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Per Halkjær Nielsen

Per Halkjær Nielsen

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Biology and Biochemistry
Denmark
2026

D-Index & Metrics

Biology and Biochemistry

D-Index
119
Citations
50564
World Ranking
674
National Ranking
6

Research.com Recognitions

  • 2026 - Research.com Biology and Biochemistry in Denmark Leader Award
  • 2025 - Research.com Biology and Biochemistry in Denmark Leader Award
  • 2023 - Research.com Biology and Biochemistry in Denmark Leader Award
  • 2022 - Research.com Biology and Biochemistry in Denmark Leader Award

Overview

Per Halkjær Nielsen is affiliated with Aalborg University in Denmark and has a significant body of research focused on environmental science. Their extensive publication record reflects substantial work in pollution, ecology, molecular biology, environmental engineering, and health, toxicology, and mutagenesis.

Their main research topics include:

  • Wastewater Treatment and Nitrogen Removal
  • Microbial Community Ecology and Physiology
  • Genomics and Phylogenetic Studies
  • Microbial Fuel Cells and Bioremediation
  • Anaerobic Digestion and Biogas Production
  • Water Treatment and Disinfection
  • Constructed Wetlands for Wastewater Treatment

Prominent recent publications by Nielsen include:

  • The biofilm matrix: multitasking in a shared space (2022, Nature Reviews Microbiology)
  • MiDAS 4: A global catalogue of full-length 16S rRNA gene sequences and taxonomy for studies of bacterial communities in wastewater treatment plants (2022, Nature Communications)
  • Connecting structure to function with the recovery of over 1000 high-quality metagenome-assembled genomes from activated sludge using long-read sequencing (2021, Nature Communications)
  • MiDAS 3: An ecosystem-specific reference database, taxonomy and knowledge platform for activated sludge and anaerobic digesters reveals species-level microbiome composition of activated sludge (2020, Water Research)
  • Novel syntrophic bacteria in full-scale anaerobic digesters revealed by genome-centric metatranscriptomics (2020, The ISME Journal)

Frequent co-authors collaborating with Nielsen are:

  • Morten Simonsen Dueholm
  • Caitlin M. Singleton
  • Marta Nierychlo
  • Mads Albertsen
  • Francesca Petriglieri

Their work has appeared repeatedly in key publication venues within their field, including:

  • bioRxiv (Cold Spring Harbor Laboratory)
  • Water Research
  • The ISME Journal
  • Nature Communications
  • Frontiers in Microbiology

Nielsen is also credited with contributions to books, notably with a publication titled "How a Water/Wastewater Utility Has Successfully Incorporated the UN Sustainable Development Goals in Their Daily Operations," published by the Water Environment Federation in 2020.

Best Publications

  • Extraction of extracellular polymers from activated sludge using a cation exchange resin

    Bo Frølund;Rikke Palmgren;Kristian Keiding;Per Halkjær Nielsen

  • Complete nitrification by Nitrospira bacteria

    Holger Daims;Elena V. Lebedeva;Petra Pjevac;Ping Han

  • Complete nitrification by a single microorganism

    Maartje A. H. J. van Kessel;Daan R. Speth;Mads Albertsen;Per Halkjær Nielsen

  • Enzymatic activity in the activated-sludge floc matrix

    B. Frølund;T. Griebe;P. H. Nielsen

  • Genome sequences of rare, uncultured bacteria obtained by differential coverage binning of multiple metagenomes

    Mads Albertsen;Philip Hugenholtz;Adam Skarshewski;Kåre Lehmann Nielsen

  • In Situ Characterization of Nitrospira-Like Nitrite-Oxidizing Bacteria Active in Wastewater Treatment Plants

    Holger Daims;Jeppe L. Nielsen;Per H. Nielsen;Karl-Heinz Schleifer

  • Combination of fluorescent in situ hybridization and microautoradiography-a new tool for structure-function analyses in microbial ecology

    Natuscka Lee;Per Halkjær Nielsen;Kjær Holm Andreasen;Stefan Juretschko

  • Global diversity and biogeography of bacterial communities in wastewater treatment plants

    Linwei Wu;Daliang Ning;Bing Zhang;Yong Li

  • Measurement of pools of protein, carbohydrate and lipid in domestic wastewater

    Kamma Raunkjær;Thorkild Hvitved-Jacobsen;Per Halkjær Nielsen

  • The activated sludge ecosystem contains a core community of abundant organisms.

    Aaron Marc Saunders;Mads Albertsen;Jes Vollertsen;Per Halkjær Nielsen

  • Microbial Ecology of Activated Sludge

    Robert Seviour;Per Halkjær Nielsen

  • Back to Basics – The Influence of DNA Extraction and Primer Choice on Phylogenetic Analysis of Activated Sludge Communities

    Mads Albertsen;Søren Michael Karst;Anja Sloth Ziegler;Rasmus Hansen Kirkegaard

  • Role of sulfate‐reducing bacteria in corrosion of mild steel: A review

    Whonchee Lee;Zbigniew Lewandowski;P. H. Nielsen;W. A. Hamilton

  • Expanded metabolic versatility of ubiquitous nitrite-oxidizing bacteria from the genus Nitrospira

    Hanna Koch;Sebastian Lücker;Mads Albertsen;Katharina Kitzinger

  • Low Temperature Partial Nitritation/Anammox in a Moving Bed Biofilm Reactor treating low strength Wastewater

    Eva Gilbert;Shelesh Agrawal;Søren Michael Karst;Harald Horn

  • Conceptual Model for Production and Composition of Exopolymers in Biofilms

    Per Halkjær Nielsen;Andreas Jahn;Rikke Palmgren

  • Amyloid adhesins are abundant in natural biofilms.

    Poul Larsen;Jeppe Lund Nielsen;Morten Simonsen Dueholm;Ronald Wetzel

  • Identity and Ecophysiology of Uncultured Actinobacterial Polyphosphate-Accumulating Organisms in Full-Scale Enhanced Biological Phosphorus Removal Plants

    Yunhong Kong;Jeppe Lund Nielsen;Per Halkjær Nielsen

  • Ammonia and temperature determine potential clustering in the anaerobic digestion microbiome.

    Jo De Vrieze;Aaron Marc Saunders;Ying He;Jing Fang

  • Back to basics – the influence of DNA extraction and primer choice on phylogenetic analysis in activated sludge communities

    Mads Albertsen;Søren Michael Karst;Anja Sloth Ziegler;Kåre Lehmann Nielsen

Frequent Co-Authors

Jeppe Lund Nielsen
Jeppe Lund Nielsen Aalborg University
Michael Wagner
Michael Wagner University of Vienna
Daniel E. Otzen
Daniel E. Otzen Aarhus University
Robert J. Seviour
Robert J. Seviour La Trobe University
Thorkild Hvitved-Jacobsen
Thorkild Hvitved-Jacobsen Aalborg University
Holger Daims
Holger Daims University of Vienna
Stefan Wuertz
Stefan Wuertz Nanyang Technological University
Gunna Christiansen
Gunna Christiansen Aalborg University
Thomas Bjarnsholt
Thomas Bjarnsholt University of Copenhagen
Niels Høiby
Niels Høiby University of Copenhagen

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