Systems utilizing chloramines for residual disinfection often are required to stopammonia addition for at least one month per year. This time is utilized to burn orflush the system with a high strength disinfectant and is typically accompanied by aprogram of hydrant flushing to ensure the chlorinated water travels completely throughthe distribution system. A previous study indicated that switching from chloraminesto free chlorine residual disinfectant reduced bacteria levels as measured by heterotrophicplate count (HPC); the effect was temporary, however, because the levels increased againupon return to chloramination. To build upon this work, one of the project goals was toexamine the effect of switching from combined to free chlorine and then back tocombined chlorine on bacteria levels in two neighboring distribution systems (DS-1 andDS-2) with similar raw water quality, and to link these effects to water age and waterquality parameters including disinfectant residual, assimilable organic carbon, andnitrogen species (nitrate, nitrite, ammonia).A second project goal involved examining a dead-end site in the distribution system forbacterial growth after periods of unsustained chlorine residuals. Additionally, nitrogenspecies were analyzed to examine the possibility of nitrification at the site. Includes 15 references, table, figures.
Keywords: Bacteria; Disinfection; Distribution Systems; Disinfection Residuals; Organic Carbon; Nitrogen; Chlorine; Ammonia; Nitrification; Nitrates; Nitrites
