Membrane bioreactors (MBR) represent a new generation of processes that can be applied to the treatment of municipal and industrial wastewater. Their main advantage is their ability to keep all biomass in the bioreactor, thus removing all suspended solids from the treated water and disinfecting it according to the membrane cut-off threshold. Perfect control as well as separation of hydraulic (HRT) and biomass retention times (SRT) also means better control of biological activity. Treatment of municipal wastewater on a semi-industrial aerobic pilot-scale MBR (HRT: 24 hr; SRT: 25 days) resulted in complete nitrification and from 93 to 99.9% removal of COD, N-NH3 and suspended solids. The COD removed loading rate was equal to 0.2 kg/kg VSS.day and the average sludge production was around 0.2 kgSS/kgCOD. Filtration through 0.1 µm ceramic hollow fibres (Surface = 1.1 m2) under moderate conditions (1.5 to 3.5 m/s; TMP < 2 bars) maintained good flow rates of 60 to 80 1/hr at 20°C for over 15 days without chemical washing. The performances shown here over a total period of 100 days emphasize perfect stability of the MBR process in treating municipal wastewater.

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