Hydraulic conditioning to manage potable water discolouration

Results are reported from studies conducted using a unique laboratory-based, full-scale, temperature-controlled pipe facility to examine the impact of conditioning shear stress on discolouration risk, as characterised by bulk water samples (turbidity, iron and manganese) and biofilm pipe wall measurements. The facility uniquely allowed for replication of the dynamics of an operational network but with rigorous control, thus yielding fully representative results overcoming the limitations of bench-scale or operational studies. The effect of the daily variation in flow (and boundary shear stress) was observed to be greater than the effect of the average daily flow rate at reducing discolouration risk. This is useful for informing operation and maintenance strategies, specifically that regularly imposing cycles of flow variation are more effective than increasing total average flow rates at limiting discolouration risk. The application of such knowledge aids the development of cost-effective, proactive, operational interventions to manage discolouration

Understanding microbial ecology to improve management of drinking water distribution systems

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 behaviour can be broadly classified as common or complex. Common behaviour 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 pro-active management and operation benefits to these critical yet ageing systems, protecting water quality and public health in the process

Case-Based Reasoning Approach For Managing Water Quality Incidents In Distribution Systems

Access to safe drinking water is universally considered as a fundamental human right and customers regard a reliable supply of safe, clean water as the most important aspect of the water supply service. However, water quality failures do occur, with some of the hardest to understand and manage occurring within distribution systems. In the UK, a regulatory process is applied in which water companies must report on significant water quality incidents, their causes, actions, responses, and outcomes. The Drinking Water Inspectorate (DWI) assesses these reports on an annual basis and their findings are made publically available. It is hypothesised here that these reports form a valuable resource that can be ‘data mined’ for improved understanding and to help with future incident management. Developed in the late 1970s, case-based reasoning (CBR) is a knowledge-based problem-solving technique that relies on the reuse of past experience. It is based on the assumption that similar problems have similar solutions and hence new problems can be solved by reusing (and adapting) solutions. The WaterQualityCBR software system, reported on here, was developed as a decision support tool for water companies to deal more effectively with water quality incidents (e.g. water discolouration, contamination and loss of supply) by using information from previous incidents. The tool manipulates a database (compiled in XML) of past significant events from several years DWI reporting. The system can provide information at a strategic level, for example to help inform policy or water company guidance documents. In addition, a complete closed CBR cycle is possible for operational event management providing information from similar cases from the past and, importantly, ranking past actions in response to similar incidents. Examples are provided to illustrate both aspects of the software, demonstrating how the CBR methodology can support decision-making for water utilities in managing drinking water incidents

Biofilm microbiome (re)growth dynamics in drinking water distribution systems are impacted by chlorine concentration

Biofilms are the dominant form of microbial loading (and organic material) within drinking water distribution systems (DWDS), yet our understanding of DWDS microbiomes is focused on the more easily accessible bulk-water. Disinfectant residuals are commonly provided to manage planktonic microbial activity in DWDS to safeguard water quality and public health, yet the impacts on the biofilm microbiome largely unknown. We report results from a full-scale DWDS facility used to develop biofilms naturally, under one of three chlorine concentrations: Low, Medium or High. Increasing the chlorine concentration reduced the bacterial concentration within the biofilms but quantities of fungi were unaffected. The chlorine regime was influential in shaping the community structure and composition of both taxa. There were microbial members common to all biofilms but the abundance of these varied such that at the end of the Growth phase the communities from each regime were distinct. Alpha-, Beta- and Gammaproteobacteria were the most abundant bacterial classes; Sordariomycetes, Leotiomycetes and Microbotryomycetes were the most abundant classes of fungi. Mechanical cleaning was shown to immediately reduce the bacterial and fungal concentrations, followed by a lag effect on the microbiome with continued decreases in quantity and ecological indices after cleaning. However, an established community remained, which recovered such that the microbial compositions at the end of the Re-growth and initial Growth phases were similar. Interestingly, the High-chlorine biofilms showed a significant elevation in bacterial concentrations at the end of the Re-growth (after cleaning) compared the initial Growth, unlike the other regimes. This suggests adaptation to a form a resilient biofilm with potentially equal or greater risks to water quality as the other regimes. Overall, this study provides critical insights into the interaction between chlorine and the microbiome of DWDS biofilms representative of real networks, implications are made for the operation and maintenance of DWDS disinfectant and cleaning strategies

The Impact of Ground Heat Capacity on DrinkingWater Temperature

Temperature is known to impact physical, chemical and biological processes in DrinkingWater 1Distribution Systems (DWDS), but it is rarely considered or modelled. This research evaluates the impact of considering a finite heat capacity for the ground, which has been assumed infinite in previous DWDS research. The aim of this work is to explore and quantify the region where the difference between considering infinite or finite heat capacity for the ground is significant, i.e. the distance over which water-ground heat transfer interaction is important. A detailed model comparison is carried out for key pipe materials, diameters and hydraulic conditions. Temperature effects are found to 23 exist for up to tens of kilometres (i.e. several hours) into the DWDS. While the differences found were only a few degrees Celsius, this will affect all reaction rates, such as chlorine decay, and is at the start of the DWDS so will impact the entire downstream network. This work highlights the importance of considering temperature in DWDS, and in particular the finite heat capacity of the ground, in ensuring the provision of safe drinking water.Se sabe que la temperatura influye en los procesos físicos, químicos y biológicos de los sistemas de distribución de agua potable, pero rara vez se tiene en cuenta o se modela. Esta investigación evalúa el impacto de considerar una capacidad calorífica finita para el suelo, que se ha supuesto infinita en anteriores investigaciones sobre DWDS. El objetivo de este trabajo es explorar y cuantificar la región en la que la diferencia entre considerar una capacidad calorífica infinita o finita para el suelo es significativa, es decir, la distancia en la que la interacción de transferencia de calor agua-suelo es importante. Se lleva a cabo una comparación detallada de modelos para los principales materiales, diámetros y condiciones hidráulicas de las tuberías. Se observa que los efectos de la temperatura existen hasta decenas de kilómetros (es decir, varias horas) en el interior del DWDS. Aunque las diferencias encontradas son sólo de unos pocos grados centígrados, esto afectará a todas las velocidades de reacción, como la descomposición del cloro, y se encuentra al principio del sistema de alcantarillado, por lo que repercutirá en toda la red aguas abajo. Este trabajo pone de relieve la importancia de tener en cuenta la temperatura en los sistemas de abastecimiento de agua potable y, en particular, la capacidad calorífica finita del suelo para garantizar el suministro de agua potable

Self-Organizing Maps For Knowledge Discovery From Corporate Databases To Develop Risk Based Prioritization For Stagnation

Stagnation or low turnover of water within water distribution systems may result in water quality issues, even for relatively short durations of stagnation / low turnover if other factors such as deteriorated aging pipe infrastructure are present. As leakage management strategies, including the creation of smaller pressure management zones, are implemented increasingly more dead ends are being created within networks and hence potentially there is an increasing risk to water quality due to stagnation / low turnover. This paper presents results of applying data driven tools to the large corporate databases maintained by UK water companies. These databases include multiple information sources such as asset data, regulatory water quality sampling, customer complaints etc. A range of techniques exist for exploring the interrelationships between various types of variables, with a number of studies successfully using Artificial Neural Networks (ANNs) to probe complex data sets. Self Organising Maps (SOMs), are a class of unsupervised ANN that perform dimensionality reduction of the feature space to yield topologically ordered maps, have been used successfully for similar problems to that posed here. Notably for this application, SOM are trained without classes attached in an unsupervised fashion. Training combines competitive learning (learning the position of a data cloud) and co-operative learning (self-organising of neighbourhoods). Specifically, in this application SOMs performed multidimensional data analysis of a case study area (covering a town for an eight year period). The visual output of the SOM analysis provides a rapid and intuitive means of examining covariance between variables and exploring hypotheses for increased understanding. For example, water age (time from system entry, from hydraulic modelling) in combination with high pipe specific residence time and old cast iron pipe were found to be strong explanatory variables. This derived understanding could ultimately be captured in a tool providing risk based prioritisation scores

Physical investigation into the significance of ground conditions on dynamic leakage behaviour

Effective leakage models are crucial for leakage assessment and control strategies to improve the sustainability of vital water distribution, and other pipeline, infrastructure. This paper evaluates the interdependence of leak hydraulics, structural dynamics and soil hydraulics, particularly considering the significance of the soil conditions external to longitudinal slits in viscoelastic pipe. Initial numerical exploration and unique physical experimental results are presented exploring this complex physical phenomenon. The existence of an idealised fully restrained porous medium was shown to significantly increase the pressure- and time-dependent leak opening area whilst reducing the leak flow-rate, compared to a leak into water only. The research highlights the limitation of existing dynamic leakage modelling approaches which greatly simplify or neglect the influence of the soil conditions. Incorporation of this understanding into leakage modelling will enable more accurate estimation of leakage rates and hence the effects of management and control strategies

Experimental study exploring the interaction of structural and leakage dynamics

Strategies for managing leakage from water distribution systems require the ability to effectively evaluate such real losses through the understanding of the behavior of individual leaks, including their response to changes in pressure regime due to demand or management strategies. This paper presents the results from an innovative experimental investigation aimed at understanding the response of longitudinal slits in pressurized viscoelastic pipes, specifically considering the interaction between the structural and leakage dynamics. For the first time, leakage flow rate, pressure, leak area, and material strain were recorded simultaneously, providing new knowledge of the complex interaction of these factors. The paper shows that strain and area are directly related, hence it is possible to employ strain as a predictor of leak area, calculated using a calibrated viscoelastic model. Using such an approach, the leakage flow rates under a range of quasi-static pressures were accurately predicted and validated. Overall the paper demonstrates that the orifice equation, with a constant coefficient of discharge, is suitable for accurately estimating dynamic leakage flow rates from longitudinal slits, provided that the leak area is suitably incorporated

Non-destructive in-situ condition assessment of plastic pipe using ultrasound

Pipelines in potable water distribution system are a vital part of modern infrastructure, providing one of the most important services for society. This vital, complex infrastructure is endemic to our urban environments but is ageing, with current average age of around 70 years and with current replacement rates an inferred serviceable asset life of hundreds of years. Hence it is important that we develop technology that will enable pipeline condition assessment without service interruption. Due to environmental and operational stresses acting upon these pipelines, the common structural health problems include stress corrosion, thermal degradation, cracks or even leaks [1]. In particular, it has been suggested that void formation external to buried pipe wall is a crucial factor in pipe breakages due to lack of structural support [1, 2]. This paper presents the development and laboratory testing of ultrasonic non-destructive inspection technology for the condition assessment of plastic pipes, provide a measure of the structural integrity of the pipe, as well as 'looking' through the pipe wall to assess void formation and critical loss of support. Ultrasonic detection results are presented for grooves and cracks with two common plastic pipe materials, HDPE (High-density polyethylene) and PVC (Polyvinyl chloride) in order to simulate material loss in pipe wall. In addition, four voids in the ground external to plastics with varying shapes and dimensions were detected. Tested soils include two particle sized sands and two particle sized gravels. The study demonstrates the feasibility of developing a new technique for condition and health assessing for buried water plastic pipes