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Tech Researchers discover polymer to improve reverse osmosis

September 18th, 2006

Jessie Gemmer, CT Staff Writer

Researchers at Virginia Tech discovered how to make a polymer membrane that will improve the process of reverse osmosis. Before this discovery, the polymer material in thin film composite membranes, typically used in RO, broke down with the use of chlorine for disinfection. The new chlorine-resistant filter will make it easier and faster to produce freshwater from saltwater.

Reverse osmosis is a widely used process to separate a solute from a solvent. A semi-permeable membrane that acts as a filter through which a solvent passes when pressure is applied to a solution separates two compartments. Because the membrane has no pores, the separation takes place in a dense polymer layer of only microscopic thickness.

In most cases, the membrane is designed to only allow water to pass through. For 40 years, the polymer material has been too fragile to be treated with chlorine, but the new discovery has made a stronger polymer structure that improves the process and allows water to be disinfected during the separation process.

The researchers presented a paper, “Synthesis of di-sulfonated poly (arylene ether sulfone) random copolymers as novel candidates for chlorine-resistant reverse osmosis membranes (PMSE 494),” Wednesday.

The paper detailed how the membrane is made and how it will be used. The authors are post-doctoral associate Zhong-Biao Zhang, James McGrath, University Distinguished Professor of Chemistry at Tech, Tech graduate students Guang-Yu Fan and Mehmet Sankir, Ho Bum Park, and Benny D. Freeman, chemical engineer at the University of Texas, Austin. Freeman tested sample materials of the membrane for the researchers at the University of Texas. Freshman mechanical engineering major Matt Allen was impressed by the university’s discovery. “I think it’s great to be in a place that not only teaches science but makes scientific advances that other places will teach about.”

The film created, though effective, is too thick for professional use. It consists of a skin braced by a thick foam layer, which strengthens to skin but makes the membrane 10 to 100 times bigger than it should be in order to be widely used.

Tim Good, a sophomore building construction major, said that he “always knew that Tech was a research institute, but to think that something discovered by students will change every day life for people and businesses all around the world is really impressive.”

Reverse osmosis is commonly used to purify water for household use, but also has become an efficient way to make undrinkable water potable. Rainwater collected from sewer drains is purified with reverse osmosis water processors and used as tap water in Los Angeles and other cities as a solution to the problem of water shortages.

In industry, reverse osmosis removes minerals from boiler water at power plants. It is also used to clean effluent and brackish groundwater. The new membrane will affect the use of reverse osmosis in many different fields. In places where saltwater is more plentiful than freshwater or where water has to be recycled, this discovery will make it easier for people to be supplied with drinkable water.