The Rotating Biological Contactor (RBC) is a type of:

Question

The Rotating Biological Contactor (RBC) is a type of:

1. A. Suspended-growth biological system
2. B. Attached-growth biological system (Correct answer)
3. C. Physical sedimentation unit
4. D. Chemical coagulation unit

Correct Answer

Option B — Attached-growth biological system

Detailed Solution & Explanation

The correct answer is Attached-growth biological system.

Key Points

• A Rotating Biological Contactor consists of closely spaced circular discs mounted on a horizontal shaft, rotating slowly through a tank of wastewater. Micro-organisms grow as a biofilm fixed to the disc surface, which makes it an attached-growth, or fixed-film, system.
• Roughly 40% of the disc area is submerged at any moment. Rotation alternately immerses the biofilm in wastewater, where it absorbs organic matter, and lifts it into the air, where it takes up oxygen — so no separate aeration equipment is required.
• It is not a suspended-growth system (that is the activated sludge family), nor a physical or chemical unit.

Additional Information

• The two families are worth holding side by side. Attached growth: trickling filters, RBCs, biological filters. Suspended growth: activated sludge and all its modifications, oxidation ditches, aerated lagoons, SBRs.
• Attached-growth systems are valued for low power consumption, simple operation, resistance to shock loads and freedom from sludge-bulking problems; their drawbacks are higher capital cost and shaft or media failures.
• Excess biofilm periodically sloughs off the discs and is carried forward, so an RBC still needs a secondary clarifier downstream.
• RBCs are usually built in stages in series, with the first stage carrying the heaviest organic load and later stages achieving nitrification.