The bacteriological composition of biomass recovered by flushing an operational drinking water distribution system

Abstract

This study investigates the influence of pipe characteristics on the bacteriological composition of material mobilised from a drinking water distribution system (DWDS) and the impact of biofilm removal on water quality. Hydrants in a single UK Distribution Management Area (DMA) with both polyethylene and cast iron pipe sections were subjected to incremental increases in flow to mobilise material from the pipe walls. Turbidity was monitored during these operations and water samples were collected for physico-chemical and bacteriological analysis. DNA was extracted from the material mobilised into the bulk water before and during flushing. Bacterial tag-encoded 454 pyrosequencing was then used to characterize the bacterial communities present in this material. Turbidity values were high in the samples from cast iron pipes. Iron, aluminium, manganese and phosphate concentrations were found to correlate to observed turbidity. The bacterial community composition of the material mobilised from the pipes was significantly different between plastic and cast iron pipe sections (p < 0.5). High relative abundances of Alphaproteobacteria (23.3%), Clostridia (10.3%) and Actinobacteria (10.3%) were detected in the material removed from plastic pipes. Sequences related to Alphaproteobacteria (22.8%), Bacilli (16.6%), and Gammaproteobacteria (1.4%) were predominant in the samples obtained from cast iron pipes. The highest species richness and diversity were found in the samples from material mobilised from plastic pipes. Spirochaeta spp., Methylobacterium spp. Clostridium spp. and Desulfobacterium spp., were the most represented genera in the material obtained prior to and during the flushing of the plastic pipes. In cast iron pipes a high relative abundance of bacteria able to utilise different iron and manganese compounds were found such as Lysinibacillus spp., Geobacillus spp. and Magnetobacterium spp.

A Keystone Methylobacterium Strain in Biofilm Formation in Drinking Water

“…Thus, a relative abundance of a strain at 1% is considered to be a low abundance in a mixed population. Also, Methylobacterium species have been found to be present in drinking water in the United Kingdom [46,47] but they have not been found to be abundant in Glasgow tap water [40]. Here, only the case in which Methylobacterium was inoculated at the lowest relative abundance of 1% is reported.…”

Biological Instability in a Chlorinated Drinking Water Distribution Network

“…According to Antoun and co-workers [40] low-veocity flushing (below 0.3 m s −1 ) does not cause any scouring actions. However, it should be considered that part of the samples, especially during the first minutes of the flushing, can cointain biofilm bacteria detatched in a result of pre-flushing [35].…”

“…For example, increased water temperature can accelerate chlorine decay and favor bacteria growth [19], [31], while changes in hydraulic conditions can alter nutrient supply for microorganisms in biofilms and/or bacteria detachment from the pipe surfaces [32], [33]. Finally, the quality of materials in contact with drinking water, as well as the presence of sediments and loose deposits, can both affect the general microbial quality of the water [6], [34], [35].…”

Distribution System Water Quality Affects Responses of Opportunistic Pathogen Gene Markers in Household Water Heaters

“…52 Iron pipes were also able to select for a variety of bacteria capable of utilizing different iron and manganese constituents, such as Lysinibacillus spp., Geobacillus spp., and Magnetobacterium spp., which, incidentally, were not identified in the present study. 49 Decreased pipe material effects with time might be associated with temporal variation of influent waters from SDSs. For example, development of distinct microbial communities in chlorinated iron 3.6 days SWH samples relative to other iron SWH samples occurred together with a ∼1-log reduction of 16S rRNA genes during Stage 2.…”