The effect of alum coagulation for in-lake treatment of toxic Microcystis and other cyanobacteria related organisms in microcosm experiments

Microcosm and bottle experiments were conducted to evaluate the effects of alum treatment on cyanobacteria-lysing organisms and microcystin-degrading bacteria as well as Microcystis cells, and to provide detailed evidence of Microcystis cell damage by investigating precipitated Microcystis cells. The alum concentration to be pH 6.0 is the maximum which does not cause toxicity by monomeric Al, therefore, this concentration was defined as maximum dose. Microcystis cells were considerably damaged by the alum treatment with maximum dose and long contact time. Seven days post-treatment, intracellular microcystin-LR was released into the extracellular environment in excess of 95 percent and chlorophyll a is not easily released from inside the cell, chl.a of precipitated Microcystis cells was also decreased to approximately 50 percent. Moreover, alum treatment caused damage to cyanobacteria-lysing organisms and microcystin-degrading bacteria, as well as to Microcystis cells. Therefore, it could be concluded that alum treatment with maximum dose (48 mg L−1 as AI) is not suitable for removing cyanobacterial bloom without the release of cyanotoxin in reservoirs and ponds.