Understanding of membrane fouling processes in membrane bioreactors (MBR) treating municipal wastewater is essential for proper design and operation of full-scale MBR wastewater treatment plants. One of the tools in investigating this subject must be a well-defined measuring protocol to quantify the filterability of activated sludge. Such a method was developed and a filtration apparatus was built by Delft University of Technology [1]. This article describes the results of applying the mentioned filtration characterisation method at three MBR pilot locations in the Netherlands. The measurements were sustained by EPS analyses in the water phase of the respective activated sludge broths. Each MBR installation produces an activated sludge with a specific filterability, which can be quantified by the proposed measuring protocol quite well. Activated sludge from each installation could be filtered under subcritical conditions, i.e. without filtration resistance increase for at least thirty minutes of filtration. Photometric EPS analyses of the water phase and obtained permeate seem to be too weak to explain the differences in filtration behaviour.