Removal of algae from raw water by ultrasonic irradiation and flocculation: a pilot scale experiment

Using Chl alpha removal rate as index, a 28 kHz/900w ultrasonic cleaning machine was applied to testify algal removal by ultrasonic irradiation from raw water of a pool, where Microcystis aeruginosa colonies is absolutely dominated with temperature being over 20 degrees C, and the irradiation lasted for 5 min. PAC was used as flocculant at the dose of 60 mgl(-1), jar tests were done to investigate the Chl alpha removal by flocculation. The results showed that ultrasound raised the water temperature instantly but did not lead to a regular pH change pattern in all the treated samples. Ultrasound could remove more than 90% of Chl alpha from raw water with temperature over 31 degrees C, but less than 20% of Chl alpha or even increased Chl alpha concentration in some samples with temperature lower than 31 degrees C. Compared with the algal removal effects by direct raw water flocculation with PAC, ultrasound did not enhance markedly the flocculation effects on algae removal, which was not in agreement with the findings reported. The reason might be due to morphology and characteristics of natural algae differed greatly from that of algae cultured in laboratory.