AGNES – Aerobic Granular sludge

The aerobic granular sludge (AGS) technology is an innovative, compact and energy efficient wastewater treatment process that seems to be mature for full-scale implementation around the world.

More stringent discharge limits and increased load due to population growth and centralisation create needs of upgrading and enlarging the existing municipal wastewater treatment plants (WWTPs). Also expansion of housing areas close to the treatment plants increase the demands of retrofits and upgrades that are space efficient. At the same time we want the treatment methods to be robust, energy, carbon and chemical efficient, have low carbon footprint and facilitate recovery of plant nutrients.

The aerobic granular sludge (AGS) technology is an innovative, compact and energy efficient wastewater treatment process that seems to be mature for full-scale implementation around the world. Therefore, Sweden Water Research has initiated a research and development programme on this technology. The programme is called AGNES, which is an acronym for Aerobic Granular sludge – Nutrient removal and recovery Efficiency in Sweden. In AGNES we cooperate with many stakeholders such as universities, companies and utilities that are interested in research and development and implementation of the AGS technology.

AGNES I – knowledge about AGS technology

Our first project Aerobic granules, a new technology for municipal wastewater treatment – the state-of-the-art (AGNES I) was a project co-financed by the Swedish Water & Wastewater Association (project no. 2017-19) which was performed to increase the knowledge about the AGS technology in Sweden.

Aerobic granules are distinguished from activated sludge flocs through their larger size and more compact and spherical structure. Due to these properties, granules settle rapidly and can therefore contribute to compact treatment processes through high sludge concentrations and short settling times. The most important factors to promote granulation include exposing the biomass to relatively high concentrations of contaminants in sequencing batch reactors (SBRs), promoting slow-growing microorganisms and applying a relatively short settling time. Enhanced biological phosphorus removal is preferably integrated with AGS and the large size of the granules makes simultaneous nitrification (at the surface of the granules) and denitrification (at the inner, anoxic parts) feasible. The AGS technology is energy efficient due to its lack of need of mixers and return pumping of sludge and nitrate, and its operation at low dissolved oxygen concentrations.

AGNES II – a full-scale study

At Österröd WWTP in the municipality of Strömstad the first AGS plant in the Nordic countries will be started during the summer of 2018. A new project, also co-financed by the Swedish Water & Wastewater Association, called Implementation of aerobic granular sludge in Sweden – a full-scale study (AGNES II), will evaluate and document the start-up and the first years of operation of the AGS plant at Österröd WWTP. Jennifer Ekholm is the PhD-student working with AGNES II.

A stakeholder group, consisting of the municipalities of Strömstad and Tanum, Chalmers University of Technology, Sweden Water Research, H2OLAND, Uppsala Vatten och Avfall, Gryaab, the Käppala Association, VA SYD, Västervik Miljö & Energi, TU Delft and Royal HaskoningDHV, contributes with knowledge and cash money in the project, which should increase the knowledge of granular based WWTP operated at Nordic conditions.



Bengtsson, S., de Blois M., Flodin, J., Olsson, J., Jonstrup, M., Myring, K., Johansson, J., Wilén, B.-M., Gustavsson, D.J.I. (2017) Aeroba granuler, en ny reningsteknik för kommunala avloppsreningsverk. En kunskapssammanställning. (In Swedish) Svenskt Vatten Utveckling rapport nr. 2017-19.,

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Bengtsson, S., de Blois, Mark., Wilén, B-M., Gustavsson, D. (2018) A comparison of aerobic granular sludge with conventional and compact biological treatment technologies Environmental Technology,

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Bengtsson, S., de Blois, M., Wilén, B-M., Gustavsson, D. (2018) Treatment of municipal wastewater with aerobic granular sludge Critical Reviews in Environmental Science and Technology, pp. 119-166. DOI:

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Jennifer Ekholm, Frank Persson, Mark de Blois, Oskar Modin, Mario Pronk, Mark C. M. van Loosdrecht, Carolina Suarez, David J. I. Gustavsson and Britt-Marie Wilén (2022) Full-scale aerobic granular sludge for municipal wastewater treatment – granule formation, microbial succession, and process performance Environmental Science: Water Research & Technology,

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Project members from Sweden Water Research and and its owners

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