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UV LEDs sterilize water

12 May 2004

Scientists demonstrate the first direct germicidal effect with an ultraviolet LED source.

A US collaboration has reduced levels of E.coli. bacteria in water by over five orders of magnitude using 280 nm excitation from GaN-based ultraviolet LEDs.

The proof-of-concept experiment involved exposing a 1 ml E.coli. spiked water sample to 50 µW emission from two ultraviolet LEDs.

The experiment was conducted at the University of Maine, with input from local company Hydro-Photon and ultraviolet LEDs provided by Shuji Nakamura’s UCSB group.

The technology is not restricted to just the sterilization of E.coli. Miles Maiden, president of Hydro-Photon, says “anything with DNA or RNA will work.” He added that the experiment was the first demonstration of a direct germicidal effect by ultraviolet-emitting semiconductors.

Hydro-Photon previously developed portable mercury lamps emitting in the ultraviolet. However, these units were expensive, needing components to provide high frequency, high voltage sources for the lamp.

LED sources of ultraviolet light offer many benefits over mercury lamps. They are “instant-on”, potentially much cheaper, easily portable, and have a higher theoretical efficiency.

The global market for ultraviolet water treatment is huge, says Maiden. For example, practically all bottled water in the developed world is treated by ultraviolet light prior to shipment.

Hydro-Photon’s next project, which also forms part of DARPA’s SUVOS program, involves developing in-line water treatment for the armed forces.

A small device will form part of a portable system similar to that used by many hikers. Ultraviolet LEDS at both the inlet and outlet of the device will emit instantaneously when water is extracted, providing sterilization.

From Compound Semiconductor

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