Chlorination of Microcystis aeruginosa: toxin release and oxidation, cellular chlorine demand and disinfection by-products formation.

Direct chlorination of toxic cyanobacteria cells can occur at various stages of treatment. The objectives of this work are to determine and model the extent of Microcystis aeruginosa cells lysis, toxins and organic compounds release and oxidation, and quantify the subsequent disinfection by-products formation. Chlorine exposure (CT) values of 296 and 100 mg min/L were required to obtain 76% cell lysis and oxidation of released cell-bound toxins at levels below the provisional World Health Organisation guideline value (1 μg/L MC-LR). Toxin oxidation rates were similar or faster than cell lysis rates in ultrapure water. This work presents much needed unit M. aeruginosa cellular chlorine demand (5.6 ± 0.2 pgCl(2)/cell) which could be used to adjust the chlorination capacity to satisfy the total chlorine demand associated with the presence of cells. Furthermore, a novel successive reaction kinetics model is developed using the kinetics of the chlorine reaction with cyanobacterial cells and cell-bound toxins. Chlorination of dense cell suspensions (500,000 cells/mL) in ultrapure water at CT up to 3051 mg min/L resulted in modest concentrations of trihalomethanes (13 μg/L) and haloacetic acids (below detection limit).