Effect of silver in severely nitrified chloraminated bulk waters

Chloramine has been widely used in many water utilities as a secondary disinfectant because of increased concern over disinfection by-products (DBPs) formation. However, its popularity has been affected due to microbial acceleration, which is traditionally believed to be by nitrifying organisms or their products such as nitrite and pH value which change substantially under nitrifying conditions. With the traditional belief in mind, the conventional approach to solve ‘chloramine decay’ was aimed at killing or flushing out nitrifiers. We have recently shown that either soluble microbial products (SMPs) released by microbes or changes in natural organic matter (NOM) characteristics under nitrified conditions could be responsible for the acceleration. With this new insight, a new control strategy was attempted by dosing silver at a concentration of 0.1 mg-Ag/L to the nitrified bulk waters obtained in a laboratory scale system. Accelerated chemical and microbial chloramine losses were significantly reduced after the addition of silver. These results are very promising for future applications.