AWWA PATH50777

The objective of this work was to define the inactivation of Legionella pneumophila as a function of free chlorine levels at a spectrum of pH, temperature, and dose conditions that might be employed under typical water treatment practice. Batch experiments were conducted at pH 6, 7 and 8, temperatures of 5, 15 and 25C, and initial doses of 1,2 and 4 mg/L. A total of 36 experiments were run under these 27 conditions (thereby allowing assessment of replication error). A batch contacting methodology was used. L. pneumophila cultures were prepared, dosed into buffered chlorine demand-free water, disinfectant was added, and viability was assessed by plating at subsequent times. Decay of controls (in the absense of chlorine) was also monitored, as was the loss of disinfectant residual. The results were analyzed using a computational environment developed by the senior author for the analysis of disinfectant kinetics in the presence of demand. While demand was minor, over the 4-8 hour contact it could not be neglected, and it is described by a first order process with instantaneous demand. Includes 16 references, tables, figures.