Ultrasonic algae control
Algal blooms cause reduced light penetration, depletion of oxygen, and a release of toxins from the algae, which are all unfavourable conditions for fish and plants. When there is an imbalance in the ecosystem, it is important to control algae growth. At specific frequencies, low-power ultrasound at frequencies higher than the upper audible limit of human hearing (22 kHz) can be used to control algae growth. It is an environmentally-friendly alternative to chemical usage that is harmless to fish and plants. Ultrasound can be used in both fresh water surfaces such as lakes, drinking water reservoirs, and irrigation basins, as well as in maritime environments. By controlling the algae, it is possible to improve the clarity of the water, resulting in plant growth and increased oxygen levels.
LG Sonic algae control devices make use of specific and low-power ultrasound (5W per transmitter). It is an environmental friendly technology which is harmless to fish and plants. Other ultrasonic methods involve the production of cavitation by using ultrasound with a high-power output. Cavitation is a phenomenon where high power ultrasound causes the formation of bubbles that implode upon themselves causing intense heat and pressure, which can destroy cells, and has been known to have a harmful impact on the ecosystem. Also, due to the high power-requirements, it is not possible to use this method for the treatment of lakes or any large water surface.
Effects of ultrasound on the algae
To understand how ultrasound waves target blue-green algae, it is important to know their growing mechanism. Cyanobacteria use gas vesicles for buoyance and depth regulation. During the day algae are photosynthesizing in the top layer, using carbon dioxide and dissolved nutrients from the surrounding water to produce oxygen and polysaccharides. At night, or during events of high UV irradiation, the cyanobacteria cells empty their gas vesicles (vacuole) to sink to the bottom and use oxygen and nutrients (nitrogen and phosphorus) to produce biomass.
To control the algae, LG Sonic ultrasound technology transmits specific ultrasonic waves is installed in the water. The sound waves can spread through the water column over hundreds of meters. The ultrasound waves create a sound layer in the top layer of the water which affects the buoyancy regulation of the algae, fixing them in the water column. The algae cells sink to the deeper and darker layers of the water column where they are not able to photosynthesise, and eventually die due to a lack of light. However, it is important for the efficiency of the technology that specific frequency programs are used, based on the algae that require a control strategy.
Due to the adaptability of algae during seasons within a lake, the ability to change these ultrasonic frequencies is of importance for the long-term effects of the technology.
In general, ultrasonic algae control does not significantly alter the basic level of algae present in a lake. However, due to the direct effect of the ultrasound on the vertical distribution of algae in the water column, the ultrasound directly influences the capability of an algal species to form a bloom. In general, these blooms can be reduced by 70-90% in concentration, compared to no treatment.
- LG Sonic ultrasound technology creates a sound layer in the top layer of the water.
- The ultrasound affects the buoyancy of the algae, fixing them in the water column.
- Due to a lack of sunlight and nutrients, the algae will die and sink to the bottom of the reservoir.
- The algae are degraded by the bacteria present.
What happens when the algae die?
LG Sonic ultrasound technology affects the buoyancy regulation of algae, fixing them in the water column. Due to a lack of sunlight and nutrients, the algae will sink to the bottom of the reservoir where they die, and eventually decompose.
Does the ultrasound cause a release of toxins?
Algae control by ultrasound is based on interference with their buoyancy, in turn preventing their photosynthetic activity. Ultrasound does not break or lyse the cells, as such, toxins are not released into the water. As the ultrasound process is generally a two-to-three-week process in which growth of new algae is being prevented, you will see a gradual reduction in toxin concentration once the ultrasound has been introduced. The ultrasonic treatment will result in a lower release of toxins compared to no treatment or to the use of chemicals.
Is the ultrasound harmful to fish, plants and zooplankton?
LG Sonic ultrasonic algae control systems are developed together with several European Universities and research institutes to provide an environmentally friendly alternative to the use of chemicals. The University of Portsmouth, UK; UNICET Catania, Italy; and BOKU, Austria have all found that LG Sonic systems are safe for fish. LG Sonic devices have also been tested on zooplankton, and no negative effect was found.
Which algae types can be controlled with ultrasound?
The ultrasound can control common types of green and blue-green algae such as spirogyra, microcystis, and anabaena.
How long does it take before the algae die?
There are different types of algae in existence which react in various ways to the ultrasonic treatment. On average, it takes two to three weeks for the treatment to take effect.