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Media Effects on Nitrosomonas Europaea Monochloramine Disinfection Kinetics Using Propidium Monoazide Quantitative Real-time PCR
Citation:
WAHMAN, D., K. A. WULFECK-KLEIER, AND J. G. PRESSMAN. Media Effects on Nitrosomonas Europaea Monochloramine Disinfection Kinetics Using Propidium Monoazide Quantitative Real-time PCR . Presented at 2010 AWWA Water Quality and Technology Conference, Savannah, GA, November 14 - 18, 2010.
Impact/Purpose:
To inform the public.
Description:
Monochloramine use as a secondary disinfectant in the United States is predicted to increase to 57% of all surface and 7% of all ground water systems. With monochloramine addition, there is a risk of nitrification in the distribution system by ammonia-oxidizing bacteria (AOB). Nitrification in drinking water distribution systems is undesirable and may result in degradation of water quality and subsequent non-compliance with existing regulations. Thus, nitrification control is a major issue in practice and likely to become increasingly important as monochloramine use increases. Previous research has shown that water quality and ionic environment impact disinfection kinetics. Therefore, it was necessary to understand more fully the impact of conducting batch laboratory experiments in various media compositions versus typical distribution system waters. As a first step in exploring possible media composition effects on disinfection kinetics determined using two culture-independent methods, Live/Dead BacLight (LD) and propidium monoazide qPCR (PMA-qPCR), batch disinfection experiments were conducted with three different phosphate buffers (1, 10, and 50 mM Na2HPO4 (PB), pH 8.0) to supplement and compare with previous research that used 10 mM phosphate buffer saline (PBS; 10 mM Na2HPO4 and 130 mM NaCl, pH 8). The media compositions were chosen to cover typical drinking water ionic strengths (less than 12.5 meq/liter based on the Secondary Maximum Contaminant Level for total dissolved solids of 500 mg/liter and the Langelier correlation) and to evaluate phosphate concentration because monochloramine decomposition is general acid catalyzed and various strength phosphate buffers are commonly used in disinfection experiments. Overall, changing from relatively high (120-150 meq/liter) to low (2.8-27 meq/liter) ionic strength media led to an increase in disinfection kinetics while the effect of phosphate concentration was inconclusive. Depending on the media, delayed Chick-Watson kinetic parameters varied by a maximum factor of 13 (LD) and 5.4 (PMA-qPCR) for the lag coefficient (b) and 2.3 (LD) and 6.0 (PMA-qPCR) for the rate constant (k). As typical drinking water would represent lower ionic strength conditions, it is expected that results performed in drinking water will more closely approximate the lower ionic strength (1 and 10 mM PB) experiments. At these lower ionic strength conditions, both LD and PMA-qPCR methods resulted in similar, yet statistically different, kinetic parameters. The media choice for disinfection experiments should be considered another experimental parameter that needs resolution to find a drinking water representative media, and serve as a baseline for future experiments with finished drinking waters.
