FEATURE — Summer 2005
   

 
Professor Pratim Biswas (left) and doctoral student Rafael McDonald work with a flame aerosol reactor, which is used to synthesize nanosized titanium dioxide (Ti02). The nanostructured Ti02 has many different applications: one is photosplitting water to produce hydrogen, the other is to control mercury emissions from combustion systems.

Clearing the Air, Cleaning the Water

Engineering Professor Pratim Biswas develops innovative techniques to help solve global environmental problems, from mercury pollution to groundwater contamination.

By C.B. Adams

In March 2005, the Environmental Protection Agency (EPA) issued new, stricter regulations intended to reduce mercury emissions from power plants from the current 48 tons a year nationwide to 38 tons by 2010 and to less than 25 tons by 2018. That was good news for Pratim Biswas, the Stifel and Quinette Jens Professor of Environmental Engineering Science at Washington University. For the past several years he has been working on a new technology to remove mercury from fossil fuel combustion exhausts. In fact, he holds a patent for the technique that uses nanoparticle agglomerates, or clusters, of titanium dioxide to firmly bind and remove mercury in the power-plant stack. Biswas calls titanium dioxide a "wonder chemical" with many potential applications in environmental technologies. 

"Mercury occurs naturally in trace amounts in coal. It is a toxic pollutant, which is very problematic not only in the United States but globally," Biswas says. "The main source of mercury pollution comes from combustion systems—mostly stationary, coal-fired combustors, which are used for power generation. Trying to capture mercury using conventional pollution control systems is very difficult.

"We knew the EPA was going to pass new mercury emissions regulations, and since then, we have seen a mad dash by others trying to come up with new, less-expensive technologies," he continues. "We believe our technique will work very well in a full-scale system."

Mercury in the Environment

Pratim Biswas began his search for a better way to capture mercury as the evidence grew about its adverse effects on the environment.

Because mercury is the only metal that is liquid at room temperature, it quickly evaporates and spreads into the environment.

Mercury poisons wildlife and causes brain and nervous system damage in fetuses and children.

The Natural Resources Defense Council has reported that mercury pollution in the United States alone has contaminated 12 million acres of lakes, estuaries, and wetlands, as well as 473,000 miles of streams, rivers, and coasts.

For Biswas, the "how" of his patented technique is only as important as the "why" behind it. Biswas began his search for a better way to capture mercury as the body of evidence grew about its adverse effects on the environment. Because mercury is the only metal that is liquid at room temperature, it quickly evaporates and spreads into the environment. It poisons wildlife and causes brain and nervous system damage in fetuses and children. The Natural Resources Defense Council, a research and advocacy group, has reported that mercury pollution in the United States alone has contaminated 12 million acres of lakes, estuaries, and wetlands, which is 30 percent of the total, as well as 473,000 miles of streams, rivers, and coasts. Perhaps even more troubling is that at least 40 percent of the mercury polluting the United States was generated abroad.

"Mercury that is emitted from a Chinese power plant, for example, can traverse the globe several times for up to a year before it eventually deposits in, say, the Great Lakes. That's what makes mercury such a global concern," Biswas says. In layman's terms, Biswas' technique injects titanium dioxide, a non-toxic compound whose variants are used in many commercial applications ranging from food products to paint, into the power plant's combustion chamber. This forms nanoparticle clusters of titanium dioxide that trap the mercury and bind it on the surface when exposed to the ultraviolet light found in industrial pollutant—capturing devices called electrostatic precipitators. The agglomerates are then readily removed in conventional particle control devices.

"We have successfully used this process to trap mercury in a laboratory-scale system," Biswas says. "A relatively small amount of titanium dioxide was needed to prevent the emission of mercury, which means the process does not generate a large amount of waste, unlike other processes. At present, we are seeking to collaborate with some utility companies and determine whether our process can be scaled up and then used in full-scale power plants."

Biswas, who joined the University almost five years ago, is principal investigator and one of six core aerosol researchers involved in research and education related to particulate matter and the synthesis and environmental impact of nanoparticles. These scientists work in the Environmental Engineering Science Program and its laboratories, such as the Aerosol and Air Quality Research Laboratory. Washington University now has one of the largest aerosol research programs in the nation.

Integrated and multidisciplinary, the Environmental Engineering Science Program provides a scientific education for individuals interested in focusing on the improvement and management of the quality of the environment. The program's mission is to educate the future generations of engineers and scientists who will tackle and solve the complex environmental issues being faced today and in the future.

 "Pratim has been a passionate researcher and an inspirational leader whose goal for this program is nothing less than to have it become a national and international powerhouse. It is a pleasure for faculty, staff, and the students to work with him," says School of Engineering & Applied Science Dean Christopher I. Byrnes, the Edward H. and Florence G. Skinner Professor of Systems Science and Mathematics.

Rafael McDonald, M.S. '03, came to the University after obtaining his Bachelor of Science from Princeton University in 2001 to work toward his master's degree in environmental engineering. He relished the experience—and the guidance of Biswas—so much that he decided to stay and work on his doctorate.

"Professor Biswas is very easy to work with, and he doesn't micromanage his students," McDonald says. "He's more of an idea person and a manager than our boss. He really helps us get things done in the lab and makes sure we create something good from our research."

"We are trying to understand what causes some of the major environmental problems and then develop technologies to prevent them at the source," Biswas says. "Our primary goals remain not to have to deal with cleaning problems up as well as to prevent any adverse health effects later on."

This focus on preventing environmental troubles at the source is important to Biswas and his team because sometimes the response to a particular issue can be as bad as the initial problem. Such is the case with methyl tertiary butyl ether (MTBE). MTBE is an oxidative compound added to gasoline to reduce air pollution—something it does very well as an alternative to octane-enhancing lead additives. Unfortunately, MTBE has been increasingly detected at low levels in municipal water sources across the United States. In several cases it has made its way into tap water. MTBE has an unpleasant odor and is considered a carcinogen. Entering the groundwater from leaking underground gasoline storage tanks, it can traverse long distances before entering the water supply. Conventional water purification techniques are not effective in removing this compound.

"Along with my graduate students, we were playing around with a nanostructured form of titanium dioxide. We thought we'd give it a shot in terms of how it would react as a catalyst to MTBE," Biswas says. "We discovered the compound causes MTBE to react with dissolved oxygen. The MTBE oxidizes on the surface of the titanium dioxide and produces carbon dioxide, a harmless gas. We engineered nanostructure configurations of this catalyst to optimally degrade the pollutant."

Biswas' process also features an innovative micro-lamp, or corona, that emits a glow when an electrical current is run through it. In addition, the system can be engineered to produce ozone that increases the oxidation of MTBE to carbon dioxide. The original device was 18 by 6 inches, but Biswas is collaborating with companies, including Salt Lake City-based Ceramatec, to develop full-scale purifying units.

"Mercury that is emitted from a Chinese power plant, for example, can traverse the globe several times for up to a year before it eventually deposits in, say, the Great Lakes. That's what makes mercury such a global concern," Biswas says.

Another of Biswas' four patents is for a device that traps and deactivates microbial particles. The device combines conventional electrostatic precipitators (similar to electronic air cleaners), miniaturized X-ray systems developed in Japan, and "smart" catalysts to capture and destroy bioagents.

"We were trying to come up with designs that would improve the low capture efficiency in ultrafine particle sizes of the existing electrostatic precipitators. Very fortuitously, we tried out this combination and found that not only could we trap and capture ultrafine particles, including viruses, but we could also completely inactivate them," Biswas says.

In tests, the device has achieved a 99.9999 percent kill rate for difficult-to-capture virus particles. The device has numerous potential applications, from common indoor air filtration in buildings, hospitals, and aircraft cabins to the war on terrorism. It can deactivate airborne bioagents and bioweapons such as the smallpox virus, anthrax, and ricin. Biswas is collaborating with Midwest Regional Center of Excellence for Biodefense and Emerging Infectious Disease Research, researchers from the School of Medicine, and the Boeing Company, among others, to develop applications for the device.

Biswas lends his expertise to a variety of other research projects as well. He is working on a National Science Foundation project to synthesize small magnetic oxide nanoparticles that can be injected into the bloodstream to deliver medication to specific parts of the body. He is also working with the U.S. Army to develop a system to capture and remove heavy metals from ammunition incinerators. And, he and his fellow researchers have had collaborations in other countries, including Japan, China, Korea, India, and Europe.

"Environmental problems have global importance. In the U.S., we are technology leaders, and we have the means to take care of our own environmental problems," Biswas says. "As the developing countries come up to speed, we have to ensure that some of these technologies are used right from day one so that former mistakes are not repeated. In some parts of the world, there is a great need for new technologies. Finding innovative and less-expensive solutions to the world's environmental problems motivates me and my research."

C.B. Adams is a free-lance writer based in St. Charles, Missouri.

Please visit http://www.uspto.gov/patft/index.html, and search by "patent number" for more detailed abstracts of Professor Biswas' patents: U.S. Patent 6,861,036; U.S. Patent 6,777,374; U.S. Patent 6,248,217; U.S. Patent 5,888,926.