Removal of Micropollutants from Wastewater in Aerobic Granular Sludge and Activated Sludge Systems
Doctoral thesis, 2022

The presence of organic substances in the aquatic environment, such as pharmaceutically active compounds, antibiotics, and personal care products, has become a worldwide issue of increasing environmental concern. As they are present at nano- to microgram per liter concentrations, they are defined as organic micropollutants (OMPs). Understanding the removal of micropollutants mediated by biological processes in wastewater treatment plants is the key to developing and deploying strategies to efficiently reduce environmental exposure to such contaminants. The biomass configurations (suspended growth systems or biofilms) can affect the removal of OMPs, and the underpinning mechanisms need to be substantiated. Aerobic granular sludge (AGS) is a form of free-floating biofilm technology for the simultaneous removal of organic carbon, nitrogen, and phosphorus in a single process step. The features of AGS make this technology very attractive for the removal of OMPs, but an in-depth understanding of the fate of OMPs in such systems under different operational conditions is still required.

The present work investigated the removal mechanisms of OMPs in biological treatment processes with a focus on AGS. Removal performances were evaluated by measuring the presence of OMPs in the water phase at both full-scale treatment plants and laboratory-scale reactors. The kinetics of transformation and sorption behavior were assessed in batch experiments with different biomass types. The microbial communities and antimicrobial resistance genes of the activated sludge and granular sludge systems were compared. The spatial distributions of a few pharmaceuticals inside the biological matrix of AGS were imaged and analyzed together with the endogenous biofilm molecules by secondary ion mass spectrometry.

A higher transformation capacity for most of the investigated OMPs was observed for the activated sludge compared to the granular sludge system, both at the full-scale treatment plant and in the batch experiments. Despite the differences in microbial composition and diversity, the two systems shared similar antimicrobial resistance gene profiles. Micropollutant exposure to the biomass or mass transfer limitations in the dense matrix of AGS likely played an important role and could explain the observed differences in OMP removal. Oxic conditions seemed to support the microbial transformation of several micropollutants with a faster and/or comparable rate compared to anoxic conditions. Sorption of OMPs to the biomass was observed to be an important removal mechanism for a few compounds. Partitioning of the pharmaceuticals to AGS occurred quickly and increased over time for most pharmaceuticals, suggesting that the compounds can penetrate the deeper biofilm matrix. This observation was also confirmed by the chemical analysis of the biofilm matrix of AGS. The spatial distributions of the pharmaceuticals inside the biological matrix of AGS revealed that the interactions between the OMPs and the biomass happen at specific receptor sites distributed across the biofilm.



Aerobic Granular Sludge

Microbial Community

Organic Micropollutants




SB-H5, Samhällsbyggnad, Sven Hultins Gata 6, Chalmers.
Opponent: Paola Verlicchi, Associate Professor, Department of Engineering, University of Ferrara, Italy.


Cecilia Burzio

Chalmers, Architecture and Civil Engineering, Water Environment Technology

"Burzio C., Mohammadi A. S., Smith S., Abadikhah M., Svahn O., Modin O., Persson F., Wilén B.M. Pharmaceutical sorption to aerobic granular sludge and air-induced foam"

Chemical Imaging of Pharmaceuticals in Biofilms for Wastewater Treatment Using Secondary Ion Mass Spectrometry

Environmental Science and Technology,; Vol. 57(2023)p. 7431-7441

Journal article

"Burzio C., Ekholm J., Tang K., Mohammadi A. S., Abadikhah M., Modin O., Persson F., Wilén B.M. Dissolved oxygen concentration impacts nutrient and pharmaceutical removal by aerobic granular sludge"

Removal of organic micropollutants in the biological units of a Swedish wastewater treatment plant

IOP Conference Series: Materials Science and Engineering,; Vol. 1209(2021)

Paper in proceeding

Exploring the potential of microorganisms to clean wastewater from pharmaceuticals

The water discharged in our daily life from showers, toilets, dishwashers, and washing machines, so-called wastewater, is collected and diverted to wastewater treatment plants. This wastewater is contaminated by a variety of pollutants, such as nutrients, toxic compounds, and pathogenic microorganisms. Wastewater treatment plants commonly apply biological processes, exploiting the natural ability of microorganisms to remove these pollutants, that if released into the environment, would cause its deterioration. Unfortunately, some pharmaceuticals that humans consume and excrete in the wastewater can escape the treatment processes. Even though they are present in low concentrations, hence the name micropollutants, they can cause a significant impact on the environment.

In this thesis, the potential of biological processes to remove pharmaceuticals was explored and the mechanisms and efficacy to remove micropollutants from wastewater were assessed, both in the laboratory and at the wastewater treatment plants. Two biological systems were compared: activated sludge, where the bacteria grow in small aggregates, and granular sludge, where the microorganisms grow in dense spherical layers.

This work opens a route towards understanding the natural potential of microorganisms to purify the wastewater from pharmaceuticals, which is fundamental for maintaining a healthy aquatic ecosystem and avoiding the use of expensive and energy-demanding technologies to remove organic micropollutants.

Subject Categories

Environmental Engineering

Water Engineering

Other Electrical Engineering, Electronic Engineering, Information Engineering



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5208



SB-H5, Samhällsbyggnad, Sven Hultins Gata 6, Chalmers.


Opponent: Paola Verlicchi, Associate Professor, Department of Engineering, University of Ferrara, Italy.

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