AWWA JAW24265

Derivations from first-order inactivation of microorganisms are commonly observed during disinfection. These have been attributed to aggregation, decreasing concentration of disinfectant, or biological heterogeneity. The phenomenon, however, has not been properly investigated. During this study, chemostat-grown and batch-grown populations of Legionella pneumophila and Escherichia coli were dosed with chlorine dioxide (ClO2) to achieve an initial concentration of 0.75 mg/L. Results indicated that a resistant fraction of cells survives in the absence of aggregation and with a constant ClO2 residual. The resistance is a phenotypic characteristic that can be manipulated by altering the antecedent growth environment. Growth rate and temperature were important determinants of the size of the recalcitrant population. Includes 38 references, tables, figures.