Application of micro cavitations bubbles for mitigation of harmful phytoplankton in seawater

Abstract

The representative species cause harmful algal bloom (HAB, called red-tide) in the coastal waters of Korea is a dinoflagellate (Cochlodinium polykrikoides) that gives serious damages to marine ecology, fisheries, and related industry during summer season. When the red-tide occurred in the ocean, as a natural absorbent material of red-tide, amount of clay to mitigate red-tide have been sprayed in Korea. The method for red-tide mitigation involves considerable human power and cost and may make a harmful effect on the coastal ecosystem. As a pilot study, we considered physical approach to mitigate or eliminate of the red-tide. In physics, if propeller with a blade rotates in water with very high speed, the propeller makes mass cavitation bubbles around water. When the cavitation bubble returns to liquid condition from vapor, surrounding waters of the bubbles accelerate into the bubble inside, finally the bubbles suddenly collapsed. With the principle, we have a hypothesis that the returning power or speed (>1000 m/s) of the cavitation bubble can break red-tide cell in the water. We, therefore, tried to make micro cavitation bubbles under the various tiny propellers with a high speed motor (3000 rpm) and red-tide species was instantaneously exposed to mass cavitation bubbles. From the measurements, most of cell population was apparently reduced under the laboratory condition. In the field measurement of the red-tide water, cell numbers were compared with before and after of the cavitation bubbles experiment from the cell counting. After cavitation bubbles experiment in the red-tide blooms water, the cells density has a tendency to rapidly decrease and chain of cell was broken. These results suggest that it may be possible to decease of harmful algal blooms from cavitation bubbles.