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Free Chlorine and Monochloramine Application to Nitrifying Biofilm: Comparison of Biofilm Penetration, Activity, and Viability
Citation:
Lee, W., D. G. WAHMAN, P. L. Bishop, AND J. G. PRESSMAN. Free Chlorine and Monochloramine Application to Nitrifying Biofilm: Comparison of Biofilm Penetration, Activity, and Viability. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 45(4):1412-1419, (2011).
Impact/Purpose:
To inform the public.
Description:
Biofilm in drinking water systems is undesirable and effective biofilm control maintains public health. Free chlorine and monochloramine are commonly used as secondary drinking water disinfectants, but monochloramine is perceived to penetrate biofilm better than free chlorine. However, this hypothesis remains unconfirmed by direct biofilm monochloramine measurement. This study compared free chlorine and monochloramine biofilm penetration using microelectrodes and assessed the subsequent effect on biofilm activity and viability using dissolved oxygen (DO) microelectrodes and confocal laser scanning microscopy (CLSM) with LIVE/DEAD® BacLight™. For equivalent chlorine concentrations, monochloramine initially penetrated biofilm 170 times faster than free chlorine, and even after subsequent application to a monochloramine penetrated biofilm, free chlorine penetration was limited. DO profiles paralleled monochloramine profiles, providing evidence that either the biofilm was inactivated with monochloramine’s penetration or its persistence reduced available substrate (free ammonia). While this research clearly demonstrated monochloramine’s greater penetration, this penetration did not necessarily translate to immediate viability loss. Even though free chlorine’s penetration was limited compared to monochloramine, it more effectively (on a cell membrane integrity basis) inactivated microorganisms near the biofilm surface. Limited free chlorine penetration has implications when converting to free chlorine in full-scale chloraminated systems in response to nitrification episodes.
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FREE CHLORINE AND MONOCHLORAMINE APPLICATION TO NITRIFYING BIOFILM: COMPARISON OF BIOFILM PENETRATION, ACTIVITY, AND VIABILITY
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