| 1. |
- Müller, Alexandra
(author)
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An evaluation of sources contributing to urban runoff pollution
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Urban runoff is a significant pathway for the transport of diverse substances from the urban environment to receiving water bodies. Many of these substances are pollutants of environmental concern with potentially harmful effects on aquatic life. Detailed knowledge of the sources of pollutants entering stormwater runoff is needed to mitigate these effects.The overall aim of this doctoral thesis is therefore to provide new knowledge on the sources contributing to urban runoff pollution and to evaluate the specific contributions of micropollutants from two known major sources: building and structure surface materials, and vehicular activities. The work presented herein also (i) identifies pollutants that are expected to occur in runoff from buildings and other structure surfaces in the urban environment as well as in runoff from the road environment, (ii) estimates the concentrations of these pollutants released into runoff, and (iii) evaluates methods for identifying sources contributing to the pollution of urban stormwater runoff.The novel work presented in the thesis includes a critical review of the literature on sources contributing to urban runoff pollution, laboratory leaching tests and open-air sampling of pilot panels of building and structure surface materials, and field sampling of urban roadside snow. The literature review was not restricted in terms of type of pollution, while the experiments focused on selected metals and organic micropollutants including phthalates, alkylphenols, bisphenol A, and polycyclic aromatic hydrocarbons (PAHs).According to the literature review, atmospheric deposition, vehicular activities, and metallic building envelopes are the major pollution sources in the urban environment and have been studied far more extensively than other sources. Moreover, their dominance is likely to continue given their central roles in urban environments. The experimental results confirmed that vehicular activities were sources of octylphenols, bisphenol A, and phthalates as well as the metal(loid)s Sb and W, both of which were rarely determined in previous studies on urban runoff. Building and structure surface materials such as copper sheets, zinc sheets, and polyvinyl chloride (PVC) roofing membranes were found to release Cu, Zn, nonylphenols, and phthalates. Among alkylphenols, nonylphenols were predominantly found in building surface runoff while octylphenols occurred predominantly in roadside snow. Metals occurred more commonly in dissolved (<0.45 μm) form in building surface runoff than in roadside snow, where metals were mainly attached to particles.A comparison of methods for identifying building surface materials contributing to runoff pollution showed that laboratory leaching tests were generally effective for source identification but not for estimating concentrations in actual runoff, whereas open-air pilot studies were resource-intensive but give results that agree well with analyses of real runoff. In addition, the release of pollutants from building surface materials subjected to in-situ ageing was investigated and the water quality of rainwater-induced runoff was compared to that of snowmelt-induced runoff; neither of these issues were adequately addressed in the previous literature. These studies showed that pollutant concentrations were generally higher in rain runoff than in snowmelt runoff and that pollutant releases from most materials and substances exhibited no decreasing or increasing trend over time. However, the release of nonylphenols from one of the PVCs did decrease over time, possibly because of washing out and material ageing.
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| 2. |
- Beryani, Ali
(author)
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Organic micropollutants in highway stormwater and the role of a gross pollutant trap-biofilter stormwater treatment train
- 2023
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Licentiate thesis (other academic/artistic)abstract
- The studies which this thesis is based on assessed the stormwater quality in a highway catchment located in Sundsvall, Sweden, and examined the performance of a gross pollutant trap (GPT)-biofilter stormwater treatment train (TT) downstream of the catchment, in terms of removal efficiency, intra-event variability, and environmental risk reduction of organic micropollutants (OMPs) for the receiving water body. Assessing the occurrence and event mean concentrations (EMCs) of all OMPs in the catchment revealed that bisphenol A (BPA), octylphenol (OP), nonylphenol (NP), five carcinogenic and four non-carcinogenic polycyclic aromatic hydrocarbons (PAHs), and C16-C40 fractions of petroleum hydrocarbons (PHCs) all potentially pose an environmental risk to freshwater (EMCs >PNEC: predicted non-effect concentration), while alkylphenolethoxylates, six low- molecular weight PAHs, and lighter fractions of PHCs (C10-C16) do not occur at problematic levels.In order to assess the impact of the downstream TT in mitigating the risks of the studied OMPs, the performance of the TT compartments (a GPT followed by three filter cells) was analyzed and then compared with each other to identify the importance of each design feature (i.e. pre-treatment GPT, sand-based filter media, vegetation, and chalk amendment). Overall, the TT removed most OMPs from highway runoff effectively. The GTP did not contribute to this treatment, thus, the filter sections were responsible for most of the OMP removal. The results showed that, although the non-vegetated sandfilter (SF) could moderately (<50% removal for phenolic substances) to substantially (50–80% removal for PAHs and PHCs) treat the OMPs, the vegetated biofilters (BF and BFC) considerably improved the removal performance, especially for BPA, OP, and suspended solids (TSS). This observation was explained by additional filtration processes provided by the vegetation topsoil layer, which not only enhanced the particulate/particle-bound OMP physical retention but also physiochemical adsorption of colloidal and soluble substances/fractions (such as BPA and OP).Further analysis of intra-event concentration (IEC) variations of OMPs and TSS showed that the IECs in the highway stormwater and GPT outflow varied considerably without any particular patterns over the course of the events, but first flush rarely occurred. The IEC variations were attenuated by the SF and BFC cells so that more even pollutant load discharge with no first flush was observed during the filter cells’ outflow events. Yet, the IECs for the SF cell revealed that the IECs often peak at the beginning of the effluent events (within the first 100 m3 out of maximum record of ⁓600 m3) and then decrease and become stabilized towards the end of the event. The early-phase concentration peaks exceeded the PNECs for TSS, five PAHs, BPA, and OP, a fact that was not shown by the EMC-based analysis, thus highlighted the advantage of the IEC analysis.
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| 3. |
- Broekhuizen, Ico, 1993-
(author)
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Uncertainties in rainfall-runoff modelling of green urban drainage systems : Measurements, data selection and model structure
- 2019
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Licentiate thesis (other academic/artistic)abstract
- Green urban drainage systems are used to avoid flooding and damages to people and property, while limiting the downstream flooding and water quality problems caused by pipe-based drainage systems. Computer models are used to analyse and predict the performance of such systems for design and operation purposes. Such models are simplifications of reality and based on uncertain measured data, so uncertainties will be involved in the modelling process and its outcomes, which can affect the design and operation of these systems. These uncertainties have been investigated extensively for traditional pipe-based urban drainage systems, but not yet for green alternatives. Therefore, the overall objective of this thesis is to contribute to improved applicability and reliability of computer models of green urban drainage systems. Specifically, the thesis aims to (1) improve understanding of the uncertainties arising from (a) model structure and (b) calibration data selection, (2) evaluate two alternative calibration methods for green urban drainage models, (3) discuss desirable structural features in urban drainage models, and (4) evaluate several sensors for hydrometeorological measurements in urban catchments.The effects of model structure uncertainty were investigated using long-term simulations of synthetic catchments with varying soil types and depths for three different models. First, it was found that surface runoff could be a significant part of the annual water balance in all three models, depending on the soil type and depth considered. Second, differences were found in how sensitive the different models were to changes in soil type and depth. Third, the variation between different models was often large compared to the variation between different soil types. Fourth, the magnitude of inter-annual and inter-event variation varied between the models. Overall, the findings indicate that significant differences may occur in urban drainage modelling studies, depending on which model is used, and this may affect the design or operation of such systems.The uncertainty from calibration data selection was investigated primarily by calibrating both a low- and high-resolution stormwater model using different sets of events. These event sets used different rainfall-runoff statistics to rank all observed events before selecting the top six for use in calibration. In addition, they varied by either calibrating all parameters simultaneously, or by calibrating parameters for impervious and pervious surfaces separately. This last approach sped up the calibration process. In the validation period the high-resolution models performed better than their low-resolution counterparts and the two-stage calibrations matched runoff volume and peak flows better than single-stage calibrations. Overall, the way in which the calibration events are selected was shown to have a major impact on the performance of the calibrated model.Calibration data selection was also investigated by examining different ways of including soil water content (SWC) observations in the calibration process of a model of a swale. Some model parameters could be identified from SWC, but not from outflow observations. Including SWC in the model evaluation affected the precision of swale outflow predictions. Different ways of setting initial conditions in the model (observations or an equilibrium condition) affected both of these findings.The precipitation sensors used in this thesis showed generally satisfactory performance in field calibration checks. Different types of precipitation sensors were associated with different requirements for maintenance and data acquisition. Sensors for sewer pipe flow rates showed good agreement with a reference instrument in the laboratory, as long as installation conditions were good. Higher pipe slopes and upstream obstacles lead to larger measurement errors, but this last effect was reduced by increasing water levels in the pipe. Sensor fouling was a source of errors and gaps in field measurements, showing that regular maintenance is required. The findings show that the evaluated flow sensors can perform satisfactorily, if measurement sites are carefully selected.
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| 4. |
- Galfi, Helen
(author)
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Assessment of stormwater and snowmelt quality based on water management priorities and the consequent water quality parameters
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Stormwater and snowmelt pollution contributes to degradation of quality of the receiving waters. For assessing such impacts, it is effective to focus on specific causes of degradation, as done in this study of the quality of stormwater and snowmelt discharges into the receiving waters serving for supply of raw drinking water and water-based recreation. While the main priority were faecal indicator bacteria (FIBs), the understanding of their occurrence, and of other potential effects on the receiving waters, required addressing additional water quality parameters as well. Exports of FIBs in stormwater and snowmelt discharged from four urban catchments yielded the following findings: (a) E.coli, with mean concentration of all stormwater data Cmean = 430 cfu (colony forming units)/100 mL, and enterococci (Cmean=1380 cfu/100 mL) were the best indicators of faecal pollution of stormwater, but total coliform (Cmean=3130 cfu/100 mL) and C. perfringens (Cmean=150 cfu/100 mL) were much less effective: the former indicator includes non-faecal bacteria and the latter one barely varied; (b) Among the different catchments, the central catchment with mixed land use produced the highest concentrations of FIBs; (c) FIB concentrations in snowmelt were significant only in the case of enterococci (400 cfu/100 mL); and, (d) Baseflows in two catchments were practically devoid of FIBs, with Cmean=10 cfu/100 mL for both E.coli and enterococci. Hence, there were no contributions of sanitary sewage to the storm sewer baseflows.FIB concentrations varied with stormwater or snowmelt quality, described by associated parameters, which were identified by cluster analysis as: temperature, conductivity, TSS, flow rate, and TP. Such findings were used in statistical regressions indicating that E. coli and enterococci could be statistically modelled in three of the four catchments, with determination coefficients R2 ranging from 38-66%. In spite of uncertainties, such modelling would be useful for future FIB monitoring, or for comparing remediation alternatives. Estimation of FIBs by microbial partitioning to settleable solids (represented by gully pot sediments) was infeasible, because these highly mineral sediments contained little FIBs.Storm sewer outfall effluents were also analyzed for mineral (Al, Ca, Fe, K, Mg, Na) and anthropogenic indicator trace metal (TM) inorganics (Cd, Cr, Cu, Ni, Pb, Zn). The total mass of inorganics exported from the catchments by runoff or snowmelt was dominated by mineral inorganics, which were particularly high in baseflows. TM concentrations were compared to the tentative guidance limits suggested in Sweden as annual mean, or maximum event mean, total TM concentrations. Effluents from the catchments studied clearly exceeded the recommended values 5 times in the case of Zn.Field studies drew attention to uncertainties in measured FIBs and solids. Automated sampling of greatly varying FIB concentrations was affected by sampling line water residuals, which can be minimized by short sampling lines and avoidance of sags in the sampling line. Stormwater and snowmelt solids were underestimated by the conventional TSS method requiring withdrawal of aliquots from total samples. This bias can be eliminated by using whole-sample methods; either the existing SSC (suspended sediment concentration) method, or the newly proposed (and easier to use) multiple filter procedure (MFP), filtering whole samples through progressively finer filters (pore sizes 25, 1.6 and 0.45 µm). The MFP produced data equivalent to those obtained with SSC, as confirmed by the Limits of Agreement (LoA) statistical procedure.
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| 5. |
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| 6. |
- Okwori, Emmanuel, 1988-
(author)
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Analytics-driven approaches supporting asset management of sanitary sewer networks
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Sewer blockages can cause overflows and flooding, with consequences such as damage to property and environmental pollution, risks to public health and economic loss. Despite the causes being understood, blockages in sewer networks may occur unpredictably. The responsible staff for sewer networks at water utilities need to efficiently determine the most effective action (what), the specific network location needing attention (where), the optimal timing for intervention (when), and the appropriate remedial task (how), especially given the unpredictability of blockages. Today a reactive approach to asset management and maintenance is often adopted. Additionally, data availability, quality and interoperability between systems are not always at levels that can support decided objectives, proactive maintenance planning and asset management of pipe networks. Thus, the aim of this thesis is to propose and evaluate approaches that can support analytics-driven maintenance planning and asset management for sewer networks. These approaches aim to contribute to mitigating the impact of siloed data structures and enhance the understanding of blockage root causes from a spatial perspective.In this thesis, the challenges of data management in the asset management of pipe networks were investigated through focus group workshops and questionnaire surveys. A conceptual framework was developed based on findings from focus group workshops and surveys. The framework combines data quality assessments, interoperability evaluations between asset management tools, data collection, and informational benefits analysis. This framework aimed to identify the presence of data silos and plausible pathways towards more data-driven data management strategies. A performance assessment combining performance indicators associated with blockages and partial least squares regression (PLS) was conducted to draw inferences that could be useful at a strategic level. Furthermore, a spatial heterogeneity assessment of blockages and factors affecting blockages was carried out. This approach combined network kernel density estimation (NKDE), network k-function, and geographically weighted Poisson regression (GWPR). Lastly, a vulnerability assessment was carried out that combined topological analysis using edge-based centrality measures and network cross-k-function. These approaches were applied to three sewer networks.The focus group workshops and questionnaire surveys identified several challenges affecting data management in the context of pipe network asset management. Many of the challenges could be ascribed to issues related to data quality and interoperability. Results from the preliminary application of the conceptual framework showed how it could be applied for identifying data silos and pathways to data-driven decision-making towards proactive management blockages in sewers. The observed spatial trends and patterns from network k-function analysis and network kernel density estimation showed spatial variability in the occurrence of blockages (single occurring and recurring). Geographically-weighted Poisson regression analysis showed spatial heterogeneity in factors influencing blockage propensity. The network cross-k-function analysis demonstrated that pipes with historical blockage incidents tend to be clustered around critical pipes with higher centrality values. These results could support vulnerability assessments in sewer networks and the development of targeted maintenance strategies. These approaches together could aid data-informed maintenance planning and asset management at the strategic, tactical and operational levels.
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| 7. |
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| 8. |
- Wei, Haoyu
(author)
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Accumulation and Composition of Gully Pot Sediments under Varying Anthropogenic Activities
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Gully pots (GPs) are an integral urban drainage component, contributing to conveying runoff from urban surfaces and reducing the load of solids and associated contaminants entering downstream piped systems and receiving waters. Over time, the silting-up of GPs impairs their hydraulic performance, increasing the risk of GP blockage-induced flood events and reducing solids retention performance. These challenges are typically addressed through GP emptying programmes. However, current GP maintenance strategies lack clear aims and a robust evidence-base, against which their effectiveness can be benchmarked. The overall aim of this doctoral thesis is to enhance understanding of the factors influencing the physicochemical properties and accumulation of solids in GPs, thereby laying the groundwork for further assessment and optimisation of GP maintenance strategies. The study encompasses various anthropogenic factors such as land use types, seasonal activities, traffic conditions, environmental regulatory measures, GP design and catchment characteristics. Research reported in this thesis includes both desk-based modelling (e.g. a study on sediment scour behaviours), and the results of an extensive field sampling campaign (sediments from a total of 87 GPs were assessed for dry masses, particle size distribution (PSD) and a range of conventional and emerging urban and traffic-related substances).The considerable variations in physicochemical properties, mass accumulation rates of sediments and associated contaminants in GPs question the utility of the prevalent generalised maintenance strategy. Although GPs in trafficked roads showed significantly higher solids mass accumulation rates compared to those in non-trafficked catchments, this factor alone could not fully explain observed variations. For example, whilst selected typically traffic-sourced contaminants such as 4-tert-octylphenol (OP) and heavy-molecular-weight polycyclic aromatic hydrocarbons (PAH-H) exhibited significantly higher concentrations in GP sediments from trafficked roads, further typically-traffic-related pollutants (e.g. aliphatic hydrocarbon > C16-C35 and Zn), as well as 4-nonylphenol (NP) and monobutyltin (MBT) were reported for GPs located in commercial and car parking land-use types. In terms of temporal dynamics, winter-spring road safety measures did not consistently result in significantly higher solids mass accumulation rates compared to summer-autumn accumulation data. However, where present, a greater influence of winter-spring road safety measures was identified under certain conditions. For example, GPs along straight roads with adjacent pedestrian/bicycle paths showed an up-to 130-fold increase in solids accumulation rates following winter-spring accumulation, largely due to the practice of using coarse traction grits in this road feature type. Synergistic impacts of winter-spring road safety measures and road layout features were also observed. This includes amplified tyre and road wear (a function of the combined use of studded tyres, traction grits and frequent braking at roundabouts) is identified as contributing to e.g. significantly higher mass fraction of <63 µm sediments and concentrations of Zn, Cd, OP, selected PAHs and phthalates in corresponding GPs following winter-spring accumulation. Additionally, significant temporal changes in basic parameters of GP sediments such as pH, electrical conductivity (EC) and total organic carbon (TOC) were identified, indicating substance phase changes (e.g. adsorption/desorption) at solid-liquid interfaces should be anticipated, and their impact considered when assessing GP sediment management needs.This research also contributes to sediment management through the characterisation of GP sediments for a broad list of contaminants. The comparison of sediment substance concentrations with Predicted No-Effect Concentrations (PNECs) (and, where these are not available, with Norwegian guideline values) indicated that 31 substances in at least one investigated GP exceeded threshold values. This demonstrates that GPs can accumulate contaminated sediments and underscores the need to revisit the role of GPs in mitigating runoff quality (and quantity) as part of an integrated urban stormwater management plan.
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