Acoustical technology developed at CU-Boulder helps make clean water

October 31, 1999

A new University of Colorado at Boulder technology that uses an acoustical device similar to a medical ultrasound probe is providing a promising new technique to inspect the fouling of thin membranes used to purify drinking water.

The membranes have pores so small they can let water molecules pass through while excluding unwanted molecules and particulates such as salts, viruses and bacteria, said chemical engineering Professor William Krantz. The technique involves bouncing acoustic waves from the surface of a porous membrane, he said.

"The technology allows engineers to determine whether fouling deposits exist on the surface of membranes," said Krantz, who co-directs the Center for Membrane and Applied Sciences and Technology, or MAST, headquartered in the chemical engineering department. "These fouling deposits must be detected and removed to enable the efficient performance of membranes."

Krantz said that applying acoustical technology to membranes is far more challenging than using it in medical ultrasound analyses. "A doctor might use ultrasound to scan for a walnut-sized organ in your body such as your gall bladder. In this application we need to detect fouling deposits that might have a thickness of only one-10th the diameter of a human hair."

"We need to tackle membrane fouling because it is a critical problem in liquid separations using membranes in cases like the production of drinking water from seawater," said mechanical engineering Professor Alan Greenberg, who is directing the research in collaboration with Krantz. "We wanted a technique that was non-invasive and non-destructive that we could use in real-time."

The advantage of the acoustical technique is that it is relatively simple and inexpensive, said Greenberg. The team uses an electrical transducer to send high-frequency pulses to the surface of the membrane that bounce back and reveal areas of fouling. By using the technique to determine if fouling deposits are present, it is possible to minimize the chemicals needed and the time required to clean clogged membranes.

Greenberg and Krantz, along with co-investigators Guo-Yong Chai and Leonard Bond, have filed a patent on the process. They are working with Jay Dusenbury of the U.S. Army's Tank and Automotive Research Center's Petroleum and Water Division in Warren, Mich., to test the acoustical technology.

The U.S. military requires large amounts of purified water in land operations in arid regions such as the Mideast, as evidenced by the 1991 Desert Storm conflict. Mobile membrane units towed by tanks or humvees can process up to 100,000 gallons of drinking water per day.

"We are excited about the potential of this technology," said Dusenbury. "From what we have seen so far, it could be of great value in the field when we need to fill these units from rivers, lakes, wells or even the ocean."

MAST is a National Science Foundation Industry/University Cooperative Research Center and the only such center in the United States focused on membrane technology. Some current applications of membrane technology in addition to water purification include environmental restoration and cleaning of water and solvents used in semi-conductor microfabrication, said MAST's other co-director, chemical engineering Professor Richard Noble.

The technology also is used in other industrial and medical fields, including devices like the artificial kidney and membrane lung oxygenator, he said.

The center is unique because industry sponsors define research topics, prioritize them and select faculty proposals for funding. Industry sponsors also work closely with faculty and graduate students, Noble said.

Since it's inception, MAST has supported 39 research projects that have led to 20 doctoral degrees and 18 master's degrees and provided $360,000 in support for 128 undergraduates, including 53 women and 17 minorities, said Noble.

Three new undergraduate and graduate membrane science courses have been created, and seven patents and more than $5.5 million in follow-up contracts have resulted from MAST research.

University of Colorado at Boulder

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