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3.
Structure and operating principle
The system consists of several preliminary sedimentation tanks. Settleable materials settle in the
preliminary sedimentation stage while floating materials are held back. An outlet scum baffle is fitted on
the outlet pipe of each preliminary sedimentation tank. After the preliminary sedimentation tanks, the
waste water flows into one or more fluid bed tanks where biological cleaning is carried out.
The waste water enters the fluid bed tank through an inlet scum baffle which prevents the carrier material
passing back into the preliminary sedimentation tanks. There is also a baffle on the outlet side which
prevents the carrier material being flushed out of the tank. There are several membrane pipe aerators on
the base of the tank which bring in air.
After the biological stage, the water flows into the final sedimentation tank(s). The excess sludge is
deposited in the final sedimentation tanks and is pumped back to preliminary sedimentation via an air lift
pump. In systems sized for 90 or more inhabitants, the sludge is returned to a separate sludge
accumulator tank. The final sedimentation tanks feature an outlet scum baffle to retain floating particles.
In systems with separate sludge accumulator tanks, the sludge accumulator overflows into the 2
nd
preliminary sedimentation tank via the dome shaft.
4.
Fitting the set-up kit
4.1
Drilling in the final sedimentation dividing wall (only for systems sized for 20-70 inhabitants)
Graf Fluid bed systems with only
one final sedimentation tank (up to
70 inhabitants) need a dividing wall
to improve the effectiveness of final
sedimentation.
A DN 70 opening should be drilled
in the dividing wall as shown in the
drawing on the right.
