Can microbes significantly accelerate chloramine decay without severe nitrification?

The ability of microbes to accelerate chloramine decay to the same degree as under severe nitrification, but without the signs of severe nitrification is reported. Traditionally, only nitrification is believed to microbiologically challenge the stability of chloramine. Chloraminated water containing high amount of natural organic matter (10-12mgL-1 of dissolved organic carbon (DOC)) was fed to four lab scale reactors connected in series. Each reactor had one day retention time with a total of four days in total. The decay coefficient was observed to be a maximum of 0.06h-1 without substantial changes in ammonia, nitrite or nitrate levels. Despite very low chloramine residuals, nitrite only increased to less than 0.012mg-NL-1, indicating a mildly nitrifying condition. Previously reported decay coefficient (0.001-0.006h-1) for the condition was an order less. Changing of the feed to a new water from the same source, but with a low DOC (of 4mgL-1) led to the onset of nitrification complying biostability. The maximum observed chloramine decay coefficient with severe nitrification was 0.085h-1. Therefore, microbes present under mildly nitrifying condition can be as destructive as that in severely nitrifying condition. For better control of chloramine, attention on microbes present under mild nitrification is needed.