AWWA WQTC69432

Microbial communities associated with the problem of bacterial regrowth in chloraminated drinking water distribution systems (DS) have two main components: the autotrophic nitrifiers growing on ammonia released from chloramine decay; and, the heterotrophs relying on biodegradable organic material. While nitrifying populations have been extensively studied, microbial ecological knowledge on heterotrophic populations is limited even though some studies have indicated that heterotrophs may be the dominant component, or could even initiate regrowth in DS. The types of heterotrophic organisms inhabiting chloraminated DS can potentially influence disinfection strategies. The objectives of this study were to: identify heterotrophic bacteria in pilot- and full-scale DS using culture-independent methods; and, comparatively evaluate heterotrophic communities to understand if pilot-scale adequately represents the real scale. Monthly samples were obtained from two parallel pilot-scale DS with high and low chloramine dose, and three full-scale systems at a geographically different location, which included finished water and two separate tanks in downstream DS. Two additional pilot systems were run for a shorter period and sampled for the observation of early community development. Organisms in DS samples were identified based on their 16S rRNA sequences and community fingerprints were generated using automated ribosomal intergenic spacer analysis (ARISA). Most of the retrieved 16S rRNA sequences (>95%) were related to heterotrophic bacteria. Both phylogenetic analyses and community fingerprints showed that the heterotrophic communities in pilot- and full-scale were significantly different. However, a significant number of sequences common to all systems excluding finished water indicated organisms that are well-adapted to chloraminated environments. These included bacteria from the Sphingomonadales order, Mycobacterium and Curvibacter genera, and an uncultured lineage of Rhizobiales. In addition, there were full-scale distribution system sequences, previously not reported in other environments related to drinking water. In conclusion, pilot-scale DS are useful for investigating certain subpopulations of microbiota in chloraminated distribution systems, but are not perfect models that can simulate the overall microbial dynamics in the full-scale. Culture-based methods are needed to determine the potential environmental roles of the chloraminated distribution system organisms discovered in this work using molecular techniques. Includes 32 references, tables, figures.