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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The sludge is withdrawn from the clarifier for further treatment.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: |
