6.3 Converting wastewater treatment facilities into resource factories: Producing biopolymers for the bioplastic and chemical industries

A current societal challenge is to achieve higher value conversions from organic residuals to renewable platform materials and chemicals. Wasted activated sludge is rich in microbial metabolic activity and it can be a functional resource. To this end, harvested surplus biomass has been demonstrated to offer significant capacity for intracellular biopolymer accumulation. Waste municipal activated sludge can be made to accumulate approximately its organic weight in polyhydroxyalkanoates (PHAs) when fed regionally available sources of fermented organic residues. Surplus activated sludge from industrial biological wastewater treatment processes can be made to accumulate significantly higher levels of PHA. PHAs are biobased and biodegradable polymers with established commercial potential as ingredients for the bioplastics, biofuel, and chemical industries. Societal water quality management infrastructures can gain a duality in function as renewable resource (biopolymer) production facilities, if the biomass response and PHA production yields in PHA accumulation bioprocesses are robust and productivities are optimized. Efficient and reliable PHA production methods and processes that can be integrated into the material flows and economies for the regional realms of industrial and municipal water quality management activities would enable maximal leverage in value. The commercial challenge is to stimulate confidence for investments for regional PHA value-chain infrastructure with goods and services from these biopolymers. The technical challenge is to secure up- and downstream confidence in the bioprocess engineering for integration of commercially relevant raw product production flows.

Research challenge
The principal input raw material for a PHA production bioprocess is surplus activated sludge with significant PHA accumulation potential. A given type of polymer can be produced reliably but industrial steps and methods that will ensure reproducibly consistent efficiency in production are not well established. Ideally, one should reach a maximal content of PHA, with the highest possible molecular weight, in as much biomass as possible, within the smallest volume, in the shortest time, and with the least amount of input substrate. The objective of this project will be to build on the already existing wealth of experience within the project partner team and establish fundamental as well as engineering principles to ensure a consistent biomass response to PHA accumulation conditions, and ultimately to reach novel strategy in bioprocess operation and control that is meaningful for practical implementations.

The qualifying candidate has an MSc degree in chemical and/or environmental engineering with strengths and aptitude in applied microbiology and bioprocess engineering, alongside analytical skills with principles of testing through practical laboratory experiments. Development of bioprocess monitoring and control strategies will require furthermore an interest in measurement methods potentially involving process modelling, soft sensing, and chemometrics. The ideal candidate will be able to blend hands-on efforts within well-grounded theoretical perspectives towards bioprocess innovations that are intended to be applied in the field.

This project falls under the Wetsus research theme Bioplastics. The theme stakeholders are: Paques BV (, STOWA (, and SNB (

Promotor: Mark van Loosdrecht (TU Delft)
Co-promotor: Robbert Kleerebezem (TU Delft)

Wetsus supervisor: Dr. Alan Werker (contact for information,

Wetsus, Leeuwarden, The Netherlands


combining scientific excellence with commercial relevance