Abstract
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 × 103 ± 0.5 × 103 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 × 103 ± 1.3 × 103 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.
Highlights
Drinking water is delivered to the consumer through kilometres of pipes and maintenance of water quality in these drinking water distribution systems (DWDSs) is a prime concern for drinking water providers
The permeate had a total cell concentration (TCC) below the quantification limit, at around 200 cells mL−1,16 and this was reflected by the instantaneous reduction in TCC at all distribution points (DP), and time points sampled after UF installation (Fig. 2)
This TCC in the distributed water included bacteria released from pipe biofilm and those added during the pH adjustment
Summary
Drinking water is delivered to the consumer through kilometres of pipes and maintenance of water quality in these drinking water distribution systems (DWDSs) is a prime concern for drinking water providers. Bacteria in loose deposits and pipe biofilm were estimated to contain >98% of the bacteria in a DWDS7 and release of these cells can alter the bulk water.[8] This must always be occurring to some extent,[9] most studies have focussed on large changes due to season, water pressure or flow in the microbial communities in the biofilm or distributed water.[10,11,12]
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