CHLORAMINATION - ITS EFFECT ON DISTRIBUTION-SYSTEM WATER-QUALITY

Postdisinfection using chloramines can limit coliform regrowth in pipe line biofilms and formation of disinfection by-products (DBPs) in dist ribution systems. Two utilities that have had occurrences of total col iform converted from free chlorine to chloramines. Water in both distr ibution systems was monitored for biological and chemical quality for a year after the conversion, Coliform occurrences were eliminated in o ne system and reduced fourfold in the other. However, excessive concen trations of assimilable organic carbon (up to 375 mu g/L) were charact eristic of the latter system, as was pitting corrosion. Both factors m ay play a critical role in limiting coliform occurrence. Postdisinfect ion using chloramines rather than free chlorine has advantages includi ng decreased coliform concentrations, decreased heterotrophic plate co unt and DBPs, and improved maintenance of a disinfectant residual. How ever chloramination alone may not be sufficient to control coliform co ncentrations in all distribution systems.