AWWA ACE58207

As part of the Water Quality Master Plan Update for the City of Phoenix (City), Carollo Engineers, Malcolm Pirnie, Inc., and Narasimhan Consulting Services worked to identify treatment strategies to facilitate the City's compliance with future regulations. Due to warm summer temperatures and high total organic carbon (TOC) in the City's raw water sources, the City may have difficulty meeting the anticipated future regulated levels for disinfection byproduct (DBP) formation as required by the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Stage 2 Disinfectant/Disinfection Byproduct (D/DBP) Rule. One treatment alternative under consideration is using chloramines as a secondary disinfectant. Research has shown chloramines to be an effective control strategy for trihalomethanes (THMs) and haloacetic acids (HAAs); however, there are also drawbacks to the process such as nitrification and formation of other DBPs (e.g., n-nitrosodimethylamine (NDMA) and cyanogen chloride (CNCl)) that may limit its practicality for the City. This paper presents results of field testing that evaluated the use of chloramines. The objectives of the study were to: evaluate chloramine residual decay in the distribution system; evaluate nitrification potential in the distribution system under chloraminated conditions; evaluate effectiveness of engineering controls to minimize nitrification; and, evaluate DBPs associated with chloramines in the distribution system. A pipe-loop apparatus was constructed to simulate the City's distribution system, and tests were conducted to meet the objectives. In addition, some bench-scale simulated distribution system (SDS) testing was completed to compliment the results of the pilot-scale pipe-loops. Includes tables, figures.