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Appl. Environ. Microbiol., 04 1995, 1246-1251, Vol 61, No. 4
AA van de Graaf, A Mulder, P de Bruijn, MS Jetten, LA Robertson and JG Kuenen
A newly discovered process by which ammonium is converted to dinitrogen gas
under anaerobic conditions (the Anammox process) has now been examined in
detail. In order to confirm the biological nature of this process,
anaerobic batch culture experiments were used. All of the ammonium provided
in the medium was oxidized within 9 days. In control experiments with
autoclaved or raw wastewater, without added sludge or with added sterilized
(either autoclaved or gamma irradiated) sludge, no changes in the ammonium
and nitrate concentrations were observed. Chemical reactions could
therefore not be responsible for the ammonium conversion. The addition of
chloramphenicol, ampicillin, 2,4- dinitrophenol, carbonyl cyanide
m-chlorophenyl-hydrazone (CCCP), and mercuric chloride (HgIICl2) completely
inhibited the activity of the ammonium-oxidizing sludge. Furthermore, the
rate of ammonium oxidation was proportional to the initial amount of sludge
used. It was therefore concluded that anaerobic ammonium oxidation was a
microbiological process. As the experiments were carried out in an
oxygen-free atmosphere, the conversion of ammonium to dinitrogen gas did
not even require a trace of O2. That the end product of the reaction was
nitrogen gas has been confirmed by using 15NH4+ and 14NO3-. The dominant
product was 14-15N2. Only 1.7% of the total labelled nitrogen gas produced
was 15-15N2. It is therefore proposed that the N2 produced by the Anammox
process is formed from equimolar amounts of NH4+ and NO3- .
Copyright © 1995, American Society for Microbiology
Anaerobic oxidation of ammonium is a biologically mediated process
Kluyver Laboratory of Biotechnology, Department of Microbiology and Enzymology, Delft University of Technology, The Netherlands.
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