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Operation and maintenance
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Determination of the sludge removal
7.3
Definition:
A settlement sample should be taken at the maintenance intervals to determine whether the wastewater
treatment system requires sludge removal. The SV30 (VS) is measured for this settlement sample. The
SV30 is the volume of sludge that 1000 ml of aerated sludge absorbs after a settlement period of 30
minutes. It is a measurement of the amount of sludge present in the wastewater treatment system.
Determination of the sludge volume is regulated in DIN EN 14702-1.
If the sludge volume is high (> 250 ml/l), the values of an undiluted SV30 measurement according to the
standard are not representative.
Reason: The settlement process in the comparatively narrow measuring cylinder is different because the
walls of the vessel and interactions of individual flakes interfere with one another.
A diluted sample should therefore be measured for higher volumes of sludge (> 250 ml/l). Another sample
with discharge water must be diluted for this purpose, taking water from the sample or clear water excess.
The volume ratio may be 1+1, 1+2 or 1+3 and may be multiplied by the dilution factor of 2, 3 or 4. The
diluted sample in which the value first falls below 250 ml/l is used to determine the sludge volume.
Implementation (recommendation):
1. Series of measurements:
The 1st measurement cylinder is filled up to the 1000 ml mark with the sludge sample. This sam-
ple is the undiluted sludge volume. If SV30 < 250 ml/l, this value is representative.
At the same time, a diluted sample in placed in the 2nd measurement cylinder. We recommend
diluting to a ratio of 1+2 (330 ml sludge and 670 ml discharge). The value read off is then multi-
plied by the dilution factor of 3 (see table below).
2. Series of measurements:
If the sludge volumes in the two measurement cylinders of the 1st series of measurements > 250
ml/l, the measurement should be repeated with the 1+3 dilution.
Sludge removal is needed as soon as the results of both the diluted and undiluted measurement produce
a SV30 of > 700 ml/l.
The table below can be used to assess the SV30 measurement.
Vers.
no.
Measurement cylinder
filled with
Reading,
diluted
ml/l
E V A L U A T I O N
Aerated
sludge
ml/l
Discharge
ml/l
Dilution
Dil.
factor f
SV30
ml/l
SV30 entry
ml/l
e.g.
500
500
225
500 + 500 = 1+1
2
225 x 2 = 450
450 (225 x 2)
e.g.
330
670
210
330 + 670 = 1+2
3
210 x 3 = 630
630 (210 x 3)
Table: Evaluation for undiluted SV30 > 250 ml/l
Summary of Contents for one2clean+ XXL
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