Key features of the process consisting in coupling biological treatment with membrane separation are described for wastewater treatment. The process development started in the early 1970s with small flow rate applications for on-site commercial development applications and industrial wastewater treatment. The introduction of immersed membrane in the early 1990s allowed the process to be used for municipal wastewater treatment. The results from the 1st year of operation of a 3,800 m 3 /d plant are presented.