water.

PARC researchers call their device the spiral concentrator. It is a spiral-shaped, 50-centimeter-long piece of plastic tubing that's one millimeter in diameter. As water is pumped through one end of the device, particles in the water are pressed up against the walls of the tubing. Particles as small as one micron in size are separated out by centrifugal force and shunted away from the clean water via diverging forks in the spiral concentrator.

The advantage of this approach is that it doesn't require as much energy as it would to push contaminated water through a membrane. Such membranes are typically built from resin and have many tiny holes perforated in them, ranging in size from a few micrometers to a few nanometers.