| 1. |
- Lindhe, Andreas, 1981
(författare)
-
Risk Assessment and Decision Support for Managing Drinking Water Systems
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The vital importance of a reliable and safe drinking water supply makes efficient risk management necessary for water utilities. Risks must be assessed and possible risk-reduction measures evaluated to provide relevant decision support. The World Health Organization emphasises the use of an integrated approach where the entire drinking water system, from source to tap, is considered when assessing and managing risks. Integrated risk assessments are important in order to avoid overlooking interactions between subsystems and events and to minimise sub-optimisation of risk-reduction measures. Methods for integrated risk assessment are, however, limited. A dynamic fault tree method is presented that enables quantitative, integrated risk assessment of drinking water systems. An approach for approximate dynamic fault tree calculations has been developed to minimise computational demand. It is shown how the method can be used to evaluate uncertainties and provide information on risk levels, failure probabilities, failure rates and downtimes of the entire system and its subsystems. The fault tree method identifies where risk-reduction measures are needed most and different risk-reduction alternatives can be modelled, evaluated and compared. The method is combined with economic analysis to identify the most cost-effective risk-reduction alternative. Integrated risk assessments of drinking water systems are commonly performed using risk ranking, where the probability and consequence of undesired events are assessed using discretised scales. There is, however, no common, structured way of using risk ranking to prioritise risk-reduction measures. Two alternative models for risk-based, multi-criteria decision analysis (MCDA) for evaluating and comparing risk-reduction measures have therefore been developed. The MCDA models are based on risk ranking, they can consider uncertainty in estimates and include criteria related to, for example, different risk types and economic aspects. In summary, this thesis provides methods for integrated risk assessment that make it possible to prioritise risk-reduction measures. It is concluded that the methods provide relevant decision support for efficient risk management in water utilities.
|
|
| 2. |
- Bergion, Viktor, 1986
(författare)
-
Risk-Based Decision Model for Microbial Risk Mitigation in Drinking Water Systems
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microbial risks in drinking water systems can cause sporadic pathogenic infections and waterborne outbreaks resulting in large costs for society. In 2010 for example, around 27,000 persons were infected with Cryptosporidium in Östersund, Sweden. It is so far the largest waterborne outbreak in Europe, and societal costs were estimated at SEK 220 million (approx. 20 million €). To achieve a safe drinking water supply, assessment of microbial risks and, when needed, implementation of risk mitigation measures is necessary. However, drinking water systems are complex, and risk mitigation measures are expensive. A thorough evaluation of possible mitigation measures is thus essential for identification of the most suitable alternative and efficient use of societal resources. In this thesis, a risk-based decision model for evaluating and comparing microbial risk mitigation measures in drinking water systems is presented and illustrated using two Swedish case studies. The decision model combines quantitative microbial risk assessment and cost-benefit analysis in order to evaluate decision alternatives from the perspective of social profitability. The quantitative microbial risk assessment is complemented with water quality modelling and consideration of unexpected risk events, such as extreme weather events and combined sewer overflows, in order to reflex the complexity of drinking water systems. To facilitate transparent cost-benefit analyses, the effect of different health valuation methods on the output from the decision model is presented. In the decision model, health benefits and other benefits are monetised for each mitigation measure and compared to the costs for implementing the measure. It is possible to combine decision criteria such as tolerable risk levels and maximising the net present value when applying the decision model. The decision model integrates several scientific disciplines, thus constituting a novel approach to evaluate microbial risk mitigation measures in drinking water systems and provides a structured analysis that includes often neglected aspects. The model provides transparent and holistic decision support and facilitates well-founded decisions balancing risks, costs and societal benefits.
|
|
| 3. |
- Ekholm, Jennifer, 1992
(författare)
-
Application of aerobic granular sludge for municipal wastewater treatment - Process performance and microbial community dynamics under fluctuating conditions
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pressures of growing cities, competition for use of urban areas and higher influent loads, are pushing for innovative technologies for wastewater treatment with low demands for land footprint and costs. Furthermore, wastewater treatment is needed to move towards a circular economy by harvest of valuable resources such as nutrients and energy. Aerobic granular sludge (AGS) is a biofilm process without a carrier material for wastewater treatment, exhibiting efficient treatment performance, excellent settleability, high biomass retention, tolerance to toxicity and high loads of organic matter. In this thesis, the first implementation of the AGS process in the Nordic countries was studied to assess the treatment performance, microbial community structure, energy usage, land footprint, and volume needs. The results in this project suggested that selective sludge withdrawal, retaining long solids retention time, sufficient substrate availability, and operational flexibility are important factors for granulation. Both the AGS and parallel conventional activated sludge (CAS) process achieved stable organic matter, nitrogen, and phosphorus removal with low average effluent concentrations. Seasonal variations and environmental factors were identified as important for microbial community succession. The granular biofilm demonstrated higher biomass concentration, diversity, and lower seasonal fluctuations in community composition than the flocculent sludge. A one-year energy comparison resulted in lower specific energy usages (kWh m-3 and kWh reduced P.E.-1) and land footprint for the AGS compared to the CAS process. However, a potential for decreased energy usage was recognised for both systems, leading to the conclusion that operational optimisation and process design might be as important as the type of technology. Additionally, the influence of decreasing temperature on AGS was studied in lab-scale reactors, revealing different responses of the functional groups in the microbial community, and even various response of ASVs at the genus level. In conclusion, the AGS technology for municipal wastewater treatment under fluctuating conditions achieved low average effluent concentrations, was more compact and energy efficient compared to the CAS.
|
|
| 4. |
- PALALANE, JAIME
(författare)
-
Processes of long-term coastal evolution and their mathematical modelling : Application to the Mozambican coast
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different processes in response to the action of natural driven forces and the human interference on coastal systems act together, contributing to shape the coast. Coastal evolution models have been developed as useful tools to better understand the contribution of different processes on observed coastal changes, and also to anticipate future evolution in response to different actions and interventions taking place along the coast.The predominant practice in coastal modelling is to have models that address separately the evolution as a result of cross-shore sediment transport processes from the ones caused by processes with main effects on the alongshore sediment transport. However, if longer time and spatial scales are to be covered by such models, a combination of cross-shore and longshore processes is crucial. In this context, the thesis explores the possibility of improving the mathematical modelling of long-term coastal evolution by integrating cross-shore evolution processes into a regional coastal evolution model.The developed models were satisfactorily tested against available data, as they could reproduce the observed coastal evolution. The model development stage was followed by its application to simulate the long-term coastal evolution of selected coastal stretches of Mozambique’s 2800-km-long coastline. Based on a literature review of different processes influencing the evolution of the Mozambican coast, the potential contribution of mathematical models to improve the local coastal planning and management was explored.With the model application to the Mozambican coast, it was possible to estimate sediment transport rates, and to reproduce the long-term evolution of the coast, for a period up to nearly two decades. For that reason, mathematical models are considered a valid tool to improve the understanding of the historical long-termcoastal evolution, and to anticipate how it will change in the future. The latter information would be valuable for the improvement of the protection of coastal sensitive systems, reinforcing the integration component, the use of soft approaches in coastal protection projects, and for the definition of setback lines.
|
|
| 5. |
- Teng, Penghua
(författare)
-
CFD MODELLING AND EXPERIMENTS ON AERATOR FLOW IN CHUTE SPILLWAYS
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A chute spillway is a typical component of large dams for discharging floods. Because of the high water head, the flow velocity in the chute is often in excess of 20 m/s. Consequently, the structure is usually prone to cavitation damages. Flow aeration is evidenced to efficiently eliminate or to mitigate the damages. An aerator is a device that entrains air into the water flows and is an effective technical measure to counter the cavitation damages.Aerator flow includes intense air-water exchange and involves a process of air entrainment, transport, and detrainment. Because of the complex phenomena, it is still a challenge to investigate the behaviors of interaction between air and water. It is fundamental to understand the flow behaviors downstream of the aerator. This thesis investigates the aerator flow features using both the Computational Fluid Dynamics (CFD) and advanced measurement techniques.The CFD method presents three two-phase flow models to describe the aerator flows, namely, the Volume of Fluid Model, the Mixture Model, and the Two-Fluid Model. They are applied and evaluated via practical engineering projects and experimental data. The Volume of Fluid model leads to reasonable results regarding the water flow discharge and flow fields. For predicting the air concentration distribution and air bubble transport processes, the Two-Fluid Model is superior to others because it includes forces acting on the air bubbles. However, the model still overestimates the air content near the chute bottom. Based on the aerator flow from a chute spillway in Sweden, three two-phase flow models are applied and compared.Physical model tests are commonly conducted to investigate aerator flow features. Because of the scale effects, the results may lead to a discrepancy in the flow behaviors compared with the prototype. Thus, CFD modeling becomes an alternative tool when seeking the reason for the difference. Based on the aerator flow in a real spillway, CFD is applied to reproduce the flow; the discrepancy between the model tests and prototype observations is evidenced. The results show similar flow features with the prototype but differ from those of the model tests. An explanation for the discrepancy is discussed in terms of flow features, effect of surface tension in model tests, and the prerequisite for air entrainment of the free-surface flow.Laboratory experiments are conducted to study the aerator flow in a chute. Four image-based measurement techniques－i.e., high-speed particle image velocimetry (HSPIV), shadowgraphic image method (SIM), bubble tracking method (BTM), and bubble image velocimetry (BIV)－are employed. The study focuses on issues of exploring characteristic positions of water-air interfaces, interpreting the evaluation process of air bubbles shed from the tip of the air cavity, identifying the probabilistic means for characteristic positions near the fluctuating free surface, and obtaining the flow field both water flow and air bubbles features of the aerator flow. The application of these techniques leads to a better understanding of two-phase flow characteristics of the chute aerator.
|
|
| 6. |
- Ezz-Aldeen Mohammad, Mohammad
(författare)
-
Sedimentation and Its Challenge for Sustainability of Hydraulic Structures : A Case Study of Mosul Dam Pumping Station
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A successful management and operation of water resources projects are essential to maintain their functions. Dams and reservoirs are one of the largest worldwide infrastructures. They serve one or more functions; reliable store and release of water for different purposes, hydropower generation and flood and draught controls. Sedimentation is one of the serious problems that affects the reservoir`s efficiency; it leads to reduction in storage capacity and reliability for water supply. Furthermore, deposition of sediment near and inside the intakes and hydropower plants cause a negative effect on plant efficiency and corrosion of turbines and pump`s impeller. Generally, degradations of the watersheds, surface runoff and river flow are the main sources and transporters of the reservoir’s sediment. Sediment management techniques are the most economical and efficient approach for sustainability of reservoirs and attached structures. Pumping rate, operation schedule, sub watersheds sediment control and earth dike is the reasonable alternatives that were applied in this study for sediment control and sustain water intakes. In Mosul Dam reservoir, the pumping station is considered as a case study, the station is suffering from sediment accumulation in front and inside the intake. The work includes application of Soil and Water Assessment Tool (SWAT) models to estimate the runoff and sediment load delivered by sub watersheds surrounding the studied area, and a sediment rating curve was considered to assess the sediment load carried by the main river (Tigris River). The Hydrological Engineering Centre’s River Analysis System ( HEC-RAS) model as a one dimensional model (1-D) was applied for sediment routing, and as a two dimensional model (2-D) for flow analysis. This aims to estimate the sediment load deposited in the studied reservoir and evaluated the effects of pumping rate and flow depth on flow velocity distribution, flow stream power and sediment transport. As this study focuses on the sedimentation problem on the area around the intake’s structure and due to compound flow regime and sediment transport near the intakes and withdraws outlets, a three dimensional (3-D) model is considered more suitable than a 1-D or a 2-D model. The Sediment Simulation in Intakes with Multiblock option (SSIIM) model was considered also in this study; a proper control code for studied case was developed. This model depends on Computational Fluid Dynamics (CDF) techniques as a numerical method to solve fluid motion problems.The applied models were calibrated and validated based on measured data of previous studies. The considered statistical criteria indicate that the models’ performances were reasonable for both flow and sediment assessments. The results of all applied strategies show an improvement with a different percent in the amount of sediment deposited in front and inside of the intake, in comparison with the current situation. The optimal improvement was obtained by adding a control earth dike upstream the station. It is considered the most efficient and practical strategy that can be applied for sustainability of the pumping station efficiency and lifespan with fewer dredging requirements.
|
|
| 7. |
- Ferdos, Farzad, 1984-
(författare)
-
Internal Erosion Phenomena in Embankment Dams : Throughflow and internal erosion mechanisms
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study, two major internal erosion initiation processes, suffusion and concentrated leak mechanisms, which lead to both defect formation in a dam’s body and its foundation and high throughflow in dams subjected to internal erosion were studied. This understanding has the potential to facilitate numerical modelling and expedite dam safety assessment studies. The throughflow properties of coarse rockfill material were studied by; analysing filed pump test data, performing extensive laboratory experiments with a large-scale apparatus and numerically simulating the three-dimensional flow through coarse rock materials, replicating the material used in the laboratory experiments.Results from the tests demonstrate that the parameters of the nonlinear momentum equation of the flow depend on the Reynolds number for pore Reynolds numbers lower than 60000. Numerical studies were also carried out to conduct numerical experiments. By applying a Lagrangian particle tracking method, a model for estimating the lengths of the flow channels in the porous media was developed. The shear forces exerted on the coarse particles in the porous media were found to be significantly dependent on the inertial forces of the flow.Suffusion and concentrated leak mechanisms were also studied by means of laboratory experiments to develop a theoretical framework for continuum-based numerical modelling. An erosion apparatus was designed and constructed with the capability of applying hydraulic and mechanical loading. Results were then used to develop constitutive laws of the soil erosion as a function of the applied hydromechanical load for both suffusion and concentrated leak mechanisms. Both the initiation and mass removal rate of were found to be dependent on the soil in-situ stresses.A three-dimensional electrical-resistivity-based tomography method was also adopted for the internal erosion apparatus and was found to be successful in visualising the porosity evolution due to suffusion.
|
|
| 8. |
- Haghighatafshar, Salar
(författare)
-
Blue-green stormwater systems for citywide flood mitigation : Monitoring, conceptualization, modeling, and evaluation
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Considering the growth in urbanization, leading to an increase in impervious surfaces, and the changing climate, enhancing the intensity and frequency of rainfall events, existing urban drainage networks—separate or combined sewer systems—are presumed to face substantially elevated hydraulic loads, causing pluvial floods in urban areas. There are several ways to address these challenges. Cities can invest in replacing existing pipes with new larger pipes to enhance the hydraulic capacity of the drainage network. This solution is considered to be extremely expensive and unsustainable. An alternative solution is to manipulate urban surfaces by constructing blue-green (open) stormwater systems. These systems are built on urban surfaces and include approaches that mimic natural processes, such as infiltration, evaporation, transpiration, pond storage, and slow transport of stormwater through ditches. The implementation of blue-green stormwater systems in dense cities would, to some extent, relieve the overload. However, the method for identifying urban areas in which the implementation of blue-green stormwater systems would have a larger effect hydraulically on the existing sewer network is unestablished.Thus, general aim of this thesis was to develop a method for studying the interactions between piped drainage networks and blue-green stormwater systems on the city-scale, performed in four steps, which shape the backbone of this thesis:•An existing blue-green stormwater system—i.e. the Eco-city of Augustenborg in Malmö—was examined to understand how such systems work, locally and regarding the surrounding neighborhoods.•A simple conceptual model for blue-green stormwater systems was proposed.•Based on the proposed concept, a fast, easy-to-use, and robust modeling tool was developed, making it possible to simulate the interaction between blue-green stormwater systems and sewer networks.•The modeling tool was supplemented with a hydroeconomic optimization algorithm and evaluated on the city-scale to identify the most effective site and size for blue-green stormwater systems throughout the catchment of the sewer network.The developed method and toolchain constitute a new platform for increasing our understanding of complex urban drainage networks. This platform is also a starting point for the development of a more reliable tool for the initial screening of urban catchments to identify urban areas in which it is hydraulically and economically efficient to construct neighborhood-scale blue-green stormwater systems.
|
|
| 9. |
- Malm, Annika, 1970
(författare)
-
Aspects of historical data and health criteria for drinking water network replacement strategies
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The drinking water distribution network represents a major proportion of the investments and capital assets of a water utility. Consequently, qualified insight into future replacement needs provides water utilities with a foundation for financial planning. This insight would allow responsible engineers to choose the right projects (pipes and pipe systems) for replacement. Currently, support for the correct project choice is through sophisticated methods and models. However, utilities (especially smaller) need simpler procedures as they often lack both input data and competence for advanced infrastructure asset management models, as well as the experience of using such models. The aim of this thesis has been to provide new knowledge and useful, simple and transparent tools for the assessment and evaluation of long-term needs and prioritization of drinking water pipe replacement. An assessment of the future long-term replacement needs for drinking water distribution networks can be made through a combination of lifetime distribution functions and current network age data. Reliable lifetime predictions are limited by a lack of understanding of deterioration processes for different pipe materials under varying conditions. However, in this thesis a method was applied to calculate national investment needs and the results provided a basis for estimates for Swedish utilities where there is a scarcity of data. An alternative approach, employed successfully in this thesis, was the use of real historical data for replacement over an extended time series. The verified data provided a good fit to commonly used lifetime distribution curves. Further, reasonable projections of replacement needs into an uncertain future could be made. CBA (Cost-benefit analysis) can be used to evaluate the replacement strategy for utilities’ water distribution networks. CBA was applied to evaluate how first, pipe failure data and second, leakage strategies, might be used in pipe prioritization strategies. CBA was applied to pipe failure data replacement priorities, and here the cost of replacement was compared to the benefits of fewer pipe failures. The method enabled the selection of prioritised pipe sections for replacement without the need for a range of parameters and advanced methods that are difficult to interpret. Scenario analysis showed that health aspects have a significant impact on the result, and a method for evaluating the health risk was developed. For the CBA application to leakage management, the benefits of leakage reduction were compared to the cost of alternative management options to determine which was the most cost-effective. In the case study distribution system it was demonstrated that it is significantly more cost-effective to reduce leakage volumes by reactively repairing broken pipes than to proactively replace them, despite large leakage losses.
|
|
| 10. |
- Aboulila, Tarek Selim
(författare)
-
Evaluation of Modern Irrigation Techniques with Brackish Water
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern irrigation techniques are becoming increasingly important in water-scarce countries especially in arid and semiarid regions. Higher crop production and better water use efficiency are usually achieved by drip irrigation as compared to other irrigation methods. Furthermore, by using drip irrigation simultaneously with brackish irrigation water, some of the water stress due to shortage of fresh water resources can be managed. The objective of the current study was to investigate the influence of geometric design, soil type, irrigation regime and amount, and salinity of irrigation water on soil water and salinity distribution as well as irrigation efficiency using drip irrigation techniques in Egypt and Tunisia. Field and laboratory experiments as well as numerical simulations were used to achieve these objectives. Two field experiments were conducted at two different sites and soil types in Tunisia. The first experiment was conducted to explore the effect of different drip irrigation treatment (i.e., surface drip irrigation with and without plastic mulch and subsurface drip irrigation) and regime (i.e., daily and bi-weekly) on soil water and salinity distribution as well as contaminant transport for sandy loam soil. The second experiment was carried out to investigate the mobility of different tracers (bromide and dye) under surface drip irrigation in loamy sand soil. Lab experiments using soil samples collected in Egypt and Tunisia were made to estimate soil hydraulic properties, soil texture, and soil moisture content. Numerical simulations for surface and subsurface drip irrigation and alternate partial root-zone surface and subsurface drip irrigation with brackish irrigation water were executed to investigate the effect of geometric design, irrigation regime and amount, and salinity of irrigation water on soil water and salinity distribution as well as irrigation efficiency for different soil types in El-Salam Canal project region, Egypt. Field experiments showed that maximum dye penetration depth during daily and bi-weekly irrigation occurred for subsurface drip irrigation. Also, during the bi-weekly irrigation, dye depth was not only larger but also occupied a larger soil volume than for the daily irrigation. Thus, bi-weekly irrigation increases the risk for groundwater contamination. Also, higher soil moisture content within the flow domain occurred with mulching treatment and daily irrigation. Simulations displayed a very close agreement with observed soil wetting. Multiple tracer experiments revealed that the bromide moved faster than dye. Therefore, fertilizers transport deeper than organic pollutants under surface drip irrigation in initially dry loamy sand soil. Numerical simulations verified this. On the other hand, numerical simulations for surface drip irrigation in El-Salam Canal cultivate land showed that soil hydraulic properties govern the shape of the wetted zone. The wetted depth was larger in sand while the wetted radius was lower as compared to loamy sand and sandy loam. Simulation results for subsurface drip irrigation (SDI) showed that deeper emitter depth increases the potential groundwater contamination risk and fertilizer leaching especially in sandy soil and shallow rooted plants. Also, it is preferable to control the wetted volume of any soil type by regulating the amount of irrigation water according to soil hydraulic properties. Simulation results also revealed that higher moisture content values within the flow domain and higher root water uptake rates occurred in case of short inter-plant emitter distances (IPED) under alternate partial root-zone surface and subsurface drip irrigation (APRDI and APRSDI, respectively). Therefore, Short IPED is preferable especially for root systems with limited lateral extension. Salinity results showed that as the salinity of irrigation water increased, the salinity levels at the soil surface at the location of the plant trunk under APRSDI increased. Therefore, APRSDI is more suitable with non-saline irrigation water, especially for shallow rooted plants. However, in case of using brackish irrigation water, short IPED and shallow emitter depth are recommended for reducing soil salinity below the plant trunk.
|
|
