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The Impact of Monochloramine on Ammonia-Oxidizing Bacteria in Lab-Scale Annular Reactors - abstract
Citation:
SCHRANTZ, K. A., D. WAHMAN, J. G. PRESSMAN, AND D. B. Oerther. The Impact of Monochloramine on Ammonia-Oxidizing Bacteria in Lab-Scale Annular Reactors - abstract. Presented at American Society for Microbiology, San Francisco, CA, June 16 - 19, 2012.
Impact/Purpose:
To inform the public.
Description:
Drinking water utilities use free chlorine or monochloramine (NH2Cl) as secondary disinfectants, which react with natural organic matter to form disinfection by-products (DBP). To reduce DBP concentrations and comply with the USEPA Stage 1 & 2 Disinfectant and DBP rules, some utilities have or are considering a switch from free chlorine to NH2Cl for secondary disinfection. However, ammonia (NH3) added to form NH2Cl may lead to nitrification and subsequent disinfectant residual loss. To better understand distribution system (DS) nitrification, the current research simulated long-term (2.5 years) chloraminated DS operation using two lab-scale annular reactors fed dechlorinated tap water supplemented with increasing temporal influent NH2Cl concentrations (0.0 to 3.2 mg Cl2/L) and Cl2:N mass ratios (0:1 to 3.2:1). Reactor performance was chemically monitored [pH, temperature, dissolved oxygen, NH3, nitrite, nitrate, NH2Cl, and trihalomethanes (THMs)] to allow evaluation of the nitrification index (NI) that accounts for the balance between ammonia-oxidizing bacteria (AOB) growth and inactivation. In addition, the AOB community was characterized for each influent NH2Cl concentration using AOB targeted (amoA gene) cloning and sequence analysis on (1) propidium monoazide treated (viable) and (2) untreated total (viable and non-viable) samples. In practice, increasing NH2Cl is usually ineffective to stop active nitrification, but in this study, nitrification was halted when the influent NH2Cl concentration reached 3.2 mg Cl2/L. The calibrated NI was successful in predicting this occurrence and indicated AOB inactivation was mainly due to THM cometabolism and NH2Cl disinfection. The current sequencing results indicated that (1) viable AOB were detected with 0 to 2.7 mg Cl2/L influent NH2Cl, (2) viable and total samples detected Nitrosomonas europaea and N. oligotropha related AOB and (3) N. oligotropha became the dominant viable AOB as NH2Cl increased. Previous chloraminated DS sequencing has shown N. oligotropha dominance, but no viability assessment was conducted. Overall, this study supported N. oligotropha’s importance and NI’s ability to predict nitrification.
