Membrane strip diffusers are disclosed, useful for example in aerating wastewater in activated sludge plants. These diffusers have membranes, diffuser bodies comprising gas conduits and, in addition to the conduits, integral membrane supports elongated in the same general direction. Such conduits are for example co-extruded with the diffuser bodies. The supports are apertured to discharge gas into chambers formed beneath the membranes when they inflate, and the membranes have pores to discharge the gas. Ways to edge- and end-seal the membranes to the diffuser bodies and ways to support the diffusers are also disclosed.