Pilot-scale evaluation of nitrification control strategies

A significant concern associated with chloramination is nitrification caused by the growth of ammonia-oxidizing bacteria (AOB) in the distribution system. To prevent nitrification, any measures designed to slow the decay of chloramine and its associated release of ammonia should theoretically reduce the occurrence of AOB growth. Pilot-scale studies were used to evaluate whether enhanced removal of natural organic matter and pH adjustment delayed the onset of nitrification. For the system described in this article, nitrification occurred at pH values ranging from 7.9 to 8.9, with the time to onset of nitrification being fastest at about pH 8.5. However, pretreatment with enhanced coagulation successfully delayed the onset of nitrification compared with pretreatment with conventional coagulation. Nitrification did not occur when total chlorine concentrations were 2.2 mg/L as Cl-2 or more. Similarly, nitrification did not occur in locations with biocide-to-food ratios of 1.9 mg Cl-2/mg N or more.