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Sewage Treatment Plant

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Rotating Biological Contractors (RBC)

Rotating Biological Contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBC's were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit.

Sewage entering a plant is passed through primary treatment where coarse material and grit is removed. The sewage then passes through one or more RBC units, which have historically been built in a variety of configurations.

An RBC unit comprises a series of closely spaced "circular disks" normally made from a plastic material. The disks are partially submerged in the sewage and are slowly rotated through it.

The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage.

Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.

The Submerged Biological Contactor (SBC) is the modified version of the conventional RBC where the disks are 80% -100% submerged and forced air is introduced.

Typical values for RBC's are as follows:

(mg/L) Raw Sewage Effluent DOE Standard B
Biological Oxygen Demand 200-400 10-30 50
Suspended Solids 200-350 15-40 100

RBC units are suitable where land is restricted. They are quite and consistently produce a high quality effluent. Because they are modular they are also suitable for a staged development. Operations and maintenance costs are lower than for other forms of mechanical treatment.

There are currently approximately 40 RBC plants in Malaysia.