Newest publications
Investigation of phosphorus recovery from biogas digestate: low-technology approaches for enhanced solid-liquid separation
(2025) Uppuluri, Naga Sai Tejaswi; Müller, Joachim
Phosphorus (P) is a critical nutrient for agriculture, essential for plant growth and food security. However, the global dependence on finite P reserves, primarily located in northern Africa and China, presents significant challenges, including supply chain vulnerabilities and rising fertilizer costs. Additionally, excessive P runoff into water bodies contributes to environmental issues, such as eutrophication. Addressing these challenges requires sustainable P management strategies, including P recovery from alternative sources like biogas digestate. To tackle these challenges, regulatory measures and innovative recovery techniques are being explored to improve P sustainability.
In Germany, regulations like the Fertilizer Ordinance and the Sewage Sludge Ordinance have introduced strict limits on P application and mandated the recovery of P from waste streams, promoting environmentally friendly nutrient management practices. These regulations aim to reduce environmental impacts while ensuring the efficient use of P resources. A primary objective of this research is to develop a cost-effective, practically feasible method for P recovery that can be easily integrated into existing biogas plants without requiring substantial infrastructure upgrades. This study investigated the recovery of P from biogas digestate using additives such as kieserite (MgSO₄∙H₂O), straw flour, and biochar to improve separation efficiency and nutrient recovery. The additives enhanced the P content in the solid phase, making it easier to recycle P back into agricultural systems.
The laboratory-scale separation trials were conducted to evaluate the effectiveness of three additives categorized into reactive (kieserite) and non-reactive (straw flour and biochar) groups. The separations were carried out using a hydraulic tincture press, with a pressure of 5 MPa applied for 120 seconds. The trials tested five different treatment times: 0 h, 1 h, 2 h, 8 h, and 20 h. Kieserite was tested at 25 °C and 50 °C, while straw flour and biochar were tested only at 25 °C. The results revealed that longer treatment durations with kieserite were more effective, with 61% of P shifting into the solid phase after 20 h. In contrast, treatment duration had little impact on the effectiveness of straw flour and biochar. Kieserite treatment increased NaOH-P and HCl-P, indicating the formation of more stable, non-labile P fractions due to the interaction between (Mg²⁺) ions from kieserite and phosphate (PO₄³⁻) ions. These findings concluded that kieserite, as a reactive additive, is more effective at enhancing P recovery by converting labile P into more stable, non-labile forms.
Based on the conclusions from laboratory-scale separation trials, practical scale experiments were conducted at the research biogas facility ‘Unterer Lindenhof’ at the University of Hohenheim. In these trials, straw flour and kieserite were used as additives, with treatment durations of 4 h and 22 h. The shorter duration represented same-day processing, while the longer duration simulated overnight treatment. Results showed that extending the treatment time with kieserite significantly improved P removal efficiency (PRE), reaching 67% of P shifted to the solid phase after 22 h. Straw flour, on the other hand, achieved a 52% PRE at the same duration, with most of the P remaining in labile fractions regardless of treatment time. Kieserite treatment resulted in notable changes in the distribution of P fractions, shifting from NaHCO₃-P to more stable NaOH-P and HCl-P fractions as the treatment duration increased. These experiments provide a technical proof-of-concept for the use of additives in biogas plants for digestate treatment to enhance P recovery into the solid phase, supporting more sustainable nutrient management practices.
Biochar modified with kieserite and calcium chloride (CaCl₂) was evaluated as an additive for P recovery, along with the metal salts used independently. The modification aimed to load Mg²⁺ and Ca²⁺ ions onto the biochar surface, enhancing its effectiveness. Initial separation trials established that using 5 gadditive/Ldigestate with a 22 h treatment time provided optimal conditions for solid-liquid separation. The separation trials were made in the laboratory using a hydraulic tincture press. The modification significantly increased the Mg content in kieserite-modified biochar (KIS-B) and the Ca content in CaCl₂-modified biochar (Ca-B). Both modified biochars and the metal salts increased P transfer to the solid phase, with the metal salts alone demonstrated higher PRE. KIS-B and Ca-B shifted P to non-labile fractions, while kieserite and CaCl₂ alone resulted in an even higher proportion of non-labile P fractions. Although the modified biochar showed slightly lower PRE compared to metal salts, its potential benefits in agricultural applications are noteworthy.
Future studies should include a comprehensive cost-benefit analysis to evaluate the long-term financial sustainability of implementing these recovery techniques at full scale. Reducing the reliance on expensive, finite phosphorus reserves through local recovery can lower input costs for farmers, making the process economically attractive. Additionally, plant pot trials will be essential in assessing the agronomic efficiency of P recovered from biogas digestate. These trials can help determine how effectively the recovered P promotes plant growth and nutrient uptake compared to conventional fertilizers. Ultimately, refining these recovery techniques and assessing their impact on both economic viability and agricultural productivity will play a key role in advancing sustainable nutrient management practices globally.
Straßenzeitungen in Deutschland – ein Medium im Spannungsfeld zwischen normativem Anspruch und publizistischem Erfolg
(2025) Hummel, Gerrit; Scheufele, Bertram
Straßenzeitungen sind journalistische Produkte, die in Form von Zeitungen oder Magazinen auf den Straßen in unseren Städten überwiegend von obdach- oder wohnungslosen Menschen, aber auch Menschen, die in Armut leben, verkauft werden (vgl. Kulke, 2015, S.10). Der Verkauf dieser Zeitungen soll den Betroffenen helfen, sich ein kleines Zubrot zu verdienen. Neben diesem Verdienst stellen Straßenzeitungsprojekte auch ein Angebot an sozialarbeiterischer Betreuung zur Verfügung. Durch den Verkauf der Zeitungen und den Kontakt mit den Kunden, aber auch durch die Möglichkeit zum Austausch mit anderen Mitarbeitern im Straßenzeitungsprojekt, kann der Betroffene verschiedene Arten des Empowerments (ökonomisch, sozial, psychologisch und politisch) erfahren (vgl. Magallanes-Blanco & Pérez-Bermúdez, 2009). Dieses Empowerment soll ihn befähigen, sein Leben wieder in die eigenen Hände zu nehmen und sich selbst als Teil der Gesellschaft in diese hinein zu reintegrieren (vgl. Bode, 2021, S.384).
Die Straßenzeitungen – also die journalistischen Produkte, die auf den Straßen verkauft werden – spielen dabei eine zentrale Rolle. Sie werden in den Medienorganisationen, genannt Straßenzeitungsprojekte, unter besonderen Bedingungen produziert. Straßenzeitungsprojekte verfügen über alternative Organisationsstrukturen, die Medienmacher haben oft eine andere Wahrnehmung und Rollenvorstellung als klassische Journalisten und es gibt andere Arbeitsroutinen als in den etablierten Mainstream-Medien (vgl. Scheufele & Schieb, 2014, S.31-42; oder für alternative Medien Bailey et al., 2008, S.19; Kenix, 2008). Von besonderer Bedeutung sind die Medieninhalte der Straßenzeitungen, die das Leben, die Perspektiven und Erfahrungen der Betroffenen wiedergeben sollen (vgl. Howley, 2003, S.280-281; Scheufele & Schieb, 2014, S.44). So kann auf ihre Situation und ihre Bedürfnisse hingewiesen werden und das Medium kann in die Mitte der Gesellschaft hinein seine Wirkung entfalten (vgl. Howley, 2003, S.283).
In dieser Arbeit steht die Genese der Medieninhalte von Straßenzeitungen im Vordergrund. Dabei untersuche ich, ob unterschiedliche Eigenschaften der Organisations-form, der Medienmacher und der Arbeitsroutinen Auswirkungen auf die publizierten Medieninhalte haben. Die Theorie meiner Arbeit besteht einerseits aus Ansätzen und Theorien zur Forschung von alternativen Medien und andererseits aus einem international stark zitierten und beforschten Gatekeeping-Ansatz, der Hierarchie der Einflüsse. Letztere stellt für mein Forschungsvorhaben eine verbindende theoretische Klammer zwischen den einzelnen Untersuchungsebenen dar. Die theoretischen Grundlagen zu alternativen Medien dienen mir dazu, die einzelnen beobachteten Eigenschaften auf dem Spannungsfeld zwischen alternativen und Mainstream-Medien zu verorten. Diese Kontrastfolie dient mir bei der Einordnung der Befunde als empirischer Kompass und hilft mir aufzuzeigen, wie stark die charakteristischen Merkmale einzelner Straßenzeitungsprojekte dem Ideal eines alternativen Mediums entsprechen.
Für meine Untersuchung habe ich 3 Teilstudien mit drei getrennten Erhebungen durchgeführt. Zum einen habe ich 25 Vertreter von Straßenzeitungen in Deutschland interviewt und im Anschluss eine qualitative Inhaltsanalyse am Interviewmaterial durchgeführt. Dabei wurden die Bereiche Medienmacher, Arbeitsroutinen und Organisation charakterisiert und vor dem Spannungsfeld zwischen alter-nativen Medien und Mainstream-Medien verortet. Vor dieser qualitativen Arbeit habe ich eine kurze Onlineumfrage durchgeführt, um Kerncharakteristika (zum Beispiel: Periodizität, Auflagenstärke, Verbreitungsgebiet) der Straßenzeitungen zu erheben. In einer dritten Erhebung wurden in einer quantitativen Inhaltsanalyse die Ausgaben des letzten Jahres der Straßenzeitungen erfasst. Der Fokus lag dabei insbesondere auf den alternativen Eigenschaften der Medieninhalte.
In den Analysen werden zuerst die Befunde für die jeweiligen Bereiche vorgestellt und in Teilen bereits in bivariaten Verfahren besprochen. Abschließend habe ich mit Hilfe der Qualitative Comparative Analysis (QCA) alle Bereiche in einer Between-Methods-Triangulation zusammengeführt und konnte so analysieren, welche Bedingungen für das Zustandekommen von welchen Medieninhalten von Bedeutung sind. Die Analysen bestätigen die Vermutungen: Je alternativer ein Straßenzeitungsprojekt in seiner Grundausrichtung in den Bereichen Medienmacher, Routinen und Organisation ist, umso alternativer werden auch die Medieninhalte. Hierbei scheint vor allem der Bereich der Arbeitsroutinen besonders wichtig und einflussreich zu sein.
Meine Dissertation gehört im Hinblick auf die eingenommene Mehrebenen-Logik im Bereich der Gatekeeping-Forschung zu einer der wenigen existierenden Studien, die mehr als zwei Ebenen inhaltlich und methodisch sinnvoll miteinander verknüpft und die Genese von Medieninhalten erklärt. Weiterhin schafft es meine Studie, die Leerstelle der Forschung zu Straßenzeitungen in Deutschland (vgl. Bode, 2021, S.371; Scheufele & Schieb, 2014, S.32) durch Aufarbeitung eines umfangreichen Samples zu füllen.
From spectra to traits: advancements in predicting wheat characteristics
(2025) Nagel-Held, Johannes Henrich; Hitzmann, Bernd
This thesis is driven by two primary objectives: To evaluate the potential for improving quality assessment throughout the wheat value chain and the potential for replacing protein content as the primary determinant of price and quality with spectroscopic methods. An early, fast, and well-founded decision on wheat quality leads to improved processing properties and product quality of wheat products. Given that these attributes are often more closely tied to protein quality or other components than protein quantity, a direct and precise quantification is highly desirable. The noteworthy advantage of protein content lies in its prediction through near-infrared spectroscopy (NIRS).
To augment the information available from near-infrared spectra, which are inherently limited in their insights into molecular compounds within samples, NIRS was supplemented with Raman and fluorescence spectroscopy. The thesis`s foundation comprises four distinct sample sets, encompassing both common wheat and spelt. In total, a staggering 4,237 samples of whole grain, whole grain flour, and extracted flour were analyzed to predict a wide array of 100 diverse quality parameters, spanning from measures of protein quality to dough rheological properties, baking behavior, physical and chemical characteristics and agronomic traits. To enable accurate predictions several spectra pre-processing and regression techniques were applied.
Among the spectrometers and algorithms tested, no clear recommendation can be given. In this work, NIRS was found to perform well over different levels of sample preparation, while Raman and fluorescence spectroscopy performed better on flour.
A glimpse into the findings is best exemplified by considering loaf volume, a measure of end-product quality. Prediction errors (RMSECV) ranged between 29 and 43 mL/100 g of flour, accompanied by R² values spanning 0.66 to 0.78. One major factor influencing the improvable prediction accuracy is the inherent measurement error associated with the baking trial. However, when this measurement error is known, a straightforward solution emerges: By measuring a few samples repeatedly, the prediction error can be corrected from 43 mL/100 g of flour to 28 mL/100 g, aligning with the magnitude of the measurement error itself. Simultaneously, the corrected R² value improves from 0.66 to 0.86. It has been shown that measurement error correction works for other quality characteristics, such as water absorption or baking loss, and may be applied to other parameters. The robustness of the models was evaluated by successfully predicting complex traits of unknown cultivars. However, the models proved less effective in predicting across separate locations and years. Similar robustness results were found for protein content, water absorption and grain yield. Since protein content is a well-established and predictable parameter, robust models for complex traits are also feasible.
Other well predictable parameters are protein content (R² = 0.97-0.98, RMSECV = 0.16-0.20 %), wet gluten content (R² = 0.89-0.98, RMSECV = 0.80-0.84 %), water absorption (R² = 0.68-0.83, RMSECV = 0.9-1.2 mL/100 g) and grain yield (R² = 0.73-0.85, RMSECV = 5.9-6.8 dt/ha). Examples for non-predictable parameters are starch properties measured with a rapid visco analyzer or enzyme activity. And for some parameters no clear conclusion could be drawn, such as SDS sedimentation volume, plant height, thousand kernel weight, extensograph or farinograph parameters.
The successful prediction of intricate traits can be further refined by reducing measurement errors of the reference values and using better suited spectrometers. The robustness can be increased by expanding the sample set by including data from a broader spectrum of locations and years.Implementing this proposed methodology holds the potential to instigate positive changes within the wheat supply chain, with implications for product quality, environment, and economic aspects.
Effects of pretreatment with a ball mill on methane yield of horse manure
(2023) Heller, René; Roth, Peter; Hülsemann, Benedikt; Böttinger, Stefan; Lemmer, Andreas; Oechsner, Hans
Lignocellulosic biomass is an abundant organic material, which can be utilised in biogas plants for sustainable production of biogas. Since these substrates usually have high lignin contents and consist of rather elongated particles, a special pretreatment is required for an economical and process-stable utilisation in the biogas plant. The mechanical pretreatment of horse manure was carried out with the prototype of a ball mill at different speeds. The aim of ball milling is to comminute the substrate and disintegrate the lignocellulosic bond. Mechanical pretreatment in the ball mill resulted in a significant increase in specific methane yield of more than 37% in anaerobic batch digestion (up to 243 LCH4 kgVS−1) of horse manure. The kinetics of the methane gas formation process was analysed by a modified Gompertz model fitting and showed a higher methane production potential and maximum daily methane production rate as well as a lower duration of the lag phase after pretreatment at 6 rpm. This was further confirmed by sieve analyses, which showed a significant reduction of particle size compared to the untreated variant. Thus, the use of the ball mill increases the specific methane yield and improves the fermentation of lignocellulosic substrates such as horse manure.
Computational aspects of experimental designs in multiple-group mixed models
(2023) Prus, Maryna; Filová, Lenka
We extend the equivariance and invariance conditions for construction of optimal designs to multiple-group mixed models and, hence, derive the support of optimal designs for first- and second-order models on a symmetric square. Moreover, we provide a tool for computation of D - and L -efficient exact designs in multiple-group mixed models by adapting the algorithm of Harman et al. (Appl Stoch Models Bus Ind, 32:3–17, 2016). We show that this algorithm can be used both for size-constrained problems and also in settings that require multiple resource constraints on the design, such as cost constraints or marginal constraints.