A rotating biological contactor or RBC is a biological treatment process used in the treatment of wastewater following primary treatment. The primary biological wastewater treatment grady pdf process means protection by removal of grit and sand and course material through a screening process, followed by a removal process of sediment by settling. It consists 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 surface of the discs where biological degradation of the wastewater pollutants takes place.
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Commonly used plastics for the media are polyethylene, PVC and expanded polystyrene. The shaft is aligned with the flow of wastewater so that the discs rotate at right angles to the flow with several packs usually combined to make up a treatment train. Biological growth is attached to the surface of the disc and forms a slime layer. The discs contact the wastewater with the atmospheric air for oxidation as it rotates.
The rotation helps to slough off excess solids. The disc system can be staged in series to obtain nearly any detention time or degree of removal required.
Since the systems are staged, the culture of the later stages can be acclimated to the slowly degraded materials. The discs consist of plastic sheets ranging from 2 to 4 m in diameter and are up to 10 mm thick. Carbonaceous substrate is removed in the initial stage of RBC.
Carbon conversion may be completed in the first stage of a series of modules, with nitrification being completed after the 5th stage. Most design of RBC systems will include a minimum of 4 or 5 modules in series to obtain nitrification of waste water. Biofilms, which are biological growths that become attached to the discs, assimilate 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 degradation of the pollutants being removed.