Abstract: There is disclosed a rotating trickling filter formed from an elongated, hollow, circular cylindrical shell in which fixed film contactor media is mounted. Wastewater is introduced through an inlet at one end of the shell and exits through an outlet at the opposite end. The volume of wastewater within the shell is maintained as a small fraction of the total volume within the shell and collects as a shallow pool of wastewater at the bottom of the shell. Longitudinal channels sweep through the pool of wastewater as the shell is rotated to raise wastewater and discharge it over the media, which also rotates with the shell. In one embodiment the shell is cradled on belts, one of which is driven to rotate the shell. In another embodiment, the shell is mounted within a holding tank of wastewater and is driven by the release of gas under pressure from a conduit disposed beneath the shell, with the gas being trapped in cups arranged about the perimeter of the shell.