Development of ultrasonic technology for treatment of toxic microcystis spp. in water resources

Abstract

Blooms of cyanobacteria in water bodies are serious environmental problem. Some cyanobacteria produce toxins that have been shown to be hazardous to both animals and humans. An alternative method of controlling cyanobacterial blooms is ultrasonication. This study investigated the effectiveness of ultrasonic technology on Microcystis spp. cell, microcystins and musty odors degradation in pond water at the following frequencies 29, 43, 108, 200 and 1000 kHz with a constant input power of 3 W. Results showed that irradiation volume important factor required to specify the efficiency of ultrasonic reactions while concentration of Microcystis cells has no effect on removal. Ultrasonic treatment at 200 and 108 kHz could remove more than 98% and 95% Microcystis cells with within 30 sec due to loss of buoyancy caused by the collapse of gas vesicles. Scanning electron microscopy (SEM) confirmed that sonication at a frequency of 200 kHz for 240 sec did not disintegrate Microcystis sp. cells, but easily broke up the sticky mucus layer of the scum. Moreover, mechanical damage brought to the gas vesicle and cell membrane by ultrasonic cavitation. When M. aeruginosa and M. wesenbergii were operated at frequency 200 kHz, it shown that both of cyanobacterial were removed but M. aeruginosa were removed quickly than M. wesenbergii. Moreover, ultrasonication at 200 kHz effectively reduced microcystin by 80.8% and musty odors more than 60%, at 10 min The nutrients and microcystins with different sonication time at 200 kHz which cultivated at room temperature until 20 days showed that time of sonication is effectively to variation of nutrients especially ammonium increase more than twice times and releasing microcystins because free radical from ultrasonication can attack some cell membranes of cyanobacterial cells. Refloatation behavior of sonicated cells was investigated. It was found that sonicated cells in every time did not float to the surface and did not regenerate within 20 days.