Interacties binnen het afvalwatersysteem

Civil Engineering and Geoscience

Interactions within wastewater systems

Wastewater systems consist of sewer systems and wastewater treatment works. As the performance of a wastewater treatment plant is affected by the characteristics, i.e. operation and design, of the contributing sewer systems, knowledge of the interactions between sewers and wastewater treatment works is very important when trying to understand and improve wastewater systems. The thesis comprises three main topics: Firstly, the sensitivity of wastewater treatment plant performance to influent fluctuations is discussed, based on both measurement data and model results. Secondly, the quality of model results achievable with state of the art sewer models are described for the most important in sewer processes. Finally, the impact of the interactions within the wastewater system on wastewater system performance is illustrated in a semi-hypothetical case study. The thesis concludes that knowledge on the interactions is not only essential with respect to understanding of wastewater system performance, but that this knowledge opens new ways of dealing with our existing wastewater infrastructure.Civil Engineering and Geoscience

Rethinking Wastewater Treatment Plant Effluent Standards: Nutrient Reduction or Nutrient Control?

Sanitary Engineerin

Extensive testing on PVC sewer pipes towards identifying the factors that affect their operational lifetime

Polyvinyl chloride (PVC) sewer pipes have operated for decades in a hostile environment, raising concern among sewer managers over the longevity of their drainage systems. Inspection data (CCTV and Panoramo®) reveals that severe defects have already surfaced, yet it is unknown if the material properties of PVC sewers have been affected. In order to address this issue, extensive testing (among others flexural and tensile tests, FT-IR, X-ray, viscosity measurements) was conducted on eight exhumed PVC sewer pipes (16–43 years old) with known defects and one brand-new for reference purposes. Visual examination during excavation revealed various failure causes, including uncontrolled handling of the pipes during construction or due to digging activities in the direct vicinity of the pipes. The test results indicate that physical ageing is extensively detected while other degradation mechanisms had minimal or no effect on the investigated pipes. However, mechanical testing on exhumed 3-layer pipes show that the incorporation of layered wall constructions is potentially a critical factor for the structural status of the pipe.Sanitary Engineerin

Analysing spatial patterns in lateral house connection blockages to support management strategies

The performance of lateral house connections has a direct impact on sewer serviceability. Despite the potential consequences of a blockage, these components are generally maintained with a reactive approach. As inspection data on the condition of lateral house connections are scarce, this study adopts a statistical procedure to support proactive strategies by analysing spatial blockage patterns to identify system parts with higher blockage incidences. First, a Monte Carlo simulation test provides insight into whether the spatial variation of the blockage likelihood is significant. This justifies the identification of explanatory factors by means of a bootstrapped generalised additive model. Application of the procedure to two databases containing 10 years of lateral house connection blockage data, revealed factors such as building age, sewer system type and ground settlement rate to explain spatial differences in the blockage likelihood. Furthermore, a likelihood ratio test demonstrated that the addition of a spatial smoother improved model performance. This smoother was able to account for additional spatial variation caused by explaining factors for which no data were available. The procedure provides key information for inspection and rehabilitation strategies by taking into account the model performance in assessing the trade-off between costs and benefits in terms of serviceability.Sanitary Engineerin

The role of integration for future urban water systems: Identifying Dutch urban water practitioners' perspectives using Q methodology

Urban water systems are under increased pressure from ongoing developments like climate change, population growth and urbanization. While it is clear that current urban water challenges need a more integrated approach, practitioners disagree on what such an integrated approach means exactly. Integration could therefore be described as a wicked problem, with practitioners having different understandings of integration, as well as the opportunities and challenges they should focus on; e.g., climate adaptation, resource recovery or collective replacement. This lack of consensus challenges decision-making, and thus the implementation of integration. To foster urban water systems integration, this study uses Q methodology to explore the different perspectives that Dutch urban water practitioners have on integration for future urban water systems. Our analysis reveals four salient perspectives: perspective 1 sees coordination as a means to make the system future-proof, perspective 2 focuses on climate adaptation, perspective 3 aims for recovery, and perspective 4 is all about efficiency and being in control. While all perspectives acknowledge that traditional urban water practices need to change, they differ on which sustainability challenges are considered most important and what means should be used. Practitioners need to understand these differences to deal effectively with the wicked nature of integration.Sanitary Engineerin

Identification of the information needs for sewer asset management by assessing failure mechanics

Asset management is a prerequisite for maintaining the required level of serviceability of urban drainage systems. The required asset management effort to achieve a certain level of service is unclear due to sewer systems process and structure complexity. One of the main questions of asset management is what kind of information is needed, and how this information can be obtained. Sewer failure mechanisms explain the structural/operational failures of sewer elements. This study focuses on determining the information required to be able to detect and identify sewer failure mechanisms. In order to be able to identify the failure mechanisms involved, a HAZOP approach was applied. The main processes and defects responsible for the structural/operational failures of sewer elements were identified, as well as possibility of obtaining the information about them. This information will help in estimating the probability of failure occurrence and generally it will help defining the information needed for proper serviceability.Water ManagementCivil Engineering and Geoscience

Potential of Laser Scanning for Quantification of Sediment Deposits in Sewer

There is still a long way to go in understanding the behaviour of solids in sewers due to the difficulties in obtaining sufficient monitoring data to be able to understand the dominant processes. Laser profilers have shown to be capable of measuring the pipe interior, with a high accuracy, which is sufficient to be able to detect and quantify wall losses. This paper describes the potential of laser scanning for measuring sediment volumes in sewers. In addition, the propagation of uncertainties from laser measurements to sediment volumes are discussed, with special attention to conditions that could affect the measurements. The Laser profiler has shown to be capable of measuring the pipe interior, which is sufficient to be able to detect and quantify sediment volume. Overall, this research is a first step in defining a new inspection concept that will be able to give reliable information on relevant failure mechanisms.Water ManagementCivil Engineering and Geoscience

Monitoring and statistical modelling of the solids accumulation rate in gully pots

Gully pots are utilized for conveying runoff to drainage systems, as well as for reducing the system’s solids loading by retaining suspended solids. However, the accumulation of solids in gully pots reduces their removal efficiency, leading to an increase in solids transport towards the drainage system. This article aims to identify the main drivers of the solids accumulation in gully pots and, thus the relevant processes for wash-off models. The solids accumulation rates in 407 gully pots were monitored within a period of ~14 months and were analysed by means of a linear mixed model and a regression tree. The parameters vegetation factor, rainfall volume, and filling degree are the main drivers of the accumulation process. These parameters are linked to the solids build-up in a catchment, solids transport, and solids retention in gully pots, which means that none of these 3 processes is dominant.Sanitary Engineerin