ANAEROBIC OXIDATION OF AMMONIUM IS A BIOLOGICALLY MEDIATED PROCESS

A newly discovered process by which ammonium is converted to dinitroge n gas under anaerobic conditions (the Anammox process) has now been ex amined in detail. In order to confirm the biological nature of this pr ocess, anaerobic batch culture experiments were used. All of ammonium provided in the medium was oxidized within 9 days. In control experime nts with autoclaved or raw wastewater, without added sludge or with ad ded sterilized (either autoclaved or gamma irradiated) sludge, no chan ges in the ammonium and nitrate concentrations were observed. Chemical reactions could therefore not be responsible for the ammonium convers ion. The addition of chloramphenicol, ampicillin, 2,4-dinitrophenol, c arbonyl cyanide m-chlorophenyl-hydrazone (CCCP), and mercuric chloride ((HgCl2)-Cl-II) completely inhibited the activity of the ammonium-oxi dizing sludge. Furthermore, the rate of ammonium oxidation was proport ional to the initial amount of sludge used. It was therefore concluded that anaerobic ammonium oxidation was a microbiological process. As t he experiments were carried out in an oxygen-free atmosphere, the conv ersion of ammonium to dinitrogen gas did not even require a trace of O -2. That the end product of the reaction was nitrogen gas has been con firmed by using (NH4+)-N-15 and (NO3-)-N-14. The dominant product was N-14-15(2). Only 1.7% of the total labelled nitrogen gas produced was N-15-15(2). It is therefore proposed that the N-2 produced by the Anam mox process is formed from equimolar amounts of NH4+ and NO3-.