Investigation of the microbiomes in two full-scale drinking water distribution systems
2018-08
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Investigation of the microbiomes in two full-scale drinking water distribution systems
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2018-08
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The drinking water distribution system (DWDS) microbiome can impact public health as well as distribution infrastructure. Though the majority of bacterial biomass in the DWDS is associated with biofilms on the walls of water mains and other surfaces, there is a lack of understanding about the biofilms due to the challenges of accessing them. Using culture-independent methods targeting marker genes, including real-time quantitative polymerase chain reaction (qPCR) and high-throughput sequencing of PCR amplicons, the microbiomes of two full-scale systems were investigated—a DWDS in the United States that maintains a chloramine residual and another in Norway that intentionally has very low or no residual disinfectant in the distributed water. This work demonstrates that residual chloramine is a fundamental factor affecting the microbiome in a chloraminated DWDS. Not all changes to the microbiome due to chloramine, however, may be desirable. Namely, non-tuberculous mycobacteria (NTM) and ammonia-oxidizing bacteria (AOB) in water-main biofilms benefit from residual chloramine, and both of these taxa pose possible concerns to water utilities and their consumers: NTM include some opportunistic pathogens (especially Mycobacterium avium complex, or MAC), and AOB may contribute to biologically accelerated chloramine decay. Still, chloramine appeared to generally work as desired. Biofilm biomass was significantly lower in the chloraminated DWDS, despite ostensibly more favorable conditions for bacterial growth, and most taxa in the bulk drinking water were not observed in the biofilms. Legionellae, which may include some opportunistic pathogens, were significantly reduced from the biofilms of the chloraminated DWDS, and no MAC were detected in either system. Characterization of the NTM indicated nearly all in the chloraminated DWDS were Mycobacterium gordonae-like species, while various phylogenetically-different species of novel NTM were present in the no-residual DWDS. Chloramine-derived ammonia also appeared to support an AOB community in the chloraminated DWDS comprised primarily of Nitrosomonas oligotropha-like taxa. Abiotic reaction of nitrite with the chloramine likely hinders complete biotic nitrification; nitrite-oxidizing bacteria (NOB) are denied available nitrite. Conversely, AOB, NOB, and ammonia-oxidizing archaea were all present in the no-residual DWDS despite little or no ammonia in the drinking water. Finally, corrosion-associated bacteria like Desulfovibrio spp. were common underneath corrosion tubercles in both systems. Microbiological activity may therefore contribute to corrosion of cast-iron water mains, regardless of whether a disinfectant residual is maintained in the bulk drinking water. This work provides novel evidence that residual chloramine alters the DWDS microbiome by reducing total biomass and diversity of water-main —though the remaining taxa may still pose management challenges. Future work will need to expand this type of research to other systems before general applicability to other systems can be assumed.
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University of Minnesota Ph.D. dissertation. August 2018. Major: Civil Engineering. Advisors: Raymond Hozalski, Timothy LaPara. 1 computer file (PDF); xi, 146 pages.
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Waak, Michael. (2018). Investigation of the microbiomes in two full-scale drinking water distribution systems. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/216810.
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