Abundance and activity of ammonia oxidizing archaea and bacteria in bulk water and biofilm in water supply systems practicing chlorination and chloramination: Full and laboratory scale investigations.

The abundance and nitrification activity of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) in bulk water and biofilm in chloraminated and chlorinated water supply systems were investigated. The abundance of AOB varied between cold and warm periods while that was the case for AOA only in biofilm. Lower ammonia concentrations favored the abundance of AOA over AOB. AOA and AOB were found more in distal zones of the distribution system (DS). Higher numbers of AOA and AOB were observed in DS associated with chloramination compared to those associated with chlorination. Significant positive correlations between ammonia-N in bulk water and AOA indicate a possibility of involvement of AOA in nitrification in DS. A separate laboratory-based experiment simulating DS condition was conducted to understand the effects of chlorine and chloramine dosages and temperature on AOA and AOB. AOA were inhibited less than AOB in the presence of lower concentrations of chlorine and chloramine (1.5 and 2.0 mg/L chlorine; 0.05-0.1 and 0.3-0.4 mg/L chloramine) while both of them were not detected at higher dosages (2.5 mg/L chlorine and 1.5-1.6 mg/L chloramine). At a low temperature (10-12 °C), chloramine and chlorine provided similar inhibition trends in which AOB were inhibited more than AOA. At a high temperature (25 °C), chloramine was less inhibitory to AOA and AOB than chlorine.