The performance of a submerged membrane bioreactor (SMBR), containing hollow fibre membranes, was investigated for the continuous treatment of wastewater. The hydrophilic polyetherimide membranes were characterised and tested in 5 days experiments using air backwashing to maintain permeate flux. Permeation and air backwashing cycles were investigated, varying the permeation period (15-30min) with fixed backwashing time (0.5 min). The effect of different hydraulic retention times (2-5 h) on the reactor performance was also assessed. Operation at low hydraulic retention times, with organic load up to 8 kg CODm(-3)d(-1), led to a sludge production of 0.05 kg VSSkgCOD(-1), which is considered low in comparison with conventional activated sludge process. The bioreactor produced an effluent free of turbidity and reached high COD (95-100%) and TOC (92-96%) removals. In a long-term operation assay (101-d), the reactor also maintained high COD (92%) and TOC (93%) removals. Polysaccharides content of the reactor supernatant contributed to produce a thin gel layer on the hollow fibre surface during long-term operation. (c) 2007 Elsevier B.V. All rights reserved.