Blowing Bubbles

Did you know that bubbles can clean water? Specifically, dissolved air flotation (DAF) and ultrasound are two methods of making water safer with bubbles. DAF can be used to replace sedimentation in municipal drinking water treatment. Large particles are typically settled out using gravity, but with DAF, bubbles are produced by an oxygen tank pumping air into the bottom of a basin and small particles attach to the sides of the bubbles. The bubbles rise to the top of the basin and the particles are swept off the surface of the water by a skimmer.

Dolfi ultrasonic device, photo from Indiegogo.

Ultrasound waves emit frequencies outside of the human hearing range. When ultrasound waves oscillate at a specific frequency, the change in water pressure creates bubbles. Ultrasound has been known to destroy bacteria since the 1920’s but has been perpetually written off as “too expensive” for a water decontamination method. Nevertheless, industry has found a use for ultrasound. For example, the Dolfi device is advertised as a way to clean laundry on-the-go. When it first came out, Dolfi sold for nearly 150 dollars.

Another tool, called StarStream, is used to clean medical devices. Ultrasound is even used at massage parlors for facials. If we trust ultrasound enough to wash our clothes, clean medical devices, and scrub our faces, why isn’t it used in water treatment?

“When the bubbles collapse, the gas inside of them becomes very pressurized and is at high temperatures for a very short amount of time,” lead author Inez Hua of Purdue University explains. “The temperatures and pressures are such that organic contaminants can degrade.”   -Scientific American, Cleaning Water with Ultrasound

This study featured in 2003 in Ultrasonics Sonochemistry shows that ultrasound strengthens the use of ordinary disinfectants in water. This is most likely because the scrubbing effect of cavitation allows the disinfectant to have more contact time with the water. At the moment, blowing bubbles through a straw isn’t going to revolutionize drinking water. There are additional steps that must be taken to ensure ultrasound water is pure such as filtration. However, if ultrasound is further researched and a product that caters specifically to water disinfection is produced, perhaps the price could be brought down. See my links below if you would like to read more. From, Jess 🙂


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