Cd. Norton et Mw. Lechevallier, CHLORAMINATION - ITS EFFECT ON DISTRIBUTION-SYSTEM WATER-QUALITY, Journal - American Water Works Association, 89(7), 1997, pp. 66-77
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.