Research projects
Research area D: Process chain
Research area D is at the center of WERA and interacts with the other research areas. Research area D investigates the influences on P recovery in a real, dynamic system (project D1). To this end, the adsorber materials synthesized in research area A are tested for their suitability for selective P separation and enrichment in increasingly complex, different wastewater matrices. The basic principles of precipitation and crystallization developed in research area B will be incorporated into the design of processes and experiments for P recovery from sewage sludge. The measurement techniques and separation methods developed in research areas B and C will be tested on real wastewater systems. Based on the results of the experiments, process chains are developed in research area D. The results of the experiments will be used to calibrate and verify the simulation results in research area B. In research area D, the adsorber materials developed in research area A are agglomerated into larger porous particles and the mechanical stability of the adsorber particles within the process chain is investigated (project D2).
Supervisor: Prof. Heidrun Steinmetz
PhD student: Linda Müller
The effort for phosphorus (P) recovery from sewage sludge is high, because phosphorus is transferred within the wastewater treatment into the sewage sludge mostly by precipitation with iron or aluminum salts to protect the receiving water and needs to be recovered subsequently from the sewage sludge in a multi-stage process. This process starts with the dissolution of phosphorus bound in the sewage sludge, subsequent complexation or precipitation of interfering ions like iron and renewed precipitation and crystallisation of the phosphorus in form of plant-available fertilizer.
Influences on these phosphorus precipitation and recovery steps are manifold. Technologies used for P-elimination as well as the type and composition of the sewage sludge have a significant influence on the P-recovery steps. The precipitation and crystallisation of struvite as a possible product of P-recovery depends on numerous factors, such as the pH value of the solution, the saturation, the molar ratios of various ions, the stirring speed, the temperature and the presence of foreign ions. Yet these influences are not clearly understood.
Supervisors: Prof. Sergiy Antonyuk and Prof. Heidrun Steinmetz
Postdoc: TBD
The adsorbent materials (particles or agglomerates) used in WERA are subjected to various mechanical stresses during the P recovery processes. Dynamic, multiple interactions occur between the particles themselves and with the surfaces of the equipment and tools. This often leads to undesirable abrasion and breakage of the particles, which greatly reduces their service life. It is therefore important to gain knowledge about the relationships between the microstructure and the fracture properties of particles in different P recovery processes under the stresses that occur there. Based on these findings, the strength and service life of P adsorbent materials can be increased by improving their manufacturing processes. In addition, the flow dynamics in P recovery processes can be adjusted to reduce the stresses on these materials.
The D2 project aims to investigate the mechanical stability of P-adsorber particles formulated in research area A depending on loads in the processes developed in research areas C and D. In the postdoctoral project, larger porous agglomerates are also produced from the adsorber materials for practical use in fluidized bed or rotor granulation processes. In addition, the fracture processes of agglomerates will be investigated using CFD-DEM simulations in cooperation with Prof. Antonyuk. In collaboration with Prof. Steinmetz, experiments on practical loads on particles in P recovery processes will be carried out on the basis of the pilot plant.
Supervisor: Jun.-Prof. Carlo Morandi
PhD student: TBD
Project D3 aims to address a key challenge facing the WERA graduate school: phosphorus recovery from sewage sludge. The precipitation of phosphorus (e.g. as struvite) in the sludge path of the sewage treatment plant is significantly hindered by the presence of high concentrations of iron ions. Conventionally, these interfering ions are complexed (e.g. with citric acid), which is costly and process-technologically unstable. The D3 doctoral project therefore aims to investigate the selective adsorptive removal of iron from acidified sewage sludge. Acid-resistant zeolites (e.g. mordenite and chabazite, as well as modified zeolites) will be used as the adsorbent materials. This step is intended to provide an alternative to iron complexation using citric acid, offering a low-iron phosphate stream for struvite precipitation (Project D1). The project will be developed and tested on a laboratory scale and in fixed-bed plants as pilot projects (in direct application of Project C2).
The key issues are selectivity — maximising iron binding while allowing the passage of phosphate, ammonium and potassium — and the regenerability of the adsorbers. In particular, the recovery of iron under acidic environmental conditions is being investigated. The aim is to quantify the influence of matrix conditions (the type and concentration of interfering ions, and the oxidation state of iron [Fe²⁺ vs. Fe³⁺]) on adsorption. A particular focus is on regenerating the adsorbers through desorption. Particular attention is paid to the cycle stability of the adsorbent materials. The objective is to assess the stability of the materials and determine the maximum number of loading and regeneration cycles that can be performed without experiencing a significant loss in performance.