Nitrification control is complicated and expensive, especially when nitrification has reached a severely nitrifying stage. Under this condition, utilities usually apply re-chloramination with limited success. Adjusting pH may benefit utilities. However, it is not clear whether pH should be moved up or down, and pH adjustment will also alter the chloramine decay profile (biocide) and ammonia (food) concentration. It is important to understand how this behaviour will ultimately impact nitrifying bacterial activity. We collected samples from severely nitrifying bulkwaters and adjusted the pH within a practical range to know which pH benefits the most. Results showed that even a slight increase in pH can help in protecting the chloramine residual and suppressing nitrifying bacterial activity.

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