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Biofilms are endemic in drinking water distribution systems (DWDS), forming on all water and infrastructure interfaces. They can pose risks to water quality and hence consumers. Our understanding of these biofilms is limited, in a large part due to difficulties in sampling them without unacceptable disruption. A novel, non-destructive and non-disruptive biofilm monitoring device (BMD), which includes use of flow cytometry analysis, was developed to assess biofouling rates. Laboratory based experiments established optimal configurations and verified reliable cell enumeration. Deployment at three operational field sites validated assessment of different biofouling rates. These differences in fouling rates were not obvious from bulk water sampling and analysis, but did have a strong correlation with long-term performance data of the associated networks. The device offers the potential to assess DWDS performance in a few months, compared to the number of years required to infer findings from historical customer contact data. Such information is vital to improve the management of our vast, complex and uncertain drinking water supply systems; for example rapidly quantifying the benefits of improvements in water treatment works or changes to maintenance of the network. [ABSTRACT FROM AUTHOR]

Trunk mains are high risk critical infrastructure where poor performance can impact on large numbers of customers. Both quantity (e.g. hydraulic capacity) and quality (e.g. discolouration) of trunk main performance are affected by asset deterioration in the form of particle accumulation at the pipe wall. Trunk main cleaning techniques are therefore desirable to remove such material. However, little is quantified regarding the efficacy of different maintenance interventions or longer-term changes following such cleaning. This paper presents an assessment of quantity and quality performance of a trunk main system pre, post and for 12 months following cleaning using pigging with ice slurry. Hydraulic calibration showed a 7 times roughness height reduction after ice slurry pigging, evidencing substantially improved hydraulic capacity and reduced headloss. Turbidity response due to carefully imposed shear stress increase remained significant after the cleaning intervention, showing that relatively loose material had not been fully removed from the pipe wall. Overall the results demonstrate that cleaning by pigging with ice slurry can be beneficial for quantity performance, but care and further assessment may be necessary to realise the full quality benefits. [ABSTRACT FROM AUTHOR]

This paper presents predictive discolouration modelling and subsequent field trial validation for a cast iron trunk main network. This enabled a UK water company to propose an 'operational flow conditioning' maintenance plan that reduces discolouration risk, improves network resilience and asset condition and yet does not require the trunk main to be decommissioned for invasive cleaning. This represents substantial time and cost benefits. Pre- and post-trial turbidity monitoring data are presented which identified a daily flux of material, a factor in the regeneration of material layers that have been shown to cause discolouration when mobilised. Additional data showing the occurrence of pressure transients are also presented, the latter being a possible cause of contaminant ingress and asset failure. After 6 months a second flow trial was conducted and modelled, confirming the regeneration of particulate discolouration material across the range of mobilising forces applied during the trial. It also indicated full layer development, or maximum discolouration risk, may occur in just over 2 years for this cast iron main. This highlights the need for appropriate maintenance strategies, such as periodic flow conditioning identified here, to mitigate discolouration risk and help safeguard water quality. [ABSTRACT FROM AUTHOR]

Drinking water distribution systems host extensive microbiomes with diverse biofilm communities regardless of treatment, disinfection, or operational practices. In Mediterranean countries higher temperatures can accelerate reactions and microbial growth that may increase aesthetic water quality issues, particularly where material deposits can develop as a result of net zero flows within looped urban networks. This study investigated the use of flow and turbidity monitoring to hydraulically manage mobilisation of pipe wall biofilms and associated material from the Mediterranean city of Valencia (Spain). Pipe sections of different properties were subjected to controlled incremental flushing with monitoring and sample collection for physico-chemical and DNA analysis with Illumina sequencing of bacterial and fungal communities. A core microbial community was detected throughout the network with microorganisms like Pseudomonas , Aspergillus or Alternaria increasing during flushing, indicating greater abundance in underlying and more consolidated material layers. Bacterial and fungal communities were found to be highly correlated, with bacteria more diverse and dynamic during flushing whilst fungi were more dominant and less variable between sampling sites. Results highlight that water quality management can be achieved through hydraulic strategies yet understanding community dynamics, including the fungal component, will be key to maintaining safe and ultimately beneficial microbiomes in drinking water distribution systems. Unlabelled Image • Monitoring turbidity during flushing allows network performance analysis. • Hydraulic strategies can be applied to control water quality issues from biofilms. • Controlled flushing facilitated network and pipe biofilm community analysis. • Core-community of microorganisms were present throughout the network. • Bacteria showed more diversity with fungi more dominant and stable. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Microorganisms in drinking water distribution systems (DWDS), and in particular the microbial communities that form biofilms on infrastructure surfaces, drive critical processes impacting water quality. This paper reviews knowledge, research approaches, and monitoring methods to consolidate understanding of the microbial ecology of DWDS. The review highlights how microbial characteristics and subsequent behavior can be broadly classified as common or complex. Common behavior relates to the ubiquitous and continual development of biofilms, consistent core communities, and mediated material accumulation. In contrast, the complex aspect relates to the shape, structure, and composition of the microbiome, defined by site‐specific properties such as supplied source water, pipe material, and hydraulic regimes. It is shown how the latest microbial tools and techniques can be applied to increase our understanding of DWDS ecology and how water utilities are starting to use this knowledge. This is not because of regulatory requirements, but in recognition that they provide valuable information facilitating proactive management and operation benefits to these critical yet aging systems, protecting water quality and public health in the process. This article is categorized under: Engineering Water > Sustainable Engineering of WaterWater and Life > Nature of Freshwater Ecosystems Microbial characteristics and behaviour in drinking water distribution systems can be classified as common or complex [ABSTRACT FROM AUTHOR]