New dirt-repelling tube offers cheaper water purifier

London, July 16 : American scientists have devised a novel technique to purify water, which is based on a process called the "particle-exclusion phenomenon" that was discovered by University of Washington researchers in 2003.

Gerald Pollack and his colleagues had discovered that particles dissolved in water naturally move away from a hydrophilic (water-loving) surface, leaving pure water behind.

He says that the particles can move up to several tenths of a millimetre, much further than predicted by conventional theories.

The researcher believes that the phenomenon is caused by water molecules forming into a liquid-crystal-like array that sits on the hydrophilic surface.

"This liquid crystalline zone excludes particles in much the same manner as ice excludes particles," New Scientist magazine quoted him as saying.

Pollack reckons that the phenomenon may be useful for water treatment.

He has even designed a prototype system based around a needle-sized tube made of the hydrophilic polymer Nafion.

The researcher said that he passed water containing tiny latex spheres, soil, clay, bacteria such as Escherichia coli, and viruses through the tube, and measured what came out.

According to him, the study showed that the particles would move to the middle of the tube, leaving a stream of pure water next to the tube walls.

For collecting the two different streams, the researcher inserted two concentric steel tubes into one end of the Nafion tube.

The particle-rich stream flowed into the smaller, central steel tube, while the pure-water stream was siphoned off into the outer steel tube.

Pollack believes that such a system may be quite useful for the developing world.

"The need for simple, inexpensive purification devices is huge, as the technical expertise required to maintain sophisticated systems is not always available in third-world villages. Our filtration device contains no physical filters and is therefore simple; and flow through the device can probably be achieved by gravity," he said.

Eric Hoek from the University of California, Los Angeles, who develops novel membranes for water treatment, calls this work "scientifically elegant".

The expert, however, adds that the system may be better suited for small-scale biological separations than large-scale water purification.

An article describing this work appears in the journal Environmental Science and Technology.

ANI