Browsing by Person "Dinkler, Konstantin"

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Coupled biogas and fiber production from agricultural residues and energy crops with steam explosion treatment
(2023) Hülsemann, Benedikt; Baumgart, Marian; Lenz, Leonhard; Elviliana,; Föllmer, Marie; Sailer, Gregor; Dinkler, Konstantin; Oechsner, Hans
The global demand for packaging materials and energy is constantly increasing, requiring the exploration of new concepts. In this work, we presented a bioeconomic concept that uses steam explosion and phase separation to simultaneously generate fibers for the packaging industry and biogas substrate for the energy sector. The concept focused on fiber-rich residues and fiber-rich ecological energy crops from agriculture. Feasibility of the concept in the laboratory using feedstocks, including Sylvatic silphia silage, Nettle silage, Miscanthus, Apple pomace, Alfalfa stalks, and Flax shives was confirmed. Our results showed that we were able to separate up to 26.2% of the methane potential while always extracting a smaller percentage of up to 17.3% of organic dry matter (ODM). Specific methane yields of 297–486 LCH4 kgODM−1 in the liquid and 100–286 LCH4 kgODM−1 in the solid phase were obtained. The solid phases had high water absorption capacities of 216–504% due to the steam explosion, while the particle size was not significantly affected. The concept showed high potential, especially for undried feedstock.
Effect of reactive and non-reactive additive treatment on the recovery of phosphorus from biogas digestate
(2023) Uppuluri, Naga Sai Tejaswi; Dinkler, Konstantin; Ran, Xueling; Guo, Jianbin; Müller, Joachim; Oechsner, Hans
The annual phosphate (PO43−) utilization has increased, leading to a depletion of existing sources of phosphorus (P). To overcome this, digestate as a source to recover P is being investigated. Due to the abundance of nutrients, the digestate from an agricultural biogas plant is used as fertilizer for crops. The separation of solids and liquids from the digestate by a screw press is the simplest form of concentrating, therefore, recovering PO43−. This is the most commonly employed method in existing biogas plants. However, the separation is not very efficient as only 20–30% of P is recovered in the solid phase. The goal of this study is to increase the separation efficiency and recover more P into the solid phase, in order to improve the transportability. For this, separation trials at a laboratory scale were performed for five experimental groups, with biochar and straw flour as non-reactive additives and kieserite as a reactive additive. In addition, untreated digestate was studied as a control. The control and the treatment with biochar and straw flour were carried out at 25 °C, while the treatment with kieserite was performed at 25 °C and 50 °C. The separation trails were performed at treatment times of 0 h, 1 h, 2 h, 8 h, and 20 h. The results showed that the treatment with additives had a beneficial effect on the recovery of P. It was noted that kieserite treatment at 25 °C and 50 °C bound about 61% of the total P present in the digestate to the solid phase. A sequential extraction was performed to study the effect of additives on the recovery of different P species. The results concluded that, compared to biochar and straw flour, kieserite was efficient in recovering the non-labile fractions (NaOH-P and HCl-P) of P, which act as slow-release fertilizers. This study shows that the use of additives, especially kieserite, has a positive influence on recovering P from digestate, and further research to optimize the recovery process would be beneficial.
Phosphate turnover during anaerobic digestion of chicken, pig and dairy manure
(2023) Dinkler, Konstantin; Müller, Joachim
Phosphate (P) is used extensively in agriculture. This has led to a reliance on P imports. Meanwhile, the framework for fertilization with digestate and manure in the European Union has become more stringent in recent years. Therefore, nutrients should be recovered as fertilizer to reduce dependencies, redistribute nutrient and amplify the product portfolio of biogas plants. Current nutrient recovery processes have in common that they are post digestion treatments of digestate, which neglect the phosphate behavior during digestion. It is necessary to closely evaluate P behavior during AD to optimize post digestion treatments of digestate by using digestion as a pretreatment for digestate. Therefore, it was the overall objective of this work to evaluate the turnover of P during anaerobic digestion in laboratory scale batch and continuous digestion systems. In laboratory experiments with batch reactor systems three different manures, namely pig, dairy and chicken manure were digested. Activated sludge served as inoculum. A set of 120 mL batch digesters were filled and individual bottles were opened after defined times and discarded afterwards until the last reactors were opened on day 30. The results showed that H2O-P and NaHCO3-P decreased over the digestion period by up to 40.1 %. Meanwhile, NaOH-P increased. Overall, it could be concluded that anaerobic digestion leads to a mineralization of P. The mineralization was especially profound during the first few days after the substrate was mixed with the inoculum, concluding that the ions in the inoculum played a significant role in this mineralization. In effect, AD reduces immediate plant availability but increases slow-release fertilization effects. During the batch experiments it was found that for a defined measurement wavelength for digestate the absorbance spectrum of digestate extracts needed to be analyzed and a drying temperature needed to be determined for sample treatment. For the evaluation of these two aspects samples were dried at 50°C and at 105°C and freeze dried. These samples and undried digestate were extracted by Hedley fractionation. The coloring agent was added to the extracts and the spectra between 600 nm and 1100 nm were measured. The spectral lines showed two peaks (709 nm and 889 nm). The lower wavelength proved to be more stable at low absorbance, making this the better wavelength for analysis. The analysis of the Hedley extracts showed that drying increases the H2O-P and NaHCO3-P fraction by up to 70 %. The samples were rinsed with preceding solvent to increase accuracy. Overall, the adapted method achieved higher accuracy for H2O-P, NaHCO3-P than the former method. The adapted fractionation was used for the analysis of samples during experiments in continuously stirred tank reactors. Chicken and dairy manure were each co-digested with straw and the parameters OLR and temperature were varied. The results showed that OLR had a negative correlation with H2O-P, which decreased by up to 50.49 %. Meanwhile, HCl-P increased significantly in chicken manure digestate, showing a positive correlation with OLR. It was proven that temperature has a minor effect on P transformation with a slightly higher mineralization of P under thermophilic conditions. Especially the high calcium concentration in chicken manure dominated the P turnover during the digestion, which can also be seen in the positive correlation of OLR with HCl-P as well as a high Pearson correlation coefficient above 0.85 for calcium and phosphate in chicken manure digestion. The results of this work have proven that P changes its chemical composition significantly during anaerobic digestion. The parameters of the digestion process had a decisive effect on the final composition with OLR and substrate composition being the major drivers. The results further showed that gas production and high P solubility are in conflict because for increased H2O-P OLR needs to be reduced. Future work should focus specifically on the combination of this anaerobic digestion and post-digestion treatments for cost effective recovery. This can play a key role for future profitability of biogas projects.