Safe drinking water is delivered to the consumer through kilometres of pipes. These pipes are lined with biofilm, which is thought to affect water quality by releasing bacteria into the drinking water. This study describes the number of cells released from this biofilm, their cellular characteristics, and their identity as they shaped a drinking water microbiome. Installation of ultrafiltration (UF) at full scale in Varberg, Sweden reduced the total cell count to 1.5 × 10 3 ± 0.5 × 10 3 cells mL −1 in water leaving the treatment plant. This removed a limitation of both flow cytometry and 16S rRNA amplicon sequencing, which have difficulties in resolving small changes against a high background cell count. Following installation, 58% of the bacteria in the distributed water originated from the pipe biofilm, in contrast to before, when 99.5% of the cells originated from the treatment plant, showing that UF shifts the origin of the drinking water microbiome. The number of bacteria released from the biofilm into the distributed water was 2.1 × 10 3 ± 1.3 × 10 3 cells mL −1 and the percentage of HNA (high nucleic acid) content bacteria and intact cells increased as it moved through the distribution system. DESeq2 analysis of 16S rRNA amplicon reads showed increases in 29 operational taxonomic units (OTUs), including genera identified as Sphingomonas , Nitrospira , Mycobacterium , and Hyphomicrobium . This study demonstrated that, due to the installation of UF, the bacteria entering a drinking water microbiome from a pipe biofilm could be both quantitated and described.
Water in a full-scale drinking water treatment plant was irradiated with ultraviolet (UV) doses of 250, 400, and 600 J/m 2 , and the effect on bacterial communities investigated using 16s rRNA gene amplicon sequencing, heterotrophic plate counts (HPCs), coliform, and Escherichia coli counts. The bacteria in the irradiated water were also analyzed following storage for 6 days at 7°C, to approximate the conditions in the distribution system. The log 10 reduction of HPCs at 400 J/m 2 was 0.43 ± 0.12. Phylogenetic examination, including DESeq2 analysis, showed that Actinobacteria was more resistant to UV irradiation, whereas Bacteroidetes was sensitive to UV. Phylum Proteobacteria contained monophyletic groups that were either sensitive or resistant to UV exposure. The amplicon sequence variants (ASVs) resistant to UV irradiation had a greater average GC content than the ASVs sensitive to UV, at 55% ± 1.7 (n = 19) and 49% ± 2.5 (n = 16), respectively. Families Chitinophagaceae, Pelagibacteraceae, Holophagaceae, Methylophilaceae, and Cytophagaceae decreased linearly in relative abundance, with increasing UV dose (P < 0.05, Pearson's correlation). When irradiated water was stored, Chitinophagaceae, Comamonadaceae, and Flavobacteriaceae families decreased in relative abundance, whereas ACK-M1, Mycobacteriaceae, and Nitrosomonadaceae were increasing in relative abundance. This suggests that the impact of UV irradiation cannot only be considered directly after application but that this treatment step likely continues to influence microbial dynamics throughout the distribution system.npj Clean Water (2020) 3:11 ; https://doi.
While slow sand filters (SSFs) have produced drinking water for more than a hundred years, understanding of their associated microbial communities is limited. In this study, bacteria in influent and effluent water from full-scale SSFs were explored using flow cytometry (FCM) with cytometric histogram image comparison (CHIC) analysis; and routine microbial counts for heterotrophs, total coliforms and Escherichia coli. To assess if FCM can monitor biofilm function, SSFs differing in age and sand composition were compared. FCM profiles from two established filters were indistinguishable. To examine biofilm in the deep sand bed, SSFs were monitored during a scraping event, when the top layer of sand and the schmutzdecke are removed to restore flow through the filter. The performance of an established SSF was stable: total organic carbon (TOC), pH, numbers of heterotrophs, coliforms, E. coli, and FCM bacterial profile were unaffected by scraping. However, the performance of two newly-built SSFs containing new and mixed sand was compromised: breakthrough of both microbial indicators and TOC occurred following scraping. The compromised performance of the new SSFs was reflected in distinct effluent bacterial communities; and, the presence of microbial indicators correlated to influent bacterial communities. This demonstrated that FCM can monitor SSF performance. Removal of the top layer of sand did not alter the effluent water from the established SSF, but did affect that of the SSFs containing new sand. This suggests that the impact of the surface biofilm on effluent water is greater when the deep sand bed biofilm is not established.
Microbial monitoring of drinking water is required to guarantee high quality water and to mitigate health hazards. Flow cytometry (FCM) is a fast and robust method that determines bacterial concentrations in liquids. In this study, FCM was applied to monitor the dynamics of the bacterial communities over one year in a full-scale drinking water distribution system (DWDS), following implementation of ultrafiltration (UF) combined with coagulation at the drinking water treatment plant (DWTP). Correlations between the environmental conditions in the DWDS and microbial regrowth were observed, including increases in total cell counts with increasing retention time (correlation coefficient R = 0.89) and increasing water temperature (up to 5.24-fold increase in cell counts during summer). Temporal and spatial biofilm dynamics affecting the water within the DWDS were also observed, such as changes in the percentage of high nucleic acid bacteria with increasing retention time (correlation coefficient R = −0.79). FCM baselines were defined for specific areas in the DWDS to support future management strategies in this DWDS, including a gradual reduction of chloramine.
Monochloramine is used to regulate microbial regrowth in drinking water distribution systems (DWDS) but produces carcinogenic disinfection byproducts and constitutes a source of energy for nitrifying bacteria. This study followed biofilm-dispersed microbial communities of a full-scale DWDS distributing ultrafiltered water over three years, before and after removal of monochloramine. Communities were described using flow cytometry and amplicon sequencing, including full-length 16S rRNA gene sequencing. Removal of monochloramine increased total cell counts by up to 440%. Increased abundance of heterotrophic bacteria was followed by emergence of the predatory bacteria Bdellovibrio, and a community potentially metabolizing small organic compounds replaced the nitrifying core community. No increased abundance of Mycobacterium or Legionella was observed. Co-occurrence analysis identified a network of Nitrosomonas, Nitrospira, Sphingomonas and Hyphomicrobium, suggesting that monochloramine supported this biofilm community. While some species expanded into the changed niche, no immediate biological risk to consumers was indicated within the DWDS.
While pipe biofilms in DWDSs (drinking water distribution systems) are thought to affect the quality of distributed water, studies regarding the microbial processes are impeded by the difficulties in accessing...
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