Module with AlGaN LEDs purifies flowing water

March 18, 2005
Water purification modules based on UV LEDs are a step closer after the first demonstration of bacterial destruction in flowing water with the technology.

A US team has conducted what is believed to be the first demonstration of a flow-through water purification module that uses ultraviolet LEDs.

Such purification modules, which would be far smaller and more convenient than those that use mercury lamps to kill bacteria, could become a high-volume market for UV LEDs in the future.

Although the concept of bacteria destruction with UV LEDs has been shown before with a static water sample, the purification of flowing water is critical for the technology to be commercially viable.

In collaboration with microbiologists at the University of Maine Orono (UMO), start-up company Hydro-Photon developed a bench-level prototype flowing water treatment module that uses ten AlGaN LEDs made by the South Carolina firm Sensor Electronic Technology (SET).

The SET devices used in the module, which were developed in collaboration with Asif Khan’s group at the University of South Carolina, emit at 280 nm, and the 4 cm3 aluminum treatment chamber is designed to maximize light reflection at this wavelength.

In tests using sterile tap water contaminated with E coli at a concentration of 10 000 microbes/ml, the UV LEDs destroyed at least 95.5% of the bacteria.

The best results were seen at lower flow rates, where the germ destruction was close to perfect.

“The results put us anther step closer to demonstrating the basic viability of the flow-through UV LED water purifier concept,” said Miles Maiden, CEO of Hydro-Photon, which is based n Blue Hill, Maine.

“At this point the challenge is to continue improving LED efficiency and power output. More power means faster flow and more purified water per minute.”

SET makes the short-wavelength LEDs used in the module with a novel growth technique called migration-enhanced MOCVD. This approach, which differs from normal MOCVD in regard to the way gases are flowed into the reaction chamber, improves the quality of AlN and AlGaN material in particular, while increasing the material deposition rate.

Remis Gaska, SET’s CEO, said: “We consider this to be a significant milestone in bringing our deep-UV technology to such high-volume markets as water, air and surface sterilization.”

The UV LEDs were developed under the Defense Advanced Research Projects Agency’s “SUVOS” program (see related story).