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Aerobic and Electrochemical Treatment of Process Water from Hydrothermal Carbonization of Sewage Sludge
Full text linkThis dissertation demonstrates possibilities and limitations of aerobic and electrochemical processes for the treatment of process water from the hydrothermal carbonisation (HTC) of sewage sludge. During HTC, sewage sludge is heated to around 190 to 250 °C, causing various reaction mechanisms to turn sewage sludge into a brown coal-like solid. The so-called hydrochar or biochar has a higher calorific value and better dewaterability compared to the untreated sewage sludge. This enables thermal utilisation, use as an adsorbent, or for carbon sequestration. However, the reaction mechanisms also release a large number of organic substances from the solids and partially transform them into substances that are difficult to biodegrade, inhibitory or toxic. Current research focuses primarily on optimizing the HTC process and only secondarily on treating the highly contaminated process water. Nevertheless, previous studies have shown that biodegradability of process water contaminats is limited and hindered by various inhibitors. This raises the issue of the robustness of aerobic processes and the efficiency of electrochemical oxidation to remove refractory substances. The main findings are summarized in four international publications.
Paper 1 visualizes the correlation of the process water load on various reaction parameters. For this purpose, the effect of the parameters reaction temperature (190 to 250 °C), reaction time (0.5 to 4 h) and pH value (3.9 to 6.1) on calorific value, dissolved organic carbon (DOC), and ammonium was tested using design of experiments and the Box-Behnken design. The temperature turned out to be the decisive parameter of the HTC reaction. The higher the temperature, the higher was the calorific value of the hydrochars and the lower was the concentration of DOC in the process water. Higher temperature also increased the percentage of ammonium in the total nitrogen due to the mineralisation of dissolved organic nitrogen (DON).
As the reaction temperature emerged as the decisive reaction parameter from paper 1, paper 2 focuses on the effect of temperature on aerobic bio-degradability. In Zahn-Wellens tests, the DOC removal for temperatures from 190 to 249 °C was about 81%. Continuous lab-scale tests in sequencing batch reactors (SBR, V=0.3 L) also showed similar DOC removals of 72% for different temperatures (190 °C and 217 °C). Due to the strong inhibition by substances formed during HTC, nitrification was only possible by diluting the process water 1:10. Inhibition tests according to DIN EN ISO 9509 (2006) revealed a stronger inhibition for process water at 217 °C than at 190 °C. However, the overall effect of temperature on aerobic biodegradability can be considered low. In addition, an exemplary mix calculation for a municipal wastewater treatment plant showed that the refractory organics could increase the effluent concentration of chemical oxygen demand (COD) by 24 mg/L in the worst case. Paper 3 takes up the findings of paper 2 and transfers them to the operation of a pilot plant in order to determine the limits of nitrification performance and organic removal. For this purpose, the sludge loading of a membrane bioreactor (MBR, V=170 L) and an SBR (V=300 L) was successively increased. In addition, reducing the dilution of the process water from 1:20 to 1:1 led to an increase in inhibitor concentration. The maximum sludge loading for nitrification as total nitrogen (TN) per mixed liquor suspended solids (MLSS) was 20 - 25 mg TN/(g MLSS·d) in both reactors. The nitrogen sludge loading during treatment of the undiluted process water was too high for nitrification. With nitrification, COD removal was 74.8 ± 1.9% (MBR) and 71.4 ± 2.6% (SBR). The activated sludge from the SBR adapted to inhibitors in the process water to a certain degree. The nitrification rate was inhibited by 50% at 50 mg DON (i.e. 4% v/v process water share), compared to 6.6 mg DON (i.e. 0.4% v/v process water share) for activated sludge from a municipal wastewater treatment plant. Although different process waters were treated in paper 2 and 3, both the COD removal and the inhibition of nitrification were similar. Paper 2 and paper 3 have demonstrated that 20 to 30% of the COD was not biodegradable. Following this, paper 4 presents results from the electrochemical oxidation (EO) of refractory COD using a boron-doped diamond electrode and introduced three possible treatment scenarios: (I) EO alone, (II) aerobic COD removal + EO, and (III) nitrification/denitrification + EO. In all scenarios, EO proved to be very effective and even reduced the COD to below 10 mg/L in scenario III. This low concentration was associated with an energy consumption of up to 534 kWh/kg COD. As the energy consumption of the EO largely depends on the COD concentration, it was significantly lower in scenario I and II with 31.3 and 46.6 kWh/kg COD. A concluding mass balance showed that scenario II had the lowest overall energy consumption due to the reduced COD load and yet high energy efficiency. The result of this dissertation suggest that aerobic treatment with downstream electrochemical oxidation is a conceivable solution for treating HTC process water. However, due to high inhibitor concentration, nitrification can in fact only be established by diluting the process water
People learn a two-stage control for faster locomotor interception
Full text linkPeople can use the constant target-heading (CTH) strategy or the constant bearing (CB) strategy to guide their locomotor interception. But it is still unclear whether people can learn new interception behavior. Here, we investigated how people learn to adjust their steering to intercept targets faster. Participants steered a car to intercept a moving target in a virtual environment similar to a natural open field. Their baseline interceptions were better accounted for by the CTH strategy. After five learning sessions across multiple days, in which participants received feedback about their interception durations, they adopted a two-stage control: a quick initial burst of turning accompanied by an increase of the target-heading angle during early interception was followed by significantly less turning with small changes in target-heading angle during late interception. The target’s bearing angle did not only show this two-stage pattern but also changed comparatively little during late interception, leaving it unclear which strategy participants had adopted. In a following test session, the two-stage pattern of participants’ turning adjustment and the target-heading angle transferred to new target conditions and a new environment without visual information about an allocentric reference frame, which should preclude participants from using the CB strategy. Indeed, the pattern of the target’s bearing angle did not transfer to all the new conditions. These results suggest that participants learned a two-stage control for faster interception: they learned to quickly increase the target-heading angle during early interception and subsequently follow the CTH strategy during late interception
Bachmann–Howard derivatives
Full text linkIt is generally accepted that H. Friedman's gap condition is closely related to iterated collapsing functions from ordinal analysis. But what precisely is the connection? We offer the following answer: In a previous paper we have shown that the gap condition arises from an iterative construction on transformations of partial orders. Here we show that the parallel construction for linear orders yields familiar collapsing functions. The iteration step in the linear case is an instance of a general construction that we call 'Bachmann–Howard derivative'. In the present paper, we focus on the unary case, i.e., on the gap condition for sequences rather than trees and, correspondingly, on addition-free ordinal notation systems. This is partly for convenience, but it also allows us to clarify a phenomenon that is specific to the unary setting: As shown by van der Meeren, Rathjen and Weiermann, the gap condition on sequences admits two linearizations with rather different properties. We will see that these correspond to different recursive constructions of sequences
Effective Mass of the Polaron: A Lower Bound
Full text linkWe show that the effective mass of the Fröhlich Polaron is bounded below by cα²/⁵ for some constant c>0 and for all coupling constants α. The proof uses the point process representation of the path measure of the Fröhlich Polaron
Towards a systematical approach for wear detection in sheet metal forming using machine learning
Full text linkWear is one of the decisive factors for the economic efficiency of sheet metal forming processes. Thereby, progressive wear phenome lead on the one hand to a poor workpiece quality and on the other hand to tool failure resulting in high machine downtimes. This trend is intensified by processing high-strength materials and the reduction of lubricant up to dry forming. In this context, data-driven monitoring methods such as machine learning (ML) provide the potential of detecting wear at an early stage to overcome manual and cost-intensive process inspections. The presented study aims to provide a ML based inline quantification of wear states within sheet metal forming processes. The development of this monitoring approach is based on a procedure model the Knowledge Discovery in Time series and image data in Engineering Epplications (KDT-EA) which is validated on two forming processes, blanking and roll forming, that strongly differ in their physical process behavior and their acquired process data. The presented inline quantification allows an estimation of wear states with a deviation of less than 0.83% for the blanking process and 2.21% for the roll forming process from the actual wear state. Furthermore, it is shown that combining different feature extraction methods as well as a compensation of unbalanced data using data augmentation techniques are able to improve the performance of the investigated ML models
Boolean finite cell method for multi-material problems including local enrichment of the Ansatz space
Full text linkThe Finite Cell Method (FCM) allows for an efficient and accurate simulation of complex geometries by utilizing an unfitted discretization based on rectangular elements equipped with higher-order shape functions. Since the mesh is not aligned to the geometric features, cut elements arise that are intersected by domain boundaries or internal material interfaces. Hence, for an accurate simulation of multi-material problems, several challenges have to be solved to handle cut elements. On the one hand, special integration schemes have to be used for computing the discontinuous integrands and on the other hand, the weak discontinuity of the displacement field along the material interfaces has to be captured accurately. While for the first issue, a space-tree decomposition is often employed, the latter issue can be solved by utilizing a local enrichment approach, adopted from the extended finite element method. In our contribution, a novel integration scheme for multi-material problems is introduced that, based on the B-FCM formulation for porous media, originally proposed by Abedian and Düster (Comput Mech 59(5):877–886, 2017), extends the standard space-tree decomposition by Boolean operations yielding a significantly reduced computational effort. The proposed multi-material B-FCM approach is combined with the local enrichment technique and tested for several problems involving material interfaces in 2D and 3D. The results show that the number of integration points and the computational time can be reduced by a significant amount, while maintaining the same accuracy as the standard FCM
First principles treatment of electron transfer in mixed-valent systems
Full text linkThe thesis offers insight into electron transfer mechanisms in mixed-valent compounds. A theoretical methodology based on ab initio calculations is established to identify the exact nuclear coordinate that drives intramolecular electron transfer in mixed-valent systems. By application of this methodology, the origin of the characteristic absorption band structure of the well-known Creutz–Taube ion is explained, and a quantitative measure of concertedness in proton-coupled electron transfer reactions is established. These findings allow us to understand different mechanisms of electron transfer and in turn, will help us in future to design new compounds with custom properties.
Furthermore, a simulation of the formation of a photoinduced mixed-valent excited state in an analogue of the Creutz–Taube ion is presented. Vibrational coherences induced by electronic states which do not possess mixed-valent character are characterized with a femtosecond time resolution in the calculations.
Finally, a new methodology is developed to study the charge-separation in the reaction center of Photosystem II. With the inclusion of thermal effects and the environment of the protein, the calculated electronic states are computationally processed to the correct ordering with respect to their charge transfer character. With this analysis, the pigment pair that is responsible for the charge-separation can be identified
Perspectives on data-driven models and its potentials in metal forming and blanking technologies
Full text linkToday, design and operation of manufacturing processes heavily rely on the use of models, some analytical, empirical or numerical i.e. finite element simulations. Models do reflect reality as best as their design and structure may appear, but in many cases, they are based on simplifying assumptions and abstractions. Reality in production, i.e. reflected by measures such as forces, deflections, travels, vibrations etc. during the process execution, is tremendously characterised by noise and fluctuations revealing a stochastic nature. In metal forming such kind of impact on produced product today in detail is neither explainable nor supported by the aforementioned models. In industrial manufacturing the game to deal with process data changed completely and engineers learned to value the high significance of information included in such digital signals. It should be acknowledged that process data gained from real process environments in many cases contain plenty of technological information, which may lead to increase efficiency of production, to reduce downtime or to avoid scrap. For this reason, authors started to focus on process data gained from numerous metal forming technologies and sheet metal blanking in order to use them for process design objectives. The supporting idea was found in a potential combination of conventional process design strategies with new models purely based on digital signals captured by sensors, actuators and production equipment in general. To utilise established models combined with process data, the following obstacles have to be addressed: (1) acquired process data is biased by sensor artifacts and often lacks data quality requirements; (2) mathematical models such as neural networks heavily rely on high quantities of training data with good quality and sufficient context, but such quantities often are not available or impossible to gain; (3) data-driven black-box models often lack interpretability of containing results, further opposing difficulties to assess their plausibility and extract new knowledge. In this paper, an insight on usage of available data science methods like feature-engineering and clustering on metal forming and blanking process data is presented. Therefore, the paper is complemented with recent approaches of data-driven models and methods for capturing, revealing and explaining previously invisible process interactions. In addition, authors follow with descriptions about recent findings and current challenges of four practical use cases taken from different domains in metal forming and blanking. Finally, authors present and discuss a structure for data-driven process modelling as an approach to extent existing data-driven models and derive process knowledge from process data objecting a robust metal forming system design. The paper also aims to figure out future demands in research in this challenging field of increasing robustness for such kind of manufacturing processes
KORPUSLINGUISTISCHE ANSÄTZE DER PHRASEOLOGIE – UND WAS NUN? Phraseodidaktik und die Potenziale neuerer Zugänge der Sprachdidaktik
Full text linkEine wesentliche Zielsetzung des Lehrens von Fremdsprachen ist die Förderung der fremdsprachlichen Phraseologie, d.h. das Erlernen fester Wendungen. Der phraseodidaktische Dreischritt von Peter Kühn gilt seit seiner Veröffentlichung vor dreißig Jahren als eine der wichtigsten didaktischen Grundlagen für das Lehren und Lernen von Phraseologie. Mit diesem Ausgangspunkt befassen wir uns im ersten Teil unseres Beitrags mit den phraseodidaktischen Grundlagen der Vermittlung von Phraseologie. Zuerst gehen wir der Frage nach, welche Potenziale – aber auch Begrenzungen – eine Schritt- oder Phasenmodellierung des Lernens von Phraseologie bietet und werfen zusätzlich einen Blick auf die Möglichkeiten anderer wortschatzdidaktischer Zugriffe, die wir als eine grundlegende Voraussetzung einer theoretisch-methodischen Verankerung der Phraseodidaktik betrachten. Eine solche Verankerung ist unabdingbar für die sprachdidaktische Umsetzung von Ergebnissen aus der Phraseologieforschung, darunter aus korpuslinguistischen oder kontrastiven Untersuchungen. Im zweiten Teil diskutieren wir, wie ausgewählte neuere sprachdidaktische Ansätze, wie z.B. der Plurilingualismus oder das korpusbasierte und aufgabenorientierte Lernen, zur Vermittlung von Phrasemen beitragen können
Migrationssensibler Fremdsprachenunterricht – Voraussetzungen, Lerngelegenheiten und Ziele am sogenannten dritten Ort. Einführung in den Themenschwerpunkt
Full text linkDass die neuen Bildungsstandards für die 1. Fremdsprache eine „plurilinguale und interkulturelle Diskurskompetenz“ (KMK 2023: 6) als übergeordnete Zielkompetenz setzen, ist durchaus bemerkenswert: erstens, weil erstmals in der Geschichte der Fachpräambeln für den fremdsprachlichen Unterricht der Mehrsprachigkeits- und der Kompetenzbegriff eine Verbindung eingehen; zweitens, weil nun auch eine Form von Mehrsprachigkeit adressiert wird, die nicht aus dem Fach und Bildungssystem heraus entsteht. Plurilinguale Kompetenz wird als Lernvoraussetzung gefasst, die aufgrund von „Erfahrungen mit unterschiedlichen Registern, Dialekten, Herkunftssprachen“ (ebd.) bereits vorhanden und durch die im Unterricht vermittelte(n) Fremdsprache(n) noch auszubauen sei. Auf Herkunftssprachen geht das Dokument eingangs unter Bezugnahme auf die „Heterogenität der Schülerinnen und Schüler“ und ihren „sozialen und kulturellen Hintergrund“ (ebd.: 3) ein. Während Heterogenität zunächst noch als Herausforderung für den individuellen Bildungserfolg im Sinne der Standarderreichung anklingt (vgl. ebd.), sind Herkunftssprachen im weiteren Dokument ausschließlich als Ressource markiert (diskursive und kommunikative Mittel, Strategien, Lexikogrammatik, soziolinguistisches und -kulturelles Wissen, vgl. ebd.: 7). Dabei wird herkunftssprachliches Vorwissen meist sprachlich (Standards zu Lesen, Sprechen, Schreiben, Sprachbewusstheit, Sprachlernkompetenz, vgl. ebd.: 12‒16 und 23‒25; Dietrich-Grappin 2024: 83‒86), seltener kulturell gefasst (Standards zu Mediation/Sprachmittlung, interkulturelle Kompetenz, vgl. KMK 2023: 17‒18 und 20‒21). Diese neue bildungspolitische Entwicklung in Deutschland, die ihren Ausgang auf europäischer Ebene nahm (vgl. Council of Europe 2018; Dietrich-Grappin 2024), wirft nicht nur hierzulande die Frage nach dem Verhältnis von Fremdsprachenunterricht (FSU) und Migration auf, der wir im Rahmen des vorgelegten Themenschwerpunkts nachgehen möchten. Im Folgenden stellen wir definitorische Überlegungen zum Schwerpunktthema (Kap. 1) und das Spektrum bisheriger Forschungszugänge vor, das sich in die empirische Kompetenz- und Einstellungsforschung aus der Perspektive der Lernenden (Kap 2), Einstellungsforschung zur Lehrperspektive (Kap. 3) sowie Beiträge zur Weiterentwicklung von Unterrichtsmaterial (Kap. 4) und zur Diskussion von Lern- und Bildungszielen (Kap. 5) gliedert. Die Beiträge dieses Themenhefts sind jeweils einem Forschungszugang zugeordnet und werden am Ende eines Abschnitts vorgestellt