Technische Universität Bergakademie Freiberg: Qucosa
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Modification of Liquid Steel Viscosity and Surface Tension for Inert Gas Atomization of Metal Powder
Get PDFInert gas atomization is one of the main sources for production of metal powder forpowder metallurgy and additive manufacturing. The obtained final powder size distribution iscontrolled by various technological parameters: gas flow rate and pressure, liquid metal flowrate, gas type, temperature of spraying, configuration of nozzles, etc. This work explores anotherdimension of the atomization process control: modifications of the liquid metal properties andtheir effect on the obtained powder size. Series of double-alloyed Cr-Mn-Ni steels with sulfur andphosphorus were atomized with argon at 1600◦C. The results indicate that surface tension andviscosity modifications lead to yielding finer powder fractions. The obtained correlation is comparedwith the individual modification of surface tension with S and Se and modification of viscosity withphosphorus. Discrepancy of the results is discussed. Additives of surfactants and viscosity modifierscan be a useful measure for powder fractions control
Die Nationale Forschungsdateninfrastruktur (NFDI)
Get PDFIn dieser Ausgabe wird die Nationale Forschungsdateninfrastruktur (NFDI) in ihrer aktuellen Struktur (Stand Juli 2024) kurz vorgestellt. Es werden Beispiele für Services und Tools der NFDI-Konsortien und Basisdienste genannt, die Forschende für ein erfolgreiches Forschungsdatenmanagement nutzen können
Investigation of Post-Processing of Additively Manufactured Nitinol Smart Springs with Plasma-Electrolytic Polishing
Get PDFAdditive manufacturing of Nitinol is a promising field, as it can circumvent the challenges associated with its conventional production processes and unlock unique advantages. However, the accompanying surface features such as powder adhesions, spatters, ballings, or oxide discolorations are undesirable in engineering applications and therefore must be removed. Plasma electrolytic polishing (PeP) might prove to be a suitable finishing process for this purpose, but the effects of post-processing on the mechanical and functional material properties of additively manufactured Nitinol are still largely unresearched. This study seeks to address this issue. The changes on and in the part caused by PeP with processing times between 2 and 20 min are investigated using Nitinol compression springs manufactured by Laser Beam Melting. As a benchmark for the scanning electron microscope images, the differential scanning calorimetry (DSC) measurements, and the mechanical load test cycles, conventionally fabricated Nitinol springs of identical geometry with a medical grade polished surface are used. After 5 min of PeP, a glossy surface free of powder adhesion is achieved, which is increasingly levelled by further polishing. The shape memory properties of the material are retained without a shift in the transformation temperatures being detectable. The decreasing spring rate is primarily attributable to a reduction in the effective wire diameter. Consequently, PeP has proven to be an applicable and effective post-processing method for additively manufactured Nitinol
Open Educational Resources (OER) in der Hochschullehre
Get PDFDie aktuelle Ausgabe gibt einen Überblick über das Potenzial von Open Educational Resources (OER) in der Hochschullehre und die förderpolitischen Maßnahmen, um dieses zu unterstützen. Es werden einige wichtige Beispiele für Initiativen wie OERSI und Twillo aufgeführt. Außerdem wird auf die Fortschritte in Sachsen eingegangen
Nasschemische Ätzung von Siliziumnitridschichten mit organischen Komplexbildnern
Get PDFEs wird eine Alternative zum Ätzen von Siliciumnitrid (SiNx) auf Silicium-Wafern vorgestellt. Herkömmliche Verfahren zum Ätzen von SiNx auf Silicium-Wafern arbeiten mit Flusssäure oder Phosphorsäure. Zu diesen Chemikalien werden alternative organische Komplexbildner zum Ätzen von SiNx vorgestellt, welche im Gegensatz zu den herkömmlichen Substanzen weniger giftig und umweltschädlich sind. Bei den organischen Komplexbildnern handelt es sich um die Stoffgruppen der Hydroxycarbonsäuren und Aminosäuren. Für diese Substanzen wurden die ersten wichtigen Parameter für einen Einsatz in der Halbleiterindustrie untersucht. Dabei handelt es sich um Einflüsse durch die Herstellungsprozesse des SiNx selbst, des pH-Wertes, der chemischen Struktur des organischen Komplexbildners und die Konzentrations- und Temperaturabhängigkeit. Es werden für die Reaktion auch die ersten Reaktionsmechanismen postuliert.:1 Einleitung...................... 1
1.1 NachhaltigkeitinderHalbleiterindustrie................. 2
1.2 Nasschemische Ätzmethoden für Siliciumnitrid (SiNx).......... 5
1.3 ZieledieserForschungsarbeit........................ 9
2 Material und Methoden 11
2.1 Probenkörper ................................ 11
2.2 Ätzversuche ................................. 12
2.3 Charakterisierung.............................. 15
3 Ätzmittel für SiNx 25
3.1 Chemischer Aufbau von organischen Komplexbildnern für Siliciumnitrid.... 25
3.2 UntersuchungderMorphologie....................... 25
3.3 XPS-AnalysederOberfläche........................ 33
3.4 WirksameGruppen............................. 35
4 Methodenentwicklung zur Bestimmung von Ätzraten, Selektivität und Isotropie.... 37
4.1 Ätzrate.................................... 37
4.2 Selektivität................................. 39
4.3 Methoden zur Bestimmung der Schichtdickendifferenz .......... 43
4.4 Fehlerbetrachtung und Zusammenfassung der Methoden........ 46
4.5 Zusammenfassung der Messmethoden................... 51
5 Parameter mit Einfluss auf den Ätzprozess 53
5.1 Einfluss des Herstellungsprozesses..................... 53
5.2 Einfluss des pH-Wertes auf den SiNx-Abbau ................... 55
5.3 Einfluss von Wasser auf die Reaktion ................... 56
5.4 Einfluss der Struktur ............................ 57
5.5 Konzentrations- und Temperaturabhängigkeit der Ätzrate von Ätzmitteln 60
5.6 Untersuchung des kinetischen Verlaufs der Reaktion . . . . . . . . . . . 69
5.7 Untersuchung der Isotropie......................... 72
6 Postulierte Reaktionsmechanismen 77
6.1 Abbau des Stickstoffs aus der SiNx-Oberfläche . . . . . . . . . . . . . . 77
6.2 Abbau des Si aus der SiNx-Oberfläche................... 78
6.3 Milchsäure als Katalysator zum Abbau von elementarem Si . . . . . . . 80
6.4 NMR-Analyse................................ 82
7 Zusammenfassung und Ausblick 87
7.1 Zusammenfassung.............................. 87
7.2 Ausblick................................... 89
6.5 Ergebniszusammenfassung der postulierten Reaktionsmechanismen . . . 8
Exploring Non-Smoothness in Shape Optimization: An Analysis of Shape Optimization Problems Constrained by Variational Inequalities and a Diffeological Perspective on Shape Spaces
Get PDFDiese Arbeit untersucht Nicht-Glattheiten im Bereich der Formoptimierung aus zwei verschiedenen Perspektiven.
Einerseits werden Formoptimierungsprobleme betrachtet, die durch Variationsungleichungen eingeschränkt sind. Häufig fallen diese unter die sogenannten Hindernis-Probleme.
Diese Probleme haben zahlreiche Anwendungen, beispielsweise bei der Konstruktion von Formen, die Einschränkungen durch die Lösung von partiellen Differentialgleichungen unterliegen, welche wiederum von der optimierten Geometrie abhängen.
Oft werden verschiedene Regularisierungsmethoden genutzt, um der Nicht-Glattheit und Nicht-Konvexität Herr zu werden.
Über die Nicht-Glattheiten hinaus ergeben sich weitere Herausforderungen, welche durch die Variationsungleichheiten sowie durch Nicht-Konvexität und Unendlich-Dimensionalität auftreten.
Diese Faktoren erschweren die Formulierung von Optimalitätsbedingungen und die Entwicklung effizienter Lösungsalgorithmen.
In dieser Arbeit wird ein Ansatz vorgestellt, welcher es ermöglicht, Nicht-Glattheiten ohne Regularisierung zu behandeln.
Dazu wird die Hadamard-Semiableitung verwendet.
Auf der anderen Seite steht die Frage nach geeigneten Formräumen im Fokus und motiviert den zweiten Teil dieser Arbeit.
Herkömmliche Formräume umfassen typischerweise glatte Verformungen der Kugel und sind mit einer glatten Struktur versehen.
Dadurch kommt es zu einer Vernachlässigung von Formen mit Ecken und Kanten.
Die Konstruktion eines Formraums, der nicht-glatte Formen beinhaltet, ist keine Herausforderung. Das Arbeiten mit einem solchen Raum hingegen schon.
Typische glatte Strukturen, wie die der riemannschen Mannigfaltigkeit, gehen unter Umständen verloren.
Diese Arbeit führt daher diffeologische Räume als natürliche Verallgemeinerung glatter Mannigfaltigkeiten ein.
Die Erweiterung von Optimierungstechniken von glatten Mannigfaltigkeiten auf diffeologische Räume stellt eine Herausforderung da.
Besondere Aspekte sind die Existenz nicht-äquivalenter Definitionen des Tangentialraums sowie die Notwendigkeit einer erweiterten riemannschen Struktur zur Herleitung von Gradienten.
Diese Arbeit präsentiert eine Erweiterung der bereits bekannten riemannschen Optimierung und ihrer Objekte.
Dazu gehören unter anderem Definitionen für einen geeigneten Tangentialraum, ein diffeologisches riemannsches Setting, einen diffeologischen Gradienten, eine diffeologische Retraktion und einen diffeologischen Levi-Civita-Zusammenhang.
Dies resultiert in der Formulierung eines diffeologischen Gradientenverfahrens, das auf ein Optimierungsproblem angewendet wird.:Abstract
Zusammenfassung
Acknowledgments
Preface
1 Introduction
1.1 Motivation,Aim,andScopeoftheThesis
1.2 StructureoftheThesis
2 Background Knowledge
2.1 DifferentialGeometry
2.2 ShapeOptimization
2.2.1 ABasicIntroduction
2.2.2 A Brief Overview of Variational Inequality Constraints
2.2.3 ShapeSpaces
3 A Hadamard Approach for Variational Inequality Constrains
3.1 HadamardSemiderivative
3.1.1 A Brief Introduction into Hadamard Semiderivatives
3.1.2 HadamardShapeDerivativeCalculus
3.2 HadamardOptimalitySystem
3.3 Application
4 Optimization on Diffeological Spaces
4.1 ABriefIntroductiontoDiffeologicalSpaces
4.2 Towards Optimization Algorithms on Diffeological Spaces
4.2.1 TangentSpace
4.2.2 Examples of Diffeological Tangent Spaces
4.2.3 DiffeologicalRiemannianSpace
4.2.4 Towards Updates of Iterates: Diffeological Levi-Civita ConnectionandDiffeologicalRetraction
4.3 Formulation of Diffeological Optimization Algorithms andTheirApplication
5 Conclusion
6 NotationsThis thesis is concerned with non-smoothness from two different points of view regarding shape optimization problems.
On one hand this thesis considers shape optimization problems that are constrained by variational inequalities of the first kind, often known as obstacle-type problems. These problems find numerous applications when constructing a shape that must adhere to constraints imposed on the solution of a partial differential equation dependent on the geometry being optimized. Since those problems are non-smooth and non-convex optimization problems, they are often handled using several regularization methods. Besides the non-smoothness there are complementary aspects due to the variational inequalities as well as non-linear, non-convex and infinite-dimensional aspects due to the shapes. This complicates setting up an optimality system, and thus developing an efficient solution algorithm. This thesis is presenting a way to deal with the non-smoothness without the requirement of regularizations. Therefore, the Hadamard semiderivative setting is considered. After introducing the Hadamard semiderivative and considering the Hadamard shape calculus, the Hadamard adjoint is introduced. This allows us to handle shape optimization problems that are constrained by variational inequalities of the first kind without using any kind of regularization.
On the other hand this thesis is confronted with the question of suitable shape spaces. What is a suitable space that contains all important shapes? This question is the motivation of the second part of this thesis. A common shape space usually contains some kind of smooth deformations of the sphere. Often those shape spaces are equipped with a suitable smooth structure. This can results in the neglection of shapes that have kinks and corners and are non-smooth. The construction of a shape space that includes non-smooth shapes is not a major challenge but working with such a space is. How do you optimize if your space is not a manifold? On answering this question lies the main focus of the second part of this thesis. Therefore, this thesis introduces so-called diffeological spaces. Diffeological spaces, firstly introduced by J.M. Souriau in the 1980s, are a natural generalization of smooth manifolds. To date, optimization techniques have primarily been developed on manifolds. Extending these methods to diffeological spaces presents a significant challenge for several reasons. One prominent obstacle is the existence of different definitions for tangent spaces that do not coincide with one another. Furthermore, the expansion necessitates the creation of a broader concept of a Riemannian structure to establish gradients, which are essential components for optimization strategies. The first major step is a suitable definition of a tangent space in view of optimization methods. This definition is then used in order to present a diffeological Riemannian space and a diffeological gradient, which this thesis needs to formulate an optimization algorithm on diffeological spaces. Moreover, this thesis presents a diffeological retraction and the Levi-Civita connection on diffeological spaces. As a result a diffeological version of the steepest decent method is obtained. This thesis gives examples for the novel objects and apply the presented diffeological algorithm (an algorithm for diffeological spaces) to an optimization problem.:Abstract
Zusammenfassung
Acknowledgments
Preface
1 Introduction
1.1 Motivation,Aim,andScopeoftheThesis
1.2 StructureoftheThesis
2 Background Knowledge
2.1 DifferentialGeometry
2.2 ShapeOptimization
2.2.1 ABasicIntroduction
2.2.2 A Brief Overview of Variational Inequality Constraints
2.2.3 ShapeSpaces
3 A Hadamard Approach for Variational Inequality Constrains
3.1 HadamardSemiderivative
3.1.1 A Brief Introduction into Hadamard Semiderivatives
3.1.2 HadamardShapeDerivativeCalculus
3.2 HadamardOptimalitySystem
3.3 Application
4 Optimization on Diffeological Spaces
4.1 ABriefIntroductiontoDiffeologicalSpaces
4.2 Towards Optimization Algorithms on Diffeological Spaces
4.2.1 TangentSpace
4.2.2 Examples of Diffeological Tangent Spaces
4.2.3 DiffeologicalRiemannianSpace
4.2.4 Towards Updates of Iterates: Diffeological Levi-Civita ConnectionandDiffeologicalRetraction
4.3 Formulation of Diffeological Optimization Algorithms andTheirApplication
5 Conclusion
6 Notation
Phosgenfreie Synthese von Isocyanaten unter Verwendung von CO2 und N-silylierten Aminen
Get PDFIsocyanate sind wichtige Zwischenstufen bei der Herstellung zahlreicher Alltagsprodukte, von Matratzen über Lacke und Beschichtungen bis hin zu Kosmetika. Die industrielle Herstellung erfolgt mit Hilfe des reaktiven und giftigen Gases Phosgen. Im Rahmen der vorliegenden Dissertation wird ein vierstufiger Prozess zur phosgenfreien Synthese von Isocyanaten untersucht. Ausgehend von Aminen werden N-Silylamine erzeugt, die im Anschluss mit CO2 zur Reaktion gebracht werden. Dabei bilden sich O-Silylcarbamate, die bereits die NCO-Einheit der Isocyanate tragen. Durch eine N-Silylierung werden N,O-Bis(silyl)carbamate gebildet. Die Stoffklassen der silylierten Carbamate werden durch diese Dissertation um mehrere, bislang unbekannte Vertreter erweitert. Die anschließende thermische Zersetzung liefert erfolgreich die gewünschten Isocyanate. Als Spaltprodukt bildet sich das ungiftige, inerte Hexamethyldisiloxan. Mit diesem patentierten Verfahren gelingt es, CO2 als Kohlenstoff- und Sauerstoffquelle in industriell wichtige Monoisocyanate zu überführen. Die Anwendung auf Diisocyanate wird beleuchtet und erzeugt Potenzial für fortführende Arbeiten
Effects of Plasma-Chemical Composition on AISI 316L Surface Modification by Active Screen Nitrocarburizing Using Gaseous and Solid Carbon Precursors
Get PDFLow-temperature plasma nitrocarburizing treatments are applied to improve the surface properties of austenitic stainless steels by forming an expanded austenite layer without impairing the excellent corrosion resistance of the steel. Here, low-temperature active screen plasma nitrocarburizing (ASPNC) was investigated in an industrial-scale cold-wall reactor to compare the effects of two active screen materials: (i) a steel active screen with the addition of methane as a gaseous carbon-containing precursor and (ii) an active screen made of carbon-fibre-reinforced carbon (CFC) as a solid carbon precursor. By using both active screen materials, ASPNC treatments at variable plasma conditions were conducted using AISI 316L. Moreover, insight into the plasma-chemical composition of the H2-N2 plasma for both active screen materials was gained by laser absorption spectroscopy (LAS) combined with optical emission spectroscopy (OES). It was found that, in the case of a CFC active screen in a biased condition, the thickness of the nitrogen-expanded austenite layer increased, while the thickness of the carbon-expanded austenite layer decreased compared to the non-biased condition, in which the nitrogen- and carbon-expanded austenite layers had comparable thicknesses. Furthermore, the crucial role of biasing the workload to produce a thick and homogeneous expanded austenite layer by using a steel active screen was validated
Beiträge zur Auslegung konturnaher Temperierkanäle in Werkzeugen bei variothermer Prozessführung
Get PDFIn der Arbeit wurde der stationäre wie instationäre Wärmetransport in exemplarischen Werkzeuggeometrien untersucht. Im Ergebnis konnten Wärmedurchgangswiderstände und instationäre Verläufe charakteristischer Temperaturen (Mitteltemperatur, Werkzeugwand- und Kanalwandtemperatur) in Abhängigkeit der Wand- und Kanalabstände sowie der Strömungsgeschwindigkeit bestimmt werden. Daraus wurden Auslegungsgrundlagen in Form von Gleichungen zur Bestimmung des Formfaktors der Wärmeleitung sowie der zeitlichen Verläufe der Werkzeugwandtemperatur, der Kanalwandtemperatur und der Wandtemperatur-inhomogenität erarbeitet. Dabei zeigt sich eine gute Übereinstimmung zwischen den Gleichungen sowie experimentellen und numerischen Daten. Die Gleichungen erweitern den Wissenstand zur Auslegung von Temperierkanälen von Werkzeugen in variothermen Prozessen
Characterization of anaerobic benzene degradation pathways
Get PDFBenzene is chemically stable as it has no substituents which can be biochemically attacked and a well-known toxic contaminant whose anaerobic degradation pathway is still not fully resolved. As only a very few anaerobic benzene-mineralizing pure cultures have been described yet, research was usually done with enrichment cultures dominated by specific organisms capable of benzene degradation under different electron acceptor conditions. Remarkable progress has been made in recent years with regard to the initial mechanism of benzene transformation especially on the putative genes that are involved in anaerobic carboxylation of benzene and the benzoyl-CoA central pathway. Many phylotypes described to be primary benzene degraders in anaerobic enrichment cultures at various electron acceptor conditions belong to the Peptococcaceae. Here, the thesis focused on characterizing the structure and function of anaerobic benzene-mineralizing microbial communities enriched from two hydrocarbon-contaminated sites: hydrocarbon-contaminated sediment from Ogoni in Niger Delta of Nigeria and a benzene-contaminated aquifer in Zeitz (Germany).
The Niger Delta is one of the world’s most damaged ecosystem mainly due to hydrocarbon exploration accidents. The natural attenuation potential of Niger Delta subsurface sediment for anaerobic hydrocarbon degradation was investigated using benzene as a model compound under iron-reducing, sulfate-reducing, and methanogenic conditions. Benzene was slowly mineralized under iron-reducing conditions using Fe(III) chelated with nitrilotriacetic acid, or poorly crystalline Fe(III) oxyhydroxides as electron acceptors, analyzed by measurement of 13CO2 produced from added 13C-labelled benzene. The highest mineralization rates were observed in microcosms amended with Fe(III) oxyhydroxides while microcosms amended with Fe(III) nitrilotriacetic acid produced methane. Abundant phylotypes were affiliated to Betaproteobacteriales, Ignavibacteriales, Desulfuromonadales, and Methanosarcinales of the genera Methanosarcina and Methanothrix, illustrating that the enriched benzene mineralizing communities were diverse and may contain more than a single benzene degrader. The study underpins the importance of microbial ecosystem services in contaminant degradation as a sustainable environmental means of mitigating harmful chemicals.
Benzene degradation pathways in a benzene-mineralizing, nitrate-reducing enrichment culture from Zeitz was investigated. Benzene mineralization was dependent on the presence of nitrate and correlated to enrichment of a Peptococcaceae phylotype only distantly related to known anaerobic benzene degraders of this family. Its relative abundance decreased after benzene mineralization had terminated, while other abundant taxa - Ignavibacteriaceae, Rhodanobacteraceae and Brocadiaceae - slightly increased. Generally, the microbial community remained diverse despite amendment of benzene as single organic carbon source, suggesting complex trophic interactions between different functional groups. A subunit of the putative anaerobic benzene carboxylase (AbcA) previously detected in Peptococcaceae was identified by metaproteomic analysis suggesting that benzene was activated by carboxylation. Detection of proteins involved in anaerobic ammonium oxidation (Anammox) indicates that benzene mineralization was accompanied by Anammox, facilitated by nitrite accumulation and the presence of ammonium in the growth medium. The results suggest that benzene was activated by carboxylation and further assimilated by a novel Peptococcaceae phylotype and confirm the hypothesis that Peptococcaceae are important anaerobic benzene degraders.
Only a few benzene mineralizing anaerobes have been isolated to date. In an attempt using classical isolation techniques to isolate benzene-mineralizing pure cultures from a benzene-mineralizing nitrate-reducing microbial community, two consortia were gained under nitrate-reducing conditions spiked separately with acetate and benzene as sole sources of carbon and energy with media containing ammonium or without ammonium. Both consortia – Bz4 (with ammonium) and Bz7 (without ammonium) - mineralized 13C-labelled acetate under anoxic conditions at 3.3 and 2.7 µM day-1, respectively, revealed by analysis of evolved 13CO2. However, only Bz4 mineralized 13C-labelled benzene (0.298 µM benzene mineralized day-1) generated up to 960.2 ± 0.3 ‰ ẟ13C-CO2 during 184 days while producing only slight amounts of nitrite (4.60 ± 0.004 µM). By 16S rRNA gene amplicon sequencing was determined that the isolated cultures were not pure cultures but still contained several different phylotypes. The gained Bz4 consortium that mineralized benzene under anoxic conditions can be further purified and explored for their metabolic potentials.:Acknowledgments ………………………………………………………................. ii
Table of Contents …………………………………………………………………… iii
Dissertation Summary ……………………………………………………………… vi
Dissertation Zusammenfassung …………………………………………………… viii
List of Tables ………………………………………………………………………… x
List of Figures ……………………………………………………………………….. xi
List of Appendices ………………………………………………………………….. xiii
Abbreviations .………………………………………………………….................... xv
Chapter 1: Introduction and Research Objectives ……………………………… 1
1.1 Introduction ……………………………………………………………… 2
1.2 Aims and Objectives ………………………………………………….... 4
Chapter 2: Anaerobic Benzene Degradation by Microbial Communities and Pure Cultures …… 6
2.1 Anaerobic benzene degradation – a brief introduction ...…………… 7
2.2 Anaerobic benzene degradation under different electron acceptor conditions … 9
2.2.1 Benzene degradation under methanogenic conditions ……… 9
2.2.2 Benzene degradation under sulfate-reducing conditions …… 14
2.2.3 Benzene degradation under nitrate-reducing conditions …… 20
2.2.4 Benzene degradation under iron-reducing conditions ……… 25
2.3 Anaerobic benzene degradation by pure cultures ………………… 26
2.4 Anaerobic benzene activation mechanisms and associated genes……………… 28
2.4.1 Hydroxylation of benzene …………………………………….… 30
2.4.2 Methylation of benzene ………………………………..………… 34
2.4.3 Carboxylation of benzene ……………………………....………. 34
2.5 Benzoyl-CoA central metabolic pathways ………………………… 37
2.6 Syntrophic interactions in benzene-degrading communities ……… 42
2.7 Prospects for the future ……..……………………………………………… 43
Chapter 3: Anaerobic Benzene Mineralization by Natural Microbial Communities from Niger Delta …………………………………………………………………........... 44
3.1 Introduction …………………………………………………………..... 45
3.2 Materials and Methods ……………………………………………….. 46
3.2.1 Chemicals ………………………………………………………... 46
3.2.2 Site description and sampling procedure ……………………… 47
3.2.3 Setup of enrichment cultures …………………………………… 47
3.2.4 Chemical and microscopic analysis …………………………… 48
3.2.5 Microbial community analysis …………………………………… 49
3.3 Results and Discussion …………………………………………………. 50
3.3.1 Mineralization of benzene at different electron-acceptor conditions …………... 50
3.3.2 Microbial community structure at different electron-acceptor conditions ……... 53
3.4 Conclusion ………………………………………….…………………… 61
Chapter 4: Structure and Functional Capacity of a Benzene-mineralizing, and Nitrate-reducing Microbial Community ……………………………………………......... 62
4.1 Introduction …………………………………………………………..... 63
4.2 Materials and methods ……………………………………………..... 64
4.2.1 Chemicals ………………………………………………………... 64
4.2.2 Microcosm setup and sampling ………………………………… 64
4.2.3 Chemical and physiochemical analyses ……………………… 66
4.2.4 Amplicon and metagenome sequencing ……………………… 67
4.2.5 Protein mass spectrometry ……………………………………. 67
4.2.6 Metaproteome analysis ………………………………………… 68
4.2.7 Cloning and sequencing of putative nitric oxide dismutase (nod) genes ………. 68
4.2.8 Data availability …………………………………………………… 69
4.3 Results …………………………………………………………………………. 70
4.3.1 Benzene mineralization under nitrate-reducing conditions …… 70
4.3.2 Changes in microbial diversity during benzene mineralization . 71
4.3.3 Metaproteome composition ……………………………………… 74
4.3.4 Presence of putative nitric oxide dismutase genes (nod) ……. 76
4.4 Discussion ……………………………………………………………... 76
4.4.1 Putative pathways for nitrate reduction coupled with benzene mineralization … 76
4.4.2 Elucidation of the benzene activation step ……………………… 78
4.4.3 Benzoyl-CoA central pathway ……………………………………. 79
4.4.4 Peptococcacea as putative primary benzene degraders ……… 80
4.4.5 Metabolic function of Anammox bacteria in the community …… 81
Chapter 5: Consortia Dominated by Gammaproteobacteria Isolated from a Denitrifying Benzene-degrading Enrichment Culture and their Capacity to Mineralize Benzene...................... 83
5.1 Introduction ……………………………………………………………… 84
5.2 Materials and methods ………………………………………………… 85
5.2.1 Chemicals ………………………………………………………… 85
5.2.2 Isolation procedure …………………………………………………… 85
5.2.3 Mineralization and nitrite analyses ……………………..……… 86
5.2.4 Genomic DNA extraction and 16S rRNA gene sequencing … 87
5.3 Results …………………………………………………………………. 87
5.4 Discussions …………………………………………………………… 91
Chapter 6: General Conclusions and Outlook …..……………………………… 95
6.1 Conclusions and novelty of the research …………………………… 96
6.2 Ignavibacteriales as benzene degrading consortia under iron-reducing conditions 96
6.3 Insights into benzene activation via carboxylation by Peptococcaceae … 97
6.4 Unraveling growth of Anammox bacteria during benzene mineralization … 98
6.5 Study significance ……………………………………………………… 99
6.6 General outlook ………………………………………………………… 100
References ………………………………………………………………………… 101
Appendices ………………………………………………………………………… 120
Contributions of other Authors …………………………………………………… 16