DISTRIBUTION SYSTEM WATER QUALITY PROFILES DURING NITRIFICATION

System variations of nitrates, nitrites, dissolved oxygen (DO), pH, alkalinity, temperature, heterotrophic plate counts (HPC) and chloramines residuals are discussed as a function of hydraulic residence time in pilot distribution systems (PDS) made of PVC, galvanized steel (G), line cast iron (LCI), and unlined cast iron (CI) pipe in reference to theoretical biochemical nitrification reactions. Nitrites and nitrates increased initially with time after the chloramines residual was lost in the distribution system but decreased with time if denitrification began. Ammonia also increased and decreased with residence time dependent on the rate of chloramines decomposition and nitrifier uptake. DO decreased with residence time until anaerobic conditions developed due to biological uptake and was a limiting factor for nitrifier growth. Distribution system pH decreased due to proton generation from biological growth. No significant alkalinity variation was observed in the distribution system during nitrification.