Rotating biological contactor

A Rotating biological contactor or RBC is a biological treatment process used in the treatment of wastewater following primary treatment. The primary treatment process removes the grit and other solids through a screening process followed by a period of settlement. The RBC process involves allowing wastewater to come in contact with a biological medium in order to remove contaminants in sewage before discharge of the treated wastewater to the environment, usually a river. Rotating biological contactor is a type of secondary treatment process. It is a unit consisting of a series of closely spaced, parallel discs, mounted on a rotating shaft which is supported just above the surface of the waste water. Microorganisms grow on the disc surface where aerobic degradation of the pollutants takes place.

The construction of a rotating biological contactor consists of a series of plastic discs mounted on a driven shaft which is contained in a tank or trough. Commonly used plastics for the media are polythene, PVC and expanded polystyrene. The shaft is aligned with the flow of sewage such that the discs rotate at right angles to the flow with several rotors usually combined to make up a treatment train. About 40% of the disc area is immersed in the sewage.

Biofilms, which are biological growths that becomes attached to the discs, assimilates the organic materials in the wastewater. Aeration is provided by the rotating action, which exposes the media to the air after contacting them with the wastewater, facilitating the digestion of the organic compounds that need to be removed. The degree of wastewater treatment is related to the amount of media surface area and the quality and volume of the inflowing wastewater.