Ultraviolet Light Zaps Bacteria

Updated 12:02 PM ET January 1, 2001

By SONJA BARISIC, Associated Press Writer

NEWPORT NEWS, Va. (AP) - Two researchers say they have found a cheap, effective way to kill harmful microorganisms being spread by ships traveling around the world: Zap them with concentrated ultraviolet light.

The technique involves using a lamp that emits UV rays to kill disease-causing bacteria and other microorganisms found in ballast water within the hulls of cargo ships.

"We are tanning the bacteria to death," said Mounir Laroussi, an electrical engineering research professor at Old Dominion University.

Laroussi and Fred Dobbs, associate professor of oceanography at Old Dominion, worked for a year to create a reactor built around a specially designed UV lamp. They work in a laboratory at the Applied Research Center next to the Thomas Jefferson National Accelerator Facility.

They have done tests with a tabletop prototype on organisms including E. coli, Bacillus subtilis and dinoflagellates. All perished in the UV light.

The researchers declined to give many details because they are applying for patents and want to keep the information secret. But basically, the prototype works like this:

A Plexiglas chamber about a foot tall is filled with about a half-liter of water. The Plexiglas blocks the UV, preventing the rays from escaping from the cylinder.

A tube-shaped UV lamp is fitted into a protective sleeve, which is inserted into the chamber.

The lamp is turned on and kept on anywhere from a few seconds to a few minutes; the length of the treatment varies depending upon the microorganisms present in the water.

At low doses, the UV light causes damage that prevents cells from replicating. Higher doses kill the cells, Dobbs said.

The device uses less than 300 watts of electric power per lamp and the lamp can be produced for about $7,000, the researchers said. Other more powerful, but less productive, sources cost more than that, they said.

"What we need to do is take half a liter of water up to the next step ... in order to be able to handle the tremendous volume associated with ballast water," Dobbs said.

Seagoing ships carry ballast water to keep the vessel floating right. When the cargo or the weather changes, ballast must sometimes be dumped.

Dobbs co-wrote an article in the Nov. 2 issue of the journal Nature that detailed how ballast water in the hulls of cargo ships traveling around the world is spreading harmful bacteria. (Marine ecologist Gregory Ruiz led that study at the Smithsonian Environmental Research Center in Edgewater, Md.)

Dobbs turned to Laroussi to help find a solution to the problem.

The UV light research was financed by the National Oceanic and Atmospheric Administration.