Rotating biological contactors is a remediation technology used in the secondary treatment of wastewater. This technology involves allowing wastewater to come in contact with a biological medium in order to facilitate the removal of contaminants. There are several different designs available, but in its simplest form a rotary biological contactor (RBC) consists of a series of discs mounted on a shaft which is driven so that the discs rotate at right angles to the flow of settled sewage. The discs are usually made of plastic (polythene, PVC, expanded polystyrene) and are contained in a trough so that about 40 percent of their area is immersed. The discs are arranged in groups or packs with baffles between each group to minimize surging or short-circuiting.

RBC units are usually installed in a concrete tank so that the surface of the wastewater passing through the tank almost reaches the shaft. This means that about 40% of the total surface area of the disks are always submerged. Aeration is provided by the rotating action, which exposes the disks to the air after contacting them with the wastewater.

Advantages offered by rotating biological contactors:

1. Short contact periods are required because of the large active surface

2. They are capable of handling a wide range of flows

3. Sloughed biomass generally has good settling characteristics and can easily be separated from waste stream

4. Operating costs are low because little skill is required in plant operation

5. Short retention time

6. Low power requirements

7. Elimination of the channelling to which conventional percolators are susceptible

8. Low sludge production and excellent process control