Effects of Chloramine and Coupon Material on Biofilm Abundance and Community Composition in Bench-Scale Simulated Water Distribution Systems and Comparison with Full-Scale Water Mains.

The vast majority of bacteria in drinking water distribution systems (DWDSs) reside in biofilms on the interior walls of water mains. Little is known about how water quality conditions affect water-main biofilms because of the inherent limitations in experimenting with drinking water supplies and accessing the water mains for sampling. Bench-scale reactors permit experimentation and ease of biofilm sampling, yet questions remain as to how well biofilms in laboratory reactors represent those on water mains. In this study, the effects of DWDS pipe materials and chloramine residual on biofilms were investigated by cultivating biofilms on cement, polyvinyl chloride, and high density polyethylene coupons in CDC reactors for up to 28 months in the presence of chloraminated or dechlorinated tap water. The bench-scale biofilm microbiomes were then compared with the microbiome on a water main from the full-scale system that supplied the water to the reactors. The presence of a chloramine residual (1.74 ± 0.21 mg/L) suppressed biofilm accumulation and selected for Mycobacterium-like and Sphingopyxis-like operational taxonomic units (OTUs) while the destruction of the chloramine residual resulted in a significant increase in biomass quantity and a shift toward a more diverse community dominated by Nitrospira-like OTUs, which, our results suggest, may be complete ammonia oxidizers (comammox). Coupon material, however, had a relatively minor effect on the abundance and community composition of the biofilm bacteria. Although biofilm communities from the chloraminated water reactor and the water mains shared some dominant populations (namely, Mycobacterium- and Nitrosomonas-like OTUs), the communities were significantly different. This manuscript provides novel insights into the effects of dechlorination and pipe material on biofilm community composition. Furthermore, to our knowledge, it is the first study to compare biofilm in a tap water-fed, bench-scale simulated distribution system to biofilm on water mains from the full-scale system supplying the tap water.

Sulfate Reducing Bacteria and Mycobacteria Dominate the Biofilm Communities in a Chloraminated Drinking Water Distribution System.

The quantity and composition of bacterial biofilms growing on 10 water mains from a full-scale chloraminated water distribution system were analyzed using real-time PCR targeting the 16S rRNA gene and next-generation, high-throughput Illumina sequencing. Water mains with corrosion tubercles supported the greatest amount of bacterial biomass (n = 25; geometric mean = 2.5 × 10(7) copies cm(-2)), which was significantly higher (P = 0.04) than cement-lined cast-iron mains (n = 6; geometric mean = 2.0 × 10(6) copies cm(-2)). Despite spatial variation of community composition and bacterial abundance in water main biofilms, the communities on the interior main surfaces were surprisingly similar, containing a core group of operational taxonomic units (OTUs) assigned to only 17 different genera. Bacteria from the genus Mycobacterium dominated all communities at the main wall-bulk water interface (25-78% of the community), regardless of main age, estimated water age, main material, and the presence of corrosion products. Further sequencing of the mycobacterial heat shock protein gene (hsp65) provided species-level taxonomic resolution of mycobacteria. The two dominant Mycobacteria present, M. frederiksbergense (arithmetic mean = 85.7% of hsp65 sequences) and M. aurum (arithmetic mean = 6.5% of hsp65 sequences), are generally considered to be nonpathogenic. Two opportunistic pathogens, however, were detected at low numbers: M. hemophilum (arithmetic mean = 1.5% of hsp65 sequences) and M. abscessus (arithmetic mean = 0.006% of hsp65 sequences). Sulfate-reducing bacteria from the genus Desulfovibrio, which have been implicated in microbially influenced corrosion, dominated all communities located underneath corrosion tubercules (arithmetic mean = 67.5% of the community). This research provides novel insights into the quantity and composition of biofilms in full-scale drinking water distribution systems, which is critical for assessing the risks to public health and to the water supply infrastructure.