Effects of ultrasonic irradiation on degradation of microcystin in fish ponds

Abstract

Surface cyanobacterial bloom causes deterioration of pond water and accumulation of toxins and musty odors (Geosmin & 2-methylisoborneol, MIB) in aquaculture activities. This study investigated the effectiveness of ultrasonic technology on Microcystis sp. surface scum settling, including microcystin (cyanotoxin) and musty odors degradation in pond water. Water from fish ponds, with 5.162±0.92 mg L-1of initial chlorophyll 'a' was sonicated at 5 frequencies (29, 43, 108, 200 & 1000 kHz). Ultrasonic irradiation of 200 kHz had the greatest effect in settling Microcystis scum. Moreover, ultrasonication at 200 kHz effectively reduced microcystin and musty odors. Scanning electron microscopy (SEM) confirmed that sonification at a frequency of 200 kHz for 240 s did not disintegrate Microcystis sp. cells, but easily broke up the sticky mucus layer of the scum. Thus, ultrasonification at 200 kHz is promising technique to sink Microcystis surface scum, without cell disintegration, and could be used to reduce microcystin toxin and musty odor substances in aquaculture ponds. © 2011 Friends Science Publishers.