Sonic cracking of blue-green algae

Kotopoulis, S., Schommartz, A., Michiel Postema

Appl Acoust 2009 70(10):1306-1312.


Abstract

Algae are aquatic organisms classified separately from plants. They are known to cause many hazards to humans and the environment. Algae strands contain nitrogen-producing cells that help them float (heterocysts). It is hypothesized that if the membranes of these cells are disrupted by means of ultrasound, the gas may be released analogous to sonic cracking, causing the strands to sink. This is a desirable ecological effect, because of the resulting suppressed release of toxins into the water.

We subjected small quantities of blue-green algae of the Anabaena sphaerica species to ultrasound of frequencies and pressures in the clinical diagnostic range, and observed the changes in brightness of these solutions over time. Blue-green algae were forced to sink at any ultrasonic frequency we studied, supporting our hypothesis that heterocysts release nitrogen under ultrasound insonification in the clinical diagnostic range.

Although the acoustic fields we used to eradicate blue-green algae are perfectly safe in terms of mechanical index, the acoustic pressures surpass the NURC Rules and Procedures by over 35 dB. Therefore, caution should be taken when using these techniques in a surrounding where aquatic or semi-aquatic animals are present.

Keywords: Ultrasonic algae eradication; Blue-green algae; Sonic cracking

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