The effect of chlorination on cell integrity and release of metabolites of two noxious cyanobacteria, a β-cyclocitral producer—Microcystis aeruginosa—and a geosmin producer—Anabaena circinalis—was investigated. Photos from a scanning electron microscope revealed that Microcystis cell surfaces were deformed after chlorination, and filamentary Anabaena cells were ruptured at the junction of vegetative cell units. Chlorination experiments indicated that both cyanobacteria are susceptible to attack by chlorine. A first-order decay model was used to simulate the cell-rupture kinetics during chlorination. Using laboratory cultures, the observed rate constants are 670–1,100 M−1 s−1 for M. aeruginosa, which are 1.3–5.0 times as large as those for A. circinalis. For unfiltered Microcystis-laden reservoir waters, a broader range of rate constants, 70–590 M−1 s−1, were obtained. The rate constant was reduced in more eutrophic water, due probably to the competition of chlorine with other cyanobacteria in water. Geosmin was rapidly released into water immediately after the Anabaena cells were ruptured. However, a portion of geosmin remained cell-bound. For Microcystis, the total β-cyclocitral concentration decreased quickly during chlorination in most cases. It is speculated that the enzymes leading to the formation of β-cyclocitral were inhibited by chlorine, thus causing a sudden reduction of β-cyclocitral in the system.

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