The use of polyetherimide hollow fibres in a submerged membrane bioreactor operating with air backwashing

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 (15–30 min) 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 COD m−3 d−1, led to a sludge production of 0.05 kg VSS kg COD−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.