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Gewählte Master / Diploma Thesis:

Miriam Huber (2021): Heavy metal fractionation in thermochemical fluidised bed conversion to enable P-recovery from sewage sludge ashes.
Master / Diploma Thesis - Institut für Verfahrens- und Energietechnik (IVET), BOKU-Universität für Bodenkultur, pp 87. UB BOKU obvsg FullText

Data Source: ZID Abstracts
Phosphorus recovery from sewage sludge is a central challenge for securing future food production, as fertiliser production is currently dependent on rock phosphate, a finite raw material declared a critical resource by the European Union in 2014. To face this challenge, the removal of heavy metals occurring in sewage sludge is essential, as is the bio-availability of the phosphate product to enable the application in agriculture. In this thesis, the recovery of phosphorus from sewage sludge is aimed in a single step process by thermochemical treatment. Experiments in a 10kW bubbling fluidised bed reactor are conducted to identify the behaviour of different additives (NaCl, CaCl2, MgCl2, and Na2SO4) at 800 °C and 950 °C. A higher reduction of heavy metals (Pb, Cd, Zn, Cu, Ni, and Cr) is demonstrated with an increased additive amount of 2.2 wt% Cl compared to 0.7 wt% Cl. Thereby, MgCl2 achieves the highest reduction for Cu and Zn to 67% and 48 %, and CaCl2 for Pb (54 %) and Cd (51 %), relative to samples without additives. Treatment with sub-stoichiometric oxygen supply shows a trend to higher reduction occurring for Cu, Zn, and Pb. The maximum phosphate solubility in neutral ammonium citrate of 42% is achieved with MgCl2 samples (0.7 wt% Cl). In the experiments, heavy metals accumulate in the filter ash fraction, while phosphates remain in the bottom ash fraction, that shows signifcant reduction of heavy metals. Bottom ash obtained in a single step thermochemical treatment process therefore provides the potential for further application in agriculture and for closing the gaps in phosphorus supply.

Beurteilende*r: Pröll Tobias

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