4 phosphate profile – Hach-Lange WTOS P-RTC User Manual
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Parameterization and operation
4.5.4
Phosphate profile
The same conditions as specified under
must
apply for the phosphate flow rate profile. If biological phosphate
elimination is still not effective at the measuring point, the flow
profile rate remains unaffected by the biological phosphate
elimination. If biological phosphate elimination is already effective
at the measuring point, this must also be reflected in the profile.
Note: In this case, the value zero (0) must be entered as Bio P
proportion!
For open-loop controls, the results of the online measurement
can be directly employed in the profile determination. This also
ensures that the measurement conditions are identical.
Due to missing data, the configuration for closed-loop controls
is more complex. A reliable data pool for a waste water treatment
plant can only be obtained on the basis of 2 h composite
samples. Any samples that were taken during unusual influent
events (heavy rains, unauthorized discharge) are excluded.
A sample unaffected by precipitation can only be taken from the
influent to the activated sludge plant. At this point, the organic
phosphorous has not yet hydrolyzed. If total phosphate is
determined here, the "unavoidable" biological phosphate
elimination must be considered.
Since the entry of a Bio-P amount is not possible for closed-loop
controls (option hidden), lower values can be entered directly. If
the online measurement fails, it is safer to forego a reduction.
Over the course of a week, there can be strong fluctuations in the
load on the waste water treatment plant. To ensure an accurate
representation of actual conditions, the daily profiles can be
superimposed with a weekly profile.
4.5.5
PID closed-loop (proportional, integral, differential closed-loop)
The proportional precipitant dosing quantity calculated by the
RTC module is increased or reduced by the proportional
intensification factor (
GAIN P CONTR.)
of the closed loop control.
As the precipitant has already become effective at the measuring
point, the measurement indicates the following:
•
The dosage is too low
•
The dosage is sufficient
•
The dosage is too high and must be corrected
accordingly
The proportional gain factor specifies the precipitant dosage
required based on the exceedance of the target value. Large
gains result in large changes to the dosing and therefore a high
closed-loop control speed; however, the closed-loop control
oscillations also increase in line with the gain.
The
DERIVATIVE TIME
allows the RTC module to react not only
to the absolute target value deviations but also to the speed with
which the phosphate content rises or falls. Necessary corrections
can thus be made at an earlier stage.