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