Lab-scale testing of a low-loaded activated sludge process with membrane filtration

Two membrane bioreactors (MBRs; volume = 300 L) equipped with different types of immersed membrane modules were operated simultaneously under the same laboratory conditions as a low-loaded activated sludge process without any membrane regeneration and excess sludge uptake (sludge retention time SRT up to 170 d; activated sludge concentration MLSS up to 11 g L −1 ). The aim was to verify the quality of treated water and to study the properties of "very old" activated sludge. Another aim was to compare different selected membrane types and choose the best one for further pilot-scale testing.