Abstract: A multi-function fluid treatment system which can filter liquids or diffuse gases into liquids. To achieve filtration, the system includes a housing with multiple, closely-spaced filter cartridges therein. The cartridges are connected to a drive system which rotates them in unison. Fluids to be filtered enter the housing and surround the rotating cartridges. Cartridge rotation scrubs solids from the cartridges and promotes fluid flow into the cartridges. Filtered fluids collected within the cartridges thereafter exit the system. To achieve gas diffusion, the housing is filled with a selected liquid. During cartridge rotation as discussed above, a gas is introduced into the interior of each cartridge which is constructed of a porous material. The gas diffuses outwardly during cartridge rotation, causing substantial mixing of the gas and fluid, with gas diffusion into the fluid. Cartridge rotation also prevents solids from accumulating thereon to achieve maximum gas delivery.