Nitrification and oxygen utilisation in a membrane aeration bioreactor

A laboratory-scale membrane aeration bioreactor (MABR) was operated with a nitrifying biofilm attached to the surface of oxygen-permeable hollow fibres. Pure oxygen was supplied to the biofilm via the lumen of the hollow fibres. The process achieved high rates of nitrogen removal (98%) and nitrification (83%) at a nitrogen loading rate of 1.2 kg NH4-N m(-3) d(-1). A specific nitrification rate of 5.4 g NH4-N m(-2) d(-1) and a nitrogen removal rate of 6.6 g NH4-N m(-2) d(-1) were demonstrated. Nitrification was virtually unaffected by a reduction in the oxygen supply rate up to the point where the supply matched the oxygen requirement of the wastewater. Exceptionally high oxygen utilisation efficiencies were achieved. It is proposed that interfacial oxygen mass transfer contributes to the excellent performance of the MABR at low oxygen supply rates. (C) 1998 Elsevier Science B.V.