Sludge index

The sludge volume index ISV , also known as the sludge volume index , is used in sewage treatment plants and is a measure of the settling properties of sewage sludge in the biological treatment stage .

The sludge index results from the quotient of the sludge volume V _S and the dry matter content TS of the same sludge:

{\ displaystyle I_ {SV} [{\ frac {ml} {g}}] = {\ frac {V_ {S} [{\ frac {ml} {l}}]} {TS_ {BB} [{\ frac {g} {l}}]}}}

Typical values:

- Regular mud	up to 100 ml / g
- Moderate thickening ability	100 to 150 ml / g
- Bulky sludge	from 150 ml / g.

Sludge volume:
The sludge volume is obtained when 1000 ml of a well-mixed sample is placed in a 1000 ml measuring cylinder . The sludge level of the settled sludge and the volume of the floating sludge, which are read off after 30 minutes, add up to the sludge volume . If the sludge volume is greater than 250 ml / l, the sample is diluted with run-off water and multiplied by the relevant factor during evaluation.

Dry matter content:
To determine the dry matter content, 100 ml are taken from the same sample of the sludge volume. A clean filter that has been stored in the drying cabinet and then in the desiccator is weighed on an analytical balance (this value is m ₁ ). The 100 ml sludge is then filtered through this filter and dried in the microwave , in the drying cabinet or by infrared . The filter is then weighed again (this value is m ₂ ). If you subtract m ₁ from m ₂ , you get the dry matter content in g / 100 ml. However, since the dry matter content in g / l or kg / m³ is to be used in the formula for the sludge index, the value m ₂ -m _{1 must} be multiplied by a factor of 10.

Individual evidence

^ Willi Gujer: Urban water management . 3. Edition. Springer Verlag, Berlin Heidelberg 2007, ISBN 978-3-540-34329-5 , p. 327 .