Biostability and microbiological quality in a chloraminated distribution system

In this study, two components were evaluated: biostability, measured by assimilable organic carbon (AOC) concentration; and microbiological quality, determined by heterotrophic plate counts and coliform counts. The study centered around a full-scale chloraminated distribution system. Results from full-scale monitoring showed that the water in the system was biologically stable and there was no significant microbial activity in the system in spite of a moderate to high AOC concentration of 162 ± 24 μg/L as acetate-carbon. Batch experiment results indicated that the treated water containing monochloramine was biologically stable, and removal of the residual chlorine resulted in rapid consumption of AOC and bacterial regrowth. This study suggested that the treated water's AOC concentration may not be the dominant factor for controlling bacterial regrowth in all distribution systems. Biostability can be achieved in a water supply containing a moderate to high AOC concentration by maintaining a high disinfectant residual throughout the system.