A Technical Explanation
The Hydro BioScience® Quattro-DB® and Mezzo-DB™ devices emit ultrasonic frequencies (i.e. above human hearing capability) that cause simply constructed forms of algae to vibrate at their natural frequency. Matching that frequency causes critical structural resonance to occur, much like playing the natural frequency of a crystal glass back to the glass that will cause it to vibrate violently and eventually break the glass by fatigue. Some types of algae that have complex structures are not vulnerable to this technique because their complexity does not create a central natural “vibrational” frequency.
In blue-green algae, the extremely fragile gas vesicles (walls only a protein layer thick) break, so that the gas they need for buoyancy is lost. It is not abruptly lost through the thicker outer cell wall, but by migrating to that wall and slowly diffusing out over several days. Even these organisms are not directly killed by ultrasound, but simply rendered heavier than water so they sink out of light needed for photosynthesis. Green algae and diatoms, generally much larger than the blue-green algae types, have an inner cell wall that tears from the critical structural resonance. They are also not instantly killed but the tear in the inner wall (called a plasmalemma) causes the inner cell contents to collapse when the tear deflates the plasmalemma. They finally die in about 3-4 weeks.
If the loudness of ultrasonic frequencies is high enough to achieve cavitation, aquatic life forms including algae can be damaged. Our devices output sound levels are purposely capped at a level below the threshold of cavitation. (I have been burned by such devices twice and it is not a pleasant experience). So we limited the maximum output sound level of the Quattro-DB® and the Mezzo-DB™ so this could not occur. And even in the devices that did create cavitation, you literally had to be in direct contact with the device to sense the cavitation. Sound level in water drops in dB by 20*log10 (distance in meters) as the sound spreads. This causes even more powerful devices than ours to quickly drop below the cavitation threshold. A 2 meter distance from the emitter will cause the sound level to drop by 6 dB which is equivalent to half of the sound pressure at only 1 meter away.
Aquatic life forms that are higher order organisms are complex enough that the ultrasound does not cause damage to them because they don’t easily resonate. There are many ultrasonic devices created by man that are used in aquatic zones. The most common is sonar and fish or depth finders. These devices can have a more powerful signal that our devices, yet no organisms are harmed by them. To get to the level of sound required to cause damage to large organisms like fish, you have to be at the capability of a naval submarine sonar system. Our devices use a total energy consumption of about 12.5 watts. This is below the power consumption of a refrigerator light bulb. If you have ever had a medical ultrasound procedure performed, you experienced a sound level many times more powerful than our Quattro-DB® and Mezzo-DB™ devices.
In 14 years being involved with this technology, I have never witnessed or had it reported to me that organisms other than algae were damaged by the devices. Even bacteria are not killed by it, though near the devices the sound mimics water turbulence to them and they will not colonize in the vicinity of the device. This “biofilm effect” is useful for preventing mussel growth (they consume biofilm polysaccarides) and water treatment equipment fouling in water processing plants. This reduces bacteria counts in processed water thus reducing Chlorination costs as well as reducing disinfection by-product carcinogens like THM (Trihalo Methanes) and HAA (Halo Acetic Acid).
Written by George Hutchinson
CTO, SonicSolutions Algae Control LLC