US EPA

2490419 

Journal Article 

ULTRASONIC CONTROL AND REMOVAL OF CYANOBACTERIA 

Zhang, G; Zhang, P; Hao, H 

2009 

Nova Science Publishers, Inc. 

Algae: Nutrition, Pollution Control and Energy Sources 

89-125 

English 

WOS:000283813900006 

Overgrowth of cyanobacteria has caused great serious water environment problems and threatens the drinking water supply worldwide. Many methods have been researched and practiced for its control. This paper investigates thoroughly the ultrasonic control of cyanobacteria growth in water, the ultrasonic enhancement of algal cell removal via coagulation, and the degradation of algal toxins by sonication. The paper also examines the important operational parameters and aqueous matrix factors. The results showed that proper ultrasonic irradiation could effectively control the growth of some cyanobacteria species. Gas vacuole in the algal cells can be easily destroyed during ultrasonic irradiation by acting as the 'nuclei' for acoustic cavitation and collapse during the "bubble crush" period, which results in the cyanobacteria settlement and growth inhibition. Sonication can also instantly decrease the antenna complexes like chlorophyll a and phycocyanins. Direct damage on cell surface or even cell fracturing was also observed. But the dominant mechanism is the acoustic cavitation of gas vacuole. The same mechanism also explains the enhancement of coagulation by sonication. As a result, cyanobacteria with gas vacuoles can be easily controlled using ultrasonic waves, but algae without gas vacuoles are virtually immune to sonication. On the other hand, the reason for ultrasonic degradation of algal toxins is because of the chemical changes caused by sonication, especially the formation of hydroxyl free radicals in water. Ultrasonic frequency, intensity, and duration play important roles in the algal growth control and ultrasonic-coagulation removal, and ultrasonic toxin degradation. © 2009 by Nova Science Publishers, Inc. All rights reserved. 

Ultrasonic cavitation; Cyanobacteria; Kinetics; Weak spot; Microcystins