Studies of a membrane aerated bioreactor for wastewater treatment

This study was undertaken specifically to collect engineering and process performance information on the behaviour of a membrane supported bio-film in a well-characterised bioreactor. A novel membrane aerated bioreactor has been tested in the laboratory on synthetic sewage, and also piloted for the treatment of primary effluent at a local municipal wastewater treatment plant. The reactor's design employs gas-permeable, hollow-fibre membranes that are submerged in the wastewater. Air is blown through the inside of the fibres. Aeration costs for such a reactor are likely to be lower than conventional systems because gas compression is not required. Thick bio-films grow on the outside of the fibres and effectively treat the wastewater. The bio-films grown in this manner are capable of biological oxygen demand (BOD) removal, nitrification, denitrification, and simultaneous sludge digestion. The character of the bio-film is very different from conventional bio-films grown on inert surfaces, since in this case the bio-film receives its oxygen and the wastewater components from different directions. In pilot studies, a reactor having a hydraulic residence time of 6.5 h and equipped with no sedimentation tank achieved 70–75% BOD and nitrogen removal, and produced an effluent containing less than 30 mg/l total suspended solids.