PhD for project: "Making biodegradable microbial flocculants (EPS) from wastewater"

PhD for project: "Making biodegradable microbial flocculants (EPS) from wastewater"

Published Deadline Location
12 Sep 13 Oct Leeuwarden

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Job description

Topic background

Water scarcity impacts many regions in the world. To reduce the pressure on fresh water sources, we must treat and reuse water in efficient and safe ways. Therefore, (waste)water needs to be treated accordingly to close the water loop/gap. The treatment of (waste)water demands innovative solutions that use non-toxic chemicals, generate less polluting waste streams, and reduce the carbon footprint. Flocculants such as polyacrylamide (PAM) are extensively used in applications such as drinking water production, wastewater treatment, and soil conditioning. However, these flocculants are produced from fossil sources and, therefore, have a high carbon footprint. Additionally, their fate in the aquatic environment is uncertain and such flocculants may degrade into toxic monomers.

To abate the risks posed by synthetic flocculants, we aim to produce well-defined, non-toxic and biodegradable microbial flocculants from wastewater. Production of such flocculants will combine low carbon footprint valorisation of organic pollutants in wastewater with contribution to safe environment and sustainable water treatment.

Research challenge
Organic pollutants in wastewater will be converted in open-culture bioreactors into extracellular polymeric substances (EPS), microbial biopolymers that behave as flocculants. We know that nitrogen limitation yields high amounts of EPS with high molecular weight and net negative charge. Theoretically, these should show similar mechanisms of flocculation to anionic PAM. However, in practice, their flocculation capacity varies and requires improvement. Hence, we will aim at understanding their flocculation capacity in relation to physical-chemical characteristics, the nature of the targeted colloidal matter and water chemistry in order to outperform synthetic polymers. Secondly, we will study whether superior microbial flocculants can be obtained by adjusting bioreactors operation such as retention times, temperature or limitation of other nutrients (e.g. phosphorus).

The knowledge generated in this research will broaden the range of suitable feedstocks for producing microbial flocculants, contribute to engineering EPS properties to specific applications, and accelerate the application of microbial flocculants.

Your assignment
The main aim of this project is to gain insights on how EPS properties can be fine-tuned, what is the relation between flocculant properties and flocculation performance and conditions to achieve predictable removal of colloids. This project ultimately shows controlled production of effective flocculant EPS.

You will make a first, principle-based selection of possible steering conditions that you will test in lab-scale bioreactors. You will monitor the bioreactors performance and identify operational conditions that lead to enhanced EPS production and flocculation. You will explore the microbial composition and competitive processes (e.g. PHA production) in the bioreactors. You will analyze EPS characteristics (molecular weight, monomeric composition, functional groups) using different analytical techniques (LC-OCD, GC, FT-IR). Understanding colloids aggregation by bioflocculants will be central to your research. You will perform flocculation tests with different synthetic and microbial flocculants under controlled conditions (particle charge, particle size, ionic strength) and combine insights from bioreactor experiments, EPS characterization and flocculation. Finally, these insights will be put to practice on one case study to apply the flocculants under realistic conditions.

Supervisory team: Prof. dr. ir. Huub Rijnaarts (Wageningen University), dr. ir. Dainis Sudmalis (Wageningen University), dr. Carlos Contreras Davila (Wetsus)

Project partners: Natural Flocculants


Wetsus, European centre of excellence for sustainable watertechnology


You are a highly motivated researcher who enjoys working in a multi-disciplinary, international team. You hold a MSc degree in Environmental (bio)technology, Bioprocess engineering, Chemical engineering or related. You have experience with bioreactors, a strong background on bioprocess design, microbial metabolism and high affinity for colloid science. You are fluent in English and have excellent writing skills.

Keywords: Flocculation, extracellular polymeric substances (EPS), bioreactors, bioprocess design, resource recovery

Conditions of employment

Salary and working conditions are according to the collective labour agreement of the Cooperative Association of Dutch Universities (VSNU) for PhD students.


Wetsus, European centre of excellence for sustainable water technology is a facilitating intermediary for trendsetting know-how development. Wetsus creates a unique environment and strategic cooperation for development of profitable and sustainable state of the art water treatment technology.

The inspiring and multidisciplinary collaboration between companies and research institutes from all over Europe in Wetsus results in innovations that contribute significantly to the solution of the global water problems. Wetsus’ scientific research program is defined by the private and public water sector.

Read more about our current PhD program. All info about the research at Wetsus can be found here.


  • PhD; Research, development, innovation
  • Natural sciences; Engineering
  • University graduate
  • PA Wetsus project 2023.12


Wetsus, European centre of excellence for sustainable watertechnology

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Oostergoweg 9, 8911 MA, Leeuwarden

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