Institut für Agrartechnik

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/19

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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.
An evaluation of biogas potential of cassava, yam and plantain peel mixtures using theoretical models and Hohenheim Biogas Yield Test-Based experiments
(2025) Kusi, Joseph Yankyera; Empl, Florian; Müller, Ralf; Pelz, Stefan; Poetsch, Jens; Sailer, Gregor; Kirchhof, Rainer; Derkyi, Nana Sarfo Agyemang; Attiogbe, Francis; Kusi, Joseph Yankyera; Regional Centre of Energy and Environmental Sustainability (RCEES), University of Energy and Natural Resources, Sunyani P.O. Box 214, Ghana; (N.S.A.D.); (F.A.); Empl, Florian; Hochschule für Forstwirtschaft Rottenburg, Schadenweiler Hof, 72108 Rottenburg, Germany; (F.E.); (R.M.); (S.P.); (J.P.); (R.K.); Müller, Ralf; Hochschule für Forstwirtschaft Rottenburg, Schadenweiler Hof, 72108 Rottenburg, Germany; (F.E.); (R.M.); (S.P.); (J.P.); (R.K.); Pelz, Stefan; Hochschule für Forstwirtschaft Rottenburg, Schadenweiler Hof, 72108 Rottenburg, Germany; (F.E.); (R.M.); (S.P.); (J.P.); (R.K.); Poetsch, Jens; Hochschule für Forstwirtschaft Rottenburg, Schadenweiler Hof, 72108 Rottenburg, Germany; (F.E.); (R.M.); (S.P.); (J.P.); (R.K.); Sailer, Gregor; State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, Garbenstraße 9, 70599 Stuttgart, Germany;; Kirchhof, Rainer; Hochschule für Forstwirtschaft Rottenburg, Schadenweiler Hof, 72108 Rottenburg, Germany; (F.E.); (R.M.); (S.P.); (J.P.); (R.K.); Derkyi, Nana Sarfo Agyemang; Regional Centre of Energy and Environmental Sustainability (RCEES), University of Energy and Natural Resources, Sunyani P.O. Box 214, Ghana; (N.S.A.D.); (F.A.); Attiogbe, Francis; Regional Centre of Energy and Environmental Sustainability (RCEES), University of Energy and Natural Resources, Sunyani P.O. Box 214, Ghana; (N.S.A.D.); (F.A.); Zelić, Bruno
This research aimed to evaluate the comparative biogas yields of waste (peels) of selected fibrous materials from the West African region: cassava, plantain, a mixture of cassava, plantain and yam. Three models: The Boyle model, the Modified Boyle’s model, and the Buswell and Müller’s model were used to determine the theoretical maximum biomethane potentials (TMBP), while the Hohenheim Biogas Yield test (D-HBT) was used to undertake a batch test of anaerobic digestion. The samples were co-digested with digested sewage sludge (DSS) for 39 days, with an operating temperature of 37 ± 0.5 °C. The study draws comparisons between the TBMPs and the experimental results, the experimental results of the different substrates, and the experimental results and figures reported in the literature. From the experimental results, plantain peels had the highest biogas yield (468 ± 72 mL/g oTS), followed by a mixture of yam, cassava and plantain peels (362 ± 31 mL/g oTS) and cassava peels obtained the least biogas yield (218 ± 19 mL/g oTS). TMBPS of 204.04, 209.03 and 217.45 CH4 mL/g oTS were obtained for plantain peels, a mixture of yam, cassava and plantain peels and cassava peels, respectively, evaluated using Boyle’s model. For all the samples, the TMBPS (205.56, 209.03 and 218.45 CH4 mL/g oTS, respectively) obtained using the Buswell and Mueller model were slightly higher than those obtained by both the Boyle and the modified Boyle’s model (163.23, 167.22 and 174.76 CH4 mL/g oTS, respectively). While the study result is sufficient to imply that generating biogas from fibrous waste materials in its mixture form is a valuable approach, it is not sufficient to conclude that the use of these waste materials in its naturally occurring mixture form has a technical added advantage in co-digestion over their individual potential. However, future studies could explore this possibility with different fractions of the mixture with a view to optimising generation. The study finds that theoretically modelling the biogas potential of fibrous materials is a good method for biogas evaluation despite having overestimation tendencies, as this challenge could be corrected by applying factors that result in these tendencies, biodegradability indices. The data can, therefore, find use in fibrous waste treatment and waste-to-energy technologies, especially in Africa. This application will not be negatively affected by whether single water streams are used or their mixture.
Hydrothermal treatment of residual forest wood (softwood) and digestate from anaerobic digestion - influence of temperature and holding time on the characteristics of the solid and liquid products
(2022) Sailer, Gregor; Comi, Julian; Empl, Florian; Silberhorn, Martin; Heymann, Valeska; Bosilj, Monika; Ouardi, Siham; Pelz, Stefan; Müller, Joachim
Hydrothermal treatment (HTT) offers the potential to upgrade low-value biomass such as digestate (DG) or forest residue (FR) by producing solids and liquids for material use or energetic utilization. In this study, microwave-assisted HTT experiments with DG and FR as feedstocks were executed at different temperatures (130, 150, 170 °C) and with different holding times (30, 60, 90 min) to determine the influences on product properties (ash and elemental concentrations, calorific values and chemical compounds). In general, DG and FR reacted differently to HTT. For the DG solids, for instance, the ash concentration was reduced to 8.68%DM at 130 °C (initially 27.67%DM), and the higher heating value increased from 16.55 MJ/kgDM to 20.82 MJ/kgDM at 170 °C, while the FR solids were affected only marginally. Elements with importance for emissions in combustion were leached out in both HTT solids. The DG and FR liquids contained different chemical compounds, and the temperature or holding time affected their formation. Depending on the designated application of HTT, less severe conditions can deliver better results. It was demonstrated that different low-temperature HTT conditions already induce strong changes in the product qualities of DG and FR. Optimized interactions between process parameters (temperature, holding time and feedstock) might lead to better cost–benefit effects in HTT.
Lab-scale carbonation of wood ash for CO2-sequestration
(2021) Koch, Robin; Sailer, Gregor; Paczkowski, Sebastian; Pelz, Stefan; Poetsch, Jens; Müller, Joachim
This study evaluated the CO2 sequestration potential with combustion ashes in the aqueous phase. The aim was to provide a cost-effective carbon sequestration method for combustion unit operators (flue gas cleaning) or biogas producers (biogas upgrading). Therefore, two separate test series were executed to identify the carbonation efficiency (CE) of bottom wood ash (1) at different mixing ratios with water in batch experiments and (2) under dynamic flow conditions. It was furthermore evaluated whether subsequent use of the carbonated wood ash for soil amendment could be possible and whether the process water could be passed into the sewage. The batch test series showed that different mixing ratios of wood ash and water had an influence on the CE. The flow series showed that the mean CE varied between approximately 14% and 17%. Thus, the ash proved to be suitable for carbonation processes. The process water was dischargeable, and the carbonated wood ash has potential for chalking, as no legal thresholds were exceeded. Therefore, wood ash carbonation could be used as a low-tech CO2 sequestration technology. Compared to existing energy consuming and cost intensive carbon capture and storage technologies, sequestration with ash could be beneficial, as it represents a low-tech approach.

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