Ultrasonic irradiation for blue-green algae control

Ultrasonic irradiation has recently been evaluated as a rapid alternative for algal bloom control.

In a research carried out at the Institute of Applied Biochemistry, University of Tsukuba, Japan by Lee, Nakano and Matsumara [6], the effects of ultrasonic irradiation on blue-green algae were investigated, considering the factors affecting their sedimentation and death.
Natural blue-green algae suspensions in test tubes were treated using an ultrasonic cleaner with 120 W input and 28 kHz frequency, at different exposure time of 0, 3, 5, 10, 15 and 30 seconds. Results show that this irradiation collapses the gas vacuoles of blue-green algae and effectively settles them at a short exposure time of 3 seconds.

Power and frequency have the greatest effect on the intensity of ultrasonic irradiation. Ultrasonic irradiation causes cavitations phenomena. The implosion of cavitations bubbles produces free radicals, which damage cells of blue-green algae. These radicals are keen to react with potassium iodide resulting in iodine liberation. Measuring the iodine level may then approximate the intensity of the cavitations. During the tests it was found that at a constant power of 40 W, iodide liberation is higher at the lowest applied frequency of 21.5 kHz. This frequency is then more effective for blue-algae settling.
In addition, ultrasonic irradiation (120 W, 1200 W at 28 kHz for 30 s) also inflicts immediate damage on photosynthetic activity and the degree of damage is dependent on input power and frequency. Different tests showed than once the photosynthetic apparatus in the cell is damaged by ultrasonic irradiation the photosynthetic activity does not recover and blue-green algae proliferation is inhibited under natural lake conditions.
Further experiments showed that ultrasonic irradiation of blue-green algae does not cause the release of algal toxins into the water environment.

Ultrasonic devices are already applied to ponds, pools, lakes and reservoirs to destroy algae and control their growth in an environmentally friendly way.

Their efficiency is measured in active radius, the linear distance they can irradiate. The algae will disappear approximately in a semicircular surface having the active radius correspondent to the model chosen. Of course factors as average temperature, walls consistency, presence of obstacles etc. should be considered in the efficiency estimation.

Ultrasonic devices:

AL 50
AL 50 D
AL 20
Al 10
Al 5

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Click here to learn more about the problem of eutrophication of water bodies.

Related topics

• Algae description and types

• Eutrophication
  Sources
  Effects
  Solutions: Nutrients limitation
  Algae filtration
  Ultrasonic irradiation
  Others

• Conclusions

• References

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