Potenziale der biologischen Behandlung von organischen Abfällen zur Sektorenkopplung

Die Dissertation beschäftigt sich mit der Bestimmung des stofflichen und energetischen Potenzials organischer Abfälle aus Haushaltungen in kreisfreien Städten und Landkreisen. Zur Bestimmung der stofflichen und energetischen Potenziale wurden Berechnungsformeln aufbauend auf regionalstatistischen Daten, Praxisdaten und Batchversuchen entwickelt. Durch die Kombination von Datenauswertung, Laborversuchen und Potenzialbestimmung wurde die Möglichkeit geschaffen, stoffliche und energetische Potenziale auf Kreis-, Landes- und Bundesebene abzuschätzen und zu optimieren

Influence of Acids and Alkali as Additives on Hydrothermally Treating Sewage Sludge: Effect on Phosphorus Recovery, Yield, and Energy Value of Hydrochar

The high moisture content present in sewage sludge hinders the use of sewage sludge in incineration or energy application. This limitation of moisture present in sewage sludge can be obviated by using the hydrothermal carbonization (HTC) process. In sewage sludge management, the HTC process requires less energy compared to other conventional thermo–chemical management processes. The HTC process produces energy-rich hydrochar products and simultaneously enables phosphorus recovery. This study investigates the influence of organic acids, inorganic acid, and alkali as additives on phosphorus transformation, yield, proximate analysis and the heating value of subsequently produced hydrochar. The analysis includes various process temperatures (200 °C, 220 °C, and 240 °C) in the presence of deionized water, acids (0.1 M and 0.25 M; H2SO4, HCOOH, CH3COOH), and alkali (0.1 M and 0.25 M; NaOH) solutions as feed water. The results show that phosphorus leaching into the process-water, hydrochar yield, proximate analysis, and the heating value of produced hydrochar is pH- and temperature-dependent, and particularly significant in the presence of H2SO4. In contrast, utilization of H2SO4 and NaOH as an additive has a negative influence on the heating value of produced hydrochar

Process Waters from Hydrothermal Carbonization of Waste Biomasses like Sewage Sludge: Challenges, Legal Aspects, and Opportunities in EU and Germany

Hydrothermal carbonization (HTC) has developed considerably over the last 15 years and offers a viable alternative for the utilization of municipal and industrial organic waste such as sewage sludge. However, the technology has yet to establish itself as a valorization process for waste biomasses (2024) and is not yet a recognized state of the art. Nevertheless, the HTC technology could gain greater relevance in the future, especially as an alternative valorization pathway for sewage sludge. During HTC, significant amounts of HTC process water (PW) are produced as a byproduct. The process water is inorganically and organically polluted and has to be treated, as it would be a burden on water bodies and thus on the environment if left untreated. In the EU and specifically Germany, industrial wastewater producers like HTC-plant operators are obliged to treat their industrial wastewater before discharging it into the environment. In addition to a large amount of PW and its treatment to the required limits, the organic load and possible persistent and toxic substances pose major challenges for plant operators. Many proven processes from industrial wastewater treatment were transferred for the treatment of PW. Treatment of the PW in a manner that is industrially viable, economically viable, and efficient is crucial for the effective commercialization of HTC technology. In this, the challenges and opportunities of PW composition, management, and treatment, including legal aspects, are mainly discussed. Therefore, the legal framework in the European Union and specifically for Germany will be elaborated. Furthermore, different treatment pathways are also highlighted

Cloaked contact grids on solar cells by coordinate transformations: designs and prototypes

Nontransparent contact fingers on the sun-facing side of solar cells represent optically dead regions which reduce the energy conversion per area. We consider two approaches for guiding the incident light around the contacts onto the active area. The first approach uses graded-index metamaterials designed by two-dimensional Schwarz–Christoffel conformal maps, and the second uses freeform surfaces designed by one-dimensional coordinate transformations of a point to an interval. We provide proof-of-principle demonstrators using direct laser writing of polymer structures on silicon wafers with opaque contacts. Freeform surfaces are amenable to mass fabrication and allow for complete recovery of the shadowing effect for all relevant incidence angles

Investigating the chronostratigraphy of prominent palaeosols in Lower Austria using post-IR IRSL dating

The age of most Lower Austria loess deposits is unknown; this is especially true for Middle Pleistocene loess because there is no generally applicable dating method available. Recently it has been shown that infrared stimulated luminescence (IRSL) signals measured at elevated temperatures after an infrared (IR) stimulation are more stable than the standard IRSL signal measured at 50°C. These signals offer new opportunities to extend the datable age range by minimising or circumventing the undesirable anomalous fading correction. In this study we apply, for the first time, two post-IR IRSL single-aliquot regenerative (SAR) dating protocols to polymineral fine-grain samples from three loess/palaeosol sequences in Lower Austria. The luminescence characteristics and ages derived from these protocols are compared with the IRSL results obtained at 50°C. Recycling ratios, recuperation and dose recovery tests show that these protocols are applicable to the loess under investigation. Fading rates for the post-IR IRSL signals are significantly smaller than for the IRSL at 50°C; the differences in fading rates between post-IR IRSL at 225°C and post-IR IRSL at 290°C are less obvious. Significant fading corrections are needed for the ages derived from the IRSL signal at 50°C. From our study we conclude that the fading corrected post-IR IRSL at 225°C and the fading uncorrected post-IR IRSL at 290°C provide the best age estimates; we prefer the latter because no fading correction is apparently needed. Our data strongly suggest that the pedocomplex ‘Paudorfer Bodenbildung’ developed during marine isotope stage (MIS) 5, whereas the pedocomplex ‘Göttweiger Verlehmungszone’ is significantly older (≥ 350 ka) than has been suggested in former studies

Holocene overbank sedimentation in Central Europe between natural and human drivers - The Weiße Elster River (Central Germany)

Up to several meters thick fine-grained Holocene overbank deposits are ubiquitously found in most Western and Central European lowland floodplains. However, despite their large importance for the geomorphological and geoecological floodplain properties, the interplay of different possible causes for their formation are not well understood yet. Most authors suggest human-induced deforestation as the main precondition for sediment mobilization and transport from the slopes to the floodplain, whereas others suggest a stronger influence of climatic factors. This current research gap is caused by often missing well-resolved fluvial chronostratigraphies and spatio-temporal information about former human activity within the studied catchments. To fill this gap we exemplarily studied Holocene overbank sedimentation and possible human or natural drivers in the meso-scale Weiße Elster catchment in Central Germany. To do so, we applied numerical dating as well as sedimentological and micromorphological analyses to Holocene fluvial sediments along three floodplain transects. Furthermore, we built up an unprecedented systematic spatio-temporal database of former human activity within the catchment from the Neolithic until the Early Modern Ages. Together with published paleoclimatic data, this database allowed an unprecedented, systematic comparison of Holocene overbank sedimentation phases with possible external controls. Our data show that some overbank sedimentation phases were directly linked with human activities in the affected site sub-catchments, whereas others were not. Instead, all phases seemed to be linked with natural factors. This difference with most former studies could possibly be explained by previously often limited numerical dating of the fluvial sediments and by largely missing spatio-temporally well-resolved regional settlement records, hindering a precise temporal link of fluvial sedimentation with former human settlement. Furthermore, this difference could possibly also be explained by a relatively high natural sensitivity of the landscape dynamics in the Central German lowlands, showing a subcontinental climate, towards climatic external controls

Thermodynamics of a nanowire solar cell: Towards the ultimate limit

A lossless solar cell operating at the Shockley-Queisser (S-Q) limit generates an open-circuit voltage (VOC) equal to the radiative limit. At VOC, the highly directional beam of photons from the sun is absorbed and subsequently externally re-emitted into a 4p solid angle, providing a large photon entropy loss. Moreover, due to many total internal reflections and low internal radiative efficiency, a lot of light is lost in nonradiative recombination events. In our research, we perform a nanophotonic optimization of a semiconductor nanowire geometry with a top microlens in order to decrease the photon entropy loss and to increase the photon escape probability for the nanowire, therefore increasing the output voltage. The optimization leads us to a maximum VOC of 1178 mV which is 141 mV higher than the radiative limit and 172 mV lower than the ultimate limit. The photon entropy loss is also studied fundamentally from the thermodynamics point of view to better understand where the entropy is generated during the absorption-emission processes