Selective Control of Cyanobacteria in Eutrophic Pond by a Combined Device of Ultrasonication and Water Pumps

A combined device consisting of an ultrasonic apparatus and water pumps was operated in a eutrophic pond to study its effect on the control of cyanobacteria as compared with those of a non-treated, neighboring pond. The combined apparatus seemed to be enough to spread the sonicated water to the whole surface of a 9,000 m3 pond. Although the high rainfall in 2003 resulted in an overall dominance of diatoms, cyanobacterial growth was significantly inhibited by the apparatus in the treated pond. In addition, the chlorophyll-a concentration and total algae in the treated pond were 61 and 53%, respectively, of the levels in the control pond. The reduced algal growth (7% of the control) by the combined apparatus was mainly due to the inhibition on the growth of cyanobacteria. The cyanobacterial proportion in the treated pond, however, increased significantly for several days, when the apparatus was stopped. Meanwhile, the proportion of green algae increased in the treated pond. The successful selective control ...