Ultrasound Cleans Ceramic Filters: Could Aid Water Treatment

Though early in its development, this technology may one day enable water treatment plants to purify water with ceramic membrane filters instead of harsh chemicals.

Linda Weavers and Harold Walker, both assistant professors of civil and environmental engineering and geodetic science, and doctoral students Dong Chen and Mikko Lamminen described their ultrasonic cleaning technique April 10 in a poster at the American Chemical Society meeting in Orlando.

"If water treatment plants could clean water with membrane filters, they could minimize the cost, safety and disposal issues associated with the use of harsh chemicals," Walker said.

As an alternative to chemicals, researchers are studying ceramic membrane filters -- honeycomb-like networks of tiny channels separated by thin ceramic films, or membranes. When water flows through the channels, the membranes act as sieves to catch contaminants such as clay, iron oxide, bacteria and viruses. The problem: over time, the membranes become clogged with contaminants, and must be cleaned.

Weavers and Walker took note of recent research involving ultrasound and bubbles. The idea, most recently reported by scientists at Oak Ridge National Laboratory and their colleagues, is that sound waves can form and collapse bubbles inside a liquid, releasing heat and energy.

To test whether collapsing bubbles could clean a ceramic filter, the engineers submerged a filter in water that contained latex and silica particles. They used particles in a range of sizes to mimic the contaminants found in water treatment.

They used an ultrasonic probe to vibrate the water at 20 kilohertz, or 20,000 vibrations per second -- a low frequency that is easily obtainable with typical ultrasound equipment. For example, the fetal ultrasound tests that women undergo during pregnancy employ much higher frequencies -- on the order of 10 megahertz, or 10 million vibrations per second.