ALGAL REMOVAL FROM DRINKING WATER SUPPLIES USING ULTRASONIC FLOTATION

This paper evaluates the performance and key factors of an ultrasonic flotation process to remove algae from drinking water. Two typical algal species, Microcystis aeruginosa and Anabaena flos-aquae, were used in this study. The key factors that were investigated include flocculant dosage, pH, flocculation time, flotation unit current, as well as ultrasonic frequency, and duration of treatment. And the mechanism for the ultrasonic treatment was also investigated by observing algal morphology and the fluorescence excitation-emission matrix (EEM) fluorescence spectra of the algal solution. The results showed that pH was the most important factor for the removal of M. aeruginosa and A. flos-aquae in the flocculation and flotation stages. Ultrasonication significantly improved the removal of M. aeruginosa, but not A. flos-aquae. The removal of M. aeruginosa and A. flos-aquae decreased with the frequencies. With ultrasonication, the quantity of PAC required was significantly reduced. The morphological and EEM fluorescence spectral observations, as well as the zeta potential analysis showed that the ultrasound treatment broke down the M. aeruginosa and A. flos-aquae cells in different ways, resulting in different physiochemical effects on the algal solution, and consequently the removal performance at the subsequent flocculation and flotation stage.