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Ballast Water Purified with UV Waves

Photonics Spectra
Mar 1999
Robert C. Pini

If "bioinvasions" has a futuristic sound to it, the future is now. With the speed and volume of global travel, even organisms can find themselves quickly transplanted to a new environment. In some cases, that can spell disaster for the fragile balance of the native ecosystem.
To prevent this kind of bioinvasion in marine environments, researchers at Triton Thalassic Technologies Inc. have engineered a UV light source to kill aquatic microorganisms that can stow away in the ballast water of ships traveling around the world. Exposure to UV light kills microorganisms by disturbing the replication function of their DNA.
But for it to work, microorganisms must absorb the UV light. Their size and concentration level in the water affect their absorption, as do the opacity and flow velocity of the ballast water. John Coogan, technical director at Triton, said the company developed an excimer lamp "so we can pick and choose the energy range we want to operate in and we can optimize efficiency."
Triton's systems operate from hundreds of watts to tens of kilowatts and use light from 250 to 275 nm, as appropriate. The larger systems can purify 1200 to 8000 gallons per minute for a medium or large ship. The devices are integrated with the ship's ballast water intake: As water enters the pipes, it passes into a UV treatment chamber, where it is dosed with light and disinfected before entering the ballast tanks.
A study published last year by the Battelle Memorial Institute's Duxbury Operations in Massachusetts evaluated thermal, acoustic and UV technologies for treating ballast water. The report recommended UV as the best, based on availability and cost. The choice of a technology might, in fact, be less of an issue than how to pay for it.
The practice of exchanging ballast water in midocean is seen as an inadequate solution. Although experts acknowledge the need to prevent bioinvasions, there are no laws requiring ballast water treatment. That may change, as the White House recently announced plans to create a task force to respond to the issue.
Meanwhile, the problem is worsening. "Scores of nonindigenous species are being introduced," Coogan said.

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