Turning wastewater sludge to bioplastics

What if sewage sludge could form the basis for sustainable bioplastics?

That is precisely the ambition behind PHA2USE, an innovative collaboration between local Dutch water authorities, technology partners and industry aimed at creating new value from wastewater streams. As part of this project, Colubris, in close collaboration with Waterschap Brabantse Delta, developed a pilot installation for sludge acidification. The pilot is currently operating at the Nieuwveer sewage treatment plant in Breda and is demonstrating how sewage sludge can be transformed into fatty acids, a crucial step towards the production of PHA biopolymers.

For Bart Joosse, Senior Water Chain Technologist at Waterschap Brabantse Delta, the project represents much more than technological innovation alone. It is about creating a circular future for wastewater treatment.

From sludge to valuable resources
'Everything people flush away or discharge into the sewer ultimately ends up in the sludge,' Joosse explains. 'Part of it is broken down during treatment, but a significant share of the organic material remains. What we are doing here is converting that sludge into fatty acids. Those fatty acids can then be used to produce PHAs, a biodegradable biopolymer.'
The concept builds on years of previous research. In earlier phases of the PHA2USE project, the focus was on converting fatty acids into PHA, including at a pilot plant in Dordrecht. Various waste streams were tested there, including sludge and industrial residual streams.
'We already understand the step from fatty acids to PHA quite well,' says Joosse. 'The challenge now lies in optimising the preceding step: efficiently producing fatty acids from sewage sludge.'
 

'If bioplastics such as PHA can replace even a portion of conventional plastics, we can ultimately also reduce the amount of microplastics in the environment.'
Bart Joosse | Waterschap Brabantse Delta

Scaling up laboratory research to real-world practice
According to Joosse, earlier laboratory tests showed major differences in fatty-acid yields between different types of sludge and wastewater treatment plants. This made long-term testing at pilot scale essential.
'You cannot base a multi-million-euro installation on the results of a one-litre laboratory test,' he explains. 'That is why this project focuses on testing at a larger scale and over a longer period. We want to understand the influence of seasons, rainfall, sludge composition and operating conditions.'
To enable this next phase, Colubris reused two existing 3.5 m³ digestion reactors that had previously been used in a thermal hydrolysis pilot. By optimising the installation and adapting it for sludge acidification, the pilot could be realised efficiently and fully in line with the project’s circular ambitions.
The pilot will operate in Breda for six months before moving to the sewage treatment plant in Eindhoven, where the fatty acids produced will be used as feedstock for PHA production.
 

A circular alternative to fossil-based plastics
For the water authorities, the project is not only about innovation, but also about sustainability and resource recovery. ‘At present, we mainly digest sludge to produce biogas,’ says Joosse. ‘That is valuable because it generates sustainable energy and heat. Here in Breda, we supply heat to hundreds of homes. However, converting sludge into biopolymers creates a significantly higher-value product while supporting the transition to a circular economy.’
The environmental benefits extend beyond resource recovery. Unlike conventional fossil-based plastics, PHA is fully biodegradable and does not contribute to microplastic pollution.
‘That is one of the main reasons why we see so much value in this technology,’ Joosse explains.

Collaboration based on flexibility and short communication lines
For Colubris, the pilot fits perfectly with the growing focus on innovative technologies for wastewater and sludge processing in municipal applications. Throughout the project, close collaboration between all partners has once again proved essential.
‘With pilot installations, you always encounter challenges,’ says Joosse. ‘You may face leaks, blockages or operational adjustments; that is part of the process. What matters is how you solve those challenges together.’
This collaborative approach has resulted in strong cooperation between the project team, operators and Colubris engineers.

 

'The collaboration with Colubris is very pleasant thanks to the short lines of communication and the willingness to think along in a highly practical way.’
 Bart Joosse | Waterschap Brabantse Delta
 

Looking ahead
The coming year will be crucial in determining the technology’s future potential. The results of the pilots in Breda and Eindhoven will provide the basis for assessing whether large-scale implementation is technically and economically feasible.
‘The key question is whether we can consistently achieve the fatty-acid yields from the sludge,’ Joosse explains. ‘That will ultimately determine whether we can build a viable business case for large-scale installations in the future.’
Even beyond PHA production, the fatty acids produced may offer additional opportunities in wastewater treatment, for example by supporting nitrogen-removal processes.
For Colubris, this project demonstrates how technological innovation, circular thinking and strong partnerships can transform wastewater via practical solutions into valuable and sustainable resources.

About Waterschap Brabantse Delta
Waterschap Brabantse Delta is responsible for water quality, wastewater treatment and water management in the western part of the province of North Brabant. The organisation actively invests in circular and sustainable technologies aimed at recovering valuable raw materials from wastewater streams and reducing environmental impact.