AWWA DPOC56500

Chloramine decay studies were conducted to evaluate the impact of various water quality parameters on the decay characteristics of the San Francisco Public Utility Commission (SFPUC) water, to predict disinfectant levels within the distribution system, and the potential for nitrification. The results of the studies show that overall, SFPUC water is very stable, meaning that decay rates are slow compared to other surface water supplies. The studies indicated that for SFPUC waters, pH had the most significant effect on chloramine decay; chloramine decay was slower at higher pH values (between pH 8.8 and 9.0), which are currently maintained for corrosion control. The use of booster chlorination was also evaluated as a possible means of maintaining or increasing the total chlorine residual within the distribution system. Although chlorine added to chloraminated test water combined with the free ammonia-N that was liberated as a result of chloramine decay, the ability to properly feed sodium hypochlorite is a critical factor in determining whether or not to implement this practice. An evaluation of free ammonia-N data from a similar water system supported the conclusion that boosting the chloramine residual with sodium hypochlorite is not a practical alternative for the SFPUC system. Includes 7 references, table, figures.