AWWA WQTC58848

The overall aim of this bench-scale study was to quantify differences in the inactivation kinetics of organisms of the same species obtained from various environments (disinfected and non-disinfected) versus culture collection strains of the same species. The disinfected environments included water sampled from four full-scale distribution systems. Microorganisms from non-disinfected environments included bacterial isolates from raw water (from the same four participating utilities), pure culture strains of heterotrophic bacteria and E. coli O157:H7 from ATCC, and six environmental strains of E. coli O157:H7 isolated by the Wisconsin Food Research Institute from cow manure and farm wastewater. Microbial sources from disinfected environments included isolated heterotrophic bacteria from distributed municipal water from four different locations across North America. The inactivation kinetics experiments were conducted at bench-scale at 21oC. The disinfectants tested included free chlorine and monochloramine. With monochloramine, all strains of E. coli O157:H7 tested showed approximately 2 to 3 log10 of inactivation with Ct values ranging from 20-30 mg.min/L. The Ct values for 2-3 log₁₀ of inactivation of E. coli O157:H7 using chlorine were less than 0.30 mg.min/L. All environmental strains of E. coli O157:H7 were consistently more resistant to monochloramine than the ATCC 35150 strain and these differences were statistically significant. Several strains of heterotrophic bacteria have been isolated from distributed water collected from the four participating utilities. These isolates were identified using API biochemical profiling and included various types of pseudomonads (P. fluorescens) and pseumonad-related bacteria such Brevundimonas vesicularis and Sphingomonas paucimobilis. Inactivation kinetics experiments of these isolates as well as the kinetics of culture collection strains show that there was a wide range of resistance among heterotrophic bacteria. If evidence is generated in support of the hypothesis that disinfectant-tolerant microorganisms can evolve in distribution systems, it could potentially lead to a reassessment of the practice of maintaining a steady concentration of secondary disinfectant. Strategies such as periodic changes in disinfectant concentration or type may potentially be considered. Includes 3 references, tables.