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Erskine A.,MWH UK Ltd. | Watson T.,ICS Consulting Ltd. | O'Hagan A.,University of Sheffield | Ledgar S.,Yorkshire Water Services | Redfearn D.,Yorkshire Water Services
Journal of Infrastructure Systems | Year: 2014

The replacement and maintenance of subsurface assets, such as water and wastewater pipes, is of great interest to water utilities because these infrastructure networks require large amounts of investment over time. Each asset requires investment relatively rarely, but the number of assets is so enormous that the flow of money is large. Therefore the accurate estimation of the deterioration and aging process of these assets is critical to the efficient and sustainable allocation of investment spend. The development of failure models is difficult for various reasons: short spans of data (very little longitudinal data), very sparse failure rates, inaccuracy of observational data, and accuracy and availability of potential predictor data. Technical difficulties also arise such as variability and noise, censoring effects, overdispersion, and, throughout the exercise, the large volume of data usually involved. In this paper, a new regression approach is formulated that maintains a rigorous statistical approach while still being practical and easy to apply. In addition, the formulation involved permits the individual pipe history to be used in an elegantly simple Bayesian update. The example provided refers to work done for Yorkshire Water Services in estimating probability of blockage failure for all their sewerage assets. © 2013 American Society of Civil Engineers. Source

Holme M.,MWH UK Ltd. | Berry M.,United Utilities Water
Pipelines 2012: Innovations in Design, Construction, Operations, and Maintenance - Doing More with Less - Proceedings of the Pipelines 2012 Conference | Year: 2012

United Utilities have a massive project to refurbish the Vyrnwy Large Diameter Trunk Main (LDTM). This Victorian water main supplies up to 55 million gallons per day to over 900,000 customers in Cheshire and Merseyside in the North West of England. This equates to 12% of all water supplied by the water company. The existing LDTM consists of three mains each 50 miles long and between 39" and 42" in diameter. The construction of the gravity system started in the 1890's and the first two unlined cast iron mains were installed in under 15 years, a real credit to Victorian engineering. Refurbishment of the Vyrnwy LDTM is formalised within a legal undertaking with the UK Water Quality Regulator the Drinking Water Inspectorate (DWI). The project is being carried out to reduce the risk of supplying discoloured water to customers caused by re-suspension of solids resulting from historic deposition of iron and manganese. These deposits have accumulated as a result of historically high concentrations of iron and manganese in the water supplied from Oswestry WTW, prior to the completion of work to improve the treatment process. Investigations have identified that internal corrosion also contributes to the risk of supplying discoloured water. With a project value of 250m US Dollars a unique approach was required to ensure the correct engineering solution was developed. A full review of all the cleaning and lining techniques available now and within the next five years was carried out during the outline design phase. The review confirmed that there are only a few lining techniques applicable for use on such a large diameter unlined cast iron main. In addition, cleaning techniques could be utilised on Line 3, a bitumen lined steel main. The review also showed that there are new techniques available in the market place, but these are not yet suitable for use on larger diameter trunk mains or on unlined cast iron. To enhance United Utilities Water (UUW) engineering understand of the available lining techniques two field trials were carried out using thin walled Polyethylene (PE) liners. Folded liner in 2009 and swage liner in 2010, both were carried out on a parallel 1 mile section of the Vyrnwy LDTM. This trial was carried out to test a number of engineering assumption made in the development of the ten year construction schedule and to ensure lessons learnt could be incorporated into the main works. From the work carried out to date United Utilities have developed an enhanced understanding of what to consider when refurbishing large unlined cast iron pipelines. This includes, but is not limited to, the following: • Prediction and control of discolouration events in distribution networks; • Assessment and selection of PE interactive liners; • The use of structural and semi-structural liners and end termination fittings; • Onsite experience of inserting up to 850m of PE liner in one operation; 5) The manufacturing process of cast iron mains in the late 1800's; and 6) Development of a cast iron remaining life assessment tool in conjunction with MWH United Utilities have gained a large amount of knowledge and information from this project over the last fours years and it is important that this and the lesson learnt are shared with the wider industry. © 2012 American Society of Civil Engineering. Source

Sarioglu M.,MWH UK Ltd. | Insel G.,Technical University of Istanbul | Artan N.,Technical University of Istanbul | Orhon D.,Technical University of Istanbul | Orhon D.,Turkish Academy Of Sciences
Journal of Chemical Technology and Biotechnology | Year: 2011

BACKGROUND: This study concerned the stoichiometric evaluation of simultaneous nitrification and denitrification in a membrane bioreactor. The evaluation was made to derive relevant mass balance equations for all parameters affecting nitrogen removal and to set the basis for a rational design procedure. RESULTS: The basic stoichiometry was defined to include the effect of oxygen diffusion through microbial flocs by means of half saturation constants in corresponding switching functions. The stoichiometric relationships were used as tools for the design procedure targeting the desired level of nitrogen removal. CONCLUSION: A comparison was made with the outputs associated with a conventional activated sludge system for major design parameters such as denitrification potential, active heterotrophic and autotrophic biomass, oxygen requirements, etc. The proposed rational design for nitrogen removal was tested and validated using model simulation for steady state MBR operation under selected conditions. © 2011 Society of Chemical Industry. Source

Brown L.E.,University of Leeds | Mitchell G.,University of Leeds | Holden J.,University of Leeds | Folkard A.,Lancaster University | And 27 more authors.
Science of the Total Environment | Year: 2010

Several recent studies have emphasised the need for a more integrated process in which researchers, policy makers and practitioners interact to identify research priorities. This paper discusses such a process with respect to the UK water sector, detailing how questions were developed through inter-disciplinary collaboration using online questionnaires and a stakeholder workshop. The paper details the 94 key questions arising, and provides commentary on their scale and scope. Prioritisation voting divided the nine research themes into three categories: (1) extreme events (primarily flooding), valuing freshwater services, and water supply, treatment and distribution [each >. 150/1109 votes]; (2) freshwater pollution and integrated catchment management [100-150 votes] and; (3) freshwater biodiversity, water industry governance, understanding and managing demand and communicating water research [50-100 votes]. The biggest demand was for research to improve understanding of intervention impacts in the water environment, while a need for improved understanding of basic processes was also clearly expressed, particularly with respect to impacts of pollution and aquatic ecosystems. Questions that addressed aspects of appraisal, particularly incorporation of ecological service values into decision making, were also strongly represented. The findings revealed that sustainability has entered the lexicon of the UK water sector, but much remains to be done to embed the concept operationally, with key sustainability issues such as resilience and interaction with related key sectors, such as energy and agriculture, relatively poorly addressed. However, the exercise also revealed that a necessary condition for sustainable development, effective communication between scientists, practitioners and policy makers, already appears to be relatively well established in the UK water sector. © 2010 Elsevier B.V. Source

Kalungi P.,MWH UK Ltd.
Water Distribution Systems Analysis 2010 - Proceedings of the 12th International Conference, WDSA 2010 | Year: 2012

Planning for the management of operational risk in water distribution systems (WDS) requires several issues to be considered. Water companies use models to facilitate the process. This paper highlights the importance of using All Mains, All Valve models in this process by basing the analysis on the use of the pound. The pound is defined as a collection of network components impounded by two or more closeable valves. It is central to the process of identifying critical network valves and determining the impact of unplanned interruptions on customers. Unplanned interruptions to supply (UITS) and drinking water quality are key components of the Overall Performance Assessment (OPA) system that is used by the UK regulator of water companies, Ofwat, to compare the customer service performance of the companies in England and Wales. On one extreme, water companies that prioritise unplanned interruptions to supply, aim to operate boundary valves in order to re-route the flow of water and address interruptions as the bursts are fixed. On the other extreme, companies that prioritise drinking water quality would try not to operate boundary valves to avoid worsening the problem of discolouration as the bursts get fixed. This is probably due to fact that for these companies, discolouration has a more significant impact on the OPA score thus making it more critical than interruptions. These two extreme strategies lead to different levels of valve criticality. Examples are used to demonstrate this difference and emphasize the importance of using the pound together with All Mains All Valve models in managing operational risk of WDS. © 2011 ASCE. Source

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