Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor

Authors

  • A. Mulder,

    1. Gist-brocades, Postbus 1, 2600 MA Delft, the Netherlands
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    • 1

      Present address: TNO-MW, Postbus 6011, 2600 JA Delft, the Netherlands.

  • A.A. van de Graaf,

    1. Kluyver Laboratory for Biotechnology, Department of Microbiology and Enzymology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, the Netherlands
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    • 2

      Present address: IMPULS Science and Technology Center, Postbus 421, 1000 AK Amsterdam, the Netherlands.

  • L.A. Robertson,

    1. Kluyver Laboratory for Biotechnology, Department of Microbiology and Enzymology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, the Netherlands
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  • J.G. Kuenen

    Corresponding author
    1. Kluyver Laboratory for Biotechnology, Department of Microbiology and Enzymology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, the Netherlands
      ∗Corresponding author. Tel: (31) 15 785308; Fax: (31) 15 782355.
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∗Corresponding author. Tel: (31) 15 785308; Fax: (31) 15 782355.

Abstract

Abstract Until now, oxidation of ammonium has only been known to proceed under aerobic conditions. Recently, we observed that NH4+ was disappearing from a denitrifying fluidized bed reactor treating effluent from a methanogenic reactor. Both nitrate and ammonium consumption increased with concomitant gas production. A maximum ammonium removal rate of 0.4 kg N · m−3 · d−1 (1.2 mM/h) was observed. The evidence for this anaerobic ammonium oxidation was based on nitrogen and redox balances in continuous-flow experiments. It was shown that for the oxidation of 5 mol ammonium, 3 mol nitrate were required, resulting in the formation of 4 mol dinitrogen gas. Subsequent batch experiments confirmed that the NH4+ conversion was nitrate dependent. It was concluded that anaerobic ammonium oxidation is a new process in which ammonium is oxidized with nitrate serving as the electron acceptor under anaerobic conditions, producing dinitrogen gas. This biological process has been given the name ‘Anammox” (anaerobic ammonium oxidation), and has been patented.

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