Apparatus for concentrating a nebulant comprising a nebulant flow conduit and a counter-flow conduit, or preferably, a plurality of alternating nebulant flow conduits and corresponding counter-flow conduits eg in layered or coaxial arrangement, and wherein at least a portion of the nebulant flow conduit and said counter-flow conduits define respective opposed sides of a gas permeable membrane. In use a nebuliser is in communication with the nebulant flow conduit and the nebulant flow and counter-flow are in the same or opposite directions and act to concentrate the amount of active in a droplet eg from 35 wt % to 60 wt % hydrogen peroxide in water to disinfect and/or sterilize an article.
