AWWA WQTC58883

The algal toxin microcystin-LR has been identified in source and treated drinking waters in the US (Carmichael, 2001; Karner et al., 2001). Chlorination has been shown to inactivate microcystin-LR in several cases (Nicholson et al., 1994; Tsuji et al., 1997; Hart et al., 1998; Bruchet et al., 1998). Since chlorination is extensively used in medium and large water utilities in the US it is important to establish CT (contact time chlorine concentration) values for the chlorination of microcystin-LR. The objective of this project was to conduct an evaluation of the inactivation kinetics of extracellular microcystin-LR by free chlorine. The analysis provided estimation of inactivation rate constants and CT values needed for inactivation of the toxin. Twenty-seven batch chlorine inactivation experiments of extracellular microcystin-LR were performed. The chlorination experiments were run with three different initial toxin concentrations (1, 3, and 10 ug/L), three different chlorine doses (1, 3, and 10 mg/L), and three different pH values (6.0, 7.5, and 9.0), at a temperature of 11C. All experiments were performed at five chlorination contact times, up to 100 minutes. Ascorbic acid was added as the chlorine quenching agent at the end of the chlorination time. Microcystin-LR was quantified with enzyme linked immunosorbent assay. For 19% of the samples, microcystin-LR was also quantified with high performance liquid chromatography to provide additional confidence in the laboratory results. The results of the two methods were correlated with an R2 of 0.904. Includes 6 references.