Optimising aeration is required to reduce the energy costs of activated sludge wastewater treatment plants, as aeration can represent more than half the energy demand of such a plant. This article presents the synthesis of data and experiences related to the design and the operation of fine bubble aeration systems, equipped with EPDM membranes. These devices are the most installed ones at the moment in France. This synthesis highlights the key parameters to optimise design and operation of aeration systems, in order to guaranty the best treatment efficiencies at the least cost. In addition to conventional criteria such as diffuser placement, the surface air flow rate (air flow rate divided by the total area covered by the diffuser grids) was shown to be a key parameter governing aeration performances: its value should not exceed 10 Nm3.h-1.m-2 in cylindrical tanks and 15 to 25 Nm3.h-1.m-2 in horizontal flow systems. The impact of high diffuser submergence (> 6m) and of fooling phenomenon on aeration capacities should be further investigated.