Graf oneAdvanced Operation Manual page 21

At the end of this treatment cycle, the plant pauses for the time remaining until the next cycle
start time (about 1–10 minutes). Afterwards, the cleaning process starts again with step 1.
The cycle described above is usually undertaken four times a day. The switching times and
number of cycles can be adapted following discussion with the manufacturer. They may only be
adapted by an authorised maintenance specialist.
3.2.4.3 Holiday mode
The operator can switch the plant to holiday mode when he is planning to be away for an ex-
tended period. In this event, water is no longer discharged from the plant. Aeration is minimal to
maintain the aerated sludge. In addition, a small quantity of wastewater is recirculated (in plants
larger than 10 PU) over the sludge and charging lifters inside the plant. This continues to pro-
vide nutrients to the aerated sludge.
3.2.4.4 Underload detection
Alternatively, the plant can be time-controlled to operate depending on its filled level. For this
purpose, the controller is fitted as standard with a pressure sensor that can be activated by a
specialist on request. This pressure sensor should be activated on new plants only after they
have been run in reliably.
This pressure sensor tests the level in the first chamber every six hours, or at the nominal start
of each cycle. When there is little or no inflow or the level is low, no treatment cycle is initiated.
Instead, there is minimum aeration to maintain the aerated sludge. In addition, a small quantity
of wastewater is recirculated over the sludge and feed lifters inside the plant. This continues to
provide nutrients to the aerated sludge. The controller then displays "Cycle pause". Once the
level measured in the first chamber exceeds a certain limit, a normal treatment cycle is initiated.
When fitted with underload detection, the plant can run independently of the actual hydraulic
load, helping to cut operating costs. This mode proves above all practicable when the inlet fluc-
tuates greatly over the course of the week, e.g. when the residents are not regularly at home.
Underload detection must be configured by a specialist.
3. General
Step 5:
In this phase, the excess activated sludge at the bottom is
pumped by an air lift pump from the SBR reactor chamber to
the sludge reservoir chamber, where it is stored.
Duration: 1–2 min
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Sludge return