Denitrification can occur in a traditional activated
sludge process using an aerobic bioreactor combined
with a digestion basin kept under anoxic conditions
(Aboutboul et al., 1995). A wastewater treatment plant
utilizing an anoxic/oxic concept showed a 99.9%
reduction in NO3-N (Beeman and Reitberger, 2003). In
a study by Sadick et al. (1996) that analyzed the
performance of an anaerobic fluidized bed bioreactor,
microorganisms attached to the suspended sand
particles reduced the nitrate (NO3) concentration from
7.2 mg/L at the inlet to 0.3 mg/L in the effluent. In
typical membrane bioreactor systems, the aerated and
anoxic components of the coupled nitrification and denitrification
processes are connected with a pump that
recycles water from the anoxic to aerobic tank. The
membrane component is located in the aerobic tank to
take advantage of aeration used to scour solids from the
membrane. An overflow drain from the aerobic tank to
the anoxic tank maintains a constant wastewater level in
the aerobic tank.