The combination of an activated sludge process with a UF/MF-membrane filtration is called Membrane Bio Reactor (BIOSEP^®). For separation of the purified water from mixed liquor (ML) instead of conventional processes (e. g. secondary clarification), the superior separation qualities of membrane filtration are used.

Immersed membranes are placed either directly into the aeration tank, or into an external filtration tank with ML recirculation.

MBR offers convincing benefits compared to conventional wastewater treatment:

• A substantially improved discharge quality is achieved. As the particulate components and micro organisms are rejected completely, the effluent is virtually free from solids, and a considerable reduction of the parameters COD, N, and P is achieved.
• Germs are rejected to a large extent, and the wastewater is disinfected mechanically. Therefore a direct discharge into bathing water areas is possible, or the effluent can be used for unrestricted irrigation.
• Tank volume and footprint are much lower than in conventional plants, as an MBR operates at a considerably higher MLSS (10-12 g/l compared to 3-4 g/l in a conventional plant) and secondary treatment is obsolete.
• The effluent is also suitable for re-use, i.e. as washing water or for cooling tower applications. A further treatment of the MBR filtrate by Reverse Osmosis or activated carbon is increasingly cost-efficient for industrial applications. As the influent is free from solids, better reliability, increased recovery rates and substantially longer service life are achieved.