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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. In Proceedings, 2010 AWWA Water Quality and Technology Conference, Savannah, GA, November 14 - 18, 2010. American Water Works Association, Denver, CO, ,, (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). Based on utility surveys, 30 to 63% of utilities practicing chloramination for secondary disinfection experience nitrification episodes. 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. Based on the results of this research, we expect to gain a better understanding of the disinfection kinetics of monochloramine with AOB in chloraminated drinking water distribution systems, allowing better prevention and control of nitrification episodes in practice. Previous research has shown that water quality and ionic environment impact disinfection kinetics. As a first step in exploring possible media 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 buffer medias (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 medias 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 effects as monochloramine decomposition is general acid catalyzed and various phosphate buffers are commonly used in disinfection experiments. Overall, changing from relatively high (120-150 meq/liter) to relatively 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 closer 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 these 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.
