Water Enlightenment

Disinfecting drinking water with UV is fast and efficient. A cross-disciplinary collaboration has developed a better way to monitor its efficacy.

A nasty bug made its way through the Milwaukee drinking water supply in 1993. The offending microorganism, Cryptosporidium—a mouthful in name and a stomach-turner by nature—affected more than 400,000 residents in what is now recognized as the largest waterborne outbreak in U.S. history. A highly infectious threat, “Crypto,” similar to the giardia parasite, is harmful to anyone who ingests it and possibly deadly to those with previously weakened immune systems.

For environmental researchers, the Crypto challenge sounded the alarm for improved treatment systems, including the use of ultraviolet (UV) radiation to keep drinking water clean. Ernest “Chip” Blatchley III, a professor of civil engineering, is working on that frontline battle. But because of perception problems associated with UV, the battle began uphill. “In the recent past,” Blatchley says, “as late as the late 1990s, the perception in this country was that UV wasn’t practical for drinking water applications because people had, as it turns out, incorrect information about what UV would actually do.”

UV disinfection, it now seems, is an approach whose time has come. According to Blatchley, some fairly important discoveries in the late 1990s proved UV to be a very effective disinfectant against many microorganisms that threaten drinking water supplies. “There are a few exceptions,” he says, “but it’s a much broader antimicrobial agent than people had previously believed.”

UV is also energy and cost-efficient. “The UV process is very fast,” Blatchley says, “so that means that the reactors occupy only a small amount of space.”

And it turns out that UV doesn’t use much power, which addresses the misperception of a power-intensive process. Finally, UV does little or nothing to change the chemistry of the water. Consider the use of chlorine in water, Blatchley suggests. “Chlorine reacts with many chemicals in water, and some of the products of those reactions are undesirable in terms of their effects on human health and the environment,” he says. “For the most part, UV doesn’t suffer from that.”

Because of those collective attributes, there’s tremendous interest in the use of UV applications in drinking water production. Literally thousands of utilities in the U.S. are considering it, Blatchley says, including New York City, which is the largest drinking-water supply in the country, treating up to 2.5 billion gallons of water each day.

The ability of a UV system to disinfect depends on the “dose” of UV delivered to the microorganisms in the water. However, in practical UV systems microorganisms each follow a unique path through the reactor. As a result, they each receive a different UV dose. So real UV reactors deliver a distribution of UV doses, and it is that distribution that determines the effectiveness of the reactor.

Until recently, techniques did not exist to actually measure the dose distribution delivered by a UV system. Instead, the standard practice was to measure the ability of a UV system to “kill” a standardized microorganism. This method, known as “biodosimetry,” provided a rough indication of the performance of the system; however, it gave no information about the dose distribution.

In collaboration with several other researchers at Purdue, the Blatchley group recently developed a method whereby dose distribution measurements can be collected on UV systems. This development was the result of roughly seven years of intensive research.

Collaborating Across Campus

Success within the scientific process often comes from fortuitous circumstances. For Blatchley, it followed a unique cross-disciplinary collaboration. For years, biodosimetry had been the standard (and only) method for measurement of UV reactor performance. However, the test is expensive to conduct and provides only limited information about the system. A need existed to develop a better method for characterization of performance in UV systems.

To address this need, dyed microspheres were developed. The microspheres mimic the behavior of individual microorganisms; however, the dye chosen for this application makes it possible to measure the UV dose delivered to each microsphere. “With the analytical tools we have access to, we can measure the dose of UV radiation delivered to each microsphere in a large population,” Blatchley says. Not something that can currently be done with microorganisms.

The microsphere system allows them to make quantitative, accurate statements about the distribution of doses, large or small, delivered by a UV reactor. That information allows researchers like Blatchley to make quantitative statements about how the system is going to work.

For the research to work, Blatchley needed some help from across campus. That’s where Donald Bergstrom and J. Paul Robinson came in. Bergstrom is a professor of medicinal chemistry and molecular pharmacology who has worked for many years in the area of nucleic acid photochemistry. He designed and built the microspheres. “Chip came to us with specifications,” Bergstrom says. “He needed some sort of microsphere that could mimic bacteria in size and behavior in solution.”

The microspheres also needed to be sensitive to UV radiation in a way that one could actually measure dosage of accumulated UV as the synthetic particles move through the water system. “We happened to have a molecule on the shelf that we discovered in the late 1970s that had the same properties required for the system,” Bergstrom says.

The molecule undergoes a measurable chemical change when it is exposed to UV radiation. Measurable, Bergstrom says, because the molecule is nonfluorescent before exposure to the UV radiation and fluorescent after it. Because a large number of these molecules can be attached to each microsphere, the fluorescence signal from each microsphere can be related to the UV dose it receives.

Robinson has helped take the quantification to new heights. The director of Purdue’s cytometry laboratories and a professor of both biomedical engineering and immunopharmacology, Robinson also took off-the-shelf technology and applied it to the drinking-water project. “We have some very sophisticated technologies that were developed primarily for the clinical diagnostic world,” he says. “These technologies use lasers to analyze particles. So we shoot the particles with a laser beam and collect many parameters.”

And they can shoot and analyze on the order of thousands of particles per second, resulting in some complex multivariate analyses. “It’s exciting to use existing detection technologies and then identify the specific needs for a completely different community,” Robinson says.

For the research trio, the application of the three-system approach is what’s most exciting. “It’s the right combination rather than the breakthrough,” says Bergstrom. “The collaboration among three different investigators doing different parts all created the breakthroughs.” Within their own corners on campus, a project involving a chemistry system, a UV reactor system, and a detection system all came together.

Making an Industry Splash

So what’s the next step? Robinson foresees technology leading to the development of relatively inexpensive equipment—in the $10,000 to $20,000 range—that water companies will find they need to use. “There are a lot of things that need to be done,” Robinson says, “but we’ve made an amazing amount of progress.”

The progress includes work with HydroQual, a New Jersey-based environmental company that for more than 35 years has used mathematical models to address the impacts of pollutant discharges on water quality and ecosystem health. “Greater restrictions and controls are being placed on finished water supplies, particularly with respect to disinfection byproducts and microbial contaminants such as Cryptosporidium,” says Karl Scheible, a principal at HydroQual. “The EPA has recognized UV as a best available technology and encourages its application to drinking waters. This has opened the entire water market to UV.”

It has also kept Blatchley busy and in heavy demand. “We’ve been working with the people at HydroQual to apply these microspheres at very large scales at flow rates up to 60 million gallons per day,” says Blatchley. “That would be the largest UV reactor ever developed, and what New York City would have to do if they have around 50 of these things working in parallel to treat 2.5 billion gallons of water a day.”

And the parties in that collaboration also seem to be getting along swimmingly. “We’ve followed Chip’s work for many years,” says Scheible. “He has been innovative and in the forefront in defining and researching key issues regarding the proper design and application of UV.”

The rest of the water world is taking note, too. Last year, Blatchley was awarded the William W. Edgar Pioneer Award by the Water Environment Federation (WEF). The award, given to an engineer or scientist for his or her pioneering work in the area of disinfection, was presented to him at the Disinfection 2005 conference cosponsored by WEF, the International Water Association, and the American Water Works Association.

With patents in the works and interested water utilities ranging from New York to California wanting to learn more, there’s seemingly no rest for these waterweary researchers at Purdue. But as the cross-campus collaborations continue to spawn healthy breakthroughs, they might each raise a glass of some sparkling tap-water to toast their present-day success. 

-William Meiners