Abstract
AimsTo characterize bacterial communities during the early stages of biofilm formation and their role in water discolouration in a fully representative, chlorinated, experimental drinking water distribution systems (DWDS).Methods and ResultsBiofilm development was monitored in an experimental DWDS over 28 days; subsequently the system was disturbed by raising hydraulic conditions to simulate pipe burst, cleaning or other system conditions. Biofilm cell cover was monitored by fluorescent microscopy and a fingerprinting technique used to assess changes in bacterial community. Selected samples were analysed by cloning and sequencing of the 16S rRNA gene. Fingerprinting analysis revealed significant changes in the bacterial community structure over time (P < 0·05). Cell coverage increased over time accompanied by an increase in bacterial richness and diversity.ConclusionsShifts in the bacterial community structure were observed along with an increase in cell coverage, bacterial richness and diversity. Species related to Pseudomonas spp. and Janthinobacterium spp. dominated the process of initial attachment. Based on fingerprinting results, the hydraulic regimes did not affect the bacteriological composition of biofilms, but they did influence their mechanical stability.Significance and Importance of the StudyThis study gives a better insight into the early stages of biofilm formation in DWDS and will contribute to the improvement of management strategies to control the formation of biofilms and the risk of discolouration.
Highlights
It is commonly accepted that the use of a disinfectant residual such as chlorine in drinking water distribution systems (DWDS) does not completely prevent bacterial occurrence
We explore who are the primary colonizers of a chlorinated distribution system, which bacteria are able to leave the bulk water and adhere to the pipe surfaces, how they are changing in their first month of biofilm formation and whether different hydraulic regimes affected their ability for initial adherence and the physical structure of the biofilm itself
The system has a total volume of 4Á5 m3 and consists of three 200-m-long high-density polyethylene (HDPE) recirculating loops, fed by a common pump and returning to a common closed reservoir
Summary
It is commonly accepted that the use of a disinfectant residual such as chlorine in drinking water distribution systems (DWDS) does not completely prevent bacterial occurrence. Free-living bacteria can enter the distribution system through, for example, the treatment works, crossconnections or contamination ingress and can adhere to the pipe inner surfaces and form biofilms (Szewzyk et al 2000). The process of biofilm formation on surfaces can be relatively fast even in chlorinated networks. Morvay et al (2011) reported that biofilm formation on different plumbing material in chlorinated drinking water systems reaches values of 107 cells cmÀ2 after only 30 days. Biofilms are structurally complex and consist of microorganisms attached to a surface and to each other and embedded in an extracellular polymeric matrix (EPS) made of polysaccharides, proteins, extracellular DNA, etc.
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