Membrane Bioreactors (MBRs) combine biological wastewater treatment and membrane filtration. There are two basic options for the operation of bioreactors: While anaerobic microorganisms require oxygen for the degradation of organic pollutants, anaerobic microorganisms require the absence of oxygen. The two concepts are applied for the treatment of different kinds of wastewaters.

Aerobic MBRs is especially employed for the treatment of municipal wastewaters with an average chemical oxygen demand (COD) of about 300 – 1,000 mg/L. The main byproduct is CO₂. In anaerobic MBR technology (AnMBR), biogas is generated as a valuable by-product; compared to aerobic MBRs, the amount of excess sludge is small. Anaerobic digestion has the ability to handle highly contaminated organic wastewater. Current commercial high rate anaerobic reactors can deal with a COD of up to 60,000 mg/L. Thus, this process is especially suited for the treatment of wastewater generated in the food industry (e.g. breweries, dairy industry), and in the pulp and paper industry. However, this technology has not been well established technically, yet.

In AnMBRs, suspended solids concentration can reach up to 30 g/L. For a wide range of wastewaters, COD removal of about 90 % could be achieved at temperatures about 30 °C and a methane production of 0.25 to 0.35 m³ CH₄/kg COD could be reached. The advantages of AnMBRs, as compared to conventional aerobic wastewater treatment, are...