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Prediction of water and wastewater networks rehabilitation based current age and material distribution
Abstract
Ageing drinking water, stormwater and sewer pipe networks imply an increased degree of rehabilitation. The need for rehabilitation can be predicted using lifetime distribution functions together with current network age and material distribution. In Sweden, current age and material distribution is neither documented on a national level, nor for many water utilities on a local level. In this study, current network age and material distribution was provided through a questionnaire sent to Swedish water and wastewater utilities and the data provided were extrapolated to cover the whole of Sweden. The data were then combined with lifetime distribution functions to provide predictions. One limitation is that for newer materials the lifetime is still uncertain. Predictions were made for different scenarios to reflect local differences and the medium scenario shows that while the Swedish rehabilitation rate is stable, investments in monetary terms need to double in the next 60 years. The rehabilitation rate is also dependent on the extent to which the network is expanded. This method can be used to calculate national investment needs, and the results can also provide a basis for estimates for Swedish utilities with data scarcity.
... EurEau, the European Federation of National Associations of Water Services, has indicated that the dual challenge of ageing water service infrastructure and climate change will require far-reaching adjustment measures and longterm investments at all levels across Europe. In Sweden, ageing infrastructure is increasing the need for costly investments in sewer networks (Malm et al., 2013). Concerns about organic micropollutants, such as pharmaceutical residues, will also drive increased investment due to new, expensive tertiary treatment steps (Havs, 2018). ...
This paper studies decision-making processes in relation to the implementation of innovative source-separating wastewater systems in the development area of Helsingborg called H+, and the non-implementation of the same in Stockholm Royal Seaport. Two analytical perspectives were used to identify critical organisational functions, drivers for change and the anchoring of these decisions within policy: (i) a sustainability transitions framework, and (ii) a policy trickle-down study assessing policy-concept uptake by stakeholders. Critical functions supporting implementation of source-separating systems in H+ were: common vision, leadership, cross-sectoral cooperation, and an innovative approach both within the utility and in the city administration in Helsingborg. In Stockholm, with regard to source-separating wastewater systems, there was a lack of common vision and of cross-sectoral cooperation and leadership. This was also evident in the lack of uptake by stakeholders of the policies for source separation. In Helsingborg, the main drivers for source-separating wastewater systems are increased biogas generation and improved potential for nutrient recycling. In Stockholm, these drivers have not been enough to create change, but the potential for increased heat recovery from greywater at source may be the additional driver necessary for future implementation of source-separating wastewater systems. Comparison of the stalled source-separation policy in Stockholm with a successfully implemented policy in a related field found a key criteria to be the presence of inspired individuals in positions where they had the mandate as well as the ability to create a common vision for change.
... Another aspect is that small WWTPs report difficulties in treating sludge from septic tanks under their environmental permits due to the increased load on their systems, leading to sludge being transported longer distances to larger units (Tarkka and Leppänen 2019). Moreover, considerable debts are reported in both Finland (ROTI, 2021) and Sweden (Malm et al., 2013;Hedström et al., 2016) related to the renovation of sewage networks and WWTPs. Therefore, careful consideration is needed to evaluate which solutions are worth implementing in the future, i.e., expanding the network or implementing different technologies for on-site sanitation. ...
Current practices in wastewater management lead to inefficient recovery and reuse of nutrients and can result in environmental problems. Source separation systems have been shown to be an efficient way of recovering nutrients and energy from wastewaters, both in rural and urban context. Studies on nutrient recovery potential and life cycle impacts of source separation systems are mainly limited to small systems (for example a few households) while the impacts of upscaling source separation to a regional level have hardly been studied, especially in sparsely populated areas where the cost of the connection to a main treatment plant is higher. This study examines the regional nutrient balance of two source separation scenarios—black water separation and urine diversion—and compares them to the existing conventional wastewater system. The analysis comprises three sparsely populated regions of northern Finland and Sweden, including rural, peri-urban and urban areas. In addition, climate impacts are assessed based on existing life cycle assessment (LCA) studies. According to the results, by source separation it is possible to achieve a significant increase in the recovery rate of phosphorus (41–81%) and nitrogen (689–864%) compared to the conventional system. Depending on the region up to 65% of the mineral phosphorus and 60% of mineral nitrogen fertilisers could be theoretically replaced. Furthermore, the climate and eutrophication impacts would decrease with the implementation of such systems, but an increase in acidification may occur. However, even if the benefits of source separation systems are undisputed in terms of nutrient recovery, the implementation of such systems would to a large extent require an entire system change of the wastewater treatment sector and a wide paradigm change towards a circular economy.
... It should be noted that PVC pipes are on the Algerian market only since the 2000s, which means that PVC networks are less old than others. It should be pointed out that the need for rehabilitation can be predicted using lifetime distribution functions together with current network age and material distribution (Malm et al. 2013). ...
A three steps methodological approach is developed in order to assess the effectiveness of wastewater asset management under critical conditions. Rare data and poor investments are two main causes of weakness to reach an effective asset management. They put managers under severe conditions. In the first step of the proposed methodology, results of a survey conducted amongst services of the National Sanitation Office in several Algerian cities, on wastewater assets, are presented and discussed. In total, network-related information, such as pipe materials, age, hydraulic characteristics, manholes number and types, damage nature and frequency, was acquired. Depending on the data collected and their importance for urban sanitation, statistical analyses were performed. The second step treats the efficiency of maintenance activities by analysing data collected from different technical reports of offices. In the end, an explanation of the main characteristics of the Algerian wastewater asset management system is described, as well as the efforts required to achieve the ISO-55000 standard recommendations are identified. As results, two performance indicators are proposed allowing a comparative study between the wastewater networks of two Algerian cities.
... In total, there are 242 water utilities and the trend is decreasing when more and more municipalities merge into inter-municipal organisations. According to Malm et al, (2013), drinking water network materials consist mainly of CI (35%), DI (20%), PVC (12%) and PE (22%) (see Figure 1B). Data on pipe material, dimension and PFD are uniformed collected in almost every utility in Sweden, but when it comes to data regarding failure mechanisms, soil conditions, pipe status, time for repair, different utilities are collecting, storing and analysing these data in different ways. ...
Pipe failure data provides valuable information on the mechanisms and conditions which cause drinking water pipes to break or leak. Such data feeds asset management models, helping water utilities to decide future interventions at different timelines. Among countries, and even within countries, utilities apply different pipe failure data collection methods, for a-posteriori analyses. This contribution focuses in the comparison of pipe failure data collection methods and practices in three countries: Japan, Sweden and The Netherlands. We compare their methodologies and the use that such data is given. We identify the potential for knowledge transfer of methods between the three countries. This paper stems from the Watershare knowledge sharing platform, where the three organizations are active members, along with 17 other knowledge institutes spread across the world.
... There has been various methods and tools developed over time for utilities to help them with water networks management. Herz et al. (1998) used KANEW software as an approach to study the rehabilitation needs and various strategies on water distribution networks. Malm et. al. (2013) developed a method for Swedish utilities to help them predict the rehabilitation time for their water and wastewater networks based on age and material. ...
In the recent years, many metropolitan cities are facing economic problems with the rehabilitation of their water distribution system. With time, the failure rates and leakage in the pipes will increase even with some of the rehabilitation efforts taking place. Thus, water utilities should consider seeking strategies for water pricing and the system rehabilitation to prevent their existing distribution network from deteriorating. The objective of this study was to understand how different management techniques implemented on a hypothetical water distribution networks would result in a sustainable management of water infrastructure. Using system dynamics approach, a simulation model was developed to study the impacts of management strategies on the distribution network functionality and financial health over a 100-year time horizon. The model considers the interactions among distribution network sector (existing water network differentiated by age), finance sector (user fee, profit/loss account, debt, and available cash), and lastly, consumer demand sector (change in water demand due to population). The study exhibited a comprehensive analysis for a utility on achieving financial sustainability with a comparatively lower user fees with adaptation of rehabilitation measures. Results of the current study can be used by water utilities to analyze different approaches for sustainable financial and infrastructure management.
... (3) F(t = ∞) = 0 and Terno 2003; Deb et al. 2009;Herz 1998Herz , 2002aHerz , 2002bLarge et al. 2015;Malm et al. 2012Malm et al. , 2013. Two of the most commonly used models in the European water sector are the software packages CARE-W LTP (Saegrov 2005) and KANEW (Herz 2002a;Saegrov 2005;Saegrov et al. 2003), both of which apply the Herz function and are the same models with modifications (Baur, Kropp, and Terno 2003). ...
Managing the urban drinking water system in the long term in order to maintain system performance can be challenging due to the difficulty of modelling future deterioration of the networks. This paper establishes a methodology for cohort survival models where historical (empirical) data on decommissioning ages of pipes are used to calibrate survival functions of pipe cohorts according to service level targets. The benefit of the approach is that remaining useful life of pipes, future renewal rates and investment needs can be governed by a required level of service in the network. A case study shows how the methodology can be applied to a cohort of drinking water pipes to create a ‘calibration curve’, which is a survival function calibrated with empirical data.
... [ Table 1] Table 1 is based on the experience of the authors, having working with several (mostly French) databases. However, other authors have confirmed some quality and availability issues regarding deterioration factors (Berardi et al., 2009;Malm et al., 2013;Salman, 2010). ...
The purpose of this paper is to discuss the influence of data availability and quality within a utility to prioritise inspection and rehabilitation needs. Data are required in order to predict the structural condition of assets. Lack of data and budget limitation do not encourage utilities to evolve from reactive to proactive management. Methods and tools exist; however, improving operational practices will require the demonstration of data collection benefits. In this article, asset management approaches are presented and discussed regarding influence of data; from closed-circuit television reports elaboration to prioritisation of rehabilitation needs. Bottlenecks related to uncertainty, imprecision and incompleteness of data are identified, and the authors propose approaches to study these questions. This article also highlights the use of numerical experiment to simulate asset management scenarios, to experiment methods or to demonstrate the interest of new practices. Numerical experiment allows construction and use of virtual degraded databases derived from a completely known asset stock.
Due to structural and hydraulic deterioration, urban water pipe networks have annual rehabilitation needs. Worldwide, these needs are often significantly larger than the actual amount of rehabilitation being performed, leading to increased risks of serious failures, lower performance and a growing techno-financial burden for future generations. It is well accepted that, in order to limit the multiple impacts of utility works in the urban environment, rehabilitation projects should be coordinated between water, transport, energy and telecommunication infrastructures. In practice, such coordination means that public utilities must rehabilitate assets earlier or later than technically needed, in order to engage in joint projects in which digging and resurfacing expenditures are shared. Hence, at the municipal scale, such coordination influences two variables that are key to strategic decision support: average costs (€/metre) for asset rehabilitation, and the service lifetimes of those assets. However, current models for strategic asset management do not enable practitioners to estimate how changes in the coordination process may influence the long-term financial and environmental impacts of infrastructure rehabilitation. The present study aimed at addressing this methodological gap by introducing the concept of a coordination window that quantifies to what extent utilities compromise asset rehabilitation times in order to join multi-utility projects. An algorithm for modelling the influence of the coordination window size on long-term sustainability costs is presented and applied to one Swedish municipality. The results suggested that total capital costs and carbon emissions can be lowered by 34% and 16% with a coordination window of 35 and 25 year, in comparison to the no-coordination case.
A novel modified Page Rank algorithm for pipe renewal (MPR-Pipe) is presented to realize selection sort and provide Page Rank values of static and dynamic attributions of junctions and pipes in water distribution systems. The measurement of pipe renewal significance, well defined on the grounds of economic flow and unit hydraulic gradient, can be taken as the criterion for the selection sort of pipe renewal. Theoretical calculations confirm the high efficiency of the algorithm, and engineering application cases indicate the effectiveness and feasibility of the renewal plan based on MPR-Pipe algorithm.
European Project CARE-W (Computer Aided Rehabilitation of Water Networks), which is supported by the European Commission, gathers 10 research and development organisations as well as 13 water utility managers. Its aim is to build and test a decision support system (DSS) for the rehabilitation of water networks, This DSS gathers several tools: - Care-W_PI : assessment and monitoring of network with performance indicators ; - Care- W_FAIL ; set of statistical tools for network failures pro bability forecasting ; - Care-W_REL : set of tools for network hydraulic reliability assessment ; - Care-W_LTP : long term planning tool for the definition and assessment of a rehabilitation strategy ; - Care-W_ARP ; multi-criteria tool for the annual programming of rehabilitation projects. Inside the project, the present operational decision making processes have been analysed in 14 water utility management organisations. The objectives were to identify the involved actors and their interactions, as well as the structure of the decision processes: institutional and regulatory contexts, steps of decision making, information fluxes, sharing out of responsibilities and of influence, participation of social and institutional stakeholders. Synthetic results are shown here. The cases studied are diversified on several aspects. An "average" situation could be described as showing a moderate level of confrontation, with rather formalised procedures, and very centralised decision making out ot the interrelations with road works programming. The highest diversity encountered among the utilities concerns the level of information inside the decision process: data considered, fluxes of information, "sophistication" of criteria taken into account.
This paper presents the approach taken and the tools developed and advanced within the European research project CARE-W (Computer Aided REhabilitation of Water networks) for strategic rehabilitation investment planning as a complement to short-term performance monitoring and annual rehabilitation (rehab) budget allocation planning. In a first step, future rehab needs are quantified with a cohort-survival model from the present stock of assets taking into account the specific service lives of its components. Utility managers may choose in the short and medium range from many rehab options: doing more or less, sooner or later, on particular network components and with specific rehab technologies at lower or higher cost. So, in a second step, alternative medium-term rehab programs are specified and tested for their effects. The annual costs and benefits of these alternative rehab programs are forecast with the cohort-survival model beyond the rehab program period to capture the long-term effects of rehabilitating these long-lived assets. Advantages and disadvantages of alternative rehab programs are systematically compared to find out which one is most appropriate under local constraints. However, whereas the survival of network components can be forecast over very long periods with sufficient accuracy, many other characteristics of the water supply system that must be considered for finding the best network rehab strategy may take unforeseeable paths into the far future. Therefore, a scenario writing tool was developed allowing consistent scenarios for particular water utilities to be created and to test whether the alternative rehab programs are robust enough to meet all eventualities of the future. This approach is illustrated by a case study from East Germany.
Utilities throughout the world are faced with the challenge of how best to manage their existing asset stock to provide satisfactory customer service with limited funds. Effective asset management helps utilities to meet this challenge; however, this requires the utilization of cost-effective approaches for assessing asset condition, performance and remaining service life. A key component of these approaches requires an understanding of asset lifetimes. This paper discusses the role of asset lifetimes in asset management and the current state of the art for prediction of remaining life using different approaches. It discusses very simple approaches based on assumed lives, as well as sophisticated mathematical approaches using deterministic, statistical, physical/probabilistic and artificial intelligence models. In analysing both asset management strategies and lifetime prediction methodologies, a key factor identified as missing is a standardized technique for the incorporation of lifetime models into the probability side of risk analysis. For asset management to become a valued and readily utilized tool, this issue needs to be urgently addressed.
Lifetime distribution functions and current network age data can be combined to provide an assessment of the future replacement needs for drinking water distribution networks. Reliable lifetime predictions are limited by a lack of understanding of deterioration processes for different pipe materials under varied conditions. An alternative approach is the use of real historical data for replacement over an extended time series. In this paper, future replacement needs are predicted through historical data representing more than one hundred years of drinking water pipe replacement in Gothenburg, Sweden. The verified data fits well with commonly used lifetime distribution curves. Predictions for the future are discussed in the context of path dependence theory.
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