The rotating biological contactor (RBC) treatment system is a biological treatment process which utilizes a concentrated mass of microorganisms to stabilize organic matter in the wastewater. Rather than the organisms being suspended in an aeration basin, as with the activated sludge process, the biological growth is attached to large-diameter corrugated plastic discs mounted on a horizontal shaft.
A series of these shafts are placed in a rectangular tank so that the discs are immersed to approximately 40% of their diameter. The discs are spaced so that, during submergence, wastewater can enter the separations between the corrugated surfaces, providing the microorganisms with a food source. When rotated out of the tank, the liquid trickles out of the plastic media and is replaced by air, providing a source of oxygen to satisfy the respiratory requirement of the microorganisms. The rotation of the discs and the biological activity on them maintains a constant thickness of biologic growth. Growth sloughed from the discs is separated from the flow in the secondary clarifiers.