MIDAS is a central resource for information about the microbes in the engineered ecosystem of activated sludge and similar wastewater treatment systems, such as biofilms, granules and membrane-bioreactors.

MIDAS field guide grew out of the necessity for consistent and up-to-date naming and information about activated sludge microbes. In 2006, Aalborg University began an on-going effort to characterise the diversity within the activated sludge in Danish Wastewater treatment plants with biological removal of nitrogen and phosphorus. The characterisation was initially using a suite of FISH probes but has since included the use of amplicon sequencing and metagenomics. From year 2009 on microorganisms in Danish anaerobic digesters were characterized along with activated sludge community. The activities were supported by numerous research grants along the Danish Wastewater Association, Krüger A/S, Kemira A/S and approx. 50 municipal wastewater treatment plants. 

All information in the database and all new data is manually curated by a small team of experts at Center for Microbial Communities, Aalborg University (cmc.bio.aau.dk). We invite contributions such as corrections of errors or other information that you think should be in the database.

Contact us

Do you need further information or clarification? Do you have novel relevant information? Is there an error in the information? Are we not linking to your highly-relevant paper? Please let us know at mail@midasfieldguide.org or leave a note via the comment section on the MiDAS page.

You can also sign up for the mailing list to receive the latest updates.


Use of the MiDAS database should cite:

McIlroy, S.J., Saunders, A.M., Albertsen, M., Nierychlo, M., McIlroy, B., Hansen, A.A., Karst, S.M., Nielsen, J.L. and Nielsen, P.H. (2015) MiDAS: the field guide to the microbes of activated sludge. Database, Vol. 2015, Article ID bav062; doi:10.1093/database/bav062

Use of the MiDAS taxonomy should additionally cite the SILVA database on which it is based:

Quast C., Pruesse E., Yilmaz P., Gerken J., Schweer T., Yarza P., Peplies J., Glöckner F.O. (2013) The SILVA ribosomal RNA gene database project: improved data processing and web-based tools. Nucleic Acids Res. 41: D590–6.

Read more about our conceptual model of the activated sludge ecosystem:

Saunders A. M., Albertsen M., Vollertsen J., Nielsen P. H. (2016) The activated sludge ecosystem contains a core community of abundant organisms. ISME Journal, 10(1): 11-20.

Nielsen, P. H., Saunders, A. M., Hansen, A. A., Larsen, P., & Nielsen, J. L. (2012). Microbial communities involved in enhanced biological phosphorus removal from wastewater - a model system in environmental biotechnology. Current Opinion in Biotechnology, 23(3), 452–459.

Nielsen, P. H., Mielczarek, A. T., Kragelund, C., Nielsen, J. L., Saunders, A. M., Kong, Y., Hansen, A. A., et al. (2010). A conceptual ecosystem model of microbial communities in enhanced biological phosphorus removal plants. Water Research, 44, 5070–5088.


Simon J. McIlroy, Mads Albertsen, Marta Nierychlo, Bianca McIlroy, Aviaja A. Hansen, Rasmus H. Kirkegaard, Jannie M. Kristensen, Søren M. Karst, Jeppe L. Nielsen and Per H. Nielsen

Past contributors:

Aaron A. Saunders, Artur T. Mielczarek

The online MiDAS field guide is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.


The MiDAS taxonomy is a manual curation of the Silva database and is redistributed for non-commercial use only.


Citing MiDAS: McIlroy S.J., Saunders A.M., Albertsen M., Nierychlo M., McIlroy B., Hansen A.A., Karst S.M., Nielsen J.L., Nielsen P.H. (2015) MiDAS: the field guide to the microbes of activated sludge. Database, Vol. 2015

Contact us at mail@midasfieldguide.org