Rotary biological disc (biodisk) systems are designed to provide a suitable surface for micro-organisms to be repelled by the possible corrosive nature of the incoming wastewater. It consists of a structure in which plastic materials are placed in discs on a rotating shaft, or in the form of perforated drum.
Oxygen demand is great in the air, during rotation.
Microorganisms on the surfaces of the discs form a biological film.
As the discs are partially submerged, the surface (air-contacting) cycles meet the oxygen requirement of the biofilms.
Generally applicable diameters in biodisks are 1.5-3.0 m.
40-50 discs can be placed at intervals of 2 cm per 1 meter of shaft, the discs are placed parallel and equally spaced on the shaft and the shaft is rotated with the help of a motor, made of plastic with a diameter of 2-3 m and a total length of 6 cm M.

The discs are rotated at 2-4 rpm.

In the case of filled drum types, sizing is performed in order to provide the desired total filling material surface.

Each rotating disc or drum shaft is mounted in a separate cylinder chamber (channel), with 40-45% submerged in water.

The wastewater tank is dimensioned so that there are not too many dead zones, so the tank is generally made in semi-cylindrical form, preferably in standard sizes, either as PE material or as reinforced concrete.