WUSTL

Method removes toxin from water

Pollutant thought to be a cancer-causing agent
By Doug Main

A University researcher has discovered an effective way to remove a troubling new pollutant from our nation's water sources.

Pratim Biswas, Ph.D., the Stifel and Quinette Jens Professor of Environmental Engineering Science and director of the Environmental Engineering Science Program, has found a method for removing the toxin MTBE from water.

Pratim Biswas, Ph.D. (left), and M.H. Lee, Ph.D., postdoctoral fellow in environmental engineering, discuss the nanostructured titanium dioxide reactor, which degrades the pollutant MTBE. Biswas discovered that a nanostructured form of titanium dioxide causes MTBE to react with dissolved oxygen so that it yields the harmless gas carbon dioxide.

Photo by David Kilper

Pratim Biswas, Ph.D. (left), and M.H. Lee, Ph.D., postdoctoral fellow in environmental engineering, discuss the nanostructured titanium dioxide reactor, which degrades the pollutant MTBE. Biswas discovered that a nanostructured form of titanium dioxide causes MTBE to react with dissolved oxygen so that it yields the harmless gas carbon dioxide.

MTBE (methyl tertiary butyl ether) has been detected at low levels in municipal water sources around the nation and in several cases has made its way into citizens' tap water.

Biswas discovered that a nanostructured form of a compound called titanium dioxide causes MTBE to react with dissolved oxygen so that it yields the harmless gas carbon dioxide. This reaction proceeds via oxidation of MTBE on the surface of the titanium dioxide to produce a harmless end product.

Biswas then designed nanostructure configurations of this catalyst to optimally degrade the pollutant.

"These photo-catalysts can be powered by an artificial light source or can be designed to run on solar power," Biswas said.

Biswas presented his research at the American Chemical Society's annual meeting, held recently in Philadelphia.

One of the researcher's innovations was developing a special micro-lamp (corona) that emits a glow after a current is run through it. But that's not all: This system can also be tailored to produce ozone, which speeds up the oxidation of MTBE to carbon dioxide.

Biswas felt it was important to find a way to remove this pollutant because it "is a toxin and has been implicated as a carcinogen (cancer-causing agent)," he said.

Even more immediately obvious, the chemical's presence in water produces an offensive taste and a slight odor.

Problem of tank leakage

MTBE has been used in American fuels since 1979 — even more so in recent years in California — as an alternative to octane-enhancing lead additives because it helps fuel to be completely combusted.

Thus, MTBE decreases the environmentally harmful by-products of incomplete burning without containing the toxic element lead.

The one drawback is that MTBE can be harmful to human health, too, through exposure via groundwater sources.

"One doesn't know why, but underground gas tanks consistently leak, and this problem should really be taken care of," Biswas said.

Unfortunately, when gasoline leaks out, the MTBE is very soluble in water, and even localized leaks can allow MTBE to spread widely in a relatively short amount of time.

Biswas set out to design a compact unit for MTBE removal — and he succeeded. The original device was only 18 inches by 6 inches and held 3-4 gallons of water. The reactor removed all of the MTBE within a couple hours. Companies such as Salt Lake City-based Ceramatec have collaborated with him on scaling up the purifying unit, a process that he anticipates to be rather straightforward.

Biswas is optimistic that his technology can be used around the country to removed MTBE from water.

MTBE levels in gasoline started to increase after the Clean Air Act of 1990, which mandated lower levels of harmful emissions in car exhaust. MTBE seemed like the perfect alternative, and it wasn't until high levels were detected in a Santa Monica well in California in 1996 that people began to take notice of the pollutant.

The U.S. Environmental Protection Agency (EPA) has said that levels of the pollutant below 20-40 parts per billion (ppb) are considered nontoxic, but water with considerably lower levels of the toxin can be foul-tasting.

Biswas discovered that titanium dioxide catalyzes the oxidation of MTBE, as a follow-up on his work related to removing pollutants like mercury from coal combustion exhausts.

He said that titanium dioxide is proving to be an exciting compound because it also oxidizes dirt and scum, and is already the active constituent in products like self-cleaning bathroom tiles.

He calls it a "wonder chemical" with a variety of applications in environmental technologies.

Nanoparticles also are an active area of research, and Biswas is excited to be working in this field.

These particles have many potentially beneficial applications, for example, drug delivery via aerosol spray, and production of novel materials — work that is being conducted through the auspices of the WUSTL Center for Materials Innovation.

There is some concern about the health risks of these nanoparticles.

"One needs to address the problem at the beginning, rather than discover the problems years later," Biswas said.

"Our take is that (nanoparticles) could be made safe. They can be engineered to be safe. But it is important to be careful from the start, and we are doing so."

EXPERTS @ WUSTL
Pratim Biswas
Chair of the Department of Energy, Environmental & Chemical Engineering and the Lucy & Stanley Lopata Professor
(314) 935-5482
pratim.biswas@wustl.edu
William Buhro
Professor of Chemistry and associate director of the Center for Materials Innovation
(314) 935-4269
buhro@wustl.edu