PhD-students

The research program of Wetsus is divided in several themes. Within these themes research topics have been defined, which are being addressed in the form of PhD-projects.

1.3: Biofouling control and performance restoration in full scale and point of use installations
Spiral wound RO or NF membranes are used in many water purification installations. Very often, biofilms consisting of micro-organisms and their extracellular polymeric substances (EPS) develop on the surfaces of these membranes, which might finally result in severe biofouling. This increases the pressure drop over the module, and lowers the permeate flux. For a sustainable operation of spiral wound RO or NF membranes, it is of the uttermost importance to minimize this biofouling induced pressure drop increase over the module. This will reduce the use of chemicals necessary for performance restoration, and lowers the energy required for the separation process. Consequently, operation costs will be lower, and the process can be controlled in a more effective way.

Location: Wetsus, Leeuwarden

1.4: Modeling Photosynthetic Energy Conversion in Algal Photobioreactors. Model implementation and experimental validation
In this project relevant models of the photosynthetic energy conversion will be converted into SBML format and are used in combination with a fast solver to simulate photosynthetic energy conversion in an algal photobioreactor. The student is expected to be capable of learning how to translate the models written in form of differential equations into SBML format, annotate the models in accordance with MIRIAM, and use standard solvers to simulate experimental results. Programming proficiency is essential. Further, the student is expected to propose and execute experiments to validate the models and based on the validation to adjust/improve the model structure and parameters. For that, the candidate must be versatile, capable of mastering the microbiological techniques, the reference biochemical and biophysical assays. In its final stage, the project aims at model-based optimization of the algal photobioreactors. This requires synthetic understanding of the complex biological and engineering system.

Location: Wetsus, Leeuwarden and Brno, Czech republic.

1.7: Bioenergy potential of hydrocarbonoclastic bacteria fattened up from polluted (waste)waters
The focus of this project is to explore the biotechnological potential of using hydrocarbonoclastic bacteria to obtain bacterial-oil (essentially TAG) from polluted (waste)waters. The possibility of combining this capacity with the bioremediation of hydrocarbon contaminated waters will be further assessed. For that purpose, selected TAG/WE accumulating hydrocarbonoclastic strains will be submitted to different culturing conditions in order to determine the conditions for optimal TAG production. The goal is to compare biomass growth yields and product/biomass yields for the different combinations of strain/culturing conditions. The key enzyme catalysing the last step of TAG biosynthesis in bacteria is a promiscuous wax esters synthase/acyl-CoA:DAG acyltransferase (WS/DGAT) also responsible for the synthesis of WEs. Therefore, the profile of storage lipids will be assessed and the culturing conditions that promote an increased selectivity for TAG over WEs determined. The strain exhibiting higher potential will be chosen, as case-study, to construct a genome-scale metabolic model describing TAGs biosynthesis in hydrocarbonoclastic bacteria. Experimental fermentations performed with this strain, will be used to adjust and validate the model. The ultimate goal is to set up a continuous process with the most advantageous scenario, which will be selected after a technical and economical evaluation based on mass and energy balances.

Location: Wetsus, Leeuwarden and University of Minho, Braga, Portugal

1.8: Raman spectroscopic sensing of bacteria in water using photonic crystal cavities
The goal of this project is to study and establish the physical mechanisms for sensing of bacteria in water based on a nanocavity in a two-dimensional photonic crystal (PhC). Such a crystal is a periodic modulation of the dielectric constant, with a modulation period comparable to the wavelength of light. The nanocavity is an ultra-small resonator for electromagnetic waves inside the crystal, leading to a greatly enhanced and locally concentrated optical field. This property can be applied for both optical trapping of bacteria in water and their subsequent identification by Raman spectroscopy. These functionalities of PhC cavities will lead to rapid on-line sensing and identification of bacteria in water. The PhD student will be working on trapping bacteria in photonic crystal cavities and cooperating with a PhD student focusing on Raman spectroscopy. We look for experimental physicists (M.Sc.) with a background in photonics or solid-state physics and with affinity to bio-sensing. Experience in device fabrication is helpful.

Location: Technical University Delft

19.3: Use on-line measurement of sludge filterability to control membrane operation in municipal MBRs**
In a previous study at Wetsus an improved flux-step method was developed to assess
the effects of membrane properties on membrane fouling in MBR systems for the
treatment of municipal wastewater. When applied on-line, this method can also be used to determine the optimum flux at which membranes are operated. In this manner energy can be saved which otherwise would be consumed to clean the membrane surface. This optimum flux not only depends on the properties of the membranes that are used, but in particular on the properties of the feed sludge. These properties vary in time caused by changes in wastewater quantity, wastewater composition and environmental conditions.
The research questions that need to be addresses are (1) what are typical variations in
sludge filterability, to be determined with the flux-step method, (2) how should membrane operation respond to this with a suitable control strategy and (3) are other (automated) options available to counteract (temporary) decreases in sludge filterability, f.e. the addition of additives such as powdered activated carbon.
** Final approval of this project is in progress, and is expected in first half 2009.

Are you one of the top 3 performers in your class?
Are you enthusiastic about multidisciplinary research?
If the answer to both these questions is "yes" and you have (or will
have) a university degree in environmental technology, chemical engineering, physics or a related discipline you could be the ideal candidate for a PhD project in Wetsus.

You will be working in a new, innovative, dynamic and future-directed research institute. You will be able to put your stamp on the development of new water technology. You will work in close collaboration with our industrial partners and also with top research groups at various universities.
Salary and working conditions are according to the collective labor agreement of the Cooperative Association of Dutch Universities (VSNU) for PhD students. PhD students are appointed by one of the cooperating universities but research is mainly conducted at Wetsus in Leeuwarden.

By post or email. Send your application to Wetsus, attn. Recruitment Department, PO box 1113, 8900 CC Leeuwarden, The Netherlands. Emails to .

For further information about our PhD projects or about Wetsus you can contact Dr. G.J.W. Euverink.
Phone: +3158-2843000 or Email: gertjan.euverink@wetsus.nl.