Before sludge with a very high water content is subjected to further treatment, it makes sense and is often necessary to reduce its volume by thickening. This also increases the solids content of the sludge. If sludge with a solids content of 1% is thickened to 6% solids, this gives a volume reduction of more than 80%.
The thickening of the sludge is effected by separating sludge water; thin sludge becomes thick sludge, which is viscous but still pumpable.
Sludge Volume Reduction
Sludge settles in gravity thickeners and is compressed by the weight of its own solids. Primary sludge from the primary clarifier of wastewater treatment plants and digested sludge from anaerobic sludge treatment thicken better statically than secondary sludge because of the higher density of their solids.
Secondary sludge (excess sludge) from the secondary clarifier is preferably thickened mechanically separate from the primary sludge. Polymers are mixed into the thin sludge for flocculation before the sludge is added to the thickening machine. The sludge water released by flocculation drains by gravity through a filter medium (cloth or fine screen) while flocs are retained thereon.
Mechanical excess sludge thickening is a prerequisite for the economic operation of anaerobic sludge stabilisation in a digester.
HUBER offers various machines for sludge thickening differing in design, size and throughput capacity. We offer best-performing equipment for every application.
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