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Succession of Biofilm Microbial Community during Nitrification in Lab-Scale Reactors Simulating Chloraminated Drinking Water Distribution System Conditions: the Impact of Simultaneously Increasing Monochloramine and Chlorine to Nitrogen Mass Ratios
Citation:
Gomez-Alvarez, V., K. Kleier, J. Pressman, AND D. Wahman. Succession of Biofilm Microbial Community during Nitrification in Lab-Scale Reactors Simulating Chloraminated Drinking Water Distribution System Conditions: the Impact of Simultaneously Increasing Monochloramine and Chlorine to Nitrogen Mass Ratios. Presented at American Society for Microbiology, Denver, CO, May 18 - 21, 2013.
Impact/Purpose:
To present this information and results with the scientific community.
Description:
Chloramination has been shown to promote nitrifying bacteria and 30 to 63% of utility plants using secondary chloramine disinfection experience nitrification episodes. Although nitrifying bacteria are not considered human pathogens, nitrification can affect drinking water quality. In this study, two lab-scale annular reactors (ARs) were used to evaluate the impact of increasing monochloramine (NH2Cl) concentrations (0.0 to 3.2 mg Cl2 L-1) and chlorine to nitrogen mass ratios (0:1 to 3.2:1) on biofilm. Biofilm samples (n=15) were collected over 920 days from four periods (I – IV) defined by measured chemical parameters. We analyzed the 16S rRNA-encoding gene sequences (454-pyrosequencing) from biofilm extracts to examine the viable (propidium monoazide [PMA] treated) and total (untreated) microbial community present in the ARs. Total and viable 16S gene sequence samples paralleled each other, indicating that total samples provided a representation of the underlying viable community. Approximately 65% of the total diversity was associated with the phylum Proteobacteria with minor contributions (<11%) from 10 phyla. A significant difference was observed between the community structures in each period, suggesting changes based on AR operation. Early stages of biofilm formation (Periods I & II; complete nitrification and minimal NH2Cl residual [<0.05 mg Cl2 L-1]) were dominated by Bradyrhizobium (38%), while environmental Legionella-like phylotypes peaked during Period II (19%). Nitrifying bacteria closely related to Nitrospira moscoviensis (2%) were detected in Periods I & II but decreased to <0.02% in later periods. Methylobacterium (19%) and members of the family Nitrosomonadaceae (42%) dominated Period III (complete ammonia oxidation, partial nitrite oxidation, and low NH2Cl residual [≈ 0.4 mg Cl2 L-1]). There was a striking increase in the relative abundance of haloacetic acid-degrading bacteria Afipia (from <2% to 42%) during Period IV (minimal nitrification and moderate to high NH2Cl residual [1.5 - 3.0 mg Cl2 L-1]). These results provide an ecological insight into biofilm succession and potential ability to biodegrade DBPs in monochloramine-treated drinking water. This study will enable more effective management in these engineered systems and subsequently help to safeguard human health.