Effect of Cell Density on the Removal of Microcystis by Coagulation

Abstract

Objectives: This study evaluated the removal of Microcystis by coagulation in raw waters with three different cell densities. Method: Raw waters were prepared at three different cell densities (target cell densities of 10,000, 100,000, and 1,000,000 cell/mL; actual cell densities of 9,950, 102,000, and 991,000 cell/mL) by adding Microcystis into surface water from Nakdong river. Jar-tests were conducted with PACL, alum, illite, and loess at dosages of 0-150 mg/L. Results and Discussion: Regardless of coagulant types, the removal rates of Microcystis increased as the coagulant dosages increased. PACl and alum exhibited higher removal rates than illite and loess; PACl was the best coagulant to remove Microcystis. Removal of chlorophyll-a was highest when PACl added at 20.4 mg/L, and no significant increase in removal rate was observed with higher dosages of PACl. However, removal rates of chlorophyll-a by illite and loess gradually increased as the dosages increased. Conclusions: With the coagulants tested in this study, removal rates of Microcystis increased as the coagulant dosages increased. Removal rates of Microcystis increased as the cell densities increased probably because Microcystis acted as particles which could enhance the coagulation efficiency.

Keywords

• cyanobacteria
• algal bloom
• microcystis
• coagulation
• cell density