Abstract
Biofilm formation, loose deposit accumulation and water quality deterioration in drinking water distribution systems have been widely reported. However, the accumulation and distribution of harbored elements and microbes in the different niches (loose deposits, PVC-U biofilm, and HDPE biofilm) and their corresponding potential contribution to water quality deterioration remain unknown. This precludes an in-depth understanding of water quality deterioration and the development of proactive management strategies. The present study quantitatively evaluated the distribution of elements, ATP, Aeromonas spp., and bacterial communities in distribution pipes (PVC-U, D = 110 mm, loose deposit and biofilm niches) and household connection pipes (HDPE, D = 32 mm, HDPE biofilm niches) at ten locations in an unchlorinated distribution system. The results show that loose deposits in PVC-U pipes, acting as sinks, constitute a hotspot (highest total amount per meter pipe) for elements, ATP, and target bacteria groups (e.g., Aeromonas spp., Mycobacterium spp., and Legionella spp.). When drinking water distribution system niches with harbored elements and microbes become sources in the event of disturbances, the highest quality deterioration potential (QDP) is that of HDPE biofilm; this can be attributed to its high surface-to-volume ratio. 16s rRNA analysis demonstrates that, at the genus level, the bacterial communities in the water, loose deposits, PVC-U biofilm, and HDPE biofilm were dominated, respectively, by Polaromonas spp. (2–23%), Nitrosipra spp. (1–47%), Flavobacterium spp. (1–36%), and Flavobacterium spp. (5–67%). The combined results of elemental composition and bacterial community analyses indicate that different dominant bio-chemical processes might occur within the different niches—for example, iron-arsenic oxidizing in loose deposits, bio-calumniation in PVC-U biofilm, and methane oxidizing in HDPE biofilm. The release of 20% loose deposits, 20% PVC-U biofilm and 10% HDPE biofilm will cause significant changes of water bacterial community.
Highlights
The deterioration of the quality of water during its transport through a drinking water distribution system (DWDS) has been widely observed in the form of increased particle load (Liu et al, 2016), heterotrophic plate counts (HPC), and Aeromonas plate counts; these are the traditional microbial indicators for regrowth at customers’ taps
The water-quality deterioration potential (QDP) is proposed as a parameter which describes the maximum risk that the accumulated components represent for the deterioration of the water quality
The detection of considerable amounts of elements and microbes in biofilms on both PVC-U and HDPE pipes corresponds with previous research on the biofilm matrix in DWDSs, which has been attributed to the extracellular polymeric substance (EPS) matrix produced by the microflora in the biofilm, where organics, inorganics, and cell aggregates can accumulate in (LeChevallier et al, 1987; Van Der Wende, Characklis et al, 1989; Costerton et al, 1995; Flemming and Wingender, 2010; Wang et al, 2012)
Summary
The deterioration of the quality of water during its transport through a drinking water distribution system (DWDS) has been widely observed in the form of increased particle load (Liu et al, 2016), heterotrophic plate counts (HPC), and Aeromonas plate counts; these are the traditional microbial indicators for regrowth (van der Wielen et al, 2016) at customers’ taps. A DWDS is a pressurized pipe network which delivers treated drinking water from a centralized treatment plant to the water meters at the consumers' buildings (Snoeyink et al, 2006) It is a complex system typically consisting of different kinds of pipe, including transportation pipes (which connect the treatment plant and reservoir with the supply areas, with a typical diameter of >200 mm); distribution pipes (the main pipes under the street, which distribute water within the supply area, with a typical diameter of 63e110 mm); and household connection pipes (which connect the distribution pipe networks to the water meters at the consumers' building, with a typical diameter of 25e32 mm). There are different niches present within a pipe section, e.g., pipe surfaces and loose deposits (Liu et al, 2014; Proctor and Hammes, 2015; Prest et al, 2016; van der Wielen and Lut, 2016)
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