Rotating Biological Contactor (RBC)

ROTATING BIOLOGICAL CONTACTOR

• The rotating biological contactor is a method of secondary wastewater treatment that employs principle common to the trickling filter and activated sludge process
• A rotating biological contactor (RBC) is a cylindrical media made of closely mounted thin flat circular plastic sheets or discs of 3 to 3.5 m in diameter and 10 mm thick. 
• These discs are placed at 30 to 40 mm spacing mounted on a common shaft.
• RBC's are usually made upto 8 m length and may be pllaced in series or parallel in specially constructed tanks through which wastewater is allowed to pass.
• The RBCs are immersed in wastewater by 40% of their diameter
• The RBCs are rotated arouund their central horizontal shaft at 1 - 2 RPM using power supplied to the shaft.
• Almost 95% of the surface area is thus alternately immersed in wastewater and then exposed to the atmosphere above the liquid.
• During operation, the microorganisms in the wastewater begin to stick to the rotating surfaces and grow till the entire surface area of the disc gets covered with 1 - 3 mm layer of biological slime.
• As the discs rotate, they carry a film of wastewater into the air, where it trickles down the surface of the discs absorbing oxygen.
• As the discs complete their rotation, this film mixes with the wastewater in the tank adding to the oxygen of the tank and mixing the treated and partially treated wastewater.
• As the attached microorganisms pass through the tank, they absorb other organics for breakdown
• The excess growth of microorganisms is sheared from the discs, as they move through the wastewater tank
• The dislodged microorganisms are kept in suspension by the moving discs
• The suspended growth moves with the sewage flowing through the tank to a downstream settling tank for removal
• This effluent is of a better quality than what is obtained from secondary treatment
• The quality of the effluent can be further improved by placing several contactors in series along the tank
• This method can provide a high degree of treatment including biological conversion of ammonia to nitrates