Disclosed is a fluid treatment element, such as a filter element, operable in a dead end mode or a crossflow mode. In certain embodiments, the fluid treatment element includes a multilayer composite formed into axially extending pleats. In certain other embodiments, adjoining pleats are in a laid-over state and pressed against each other over a substantial portion of their height. The fluid treatment element can be compact yet have a large surface area available for fluid treatment. Also disclosed are a fluid treatment element and a method, particularly an all fluoropolymer fluid treatment element and a method, for diffusively transferring material from one fluid stream to another fluid stream, for example, for transferring ozone into water. Further disclosed are a device and method for crossflow cleaning of fluid treatment elements.