Mit Power-to-X (PtX) wird eine Reihe von Verfahren beschrieben, die elektrische Energie in andere Kraft-, Brenn- und Grundstoffe umwandeln. Mögliche Anwendungsbereiche der strombasierten Stoffe finden sich beispielsweise im Verkehrs-, Wärme- und Industriesektor. PtX leistet damit einen wichtigen Beitrag für eine Kopplung des Verkehrs- und Energiesektors. Damit PtX einen signifikanten Anteil zum Klimaschutz leisten kann, wird als Basistechnologie die Umwandlung von erneuerbaren Energien zu grünen Wasserstoff (H2), mittels eines Elektrolyseurs, angestrebt. Für die Wettbewerbsfähigkeit von grünen H2, müssen insbesondere die Gestehungskosten gesenkt werden. Dazu werden im Bericht folgende wesentliche Einflussfaktoren identifiziert: Anlagengröße und Automatisierungsgrad der Herstellung, Anzahl der Betriebsstunden (Auslastungsgrad), Stromeinkaufspreis (aus erneuerbaren Energien), Stromnebenkosten (Steuern, Abgaben und Umlagen). Darüber hinaus spielt der Genehmigungsaufwand für die Wettbewerbsfähigkeit von Elektrolyseuren eine wichtige Rolle. Zur Optimierung dieser Einflussfaktoren in Richtung einer wirtschaftlichen und wettbewerbsfähigen Produktion von grünen H2 benennt der vorliegende Bericht verschiedene politische Handlungsempfehlungen. Grundsätzlich ist es von großer Bedeutung, ein Level-Playing-Field zu schaffen und die Energiewende konsequent voranzutreiben. Dies soll vor allem durch eine umfängliche CO2-Bepreisung aller Energieträger und einen massiven Ausbau an erneuerbaren Energien in Deutschland erfolgen. Zudem schlägt die AG 5 vor, bereits heute schon den Aufbau von zukünftigen H2-Märkten weltweit zu unterstützen. Zur Senkung der Investitions- und Stromnebenkosten empfehlen die Experten der AG 5 eine ambitionierte Umsetzung der europäischen Gesetzgebung (RED II) und die Prüfung von Beimischquoten von grünem Wasserstoff in der Wärmeversorgung. Des Weiteren spricht sich die AG 5 für eine Reduzierung von Umlagen (insbesondere der EEG-Umlage) und der Beibehaltung der Netzentgeltbefreiung aus. Ein wesentlicher Schritt zur Marktreife von grünem Wasserstoff sind Skaleneffekte bei Elektrolyseuren. Dazu muss das bereits heute bestehende Marktpotential genutzt werden. Vor allem in der Industrie und in Raffinerien bestehen große Bedarfe an H2 zur stofflichen Verwendung, die derzeit noch überwiegend durch die Dampfreformierung gedeckt werden.:1 Executive Summary 2 Ausgangslage und Zielsetzung 3 Sachstand und Fokus 4 Marktpotenzial Elektrolyse 4.1 Heutige Markte für H2 In Deutschland 4.2 Potenzielle Markte für grünen Wasserstoff 4.2.1 Warme 4.2.2 Verkehr 4.2.3 Speicher 5 Wettbewerbsfähigkeit von grünem H2 5.1 Regionale Verteilung 5.2 Transportkosten für zentrale Elektrolyse 5.3 Anwendungsfalle 5.4 Ausbaubedarf erneuerbarer Energien 6 Handlungsempfehlungen 7 Anhang 7.1 Überschlägige unverbindliche Berechnung der Transportkosten von Wasserstoff Im Gasnetz

In der vorliegenden Arbeit wird eine integrierbare Pumpentechnologie für polymerbasierte mikrofluidische Systeme entwickelt. Ausgehend von den Anforderungen für die Durchführung molekulardiagnostischer Nachweise kommen dabei Fertigungsverfahren zum Einsatz, die sich auch für Einweg-Anwendungen eignen. Das genutzte Aktorprinzip für die integrierten Mikropumpen basiert auf der Elektrolyse von Wasser. Zur besseren technologischen Integrierbarkeit wird das Wasser in Form eines Hydrogels appliziert. Der Elektrolyt wird dabei mit einer Polymermembran mit geringer Wasserdampfdurchlässigkeit verschlossen. Die Membran wird in ihrem plastischen Verformbereich genutzt. Zur Dimensionierung der Mikropumpen und des mikrofluidischen Systems werden analytische und numerische Modelle entwickelt, die eine gute Übereinstimmung mit den Messwerten zeigen. Die Funktionsfähigkeit wird anhand zweier vollständig integriert ablaufender Immunoassays demonstriert. Dabei kommt ein polymerbasierter, optischer Biosensor zum Einsatz.

In this study, the application of bipolar electrocoagulation (EC) with iron electrode has been assessed for color removal of simulated wastewater containing Reactive Red 195. The influence of initial pH, sodium sulfate concentration, initial dye concentration, electrolysis time, and electric current were examined. The optimum operational parameters were found to be pH =11, concentration of dye = 50 mg L-1, sodium sulfate concentration = 1200 mg L-1, electrolysis time = 5 min and electric current = 4 A. In such condition, color removal efficiency achieved over 99%. This result indicates that EC can be used as an efficient and “green” method for color removal from reactive dye solution. / Trong nghiên cứu này, quá trình khử màu nhuộm hoạt tính (Reactive Red 195) được khảo sát bằng hệ thống keo tụ điện hóa điện cực kép, với vật liệu sắt. Các yếu tố ảnh hưởng đến quá trình khử màu như pH, nồng độ màu nhuộm, nồng độ muối Na2SO4, thời gian phản ứng và cường độ dòng được lựa chọn nghiên cứu. Kết quả cho thấy hệ thống điện hóa trên loại gần như hoàn toàn màu nhuộm với hiệu suất đạt trên 99 % tại pH 11, nồng độ màu 50 mgL-1 và nống độ muối Na2SO4 1200 mgL-1 trong khoảng thời gian 5phút. Kết quả trên cho thấy keo tụ điện hóa có thể xem là một phương pháp xử lý hiệu quả và “xanh” trong việc loại bỏ hoàn toàn màu từ nước thải nhuộm hoạt tính.

Die galvanische Abscheidung von Iridium aus bromhaltigen Elektrolyten ist aus der Fachliteratur bekannt. Zum besseren Verständnis des Abscheidemechanismus und der nachlassenden Stromausbeute im Betrieb werden umfangreiche Untersuchungen zu den Parametereinflüssen und der Badzusammensetzung diskutiert. Im Fokus des Interesses steht der Oxidationszustand des Iridiums, der für die Abscheidung günstig ist und die Bildung eines Aquakomplexes, der zu abnehmenden Stromausbeuten mit zunehmendem Badalter führt. Die gebildeten Schichten werden hinsichtlich zweier Anwendungsfelder charakterisiert. Die Applikation geschlossener Schichten als Kontaktwerkstoff für die Beschichtung hochbeanspruchter Steck- und Schleifkontakte wird anhand von Beschichtungsversuchen an Demonstratorbauteilen diskutiert. Im zweiten Anwendungsfeld wird die galvanische Abscheidung vereinzelter Iridiumpartikel auf der Oberfläche von PEM-Elektrolyseuren mit Hilfe der Pulsstromtechnik und die katalytische Aktivität der erzeugten Oberflächen für die Sauerstoffbildungsreaktion untersucht. / The electrodeposition of iridium from bromine-containing electrolytes is well known from the literature. For a better understanding of the deposition mechanism and the decreasing current yield during operation, extensive investigations on the parameter influences and the bath composition are discussed. The focus of interest is the oxidation state of iridium, which is favorable for deposition, and the formation of an aqua complex, which leads to decreasing current yields with increasing bath age. The formed coatings are characterized with respect to two fields of application. The application of closed layers as contact material for the coating of highly stressed plug and sliding contacts is discussed on the basis of coating tests on demonstrator components. In the second field of application, the electrodeposition of isolated iridium particles on the surface of PEM electrolyzers using pulse current technology and the catalytic activity of the generated surfaces for the oxygen formation reaction are investigated.

Im Jahr 2017 konsumierten knapp 2 Milliarden Menschen fäkalkontaminiertes Wasser. Das führte zu fast 500.000 Todesfällen. Gleichzeitig werden Trinkwasserressourcen ausgebeutet und schon heute sind 4 Milliarden Menschen von Wasserknappheit betroffen. In ländlichen Entwicklungsregionen stellt, aus technischer Sicht, die Desinfektion des Wassers eine der größten Herausforderungen für die Sicherstellung einer angemessenen Trinkwasserversorgung dar. In dieser Dissertation wird die technische sowie wirtschaftliche Machbarkeit einer solar betriebenen Anlage zur Chlorproduktion mittels Inlineelektrolyse (ECl2) als Alternative zur Lieferung und Dosierung von Chlorreagenzien analysiert und bewertet. Während der ECl2 wird das gesamte aufzubereitende Wasser durch eine Elektrolysezelle geleitet und das Chlor aus dem natürlichen Chloridgehalt des Wassers „inline“ gebildet. Unter opti-malen Betriebsbedingungen kann Trinkwasser aber auch aufbereitetes Abwasser ohne Zugabe durch Chemikalien desinfiziert werden. Damit würde die Lieferung von Chlorlösung dauerhaft entfallen. Zusätzlich wurde bewertet, inwiefern die Entfernung von Eisen und Arsen durch die ECl2 sowie der Abbau von organischen Spurenstoffen durch zusätzliche Kombination mit UV-Bestrahlung zur Radikalbildung verbessert werden kann. Alle vorgestellten Feldtests wurden in Langzeitstudien unter Realbedingungen in zukünftigen Anwendungsgebieten durchgeführt. Dadurch konnten mögliche Probleme im Be-trieb der Anlagen frühzeitig erkannt und Lösungsvorschläge erarbeitet werden. Die Erfahrungen aus dem Betrieb der ECl2-Systeme stellen dabei den größten Nutzen dieser Arbeit dar. Mit den Feldversuchen konnte gezeigt werden, dass Wasser durch die Anwendung von ECl2 sicher desinfiziert und gleichzeitig ausreichend vor Wiederverkeimung geschützt werden kann. Insbesondere die Kombination mit naturnahen Verfahren zur Vorbehandlung des zu desinfizierenden Wassers hat sich als sehr vorteilhaft für die langfristig sichere Anwendung des Verfahrens herausgestellt. Für den in Uttarakhand, Indien, durch-geführten Feldtest konnte die ECl2 zusammen mit der Uferfiltration eine Logstufenreduktion von > 5.0 für Gesamtcoliforme und 3.5 für E. coli erreichen. Durch die Kombination mit einer vertikal durchströmten Pflanzenkläranlage (VFCW) konnte die Desinfektion von behandeltem Abwasser mittels Chlor erheblich vereinfacht werden. Die Pflanzenkläranlage reduzierte die Ammoniumkonzentration, den CSB sowie die Trübung und damit auch die Chlorzehrung des Wassers. Darüber hinaus wurden durch die VFCW Konzentrationsschwankungen im Zulauf erheblich vergleichmäßigt. Es wurden Logstufenreduktionen für Gesamtcoliforme von 5.1 und >4.0 für E. coli erzielt. Durch diese Verfahrenskombination werden auch Anwendungen zur Wiederverwendung von Abwasser möglich, die über die Bewässerung hinausgehen und damit wertvolle Frischwasserressourcen geschont. Durch die Behandlung von arsenkontaminiertem Grundwasser konnten mit der hier vor-geschlagenen Kombination von ECl2 und anschließender gemeinsamer Ausfällung und Filtration Entfernungsraten für Arsen von 94 % und Eisen von > 99 % erreicht werden. Da der WHO-Grenzwert für Arsen (10 µg/L) im hier durchgeführten Feldversuch mit 10 ± 4 µg/L dauerhaft nicht sicher eingehalten werden konnte, wurden weitere Optimierungsschritte identifiziert. Die Entfernungsrate für Benzotriazol von 5 % durch ECl2 allein konnte in Kombination mit UV-Lampen auf 89 % erhöht werden. Ähnliche Ergebnisse wurden für andere aus-gewählte organische Spurenstoffe erzielt. Es sind jedoch weitere Studien erforderlich, um den Abbauprozess im Detail zu verstehen und eine mögliche Zunahme der Toxizität durch die Bildung von Transformationsprodukten sowie Desinfektionsnebenprodukten zu bewerten. Die Feldversuche haben gezeigt, dass ECl2 als innovative Behandlungstechnologie in der Lage ist, Trinkwasser und behandeltes Abwasser sicher zu desinfizieren. Darüber kann mittels ECl2 u.a. die Entfernung von Arsen aus verunreinigten Rohwässern als auch der Abbau von Spurenstoffen verbessert werden. Bei härterem Rohwasser steht die rasche Verkalkung der Kathoden jedoch einem wartungsarmen Betrieb der Anlagen, trotz Polumkehr, entgegen. Die Versuche haben ge-zeigt, dass ECl2-Systeme mit den hier verwendeten Elektrolysezellen, nur in Wässern mit einem Gesamthärtewert <200 mg/L CaCO3 zuverlässig arbeiten. Da Rohwässer häufig Konzentrationen >200 mg/L aufweisen, ist der Anwendungsbereich der ECl2 begrenzt und erfordert alternative Chlorierungstechnologien zur ursprünglich geplanten Inline-Elektrolyse. Bereits während Versuchen zur Abwasserdesinfektion in Spanien wurde daher das Pilotsystem technisch dahingehend angepasst, dass nur noch ein Teilstrom von 4 bis 23 % des zu behandelten Wasservolumens durch die Elektrode floss. Dadurch konnte die Bildung von Ablagerungen vollständig verhindert und ein zuverlässiger, nahezu wartungsfreier Betrieb sichergestellt werden. Je nach dem Chlorbedarf und der natürlichen Chloridkonzentration des Wassers erfordert diese Betriebsweise in der Regel jedoch die Zugabe von Chlorid. In Anbetracht der hier ermittelten erhöhten Prozessstabilität und dem erheblich reduzierten Energieverbrauch erscheint diese Zugabe vertretbar. Laborstudien haben auch gezeigt, dass die Bildung anorganischer Desinfektionsnebenprodukte bei den „onsite chlorine generation“ (OCG) Systemen kein Problem darstellt. Um die wirtschaftliche Machbarkeit der hier getesteten Trinkwasseraufbereitungssysteme unter Realbedingungen zu bewerten, wurden der Betrieb eines in Ägypten eingesetzten ECl2-Aufbereitungssystems und zweier in Tansania und Nepal eingesetzter OCG-Einheiten analysiert. Die Studie zeigt, dass die Betriebs- und Wartungskosten solcher Einheiten dauerhaft gedeckt werden können. Für den Aufbau der Infrastruktur sind jedoch Investitionen durch entsprechende Förderprogramme erforderlich. Die hier angewandten Verfahren zur Wasseraufbereitung können eine wichtige Rolle bei der Verbesserung der Trinkwasserversorgung insbesondere in ländlichen Entwicklungsregionen und der Wiederverwendung von aufbereiteten Abwässern spielen. / In 2017 nearly 2 billion people consumed water that was contaminated with feces, causing almost 500.000 diarrheal deaths. At the same time freshwater resources are depleted and water scarcity is already affecting 4 billion people worldwide. From a technical perspective the continuous supply of chemicals needed to ensure sufficient disinfection remains a major challenge in rural water treatment, and existing technical solutions to adequately disinfect water have failed in the past. This dissertation work evaluates the technical and economic feasibility of solar-driven inline electrolytic production of chlorine (ECl2), as an alternative to external chlorine supply. During ECl2 disinfection the water passes through the cell and chlorine is produced “inline” from the natural chloride content of the water. Under optimal conditions, no chemicals are required to safely disinfect drinking water and treated wastewater. Fur-thermore, the ability of ECl2 to enhance the removal of iron and arsenic from contaminated groundwater and to degrade Trace Organic Compounds (TOrC) when combined with UV were analyzed. All relevant tests have been conducted in long-term field studies in future deployment areas. This enabled the evaluation of potential operational challenges of such systems under real-world conditions. The experiences gathered from these field trials represent the major benefit of this dissertation work. The trials have shown that with ECl2 water can be safely disinfected and supplied with an adequate amount of residual disinfectant. Here, the combination with natural pre-treatment systems has proven to be beneficial. For the drinking water trial conducted in Uttarakhand, India, the ECl2 system received bank filtrate and achieved overall log re-moval rates of >5.0 for total coliforms and >3.5 for E. coli. For the disinfection of treated wastewater, the combination with a vertical flow constructed wetland (VFCW) has largely simplified the disinfection with chlorine by equalizing wastewater (WW) inlet quality fluctuations, removing ammonium, COD, and turbidity. This has also substantially reduced the chlorine demand of the water, and pathogen indicator-free conditions were achieved with log unit removals of 5.1 and ≥ 4.0 for total coliforms and E. coli, respectively. Wastewater reuse applications that go beyond irrigation become permissible through this approach and the use of limited freshwater resources can be substituted. Removal rates for arsenic and iron of 94 % and >99 % respectively were able to be achieved by treating contaminated groundwater with the combination of ECl2 and subsequent co-precipitation and filtration proposed here. Despite effluent concentrations up to 10 ± 4 µg/L for arsenic, strict WHO guideline values could not be met. Here further optimization requirements were identified. The removal rate for benzotriazole of 5% through ECl2 alone could be increased to 89 % when combined with UV lamps. Similar results were achieved for other selected TOrCs. Still, more advanced studies are required to understand the degradation process in detail, and to evaluate a potential increase in toxicity through the formation of transformation products. The field trials have shown that ECl2 as an innovative treatment technology is capable of safely disinfecting drinking water and treated wastewater. Its application also enhances the treatment of other contaminants evaluated. However, cathode scaling has been iden-tified as the most critical technical issue - despite the use of polarity inversion. ECl2 systems could only operate reliably in waters with total hardness value < 200 mg/L CaCO3. As such concentrations are rare, the fields of application of ECl2 are limited. This required other chlorination technologies as alternatives to the originally planned inline electrolysis. An initial derivative of an ECl2 system was also applied during a wastewater disinfection trial in Spain. In this setting the portion of water passing by the electrodes and therefore the quantities of scaling agents were reduced to between 4 and 23 % of the total water volume treated. With this approach, deposit formation was completely prevented and reliable, nearly maintenance-free operation was ensured. However, such onsite chlorine generation (OCG) units commonly require the addition of chloride. From the author’s perspective and the experience collected during the field trials, the addition of NaCl is justifiable considering the increased reliability of system operation. OCG offers further advantages regarding process stability and energy demand. Lab studies have also shown that the formation of inorganic disinfection byproducts has not been an issue with OCG systems. To evaluate the economic feasibility of the drinking water treatment systems tested in real-world scenarios, an ECl2 treatment system operating in Egypt and two OCG units operating in Tanzania and Nepal were analyzed. The study shows that long-term operation and maintenance costs of such units can be covered. However, seed investment is required for the construction of the initial infrastructure. Once those costs are covered, the treatment approaches presented here can sustainably play an important role in reducing the number of people consuming contaminated water, especially in rural developing regions.

This dissertation aims to better understand the evolution of single hydrogen gas bubbles evolved during the water electrolysis at microelectrodes. In particular, the growth and detachment processes were studied in detail experimentally by means of electrochemical and optical methods in terrestrial, micro-, and hypergravity conditions. The combination of microelectrode and sulfuric acid promoting the bubble coalescence results in a periodical growth and the detachment of single bubbles. This provides a systematic view on the phenomena under study. A shadowgraphy system was used to provide general insight into the bubble behaviour, while Particle Tracking Velocimetry (PTV) was used for the flow velocity measurements around the growing hydrogen bubble. By applying high electric potentials considerably exceeding that in industrial electrolysers, it is possible to analyse the evolution of hydrogen bubbles under extreme conditions and for a wide range of electrolyte concentrations, overall shedding more light on bubble dynamics in general, and especially the underlying balance of forces. The growth of single hydrogen bubbles at micro-electrodes was studied in an acidic electrolyte over a wide range of concentrations and cathodic potentials. New bubble growth regimes were identified which differ in terms of whether the bubble evolution proceeds in the presence of a monotonic or oscillatory variation in the electric current and a carpet of microbubbles underneath the bubble. Key features such as the growth law of the bubble radius, the dynamics of the microbubble carpet, the onset time of the oscillations and the oscillation frequencies were characterised as a function of the concentration and electric potential. Furthermore, the system's response to jumps in the cathodic potential was studied. The electrode, tilted to the horizon, promotes faster growth and, therefore, earlier detachment at the smaller volume of the bubble. During its evolution, the bubble moves laterally from the electrode centre, releasing the electrode area and enabling higher electric current, therefore faster hydrogen generation and bubble-bubble coalescence rates. The duration of the bubble position oscillations found on the horizontal electrode gradually reduces upon tilt angle increase, with an almost complete disappearance at 5°. Based on the analysis of the forces involved and their scaling with the concentration, potential and electric current, a sound hypothesis was formulated regarding the mechanisms underlying the micro-bubble carpet and oscillations. A detailed look was also taken on the dynamics of single hydrogen bubbles in microgravity during parabolic flights. Three bubble evolution scenarios were identified depending on the electric potential applied and the acid concentration. The dominant scenario, characterised by lateral detachment of the grown bubble, was studied in detail. For that purpose, the evolution of the bubble radius, electric current and bubble trajectories as well as the bubble lifetime were comprehensively addressed for different potentials and electrolyte concentrations. The bubble-bubble coalescence events, which are responsible for reversals of the direction of bubble motion, were particularly analysed. Finally, as parabolic flights also permit hypergravity conditions, a detailed comparison of the characteristic bubble phenomena at various levels of gravity was drawn. Finally, the Marangoni convection at the foot of hydrogen gas bubbles mainly induced by the thermocapillary effect is systematically studied during the bubble evolution, the bubble position oscillations, at horizontal and tilted electrodes both in terrestrial and hyper-g environments. The flow structure progressively modifies with the bubble evolution or during the bubble position oscillations, i.e. as per electric current and bubble geometry variation. The velocity increases both with the bubble size and the electric current magnitude. It reaches up to 50 mm/s and 125 mm/s shortly before the bubble detachment at horizontal and tilted electrodes, correspondingly. The bubble position oscillations characterised by the large variation of the electric current govern the velocity of around ~80 mm/s at the highest and ~40 mm/s at the lowest positions. In the case of tilted electrodes, both in terrestrial and hyper-g environments, the lateral movement of the bubble enables higher values of the current and, therefore, stronger convection. The non-homogeneous distribution of the electric current lines at the tilted electrode results in the asymmetrical Marangoni convection around the bubble. There is a certain limitation in terms of the maximal magnitude of the velocity at different tilt angles, governed by the optimal size of the bubble and electric current. At last, the effects of the particles and laser used for PTV measurements were shown to reduce the duration of the oscillations and to retard the bubble evolution. Both effects were considered during the measurements.

In this study, the application of bipolar electrocoagulation (EC) with iron electrode has been assessed for color removal of simulated wastewater containing Reactive Red 195. The influence of initial pH, sodium sulfate concentration, initial dye concentration, electrolysis time, and electric current were examined. The optimum operational parameters were found to be pH =11, concentration of dye = 50 mg L-1, sodium sulfate concentration = 1200 mg L-1, electrolysis time = 5 min and electric current = 4 A. In such condition, color removal efficiency achieved over 99%. This result indicates that EC can be used as an efficient and “green” method for color removal from reactive dye solution. / Trong nghiên cứu này, quá trình khử màu nhuộm hoạt tính (Reactive Red 195) được khảo sát bằng hệ thống keo tụ điện hóa điện cực kép, với vật liệu sắt. Các yếu tố ảnh hưởng đến quá trình khử màu như pH, nồng độ màu nhuộm, nồng độ muối Na2SO4, thời gian phản ứng và cường độ dòng được lựa chọn nghiên cứu. Kết quả cho thấy hệ thống điện hóa trên loại gần như hoàn toàn màu nhuộm với hiệu suất đạt trên 99 % tại pH 11, nồng độ màu 50 mgL-1 và nống độ muối Na2SO4 1200 mgL-1 trong khoảng thời gian 5phút. Kết quả trên cho thấy keo tụ điện hóa có thể xem là một phương pháp xử lý hiệu quả và “xanh” trong việc loại bỏ hoàn toàn màu từ nước thải nhuộm hoạt tính.

In der vorliegenden Arbeit wird eine integrierbare Pumpentechnologie für polymerbasierte mikrofluidische Systeme entwickelt. Ausgehend von den Anforderungen für die Durchführung molekulardiagnostischer Nachweise kommen dabei Fertigungsverfahren zum Einsatz, die sich auch für Einweg-Anwendungen eignen. Das genutzte Aktorprinzip für die integrierten Mikropumpen basiert auf der Elektrolyse von Wasser. Zur besseren technologischen Integrierbarkeit wird das Wasser in Form eines Hydrogels appliziert. Der Elektrolyt wird dabei mit einer Polymermembran mit geringer Wasserdampfdurchlässigkeit verschlossen. Die Membran wird in ihrem plastischen Verformbereich genutzt. Zur Dimensionierung der Mikropumpen und des mikrofluidischen Systems werden analytische und numerische Modelle entwickelt, die eine gute Übereinstimmung mit den Messwerten zeigen. Die Funktionsfähigkeit wird anhand zweier vollständig integriert ablaufender Immunoassays demonstriert. Dabei kommt ein polymerbasierter, optischer Biosensor zum Einsatz.

The dynamics of hydrogen gas bubbles growing during electrolysis in H 2 SO 4 on a Pt microelectrode are studied in detail by electrochemical, shadowgraphy and PIV methods. The bubble evolution under potentiostatic conditions is presented in terms of electric current, images and radius of the growing bubble, and the velocity profiles. It allowed to resolve the carpet of microbubbles underneath the growing bubble, the transition to a new oscillatory growth regime and a Marangoni convection around the bubble foot. To substantiate the effect of coalescence and of the electrostatic effect on the bubble departure diameter, a salt (sodium sulfate) was added to regulate the pH and the ionic strength of the electrolyte.

According to estimates of the United Nations Environment Programme (UNEP), more than 1.8 billion people will be living in countries or regions with absolute water scarcity by 2025. The pressure on water resources is increased not only in arid and semiarid regions, but also in fast growing megacities around the world as a result of, amongst other factors, the changing nutritional and consumer behavior (rising living standards). Over 90 % of the annual water consumption of the newly industrializing and developing countries in the arid and semiarid climate zone is used for agricultural irrigation to ensure the nutrition of the population. Thus, since the beginning of the 20th century, the planned/controlled reuse of wastewater has developed into a central task of the sustainable water resources management. Wastewater represents a valuable resource in view of its composition (e. g. nutrients P, N for soil fertilizing) and its reliable, weather-independent availability in every household. The establishment of a closed-loop water management can enhance the efficiency of water usage. Therefore, activities in research and development are currently focused on decentralized and semi-centralized concepts, since their structures offer better conditions for the establishment of closed-loop systems and innovations in wastewater technology can be implemented more easily. In general, the hygienic quality requirements for wastewater reuse are predominantly oriented towards the planned usage. These are, in turn, regulated by thresholds and guidance values, e. g. for faecal indicator bacteria (e. g. faecal coliforms: E. coli), in widely differing norms and legal provisions specific to the respective countries. In Germany since 2005, small wastewater treatment plants can obtain the discharge class +H by the German Institute for Civil Engineering (DIBt: Deutsches Institut für Bautechnik) if secondary effluents contain less than 100 faecal coliforms (E. coli) per 100 mL. This ensures a safe effluent seepage in karst and water protection areas. Due to the infectious risk caused by a multitude of pathogens (bacteria, viruses, worm eggs, protozoa) which are still contained in wastewater after mechanical-biological treatment, specific disinfection methods are indispensable for their satisfactory reduction. Demands on disinfection methods for wastewater reclamation are quite complex. They should be characterized by a high and constant disinfection efficiency at low or moderate formation of disinfection by-products. The reclaimed wastewater should be able to be stored safely. Moreover, the disinfection method should be technically simple, scaleable, space-saving, subjected to low maintenance and realized at moderate investment and operating costs without applying external toxic chemicals. Established methods in decentralized wastewater disinfection are mainly based on membrane and UV technologies. However, these methods are currently working under high operating costs (high maintenance and cleaning efforts). Furthermore, the high investment costs of the membrane filtration are disadvantageous. In addition, both methods do not provide a disinfection residual. Thus, further research is required for the development and testing of alternative disinfection technologies. Against this background, the applicability of the electrolysis and UV/electrolysis hybrid technology for the decentralized wastewater reclamation was investigated and assessed in this dissertation. Results have shown that the electrochemical disinfection of biologically treated wastewater represents an efficient method at temperatures of > 6 °C, pH values of < 8.5 and DOC con-centrations of < 22 mg L-1. Under these conditions, an E. coli reduction of four log levels was achieved at a concentration of free chlorine ranging from 0.4 mg L-1 to 0.6 mg L-1 and at an after-reaction time of 15...20 min. However, it becomes simultaneously apparent that low temperatures, high pH values and high DOC concentrations are limiting parameters for this disinfection method to reclaim biologically treated wastewater. A high energy consumption of the electrolysis cell equipped with boron-doped diamond (BDD) electrodes (2...2.6 kWh m-3) represents a further unfavourable effect. Moreover, the undesired formation of chlorate (c = 1.3 mg L-1) and perchlorate (c = 18 mg L-1) at BDD electrodes can be considered as critical, since these disinfection by-products are, amongst others, human-toxicologically relevant. The concentration of adsorbable organically bound halogens (AOX) and trihalomethanes (THMs) proved to be marginal to moderate. Due to the synergistic effect of the combined application of UV irradiation (primary disinfection method) and electrolysis, the disadvantages of the single methods can be compensated. Decisive drawbacks of UV irradiation are photo and dark repair mechanisms of reversibly damaged bacteria. It was observed that the reactivation of reversibly UV-damaged E. coli even occurs at low temperatures (T = 10 °C) and strongly differing pH values (pH = 5.7...8.1) as well as at low light intensities and in darkness to an extent excluding a safe usage and storage of the reclaimed wastewater. The reactivation processes might be lowered by increased UV fluences. However, this is limited by high concentrations of total suspended solids (TSS). In spite of high UV fluences of > 400 J m-1, no complete removal of E. coli bacteria can be achieved at TSS concentrations of > 17 mg L-1. Therefore, it is indispensable to prevent bacterial reactivation caused by photo and dark repair processes. This topic was studied in the current work by electrochemically produced oxidants using an electrolysis cell positioned downstream of the UV unit. Results have shown that photo and dark reactivation were completely prevented by oxidants in a total concentration of 0.5...0.6 mg L-1 at a TSS concentration of 8...11 mg L-1, at pH values ranging from 5.7 to 8.1 and at temperatures ranging from 10 °C to 30 °C (t = 24....72 h). Even at a high TSS concentration of 75 mg L-1, the reactivation of E. coli (ctotal oxidants = 1.8 mg L-1) and, up to a TSS concentration of 32 mg L-1, the reactivation of total coliforms (except E. coli, ctotal oxidants = 1.0 mg L-1) can be prevented at a high initial germ concentration of 2…3 105 per 100 mL. The lowest energy consumption could be observed when mixed oxide electrodes (MOX electrodes) were applied. This result and the fact that no chlorate and perchlorate were observed at MOX electrodes argue for the application of these electrodes in practice. All in all, the UV/electrolysis hybrid technology represents an energy-efficient method for reclamation of biologically treated wastewater with TSS concentrations ranging from < 11 to 32 mg L-1 (E = 0.17…0.24 kWh m-3, MOX electrodes). Thereby, the reclaimed wastewater meet the hygienic quality requirements for a multitude of reuse categories starting from agricultural irrigation to urban and recreational reuse. Moreover, the requirements of the discharge class +H (100 faecal coliforms (E. coli) per 100 mL) are complied with reliably. The operational stability of the UV/electrolysis hybrid technology should also be ensured within the required maintenance intervals (t > 6 months). The undesired formation of coverings caused by biofouling processes on quartz glass surfaces could be prevented by electrochemically produced oxidants in a total concentration of 1 mg L-1 within an experimental duration of 5.5 months. However, the application of the UV/electrolysis hybrid technology is limited by increased particle concentrations and faecal loadings (initial E. coli concentration). The resulting enhanced demand of electrochemically produced oxidants for the prevention of bacterial reactivation results in a considerable increase of the electric charge input and energy consumption.