Graf oneAdvanced Operation Manual page 20

3. General
Step 2:
In this step, the wastewater is aerated and mixed. Membrane
pipe or plate aerators fitted on the base of the chamber aerate
the wastewater.
The plant's aeration equipment is supplied with ambient air by
a control cabinet installed separately. An air compressor pro-
duces the compressed air needed. Aeration usually takes
place intermittently.
with two simultaneous outcomes:
the microorganisms in the activated sludge are supplied
with oxygen, which is needed for their metabolism and
therefore for the pollutants to be broken down.
there is intensive contact between the wastewater and
bacteria.
Duration: approx 240 min
Step 3:
This step is a rest phase in which no aeration takes place.
The activated sludge settles with gravity (sedimentation
phase). A clear water zone forms at the top and a sludge
layer at the bottom. Any floating sludge is on top of the clear
water zone.
Duration: approx 90 min
Step 4:
In this phase, the biologically cleaned wastewater (clear wa-
ter) is drawn out of the SBR stage. It is pumped out by an air
lift (or mammoth) pump, which uses compressed air. The air
lift pump is designed not to pump out any floating sludge on
top of the clear water layer.
Duration: 5–20 min
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Aeration
Sedimentation phase
Clear water extraction