Effects of ultrasound on Microcystis aeruginosa cell destruction and release of intracellular organic matter.

Abstract

Harmful algal blooms negatively impact ecosystems and threaten drinking water sources. One potential method to effectively counteract algal blooms is ultrasonication. However, ultrasonication can easily lead to the release of intracellular organic matter (IOM). The purpose of this study was to investigate the relationship between the destruction of algal cells and IOM release at different ultrasound frequencies. Microcystis aeruginosa cells were ultrasonicated at 20kHz with an intensity of 0.038W/mL, 740kHz with an intensity of 0.113W/mL, and 1120kHz with an intensity of 0.108W/mL. The IOM release was detected by fluorescence spectroscopy in addition to the more commonly used haemocytometry and optical density. After ultrasonication for 15min, the removal rate of algal cells reached 10.5% at 20kHz, 9.46% at 740kHz, and 35.4% at 1120kHz. The 20kHz and 740kHz ultrasound caused local damage to algal cells and then disrupted them, whereas the 1120kHz ultrasound directly disrupted most algal cells. The extracellular organic matter (EOM), which was increased by ultrasonication, mainly consisted of protein-like compounds, chlorophyll, and a small amount of humic-like substances. Gas vacuoles had been destructed before the cells were broken, as indicated by the decrease of cell size and the wrinkles on the cell surface. Moreover, the removal of algae cells while upholding integrity is more conducive to the safety of the water environment.