**3.3 Rotating biological contactor (RBC)**

RBC process entails the contact between the wastewater and the biological medium that is used to degrade the organic contaminants. A RBC is described as a device that "consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the wastewater" [4, 7]. RBCs are used to remove biodegradable organic matter and convert ammonia-N and organic-N to nitrate-N. Operational problems caused by high organic loading rates restrict the use of RBCs for partial removal of organic matter (i.e. for "roughing" treatment). However, they can be used quite effectively for the substantial removal of organic matter. Process effluent (i.e. clarified) five-day biochemical oxygen demand (BOD5)

and total suspended solids (TSS) concentrations can easily be reduced to less than 30 mg/l each, and even lower can be obtained in some instances [8].
