Effectiveness of re-chloramination to control nitrification in chloraminated bulk waters

Managing chloramine residuals in water distribution systems after the onset of nitrification is a major challenge for water utilities that employ chloramine as a disinfectant. One of the strategies adopted by utilities is re-chloramination, but its effectiveness may vary depending on the stage (immediately after the onset or later) at which re-chloramination is practiced. Therefore, a systematic study of the effectiveness of re-chloramination was conducted by collecting bulk water samples from full-scale and laboratory-scale water distribution systems. The findings of this study revealed that in addition to initial dose of chloramine residuals, effectiveness of re-chloramination largely depend on the stage at which re-chloramination is practiced. Comparatively slow chloramine decay rates were observed when re-chloramination was carried out just after the onset of nitrification or after chloramine residuals dropped close to zero. However, the recurrence of nitrification is inevitable if only single dosing is practiced.