Membrane Bioreactors (MBR) are treatment processes, which integrate a perm-selective or semi-permeable membrane with a biological process. It is the combination of a membrane process like microfiltration or ultrafiltration with a suspended growth bioreactor, and is now widely used for municipal and industrial wastewater treatment with plant sizes up to 80’000 population equivalents. Due to it being a very technical solution; it needs expert design and skilled workers. Furthermore it is a costly but efficient treatment possibility. With the MBR technology, it is possible to upgrade old wastewater plants.