Those particles are in turn moved out of the clean water's path via diverging forks in the concentrator. No membranes are needed, and the required energy investment is low by comparison with conventional technologies. While the purifier needs a constant flow of water to ensure the particles continue moving in predictable patterns, this can be done using a low power pump; to further reduce its energy needs, the researchers hooked the pump up to solar panels. The concentrator's main downside is that it cannot remove bacteria, since they are smaller than 1 micron in size. To compensate for this, Scott Elrod, PARC's manager of the hardware systems laboratory, suggests adding alum, a chemical often used in water treatment facilities to bind tiny particles to larger ones (which are then separated out by gravity), to the filtered water. The centrifugal force should be more than enough to remove these larger bound particles.
Elrod and his colleagues expect a commercial version of their technology, which would scale it down into a smaller, parallel stack of concentrators, to be in the offing soon. A larger version, to achieve the maximum filtration rate of 100 L/min, is also in the works.
Via ::Technology Review: Low-Energy Water Filtration (magazine)