Two laboratory scale biological reactors with hollow fibre incorporated to provide bubbleless aeration to a biofilm attached to the membrane wall were investigated during the nitrification of a synthetic wastewater high in ammonia (30-50 mg l−1). Pure oxygen on the lumen side of the fibres was transported through the pores of the membrane wall directly to the biofilm without the formation of bubbles. As a consequence oxygen usage efficiency is significantly increased. During the 51 d investigation the volumetric nitrogen loading rate increased from 0.08 to 0.20 kg NH4-N m−3 d−1. At the highest loading rate nitrification rates approaching 0.20 kg NH4-N m−3 d−1 were achieved. The dissolved oxygen concentration in the bulk liquid phase stayed well above critical. Hollow-fibre bubbleless oxygen mass transfer membrane bioreactors (MBR) show promise in providing a small-footprint alternative to conventional tertiary nitrification processes.

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