University of Vermont

Junru Wu

Professor of physics, inventor

Junru Wu

A big cargo ship docks in the United States about every six minutes carrying cargo from potentially any port on the planet. Unfortunately, these ships also often unload invasive species — unwanted hitchhikers, like zebra mussel larvae — travelling in the ship’s ballast water. In the U.S., dumped ballast water may be the leading source of invasive species found in freshwater and marine ecosystems, according the EPA. Communities around the world have have suffered profound damage because of these intruders and efforts to remove them from ballast water have proven very difficult, often toxic, and expensive.

But Junru Wu, a physicist at the University of Vermont, has invented a promising new approach: blast them to death with sound.

He and Meiyin Wu, an ecologist at Montclair State University in New Jersey, have been collaborating for nearly a decade to create a device — they call it BallastSolution. The machine will treat ballast water, as ships take it in and dump it out, with a lethal dose of ultrasound. (Lethal, that is, to wee beasties; it’s harmless to people.)

In recent tests, “we thought we’d be happy if we could kill close to 90%” of the small clams, water fleas, and e. coli bacteria sent into the machine, said Junru Wu, “but the results were over 99%.” The U.N.’s International Maritime Organization will require all ships to have a treatment system by the end of 2016.

Purpose for faculty member's invention

“There are millions of ships out there that will have to comply with these new regulations," says Meiyin Wu.

The device relies on what physicists call “cavitation,” the formation and implosion of tiny bubbles within the organisms. These bubbles in liquid, created by mechanical waves from the ultrasound, “basically rip them apart,” says Junru Wu.

The ultrasound has advantages over other treatments, like ultraviolet light that has a hard time penetrating murky water, or chemical treatments, like chlorine, which have environmental problems. “Our goal is to produce a system that doesn’t produce secondary pollution,” says Meiyin Wu.