Influence of ultrasonic intensity on sinking of Microcystis colonies and their floating process under different light and temperature conditions

Abstract

Inhibition effect of different ultrasonic intensities was investigated by using Microcystis colonies from Lake Taihu, and the aim of this study was to obtain the optimal ultrasound parameters. The floating character of Microcystis colonies after sonication was cultured under different illumination intensity and temperature conditions. Results showed that sonication for 60 s at 0.0353 W/cm3 was an optimal parameter, which led to an immediate sedimentation (up to 80%) markedly. In the experiment, the algal cell concentration and chlorophyll-a concentration were unchanged, which suggested that algal cells remained intact and cell inclusions did not leak to contaminate water quality. Light and temperature played important roles in the floating process of Microcystis colonies, but light was a more significant factor during the process. Under 2000 lx at 25℃, the floating rate of algal cells could restore to the normal level after 120 h, while the floating rate of algal cells after sonication did not change significantly at a relatively low temperature (≤20℃). In comparison, at a higher temperature of 25℃, the floating rate increased after 72 h which could restore to 80% of the level in control group after 120 h. Therefore, the ultrasonic control of algal blooms in lakes should choose a weak illumination intensity and low temperature condition.