phd project

Green flocculants for water treatment

Very large quantities of fossil-based, water soluble polymers are employed to flocculate (aggregate) particles and in this manner facilitate solid-liquid separation. These are, for example, used for water treatment, sludge dewatering, drinking water production, wastewater treatment, for engineered applications as dredging, tunneling, prevention of soil erosion, for oil and gas production, and for harvesting of valuable biomass in biobased processes. Previous research by Wetsus in cooperation with Wageningen University has shown that extracellular polymeric substances (EPS), produced by microorganism from organic waste streams, can provide promising and sustainable alternative flocculants. Large scale transition from the potentially hazardous synthetic flocculants to their more environmentally friendly microbial counterparts requires more knowledge about (1) the effect of the type of organic waste and reactor operational conditions on the yield and properties of these microbial flocculants and (2) the effect of basic properties of the microbial polymers on flocculation mechanisms.

Research challenge
The composition of the organic (waste) feedstock, together with the reactor operation conditions not only affect the yield of EPS but also their chemical characteristics (proteins, polysaccharides and other biopolymers), overall charge density and molecular weight. Together these properties will determine the efficiency with which the microbial polymers can flocculate particles in specific surface and wastewaters. The first objective of this PhD study is to investigate this relationship between organic feedstock composition, reactor operational conditions and yield and properties of the EPS and to elucidate the role of the (mixed-culture) microbial population in this. Important research questions in this regard are the following: i) which factors determine the outcome of the competition between the production of EPS and of internal storage products such as polyhydroxyalkanoates (PHA) and ii) can  a microbial population producing large quantities of EPS maintain this capacity when fed with less favorable organic substrates. The second objective of the research is to study the relationship between EPS properties and flocculation capability, which requires more in-depth knowledge about the underlying flocculation mechanisms.

We are looking for an excellent, creative and enthusiastic candidate with an MSc degree in (environmental) biotechnology or related fields with an affinity for bioreactor operation, analytical chemistry and physical-chemical separation technology. Good organizational and communication skills are required to facilitate interaction with external parties.

The research project will be part of the Wetsus research theme “Natural Flocculants”. The following companies are part of this theme: Paques Technology B.V., Pentair X-Flow and Evides.

Promotor: Prof. Huub Rijnaarts (Wageningen University)

Wetsus supervisor: Dr. Hardy Temmink

For more information please contact


Wetsus, Leeuwarden, The Netherlands

12.4 Green flocculants for water treatment

  • Fill in the number (not the title) of the project e.g, 12.1
  • Fill in the project number
  • Fill in the project number
    i.e. in the first 4 years of your research career and not have a doctoral degree
  • Drop files here or
    Upload the required documents. Please combine all the documents (motivation letter, CV, grades, copy of master diploma, letter of recommendation(s)) in one single attachment, preferably a PDF. Only complete applications will be evaluated.