Bacterial community dynamics during the early stages of biofilm formation in a chlorinated experimental drinking water distribution system: implications for drinking water discolouration

Aims : To 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 Results : Biofilm 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. Conclusions : Shifts 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 Study : This 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

Influence of hydraulic regimes on bacterial community structure and composition in an experimental drinking water distribution system

Microbial biofilms formed on the inner-pipe surfaces of drinking water distribution systems (DWDS) can alter drinking water quality, particularly if they are mechanically detached from the pipe wall to the bulk water, such as due to changes in hydraulic conditions. Results are presented here from applying 454 pyrosequencing of the 16S ribosomal RNA (rRNA) gene to investigate the influence of different hydrological regimes on bacterial community structure and to study the potential mobilisation of material from the pipe walls to the network using a full scale, temperature-controlled experimental pipeline facility accurately representative of live DWDS. Analysis of pyrosequencing and water physico-chemical data showed that habitat type (water vs. biofilm) and hydraulic conditions influenced bacterial community structure and composition in our experimental DWDS. Bacterial community composition clearly differed between biofilms and bulk water samples. Gammaproteobacteria and Betaproteobacteria were the most abundant phyla in biofilms while Alphaproteobacteria was predominant in bulk water samples. This suggests that bacteria inhabiting biofilms, predominantly species belonging to genera Pseudomonas, Zooglea and Janthinobacterium, have an enhanced ability to express extracellular polymeric substances to adhere to surfaces and to favour co-aggregation between cells than those found in the bulk water. Highest species richness and diversity were detected in 28 days old biofilms with this being accentuated at highly varied flow conditions. Flushing altered the pipe-wall bacterial community structure but did not completely remove bacteria from the pipe walls, particularly under highly varied flow conditions, suggesting that under these conditions more compact biofilms were generated. This research brings new knowledge regarding the influence of different hydraulic regimes on the composition and structure of bacterial communities within DWDS and the implication that this might have on drinking water quality

Succession of bacterial and fungal communities within biofilms of a chlorinated drinking water distribution system

Understanding the temporal dynamics of multi-species biofilms in Drinking Water Distribution Systems (DWDS) is essential to ensure safe, high quality water reaches consumers after it passes through these high surface area reactors. This research studied the succession characteristics of fungal and bacterial communities un der controlled environmental conditions fully representative of operational DWDS. Microbial communities were observed to increase in complexity after one month of biofilm development but they did not reach stability after three months. Changes in cell numbers were faster at the start of biofilm formation and tended to decrease over time, despite the continuing changes in bacterial community composition. Fungal diversity was markedly less than bacterial diversity and had a lag in responding to temporal dynamics. A core-mixed community of bacteria including Pseudomonas, Massillia and Sphingomonas and the fungi Acremonium and Neocosmopora were present constantly and consistently in the biofilms over time and conditions studied. Monitoring and managing biofilms and such ubiquitous core microbial communities are key control strategies to ensuring the delivery of safe drinking water via the current ageing DWDS infrastructure

Investigating the microbiological risks associated with urban flooding in the UK

Over the last 30 years, the frequency and occurrence of intense rainfall, and thus extreme hydrological events –flooding- has steadily increased. Drainage infrastructure in the UK was not designed for a changing climate, and many sewer systems in densely populated urban areas, are unable to cope. Sewage overflow and surface run off in urban areas can act as vectors for the dissemination of pathogens, known to cause disease among human populations. Most of the previous studies in this field have focused on using faecal indicators such as E.coli when assessing the public health risk of floodwater [1]. However, traditional indicators do not accurately reflect the true risk that urban flooding poses [2]. Little is understood in regards to the survivability and behaviour of pathogens in different urban settings, which are fundamental to determine potential risks to public health. Previous investigations in UK waterlogged soils have shown a clear response of microbial communities to water table variation, temperature, and nutrient availability in soil profiles [3]. This research aims to investigate, using advanced molecular methods, the dynamics of pathogens (i.e. movement through soil and survival rates), and microbial interactions at the soil/water interface- collecting information from field work studies and laboratory-controlled experiments. The outcomes from this research will inform future management strategies of flooded sites that will aid to protect public health

Impact of phosphate dosing on the microbial ecology of drinking water distribution systems: fieldwork studies in chlorinated networks

Phosphate is routinely dosed to ensure regulatory compliance for lead in drinking water distribution systems. Little is known about the impact of the phosphate dose on the microbial ecology in these systems and in particular the endemic biofilms. Disturbance of the biofilms and embedded material in distribution can cause regulatory failures for turbidity and metals. To investigate the impact of phosphate on developing biofilms, pipe wall material from four independent pipe sections was mobilised and collected using two twin-flushing operations a year apart in a chlorinated UK network pre- and post-phosphate dosing. Intensive monitoring was undertaken, including turbidity and water physico-chemistry, traditional microbial culture-based indicators, and microbial community structure via sequencing the 16S rRNA gene for bacteria and the ITS2 gene for fungi. Whole metagenome sequencing was used to study shifts in functional characteristics following the addition of phosphate. As an operational consequence, turbidity responses from the phosphate-enriched water were increased, particularly from cast iron pipes. Differences in the taxonomic composition of both bacteria and fungi were also observed, emphasising a community shift towards microorganisms able to use or metabolise phosphate. Phosphate increased the relative abundance of bacteria such as Pseudomonas, Paenibacillus, Massilia, Acinetobacter and the fungi Cadophora, Rhizophagus and Eupenicillium. Whole metagenome sequencing showed with phosphate a favouring of sequences related to Gram-negative bacterium type cell wall function, virions and thylakoids, but a reduction in the number of sequences associated to vitamin binding, methanogenesis and toxin biosynthesis. With current faecal indicator tests only providing risk detection in bulk water samples, this work improves understanding of how network changes effect microbial ecology and highlights the potential for new approaches to inform future monitoring or control strategies to protect drinking water quality

Dynamics of biofilm re-growth in drinking water distributions systems

The majority of biomass within water distribution systems is in the form of attached biofilm. This is known to be central to drinking water quality degradation following treatment yet little understanding of the dynamics of these highly heterogeneous communities exists. This paper presents original information on such dynamics with findings demonstrating patterns of material accumulation, seasonality and influential factors. Rigorous flushing operations repeated over a one-year period on an operational, chlorinated system in the UK are presented. Intensive monitoring and sampling were undertaken including time series turbidity and detailed microbial analysis using 16S rRNA Illumina MiSeq sequencing. Results show bacterial dynamics were influenced by differences in the supplied water and by the material remaining attached to the pipe wall following flushing. Turbidity, metals and phosphate were the main factors correlated with the distribution of bacteria in the samples. Coupled with the lack of inhibition of biofilm development due to chlorine residual, this suggests that limiting inorganic nutrients, other than organic carbon, might be a viable component in treatment strategies to manage biofilms. The research also showed that repeat flushing exerted beneficial selective pressure, thus also a viable advantageous biofilm management option. This work advances our understanding of microbiological processes in drinking water distribution systems and helps inform strategies to optimise asset performance. IMPORTANCE: This research provides with novel information regarding dynamics of biofilm formation in real drinking water distribution systems made of different materials. This new knowledge on microbiological process in water supply systems can be used to optimise the performance of the distribution network and to guarantee safe and good quality drinking water to consumers

Decision-making tools to manage the microbiology of drinking water distribution systems

This paper uses a two-fold multi-criteria decision-making (MCDM) approach applied for the first time to the field of microbial management of drinking water distribution systems (DWDS). Specifically, the decision-making trial and evaluation laboratory (DEMATEL) was applied removing the need for reliance on expert judgement, and analysed interdependencies among water quality parameters and microbiological characteristics of DWDS composed of different pipe materials. In addition, the fuzzy technique for order preference by similarity to ideal solution (FTOPSIS) ranked the most common bacteria identified during trials in a DWDS according to their relative abundance while managing vagueness affecting the measurements. The novel integrated approach presented and proven here for an initial real world data set provides new insights in the interdependence of environmental conditions and microbial populations. Specifically, the application shows as the bacteria having associated the most significant microbial impact may not be the most abundant. This offers the potential for integrated management strategies to promote favourable microbial conditions to help safeguard drinking water quality

Amoeba & biofilms in UK chlorinated drinking water distributions systems: impact on water safety

Amoeba-related diseases have been related with the presence of certain amoebas in domestic water, including drinking water. Biofilms in drinking water distribution systems are able to support amoeba growth by providing a food source and protecting them against disinfectants. Additionally, amoeba growth can be favoured by warm temperatures and climate change appears to contribute to its geographic spread. The presence of amoeba and its association with potential pathogenic bacteria was studied in a real-scale chlorinated DWDS. The test facility comprised three independent pipe loops fed with water from the local water supply and for this study a varied flow hydraulic profile was applied based on daily patterns observed in real UK distribution networks. The daily regime was repeated for a biofilm growth phase of 30 days. Amoeba viability was tested by a culture-based method, non-nutrient agar (NNA)-E. coli plates, and then confirm by qPCR using specific primers to detect species of amoeba including Naegleria and Acanthamoeba. Amplicon sequencing of the 16s rRNA gene was used to characterise the biofilm and planktonic bacterial communities. Several amoeba species belonging to the genera Acanthamoeba, Vermamoeba and Naegleria were identified in 30-day old biofilm samples. While the bacterial communities in biofilms were dominated by Variovorax, Pseudomonas and Aquabacterium. This study yielded new insights on the dynamics of amoeba and bacterial communities in DWDS. However, more research is required to accurately establish the impact of these inter-kingdom associations on human health

Influence of phosphate dosing on biofilms development on lead in chlorinated drinking water bioreactors

Phosphate dosing is used by water utilities to prevent plumbosolvency in water supply networks. However, there is a lack of knowledge regarding biofilm formation on lead and plastic materials when phosphate concentrations are modified in drinking water systems. In this study, biofilms were grown over lead coupons and PVC tubes in bioreactors supplied with local drinking water treated to provide different phosphate doses (below 1, 1 and 2 mg/L) over a period of 28 days. A range of commercial iron pellets (GEH104 and WARP) were tested aiming to maintain phosphate levels below the average 1 mg/L found in drinking water. Changes in biofilm community structure in response to three different phosphate treatments were characterised by Illumina sequencing of the 16S rRNA gene for bacteria and the ITS2 gene for fungi. Scanning electron microscopy was used to visualise physical differences in biofilm development in two types of materials, lead and PVC. The experimental results from the kinetics of phosphate absorption showed that the GEH104 pellets were the best option to, in the long term, reduce phosphate levels while preventing undesirable turbidity increases in drinking water. Phosphate-enrichment promoted a reduction of bacterial diversity but increased that of fungi in biofilms. Overall, higher phosphate levels selected for microorganisms with enhanced capabilities related to phosphorus metabolism and heavy metal resistance. This research brings new insights regarding the influence of different phosphate concentrations on mixed-species biofilms formation and drinking water quality, which are relevant to inform best management practices in drinking water treatment

Climate change and management of biofilms within drinking water distribution systems

Climate change will increase the temperature of water in our drinking-water distribution systems, impacting the biofilms that grow in these vast infrastructure systems and hence the quality and safety of drinking water at the tap. Using a full-scale laboratory-controlled facility, we studied the impact of such temperature increase and the impacts of different control strategies. Our results show that increasing the temperature from 16 to 24°C changed the biofilm community structure and increased the potential for discoloration. Interventions of flushing only or flushing supplemented with hyperchlorination showed a similar reduction in discoloration potential and reduced the abundance of microorganisms that can compromise water quality and safety such as the bacteria Flavobacterium or Sphingobium and the fungi Fusarium and Cladosporium. However, there was no difference between the interventions, suggesting no benefit from adding hyperchlorination. This study provides useful understanding to inform strategies for managing biofilms within chlorinated HDPE DWDS, understanding and mitigating the impact of increasing temperature due to climate change