AWWA QTC97188

Coliform bacteria are still the most commonly used indicators of the sanitary quality of water. While their inability to serve as indicators for the removal of chlorine-resistant microorganisms such as viruses, Giardia, and Cryptosporidium has been confirmed, this may be caused by the fact that CT values for coliforms are based on data from inactivation experiments completed with strains cultivated in rich medium, which is not representative of natural environmental conditions. In this study, two strains of coliform bacteria (E. coli) were grown in a rich medium in batch culture and in a carbon-limited chemostat at two dilution rates and two temperatures. Bacterial counts were estimated using two enumeration methods: a direct epifluorescence viable count method with the LIVE/DEAD BacLight(TM) bacterial viability kit, and standard colony counts using M-T7 medium. The objectives of the study were to: compare the chlorination CT values for the two E. coli strains using the above two methods; measure chlorination CT values at a cold temperature to verify the acceptability of extrapolation from values at higher temperatures; and, assess the impact of growth conditions on resistance to chlorination.