Biotechnology and Bioinformatics (1+1)

6.2.4.5. Biodisks or RBC (Rotating Biological Contactors)

· Rotating Biological Contactor units contain circular disks made of Styrofoam, high-density plastic, or other lightweight material.

· Oxygen is transferred from the atmosphere to the exposed film.

· RBC's were first used in domestic sewage treatment applications.

· There are several different types that are manufactured. A typical design consists of plates or disks that are attached to a horizontal shaft. The shaft is located at the surface of the water and it is turned at a very slow speed (1-5 rpm). A series of disks are partially submerged in the wastewater at all times. As they rotate, the biofilm attached to the surface of the disk is alternately exposed to air and then submerged in the water.

· Diffused aeration may be used to enhance performance.

· The process has similarities to trickling filters and the activated sludge process but the biofilm performance is the main feature of the process.

· The original designs used an electric motor to turn the shaft. There is a new design specifically for aquaculture that uses compressed air or pumped water to drive a paddle wheel in the center of the cylinder.

· These RBC's float in the water and do not require bearings or elaborate mechanical supports.

Advantages

· offer excellent treatment efficiencies.

· require very little energy to operate and can be located in the culture tank to save space if necessary.

· do not require additional oxygen and are not limited to oxygen contained in the incoming water.

· can remove dissolved BOD or ammonia depending on nutrient levels.

· They are biologically robust and handle shock loads well.

· It is easy to observe their operation and visually monitor the biofilm.

Drawback

· They only have one major drawback besides cost and that relates to reliability.

· If there is a power failure or the cylinder stops turning for any reason, the biofilm exposed to the air can dry out.

· When this happens, the cylinder will be unbalanced and become difficult to turn.