The traditional ammonium removal used in wastewater treatment
involves two separate steps: aerobic nitrification by autotrophs
and anaerobic denitrification by heterotrophs (1).
Nitrification and denitrification are generally carried out by
adopting individual bioreactors or different aeration intervals
because of the different demands for oxygen and organic matter
(2,3). Furthermore, autotrophic nitrifiers are sensitive to high loads
of ammonium and organic matter (4), and their slow growth rate
generally make the nitrification become the rate-limiting step (2,5).
All these inevitably increase the operating cost and the difficulty in
treatment condition control. Recently, bacteria which are both
heterotrophic nitrifier and aerobic denitrifier have attracted
increasing attention. Under aerobic conditions, ammonium compounds
can be converted to gaseous products by the pure cultures
of these heterotrophic microorganisms with concomitant removal
of carbon compounds (2).