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The Impact of Monochloramine on Ammonia-Oxidizing Bacteria in Lab-Scale Annular Reactors - Poster
Citation:
WULFECK-KLEIER, K. A., D. WAHMAN, J. G. PRESSMAN, AND D. B. Oerther. The Impact of Monochloramine on Ammonia-Oxidizing Bacteria in Lab-Scale Annular Reactors - Poster. Presented at American Society for Microbiology 110th General Meeting, San Diego, CA, May 23 - 27, 2010.
Impact/Purpose:
To inform the public.
Description:
Drinking water utilities typically use chlorine or monochloramine (NH2Cl) as secondary disinfectants. In general, disinfectants react with natural organic matter, producing disinfection by-products (DBP), which are a health concern. As a result, the stage 1 & 2 disinfectant and DBP rules limit DBP concentrations in finished drinking water. To reduce DBP concentrations for regulatory compliance, some utilities are considering the use of NH2Cl, instead of free chlorine, for secondary disinfection. However, ammonia (NH3) added to form NH2Cl may lead to biological nitrification episodes and subsequent disinfectant residual loss. To better understand distribution system (DS) nitrification, the current research simulated long-term DS conditions in annular reactors, investigating reactor performance and associated ammonia-oxidizing bacteria (AOB) community structure. Two DS source waters were seeded into separate annular reactors with polycarbonate slides. Reactors were operated 893 days on dechlorinated tap water supplemented with increasing NH2Cl concentrations (0.0 to 3.2 mg Cl2/L). Bulk water samples were monitored for pH, temperature, dissolved oxygen, NH3, nitrite (NO2), nitrate (NO3), and NH2Cl. AOB biofilm community structure was assessed by taking samples from polycarbonate slides and splitting each sample into two sub-samples: propidium monoazide (PMA) treated (live) and untreated (live and dead) before conducting AOB targeted (amoA gene) TA cloning and subsequent sequence analysis. Throughout the study, both reactors behaved similarly. As NH2Cl concentration increased, reactor performance progressed through three phases: 1) NH2Cl loss and NH3 oxidized to NO3, 2) NH2Cl loss and NH3 oxidized to NO2 and partially to NO3, and 3) stable NH2Cl and no oxidation of NH3 to NO2/NO3. During the first two phases, the dominant AOB present were Nitrosomonas oligotropha and N. europaea and at the third phase, AOB were becoming undetectable. Even with changes in reactor performance resulting from an increasing NH2Cl concentration, the dominant AOB present were N. oligotropha and N. europaea.
