Oxygen supply capacity/ yield refer to full floor aeration with an arrangement density of 19% and a blow-in depth of 1,80 m. Measured in clean water according to DWA-M 209.The efficiency and reliability of NORRES membrane tube diffuser can be increased by optimising and adapting the operating parameters. The permanent elasticity of the membrane has a crucial influence on the uniformity of the opening characteristic of the slit perforation over the full operating range. This in turn ensures a largely constant performance of the fine-bubble, compressed air aeration system.