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Generating Clean Water

Assistant professor Jennifer Wilcox and professor Bob Thompson (holding model zeolites) are collaborating to best filter harmful organics out of water, while associate professor Jeanine Plummer is using sonication to destroy parasites in water.

By Michael Dorsey

Keeping our drinking water free of harmful chemicals and microorganisms is a constant and growing technological challenge. Indeed, it is one that occupies a number of research teams at WPI. Here is a look at two current programs that are developing innovative technologies for removing contaminants from drinking water before it reaches our taps.

Cryptosporidium, an intestinal parasite, is one of dozens of harmful microorganisms that can live in municipal water supplies. To destroy it, water treatment plants can use a tried and true weapon: chlorine. Unfortunately, protozoans like cryptosporidium can be resistant to chlorine. But adding larger doses of the chemical can have an unwanted side effect, as it reacts with organic material in water to generate harmful chemicals, including known carcinogens.

Jeanine Plummer, associate professor of civil and environmental engineering, is developing a new treatment technique that largely avoids the generation of byproducts. Over the past few years, Plummer has been testing the effectiveness of sonication, in which water is bombarded with ultrasonic sound waves to destroy the unwanted parasites.

“Chemical-free disinfection is something the drinking water industry has been looking into for some time,” Plummer says. “While some larger plants have adopted ultraviolet technology, it has been too expensive or complicated for many facilities. We’re hopeful that sonication will prove to be economical for smaller, rural plants, and maybe even for use in homes.”

With sonication, sound energy creates miniscule bubbles in the water. As the bubbles collapse, they generate extremely high temperatures and pressures on a microscopic scale, which can severely stress microorganisms. The collapsing bubbles also produce free radicals—highly reactive compounds that can destroy cell membranes.

In laboratory tests, the one-two punch of sonication kills off virtually all bacteria, viruses, and protozoa, given enough time. Since cryptosporidium is notoriously tough to kill, Plummer is also testing sonication in combination with chlorine. Multiple disinfectants may be just what is needed, she notes, for sonication and chlorination together can inactivate pathogens in as little as 10 seconds of exposure.

An added benefit, Plummer says, is that the heat and the free radicals also seem to destroy certain organic contaminants in water. Ongoing work in her lab is focused, in part, on further exploring the ability of the technology to attack these chemicals, and on developing new prototypes of the sonication system and testing them on a range of microorganisms.

Soaking Up and Breaking Down Contaminants
In the mid-1990s, Robert Thompson, professor of chemical engineering, and graduate student Arjan Giaya (’98 MS, ’02 PhD), were asked by a local company to see if they could find a better technology for removing toxic organic compounds from water than activated carbon filters. Carbon filters can miss some compounds, and once they fill up, they must be thrown away or regenerated, which can put the harmful chemicals back into the environment.

Thompson and Giaya, now manager of advanced materials at Triton Systems Inc. in Chelmsford, Mass., discovered that high-silica zeolites were better at adsorbing organics than carbon. Zeolites, which can be thought of as molecular sponges, are highly porous minerals that have long been used in industry as catalysts and ion exchange agents. The tiny pores in zeolites are ideally suited for trapping organic molecules, Thompson says. But, like carbon filters, once the zeolites have done their job, one is still left with concentrated organic waste that needs to be disposed. To deal with this nagging problem, the molecular sieves have been married to advanced chemical oxidation processes being developed by John Bergendahl, assistant professor of civil and environmental engineering.

Oxidizing agents, which break down organic compounds, are commonly used in water treatment. The advanced oxidation chemistry is designed to target specific compounds—for example, MTBE (methyl tertiary-butyl ether, a gasoline additive) or TCE (trichloroethylene, a widely used industrial solvent)—that are found commonly in drinking water and that pose serious health risks.

This combination of zeolites, to filter organics, and advanced oxidation chemistry, to destroy them and renew the filter, has earned Thompson and Bergendahl a provisional patent. They are currently working with other faculty in the Chemical Engineering Department to extend the technology to various scales and for other compounds.

With help from associate professor Nikolas Kazantzis and assistant professor Jennifer Wilcox, Thompson and Bergendahl are exploring ways to custom design zeolites that are perfectly matched to specific organic compounds. These “designer sorbents” should be far more effective at soaking up the compounds than any current technology, Thompson says.

The organics removal and oxidation work is one of the first projects to come under the umbrella of a proposed Water Research Center, to be part of the university’s Bioengineering Institute in recognition of the diverse strengths of WPI’s water-related research and the fundamental importance of a safe, clean water supply to public health, Thompson says.

“We’re in a building phase,” he says. “Our initial researchers have a track record of collaborating and publishing together.

“As we move forward,” he continues, “we’ll be looking to broaden the scope of the center, bringing in additional faculty and additional areas of expertise. We are also actively seeking support from corporations, foundations, federal agencies, and individual alumni who may have an interest in or applications for the technologies we are developing.”

For more information about BEI, as well as its faculty and their research, visit www.wpi.edu/+BEI.

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Last modified: May 02, 2006, 15:35 EDT
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