Can we fit activated sludge into the circular bioeconomy by getting to know its biopolymers?

During her PhD Sasmitha Aulia Zahra tackled the challenge of resolving the identity of extracellular polymeric substances (EPS) in activated sludges. EPS drives flocculation in wastewater treatment, making it arguably the most critical aspect of biological waste treatment, as well as the most abundant industrial biopolymer in the world. However, the identity of EPS in activated sludge has never been well described. Sasmitha developed an alternative strategy for recovering EPS, leading to the discovery that melanoidins dominate the biopolymer content of activated sludge EPS. This insight additionally led her to demonstrate a role for activated sludge in the circular bioeconomy, where its melanoidins can be used as reductants to synthesise catalytically active silver and gold nanoparticles. Subsequently, she demonstrated that activated sludge, like clinical model biofilms, produces non-canonical extracellular DNA under stress.

These findings bring the field closer to understanding what EPS truly is, and open new possibilities for its valorisation.

The PhD study was completed at the Department of Biological and Chemical Engineering, Faculty of Technical Sciences, Aarhus University.

This summary was prepared by the PhD student.

Time: Thursday, 3rd September 2026 at 13.00
Place: Building 1171, Room 347, Ole Worms Allé 3, 8000 Aarhus C
Title of PhD thesis: Resolving the EPS identity crisis in activated sludge
Contact information: Sasmitha Aulia Zahra, e-mail: sasmitha@bce.au.dk, tel.: +45 31405141
Members of the assessment committee:
Professor Harald Horn, Water Chemistry and Technology Division, Karlsruhe Institute of Technology, Germany 
Professor Moshe Herzberg, Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, Israel 
Chair: Associate Professor Menglin Chen, Department of Biological and Chemical Engineering, Aarhus University 
Main supervisor: Associate Professor Thomas William Seviour, Department of Biological and Chemical Engineering
Language: The PhD dissertation will be defended in English

The defence is public.
The PhD thesis is available for reading at the Graduate School of Technical Sciences/GSTS, Ny Munkegade 120, building 1521, 8000 Aarhus C.