Department of Physics
A Sound Way to Stop Stowaways
- By Joshua E. Brown
Eighty percent of world trade is carried by ships. A big cargo ship docks in the United States about every six minutes. It unloads goods that can come from any port on the planet.
Unfortunately, these ships also often unload invasive species — unwanted hitchhikers, like zebra mussel larvae and purple loosestrife seeds — travelling in the ship’s ballast water. This, too, can come from any port on the planet.
In the U.S., dumped ballast water may be the leading source of invasive species found in freshwater and marine ecosystems, according the Environmental Protection Agency. From the Caspian Sea to Lake Champlain, communities have suffered profound damage — like collapsed fisheries and clogged pipes — due to invaders that arrived in ballast water.
Efforts to remove species 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 (no relation), 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 ninety percent” of the small clams, water fleas, and e. coli bacteria sent into the machine, said Junru Wu, “but the results were over ninety-nine percent.”
Ballast water is essential to cargo ships (as well as cruise-liners and sailboats) allowing them to stay at the proper depth, steer correctly, and not tip over. But as ships take on and unload cargo, they also pump and dump enormous quantities of water. Globally, twelve billion tons of the stuff is dumped each year — with some ten thousand species being carried across the oceans each day in the ballast water of cargo ships, according to expert testimony before the U.S. Senate.
“These species introductions are one of the leading causes of losing biodiversity around the globe,” says Meiyin Wu, “so we’re trying to plug the hole.”
So are new tougher global regulations of ballast water. The U.S. Coast Guard rolled out rules in March requiring ocean-going ships to have an onboard ballast treatment system and limiting how many organisms they can release in coastal waters. And the U.N.’s International Maritime Organization will require all ships to have a treatment system by the end of 2016.
“There will be a lot of market demand for ballast treatment systems,” says Meiyin Wu. “There are millions of ships out there that will have to comply with these new regulations.”
The scientists anticipate that their machine, once commercialized, could be mounted inside the engine room of ships and available for use whenever needed, either in dock or as ships change their ballast at sea.
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.
The patented BallastSolution device, funded by a $673,000 grant from the U.S. Department of the Interior, is made from twenty ultrasound transducers, arranged in a spiral, that protrude into a pipe about ten inches wide on the interior. As the ballast water pumps through, the transducers oscillate at frequencies above the range of human hearing.
In goes a load of potential bad guys at one end -- and out comes nearly sterile water at the other.
At least that’s what the first tests have shown. The machine, built at UVM by Junru Wu and post-doctoral researcher Di Chen, was delivered to Meiyin Wu at the beginning of 2012 for testing in her laboratory in New Jersey.
“The results are fantastic,” says Junru Wu, “much better than expected.”
More demand than supply
This fall, the BallastSolution machine will be shipped to Wisconsin for a next round of testing by an independent laboratory under guidelines approved by the International Maritime Organization and the U.S. Coast Guard. If it passes these tests, it can be submitted to the IMO for approval and international use.
Current treatment technologies can cost millions of dollars to install on a medium-sized ship, Meiyin Wu says — which is why there is a global hunt to find new systems that work and are affordable.
“There are a lot of people and companies working on ballast treatments,” she says. “But there is simply no way that that the supply will be enough for the demand by 2016."
Three companies have shown interest in licensing the BallastSolutions technology, Meiyin Wu says. “We’re hoping it will be ready before 2016,” she says, noting that the cost of a commercial version of their machine is very hard to predict at this early stage -- and will depend on the size of the ship and the complexity of retrofitting it.
“We’re researchers. We’re not in the place or business to commercialize this,” she says. Which is why she and Junru Wu are looking for investors. And considering new research applications for ultrasound.
“We’re looking at ways it could be used to treat invasive jellyfish,” she says, “or clean swimming pools.”