(Blacksburg, Va., Oct. 5, 2001) -- A Virginia Tech engineering graduate student has made discoveries that may help prevent outbreaks of water-borne diseases in the future.
Paolo Scardina, a Ph.D. candidate in Virginia Tech’s Via Department of Civil and Environmental Engineering (CEE), began his research as an undergraduate on the problem of air bubbles in drinking water. Working with Marc Edwards of the CEE faculty, Scardina has continued his research as a master’s and doctoral student, and he recently won a highly competitive grant worth $150,000 from the American Water Works Association Research Foundation (AWWARF).
Scardina’s research also is being used by engineers with the California Department of Health Services to identify problems at two facilities that have experienced eruptions of air bubbles.
But why would ordinary air bubbles, which occur naturally in water, be a source of concern in drinking water treatment?
"When you open a can of soda, bubbles form and rise to the surface," explains Edwards. "The same thing can happen in water from lakes and rivers. When air bubbles are released in a ‘burp’ during the treatment process, pathogens and other particles can escape removal."
The last treatment barrier in most drinking water treatment plants is filtration, Edwards says, and a burp of bubbles can punch holes in filters—tiny holes, but large enough to let particles and pathogens escape into the water that goes out to customers.
"The field of drinking water treatment is about 3,000 years old," Edwards notes, "but in all that time, air bubbles in water have not been studied in terms of their ability to affect treatment processes."
Scardina, who began studying air bubbles at Edwards’ suggestion during his senior year at Virginia Tech, identified the causes of bubble formation while he was working on his master’s degree. "Before Paolo’s findings, we knew that bubbles could cause problems," Edwards says, "but we didn’t know how they formed or the range of the impacts."
In searching the literature about water treatment, Scardina noticed that serious problems often occurred at plants that experienced air bubble eruptions. "We thought this path was worth investigating," he says.
In addition to studying why bubbles form and how they punch holes in treatment plant filters, Scardina has made some discoveries. Air bubbles can interfere with the first drinking water treatment process—settling—where solid particles from incoming surface water drop to the bottom of treatment tanks. "If bubbles are present at this stage," Scardina notes, "pathogens and other particles can attach to them and float on through the treatment plant."
Another important discovery by the Virginia Tech student is that bubbles can cause a dilemma for treatment plant operators at the end of the process. "When bubbles form after water has gone through filtration, water quality tests may wrongly identify the bubbles as dirt particles or pathogens, even though the bubbles themselves are harmless," Edwards says. "This decreases the validity of and confidence in water quality tests."
While a master’s candidate, Scardina published two peer-reviewed papers on his findings and made a presentation at an international water treatment conference in London. "Paolo’s subject area is so new that we had a hard time finding people with enough knowledge of the field to review his papers," Edwards remarks.
On September 20, the Mendocino District Office of the California Department of Health Services flew Scardina to the West Coast to help engineers there identify the source of air bubble eruptions that have occurred at two water treatment plants. "Paolo is doing some very important work," says Guy Schott, associate sanitary engineer for the Mendocino District.
Schott found out about Scardina’s work from Edwards, with whom he had collaborated in the past. Scardina sent his graduate papers and computer models to Mendocino. "Paolo’s research has given us a good understanding of the sources of our problems," Schott notes. "He’s the only person I’ve found in the United States who does work in the field of dissolved gases and their impact on treatment."
In the plants Schott and Scardina have investigated, air bubble eruptions have carried solid particles into the filtration process, which leaves the treatment systems open to pathogen contamination. Schott is concerned about the potential for outbreaks of viruses, as well as Giardia and Cryptosporidium, both of which are microscopic parasites that can cause severe gastro-intestinal illness. These parasites are impervious to chlorine disinfection, so they must be removed through settling or filtration. A major water-borne outbreak of Cryptosporidium in Milwaukee in 1993 caused illness in an estimated 403,000 people.
These and other water-borne diseases are a threat whenever a treatment plant is compromised, which makes Scardina’s research a potentially important human health tool.
In August, the AWWARF awarded a $150,000 grant to Scardina for continuation of his air bubble research. "What’s most impressive to me is that a conservative professional organization has been persuaded to fund a student’s original research," Edwards says. "It’s unusual for a Ph.D. student to lead an effort that wins a competitive grant through AWWARF’s unsolicited proposal process."
Scardina will use the grant to "get a handle on the magnitude of the problem," he says. Working with treatment plant engineers, he is investigating air bubbles in Boulder and Denver, Colorado; Bay City, Michigan; San Diego, California; Myrtle Beach, South Carolina; and Buffalo Pound in Canada. "I’m studying parameters—such as treatment plant design and operations—that can affect formation of bubbles."
After he completes his Ph.D. in another year or so, Scardina wants to work in the water treatment industry and continue his efforts to resolve the problems posed by bubbles. "I’m studying these things so that I can help advise plant operators," he remarks. "They can’t always see bubbles in the system, and many of them haven’t thought to look."
The above story is based on materials provided by Virginia Tech. Note: Materials may be edited for content and length.
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