Jeroen Langeveld

Modelling and monitoring of integrated urban wastewater systems: Review on status and perspectives

While the general principles and modelling approaches for integrated management/modelling of urban water systems already present a decade ago still hold, in recent years aspects like model interfacing and wastewater treatment plant (WWTP) influent generation as complements to sewer modelling have been investigated and several new or improved systems analysis methods have become available. New/improved software tools coupled with the current high computational capacity have enabled the application of integrated modelling to several practical cases, and advancements in monitoring water quantity and quality have been substantial and now allow the collecting of data in sufficient quality and quantity to permit using integrated models for real-time applications too. Further developments are warranted in the field of data quality assurance and efficient maintenance.

Uncertainties of stormwater characteristics and removal rates of stormwater treatment facilities: Implications for stormwater handling

Stormwater runoff is a major contributor to the pollution of receiving waters. This study focuses at characterising stormwater in order to be able to determine the impact of stormwater on receiving waters and to be able to select the most appropriate stormwater handling strategy. The stormwater characterisation is based on determining site mean concentrations (SMCs) and their uncertainties as well as the treatability of stormwater by monitoring specific pollutants concentration levels (TSS, COD, BOD, TKN, TP, Pb, Cu, Zn, E.coli) at three full scale stormwater treatment facilities in Arnhem, the Netherlands. This has resulted in 106 storm events being monitored at the lamella settler, 59 at the high rate sand filter and 132 at the soil filter during the 2 year monitoring period. The stormwater characteristics in Arnhem in terms of SMCs for main pollutants TSS and COD and settling velocities differ from international data. This implies that decisions for stormwater handling made on international literature data will very likely be wrong due to assuming too high concentrations of pollutants and misjudgement of the treatability of stormwater. The removal rates monitored at the full scale treatment facilities are within the expected range, with the soil filter and the sand filter having higher removal rates than the lamella settler. The full scale pilots revealed the importance of incorporating gross solids removal in the design of stormwater treatment facilities, as the gross solids determine operation and maintenance requirements.

Assessing characteristic time and space scales of in-sewer processes by analysis of one year of continuous in-sewer monitoring data

Long-term and high-frequency in-sewer monitoring opens up a broad range of possibilities to study (influences on) water quantity and quality variations. Using data from the Eindhoven wastewater system in The Netherlands both dry weather flow and wet weather flow situations have been studied. For approximately 160 dry weather days mean diurnal variations of flow and pollutant concentrations have been derived. For wet weather situations (≈ 40 storm events) peak load factors have been studied. Generally, peak load factors for all considered pollutant parameters are larger than one. Peak load factors for particulate matter are larger than for dissolved constituents. Also, the smallest catchment area consistently shows the largest mean peak factors and vice versa.

Uncertainties associated with laser profiling of concrete sewer pipes for the quantification of the interior geometry

Structural strength and hydraulic capacity are two essential parameters in the assessment of the need for sewer rehabilitation. Especially concrete pipes suffer from loss of wall thickness due to biochemical corrosion and, consequently, a decreasing structural strength along with an increase of hydraulic roughness. Unfortunately, routinely used visual inspection methods do not allow a quantification of the internal pipe geometry which would enable not only detecting but also quantifying the progress of biochemical corrosion. Advances in laser technology and digital cameras theoretically allow a cost-effective application of laser profilers to measure the interior geometry of sewer pipes. An analysis of associated uncertainties revealed that the position and alignment of the laser are the main source of measurement errors. A full-scale laboratory set-up demonstrated, based on tests on a new and an 89 years old corroded sewer pipe, that laser scanning is indeed capable of measuring the interior geometry accurately enough to determine wall thickness losses for corroded pipes, provided that the position and alignment of the laser and camera are accounted for. The obtained accuracy, however, was not enough to quantify the hydraulic roughness.

Searching for storm water inflows in foul sewers using fibre-optic distributed temperature sensing

A major drawback of separate sewer systems is the occurrence of illicit connections: unintended sewer cross-connections that connect foul water outlets from residential or industrial premises to the storm water system and/or storm water outlets to the foul sewer system. The amount of unwanted storm water in foul sewer systems can be significant, resulting in a number of detrimental effects on the performance of the wastewater system. Efficient removal of storm water inflows into foul sewers requires knowledge of the exact locations of the inflows. This paper presents the use of distributed temperature sensing (DTS) monitoring data to localize illicit storm water inflows into foul sewer systems. Data results from two monitoring campaigns in foul sewer systems in the Netherlands and Germany are presented. For both areas a number of storm water inflow locations can be derived from the data. Storm water inflow can only be detected as long as the temperature of this inflow differs from the in-sewer temperatures prior to the event. Also, the in-sewer propagation of storm and wastewater can be monitored, enabling a detailed view on advection.

Settlement as a driver for sewer rehabilitation

This paper assesses the influence of (differential) settlement on sewer system functioning. Based on historical data of the vertical position of sewer invert levels, tilt measurements and in-sewer inspection videos, settlement and settlement related influences are analyzed for a case study area in Amsterdam. The average settlement rate of this system was 4 mm/year. Given this settlement rate, it is shown that settlement significantly influences sewer system functioning within the lifetime of a sewer (system).

Monitoring the performance of a storm water separating manifold with distributed temperature sensing

Storm water separating manifolds in house connections have been introduced as a cost effective solution to disconnect impervious areas from combined sewers. Such manifolds have been applied by the municipality of Breda, the Netherlands. In order to investigate the performance of the manifolds, a monitoring technique (distributed temperature sensing or DTS) using fiber optic cables has been applied in the sewer system of Breda. This paper describes the application of DTS as a research tool in sewer systems. DTS proves to be a powerful tool to monitor the performance of (parts of) a sewer system in time and space. The research project showed that DTS is capable of monitoring the performance of house connections and identifying locations of inflow of both sewage and storm runoff. The research results show that the performance of storm water separating manifolds varies over time, thus making them unreliable.

Performance evaluation of real time control in urban wastewater systems in practice: Review and perspective

Real time control (RTC) is generally viewed as a viable method for optimising the performance of urban wastewater systems. A literature review on the performance evaluation of RTC demonstrated a lack of consensus on how to do this. Two main deficiencies were identified: omitting uncertainty analysis and applying limited evaluation periods. A general methodology to evaluate the performance of RTC in practice, that takes into account these deficiencies, is proposed. The methodology is either data or model driven and the (dis)advantages of each are discussed. In a case study for a combined sewer system with limited discharge to a WWTP, it is demonstrated that the successful application of RTC and the possibility to determine a significant effect is very much dependent on the goal. It also clearly illustrates the need for taking uncertainties into account and that careful consideration in the chosen evaluation period is required.

Special Issue on ‘Sewer asset management’

Sewer systems are vital urban infrastructures, requiring appropriate asset management to safeguard serviceability and to balance service life versus costs for rehabilitation. In Europe, the total value of the sewer assets amounts to e 2000 billion. Assuming a replacement rate of once per 100 years, the annual rehabilitation costs amount to e 20 billion The shear height of these investments along with the recognition that the available knowledge on processes driving the ageing of these systems is still rather limited, should stimulate innovation on a vast scale. However, current sewer asset management has, unpurposely, been trapped in a deadlock since the 1980swithCCTV inspection as the ‘one size fits all’ source of information for sewer rehabilitation. All sewer operators throughout the EU and worldwide rely on this same source of information, which has been widely used as a basis for sewer deterioration models, decision support systems and sewer asset management approaches. Recently, however, CCTV inspection has been demonstrated not to be fully reliable and an insufficient source of information for sewer rehabilitation. The limited reliability is closely related to human errors in the assessment of CCTV footage and, in addition, CCTV cannot account for sewer conditions and failure mechanisms that cannot be observed form inside a sewer, such as exfiltration. The recognition of the limitations of using CCTV as a ‘one size fits all’ information source has opened up a newwindow of opportunity for research on sewer asset management. The papers of this Special Issue on Sewer Asset Management in the Urban Water Journal explore new directions for Sewer Asset Management by introducing inspection techniques to the ‘one size fits all’ approach, decision support systems with a broad and integrated approach, and interesting new material on lateral house connections, typically a forgotten part of the sewer system in sewer asset management. Plihal et al. developed a new method for the rapid inspection of sewer networks comprising a combination of acoustic sensors and the latest generation of manhole zoom cameras. The acoustic sensor is very powerful in detecting anomalies in the cross section of the sewer and locating these along the sewer length. Combined with a manhole zoom camera, this method is capable of providing information on the condition of the sewer comparable with traditional CCTV inspections for most type of conditions. The relative low costs of the new method will allow sewer asset managers to develop new inspection techniques for obtaining information on the hydraulic and/or structural condition. Cardoso et al. describe the application of the AWAREP procedure for planning sewer infrastructure asset management at fourteen wastewater utilities. Advanced sewer infrastructure asset management is key to achieve and ensure adequate future levels of service, in issues such as urban flooding, CSO discharges, and balancing performance, risk and costs. One of the key features in AWARE-P is to balance decision planning at three levels: strategic, tactical and operational. In order to facilitate decision making, data and information from various sources apart from the basic CCTV inspection is integrated in one system. Tscheikner-Gratl et al., describe the development of an tool for integrated rehabilitation planning of urban infrastructure systems using a street section priority model. Per street section, the condition and importance of sewers, drinking water pipes and rod construction are assessed in the street section priority model. Based on a weighed combination of condition and importance indicators, an integrated priority is given for the rehabilitation of urban infrastructures, exemplified by a case study. Ahmadi et al. describe the impact of the sample size on the calibration results of a decision-making multivariate model. They conclude that the calibration results rely heavily on the characteristics of the selected sample. As such, the reliability of the model supported decisionmaking relies strongly on the quality of its calibration, which is typically unknown to practitioners. Van Riel et al. have studied decision making for sewer asset management. Based on a survey of 150 sewer rehabilitation projects, they concluded that information on the condition of the assets is only dominant in 50% of the projects, whereas in 50% other factors play a dominant role. The other factors may range from implementing a policy to convert combined sewer systems into separate sewer systems to urban redevelopment, with a planning horizon that strongly depends on the economic development. This limits the general applicability of rational decision support models based on sewer asset information only, which might challenge further development of the decision support systems described in the preceding papers of Tscheikner-Gratl et al. and Cardoso et al.

On data requirements for calibration of integrated models for urban water systems

Modeling of integrated urban water systems (IUWS) has seen a rapid development in recent years. Models and software are available that describe the process dynamics in sewers, wastewater treatment plants (WWTPs), receiving water systems as well as at the interfaces between the submodels. Successful applications of integrated modeling are, however, relatively scarce. One of the reasons for this is the lack of high-quality monitoring data with the required spatial and temporal resolution and accuracy to calibrate and validate the integrated models, even though the state of the art of monitoring itself is no longer the limiting factor. This paper discusses the efforts to be able to meet the data requirements associated with integrated modeling and describes the methods applied to validate the monitoring data and to use submodels as software sensor to provide the necessary input for other submodels. The main conclusion of the paper is that state of the art monitoring is in principle sufficient to provide the data necessary to calibrate integrated models, but practical limitations resulting in incomplete data-sets hamper widespread application. In order to overcome these difficulties, redundancy of future monitoring networks should be increased and, at the same time, data handling (including data validation, mining and assimilation) should receive much more attention.