Removal of algae by sonication-coagulation.

Algae bloom in source water has caused serious problems in drinking water supplies, and conventional methods for its treatment have achieved only limited success. This paper reports a new technology, ultrasound assisted coagulation, for effective removal of algae cells from the source water in water treatment works. The results showed that ultrasonic pretreatment significantly enhanced the removal efficiency of algae cells. Ultrasonic irradiation for 5 s increased the algae removal efficiency by more than 20% when the coagulant dose was 0.4-0.8 mg/L. To achieve the same algae removal ratio of 90%, sonication for 5 s reduced the coagulant dose by 2/3. The optimal sonication parameters were determined as follows: sonication time of 1 s, ultrasonic power of 48 W, and solution pH of 8-9. The sound frequency had little impact on the algal removal efficiency. Ultrasonic pretreatment also significantly reduced the sample turbidity.