Bubble studies hold the key to preventing water-borne diseases

Water treatment engineers are beginning to understand why bubbles can pose a risk of water-borne diseases, thanks largely to the work of a PhD student at Virginia Tech in the US.

It has been known for a while that bubbles rising through water in treatment plants could cause problems. But since Paolo Scardina, a student at the Department of Civil and Environmental Engineering (CEE), working with Dr Marc Edwards, started to study the phenomena more closely, the full extent of the problem is only now emerging. Scardina’s work has identified the causes of bubble formations and confirmed that the release of a “burp” of air bubbles during the treatment process, could allow pathogens and other particles to escape removal. This spurt can also be strong enough to punch holes in filters that are large enough to let particles and pathogens escape.

Scardina’s work has also discovered that 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.”

Bubbles also present a problem 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 points out. “This decreases the validity of, and confidence in, water quality tests.”

Scardina is already putting his theory into practice at two Californian plants where he is helping to identify the source of air bubble eruptions. He has also recently been awarded a $150,000 grant from the American Water Works Association Research Foundation (AWWARF) to continue his air bubble research, which will focus on treatment plant design and operations, and how they can affect formation of bubbles.

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