The sludge index (SVI) is a measure of the settleability of sludge and is displayed by the ratio of the sludge volume (SV) and the dry matter content (TS) of the sludge.
Normal activated sludge has an SVI of 50 - 150 ml/g.
Upwards of a sludge index of 150 ml/g, one speaks of bulking sludge.
The sludge index is significantly influenced by the type of biocenosis (e.g., filamentous bacteria, foc structure). By means of microscopic examination and analysis of the activated sludge, one can obtain statements about the floc structure and the amount and type of filamentous organisms.
According to the occurrence of filamentous bacteria, measures must be taken to reduce the SVI. This may result in the addition of chemicals or employment of other types of sludge impact measures.
The S::Select® process is used to build a biology with granular activated sludge. The growth of filamentous bacteria is counteracted and the sludge retention time is optimized. A permanently stable and very powerful biology with excellent settling behavior (> 3m/h) is built up by S::Select®.


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