Microwaves used to kill ballast stowaways

Scientists in the US say they have developed a method that uses microwaves to kill off plants and animals hitching a lift in the ballast water on cargo ships.

The team from the Louisiana State University Agricultural Centre tested the effect of continuous microwave heating systems to kill microalgae, zooplankton and oyster larvae.

Writing in the Environmental Science and Technology journal, the researchers said that in spite of the high costs of the technique, it would be an effective solution alongside other established methods of treatment for ballast water.

The International Maritime Organization (IMO) estimates that each year about 10bn tons of ballast water are transported and exchanged around the world during maritime shipping.

Invasive aquatic species often carried in this water are seen as one of the four greatest threats to the world's ocean by the UN and IMO's Global Ballast Water Management Programme.

Dorin Boldor, assistant professor in the Biological and Agricultural Engineering Department of the LSU AgCentre and one of the authors of the study, said the system could be used in a variety of ways and operated at the flick of a few switches.

He told edie: "The system can probably be implemented in the industry in several different ways, including on-board systems, on-shore facilities, and a combination in which treatment barges based in ports pull up to ships and take their water for treatment while ships are docked or waiting to dock."

Onboard systems could be installed close to the ballast water pumps or retrofitted at the exit valves of the ballast tanks, the researchers said, but its operation would be the responsibility of the ship.

Ports could also run facilities and charge fees for treatment.

"Treatment barges are probably the most flexible option, as they can take large amounts of water in a relatively short time, then depart from the ship," Mr Boldor told edie.

The operation in general is relatively simple," he added. "All is needed is a few switches, a heat exchanger, and several valves to direct the flow of water. Microwaves turn on and off instantaneously."

Kate Martin



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