61 research outputs found
Bulking sludge control. Kinetics, substrate storage, and process design aspects
No full textThe activated sludge process is the preferred technology for biological wastewater treatment. Despite decades of progress and operation serious operating problems still occur with this process. One major problem is the regular occurrence of excessive growth of filamentous bacteria, phenomena known as filamentous bulking sludge. Poor solid-liquid separation can occur as result of this problem, leading to effluent quality deterioration and to process failure due to uncontrollable loss of biomass with the effluent. The goal of this thesis was to achieve a better understanding of bulking sludge and the relevant factors involved. To accomplish these objectives, well-controlled laboratory scale sequencing batch reactors with mixed microbial cultures and defined substrates, were operated under different conditions. Traditionally pure culture microbiology or full scale reactor observations have been the basis for the research. The choosen process engineering approach proved to be a success to study bulking sludge. Not only filamentous bacteria grew very well under specific conditions but also the results were reproducible and trends relating sludge settleability and operational conditions were identified. Design guidelines and operation aspects were proposed to control bulking sludge, leading to more robust, reliable, predictive, and sustainable activated sludge systems. Together with a literature review, the experimental results were the basis to develop a unifying hypothesis about bulking sludge - diffusion based selection. This theory can replace the existing theory based on kinetic selection. Both bacterial morphology and substrate micro-gradients inside microbial aggregates are hypothesized as playing a dominant role in selection for bulking sludge. An individual-based model, originally developed to a biofilm system, is adapted for the first time to model the competition between different bacterial morphotypes in activated sludge flocs. The first modelling results support qualitatively the hypothesis. Several chapters in this PhD thesis have been published by commercial publishers. These chapters can only be found in publications of these publishers. Bibliographical information of these publications can be found in the different chapters.Applied Science
Enabling Continuous Descent Operations in High-Density Traffic
No full textThe Air Traffic Management (ATM) community strives to reduce the environmental impact per flight. Continuous Descent Operation (CDO) has been identified by the ATM community as one of the operational improvements that could reduce aviation’s environmental impact, both in terms of aircraft noise and gaseous emissions. In the current ATM system, CDOs are only feasible in low-density traffic. The ultimate goal is an ATM system that facilitates CDOs in high-density traffic. This research described in this thesis focused on two features of such an ATM system: decision support that enables the air traffic controller to accurately set up traffic for CDO, and delegation of the spacing task to the flight crew during the CDO. Two enablers are real-time availability of meteorological data, and accurate trajectory prediction. In this thesis new methods were developed and validated to infer wind, air pressure, and air temperature profiles from aircraft surveillance data. Trajectory prediction was defined as a machine learning problem, enabling predictions based on historic aircraft trajectory and meteorological data without the need for explicit modeling of the aircraft performance and procedures. A decision support tool was developed further and tested using a human-in-the-loop experiment. The tool enabled the subjects to set up traffic for CDO in high-density traffic at an acceptable work load level and high level of situation awareness. Monte-Carlo simulations were carried out to assess the runway capacity that can be achieved when delegating the spacing task to the flight crew. These simulations showed the feasibility of CDOs in high-density traffic.Control and SimulationAerospace Engineerin
Beleidsbevoegdheid regionale luchthavens gedecentraliseerd: Een onderzoek naar de weerstand tegen de decentralisatie van het regionale luchthavenbeleid aan de hand van de situatie rondom de Rotterdamse luchthaven
No full textTechnology, Policy and Managemen
The Importance of Negativity
No full textIn a time and age where academic and scientific publishers opted again and again to publish only positive results, what would be an History of Science and Technology if there had been a different approach towards the publication of negative results
The Missing Laugh
No full textWhen we confront the absolute, i.e., the factual History, with a divergent possibility, we necessarily uncover what has been missing all along and likely did not let us go any further. Because if those that do not know History are doomed to repeat it, then those that do not discuss Alternative History are cursed to miss the early exit signs that precede the fall. 
Fatigue crack propagation behavior of old puddle iron including crack closure effects
No full textAbstractIn this paper the fatigue crack growth behavior in structural components from the old 19th century structures (e.g. bridges) has been investigated. The delivered material for investigation was extracted from a beam made of puddled iron, commonly used in 19th century. The obtained results from several ancient railway metallic bridges (located in Lower Silesia, Poland) have shown the presence of microstructural degradation processes in puddled iron. In all analyzed materials (low carbon puddled iron) microstructure degradation processes were related to: the presence of numerous precipitations of carbides and nitrides (or the carbides–nitrides) of iron inside the ferrite grains, the presence of continuous precipitations of cementite at ferrite grain boundaries. In order to restore the initial state of the microstructure, all tests were carried out in two stages of heat treatment; as-received state and after normalization (950°C, 2h, cooled in air) state. The kinetic fatigue fracture diagrams (KFFD) have been obtained. The problem of crack closure has been involved in fatigue crack growth process during the experiments and its understanding is fundamental for the analysis of stress ratio effects on KFFD. In the paper, a few experimental and numerical techniques for the evaluation of the crack closure/opening forces based on the experimental data have been compared. The implemented algorithm in the numerical environment gives promising results in description of the kinetics of fatigue crack growth of the old puddled iron with consideration of crack closure effect
The practice of Adaptive Delta Management in the Netherlands
No full textIn 2011, Adaptive Delta Management (ADM) was introduced in the Dutch Delta Program as a policy development method that incorporates uncertainty in decision-making. At this moment, little is known about the functioning of ADM in practice, while this is key for successful adaptation. This paper presents the results of research into the implementation of ADM in The Netherlands. We focus especially on the efficacy of ADM in dealing with uncertain sea-level rise.This research concludes that to enhance adaptation to sea-level rise to keep the Netherlands safe, policymakers at all levels must gain an overview of the entire solution space over time. Furthermore, actors implementing adaptation plans, like water boards and municipalities, require more insight into the combined consequences of sea-level rise and national adaptation strategies for their area. Here we propose the development of regional consequence scenarios as a promising way forward. In addition, implementing actors need to be enabled to incorporate uncertainties in their decision-making processes. Especially they need support in using the sometimes complicated instruments of ADM.Organisation & GovernancePolicy Analysi
EU Law as a Creative Process : A hermeneutic approach for the EU internal market and fundamental rights protection
No full textWhat stories about the world and about the people in it do we find in the legal reasoning of the Court of Justice of the European Union? The underlying stories in all kinds of human communication, including the law, tell us something about the worldview and the vision of humanity of the author(s). How does EU law speak about human agency and responsibility, particularly in the way in which economic interests are weighed against fundamental rights? What kind of role, what ‘self’ does the Court perform in its judgments, and how does it speak about the ‘other’?
This book invites the reader to think of the practice of EU law as a creative process. From such a perspective, the work of the Court is a cultural, literary activity, in which readers can imagine themselves participating. Thinking about the quality of legal reasoning becomes a process of ethical self-reflection, preparing jurists for future challenges that the EU legal order faces. In her dissertation, Pauline Phoa develops a new methodology to examine the textual performance of the Court, by combining the work of American ‘Law and Literature’ scholar James Boyd White with the work in hermeneutic philosophy of French philosopher Paul Ricoeur.
Two case studies, one on economically inactive EU citizens’ access to social benefits, and another on data protection and privacy, demonstrate the way in which this methodology can be used. They reveal two contradictory narratives that are at play in the case law, which raises questions about the coherence of EU law
Machining of Hybrid Composite Materials
No full textComposite materials have been having an increasing importance in the industry. Their high specific properties and their high flexibility that allows tailoring materials that suit the needs of practically every project, have been leading to a growth in the demand of this kind of materials. Fiber-Metal Laminates have an established usage on the aeronautic industry and lately have been subject of research by the automotive industry.
Since composite manufacturing methods allow the obtention of components with their final geometry, drilling is the most used machining operation in the machining of composites. Drilling of composites is very demanding from the tools point of view, with very high wear rates and several defects can occur to the workpiece like delamination, fiber pull-outs, burrs and matrix degradation. When combined with a metal, additional challenges appear in drilling these materials such as loads of different magnitudes during a single operation and surface defects on the interface because of chip removal. Orbital drilling is seen as a promising alternative to conventional drilling, presenting several advantages that result in holes with higher quality.
Given the interest the automotive industry has been showing in fiber-metal laminates constituted by steel and carbon fiber reinforced plastics (CFRP) and due to the lack of information regarding drilling of this combination of materials, the aim of this work was to evaluate the influence of the machining parameters in the quality of holes obtained by orbital drilling. A full factorial design of experiments was done and the influence of the parameters was then evaluated by means of an Analysis of Variance (ANOVA)
Global Fatigue Life Modelling of Steel Half-pipes Bolted Connections
No full textAbstractA steel hybrid structural solution for onshore wind turbine towers was proposed in the European project SHOWTIME. This solution is used in the lattice structure for the lower portion of the tower. Recently, a procedure for fatigue life estimation of steel half-pipes bolted connections applied in global structural models using multiaxial Smith-Watson-Topper (SWT) criteria was proposed by Öztürk et al. In this paper a procedure for design S-N curve modelling of steel half-pipes bolted connections is proposed. This procedure is based on a local approach using multiaxial fatigue criteria together with an elastoplastic analysis using the finite element method. The materials to be used in this analysis are the S355 and S690 steels. This evaluation to be performed is calibrated with experimental results of fatigue tests of the connection under consideration
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