Reproducible microbial community dynamics of two drinking water systems treating similar source waters

Abstract

26In addition to containing higher concentrations of organics and bacterial cells, 27 surface waters are often more vulnerable to pollution and microbial contamination 28 with intensive industrial and agricultural activities frequently occurring in areas 29 surrounding the water source. Therefore, surface waters typically require additional 30 treatment, where the choice of treatment strategy is critical for water quality. Using 31 16S rRNA gene profiling, this study provides a unique opportunity to simultaneously 32 investigate and compare two drinking water treatment plants and their 33 corresponding distribution systems. The two treatment plants treat similar surface 34 waters, from the same river system, with the same sequential treatment strategies. 35 Here, the impact of treatment and distribution on the microbial community within and 36 between each system was compared over an eight-month sampling campaign. 37 Overall, reproducible spatial and temporal dynamics within both DWTPs and their 38 corresponding DWDSs were observed. Although source waters showed some 39 dissimilarity in microbial community structure and composition, pre-disinfection 40 treatments (i.e. coagulation, flocculation, sedimentation and filtration) resulted in 41 highly similar microbial communities between the filter effluent samples. This 42 indicated that the same treatments resulted in the development of similar microbial 43 communities. Conversely, post-disinfection (i.e. chlorination and chloramination) 44 resulted in increased dissimilarity between disinfected samples from the two 45 systems, showing alternative responses of the microbial community to disinfection. 46 Lastly, it was observed that within the distribution system the same dominant taxa 47 were selected where samples increased in similarity with increased residence time. 48 Although, differences were found between the two systems, overall treatment and 49 distribution had a similar impact on the microbial community in each system. This 50 study therefore provides valuable information on the impact of treatment and 51 distribution on the drinking water microbiome. 52 53 Keywords: drinking water treatment; drinking water distribution; disinfection; 54 microbial community dynamics; Illumina MiSeq. 55 56 Highlights 57  Source waters show some dissimilarity in microbial community. 58  Treatment processes increases similarity and selects for the same dominant 59 taxa. 60  Differential response to chlorination causing increased dissimilarity and 61 variation. 62  Stabilisation of DWDS microbial community through selection of same 63 dominant taxa. 64  Microbial community dynamics are reproducible between the two systems. 65 66 Abbreviations 67 DWDS, drinking water distribution system; DWTP, drinking water treatment plant; 68 DADA2, Divisive Amplicon Denoising Algorithm; ASV, amplicon sequence variant; 69 AMOVA, analysis of molecular variance; MRA, mean relative abundance; PCoA, 70 Principal coordinate analysis; ANOVA, One-way analysis of varianc...

Microbiomes in drinking water treatment and distribution: a meta-analysis from source to tap

“…There are higher degrees of species richness and alpha diversity of taxa in the source waters that are reduced throughout treatment. This reduction is consistent with both the individual studies included in this analysis and several other pyrosequencing studies 23,31,52 . The reduction in LCBD from untreated to treated water samples supports the reduction in alpha diversity and richness.…”

“…It also suggests that although filtration is important in defining taxa in DWDS, chlorine has a more strongly selective effect. This hypothesis supports a study comparing two identical treatment systems treating the same source water, where chlorine and chloramine produced different bacterial communities 23 . Biofilms in water treatment works also had higher NST values, indicating a higher degree of determinism.…”

“…The majority of 16S rRNA amplicon sequencing studies have focused on microbial communities within DWDS, in both biofilm and bulk water. These indicate that the microbial communities within DWDS are unique to that system, influenced by the source and treatment characteristics outlined above 23,24 . DWDS microbial communities have significant temporal fluctuation 25,27 , with potential diurnal cycles in bulk-water, potentially due to flow patterns 28 .…”

“…Most 16S rRNA studies are discrete, across a single or few DWDS within a geographical area. They also tend to focus on one part of a system, e.g., source waters; efficacy of treatment processes; variations of biofilm communities in space, time, or operating conditions within a pipe distribution network; influences of domestic plumbing arrangements, or differences between the bulk water and biofilm communities (Ahmed et al, 2015;Chan et al, 2019;De Vera et al, 2018;Douterelo et al, 2019Douterelo et al, , 2017Fish and Boxall, 2018;Gerrity et al, 2018;Ghaju Shrestha et al, 2017;Gülay et al, 2016;Han et al, 2020;Hou et al, 2018;Lautenschlager et al, 2014;Liu et al, 2017b;Lührig et al, 2015;McCoy and VanBriesen, 2012;Potgieter et al, 2018;Potgieter and Pinto, 2019;Prest et al, 2014;Shaw et al, 2015;Uyaguari-Diaz et al, 2019;Vierheilig et al, 2015;Vignola et al, 2018;Wan et al, 2019;Wang et al, 2014Wang et al, , 2013Wolf-Baca and Piekarska, 2020;Wu et al, 2014;Zhu et al, 2019). While several of these studies have provided new insight into drinking water microbiomes, they tend to be descriptive and not predictive.…”

Online characterization of bacterial processes in drinking water systems

“…Bacterial growth in drinking water distribution systems (DWDSs) can lead to failure in meeting water quality guidelines, deterioration of the aesthetics of the water, and might be linked with an increased risk of diseases 1 . The microbial water quality in DWDSs can deteriorate if a suitable growth environment exists 2 . An increase in bacterial cell number or the amount of active biomass in water is caused by the degradation of biodegradable nutrients originally present in the water leaving the treatment plant and/or nutrients leaching from materials in contact with water such as pipes and reservoirs in the distribution network 3 .…”