Research projects

Supervisor: Jun.-Prof. Fabian Jirasek

The thermodynamic modeling of complex mixtures is the basis for and challenge in developing processes for recovering valuable substances from wastewater. An understanding of the thermodynamic properties of the mixtures and the components they contain is a prerequisite for designing new processes or optimizing existing processes.

This project aims to develop thermodynamic models to describe complex mixtures containing both molecular substances and electrolytes as they occur in wastewater treatment processes. A particular focus will be the simulation of processes for phosphorus recovery from wastewater by crystallization. For this purpose, novel predictive thermodynamic models for electrolyte solutions will be developed by combining classical physical models with data-driven algorithms from machine learning to yield powerful hybrid models. Furthermore, the question of dealing with uncertainties, e.g., regarding incomplete knowledge of the composition of the mixtures (so-called poorly specified mixtures), will be addressed. 

Supervisor: Jun.-Prof. Simon Stephan

The behavior of phosphate ions on adsorbent surfaces is of central importance for the technical processes addressed in WERA for P recovery from wastewater.
 
In this project, the adsorption of phosphate on adsorbent surfaces will be studied using molecular simulations based on classical force fields, which provides insights into the elementary processes at the interface that are difficult to study by experiments. In a first step, a model for the aqueous phosphate solution bulk phase will be developed and the macroscopic properties obtained from that model will be compared to experimental data. Then, the model will be used for the prediction of adsorption and desorption processes on adsorbent surfaces to elucidate the interfacial structure and process kinematics.

Supervisor: Prof. Volker Schünemann

In this project, the decisive processes in phosphate precipitation with iron salts are to be tracked. A set-up is to be realized that allows samples for Mössbauer spectroscopy to be taken from an experimental reactor for precipitation and crystallization reactions of phosphates. The project focuses on precipitation reactions with FeCl₃, FeSO₄ and K₂FeO₄.

The metal-oxide phases thus formed as a function of the process conditions and the size distribution of the micro- and nanoparticles formed during precipitation are to be determined within the framework of WERA using temperature- and field-dependent Mössbauer spectroscopy, Raman spectroscopy and supplementary electron microscopy and X-ray diffraction. A further focus of the project is on the temporal development of the nucleation process including the first fast steps in which aggregates of only a few iron centers and/or very small or amorphous particles are formed. With the help of pH jump experiments with ⁵⁷Fe-containing salt solutions and freezing of the mixture down to the millisecond range, the decisive first steps of the nucleation process during precipitation will also be investigated with the help of ⁵⁷Fe-Mössbauer spectroscopy and synchrotron-based nuclear inelastic scattering (NIS). By simulating the NIS data with the aid of quantum chemical density functional calculations, structural models for the reaction intermediates will be obtained.

Supervisor: Prof. Sergiy Antonyuk

One way of recovering P from wastewater is the precipitation and crystallization of struvite. The kinetics of precipitation and crystallization are of decisive importance for the efficiency of the process. The measurement and description of the kinetics of the precipitation and crystallization processes are important methods for understanding the influences of various process parameters such as temperature, flocculant concentration and the flow field and for optimizing the process. 

In this project, an inline measurement system based on dynamic extinction spectroscopy with high temporal and spatial resolution is to be developed, constructed and applied in order to measure the kinetics of the precipitation and crystallization processes during the formation of struvite in a test reactor with wastewater and to determine the decisive process influencing variables. The measurement method used involves passing a beam of light through the forming suspension and analyzing the measured transmission signal to determine the concentration and size of the particles in the nanometer and micrometer range. The data obtained is also used to model micro-processes of aggregation and fracture of the crystals formed using the Discrete Element Method (DEM) and the Population Balance Method (PBM).

Supervisor: Prof. Sabine Becker

Reliable P detection in wastewater is an important prerequisite for evaluating the effectiveness of P recovery. Optical sensors are of advantageous, as they enable a simple readout procedure. Current detection methods of phosphates are mostly based on the blue method, which enables a photometric quantification. However, in the trace analysis range, this method is inaccurate. It also is susceptible to other ions and the heterogeneity of the sample. To overcome these difficulties, fluorescent sensors based on zinc complexes, which enable a rapid detection and high selectivity, shall be developed.