Comparison between Decanter Centrifuge and Filter Press for Sludge Thickening

Sludge Thickening

This volume reduction, obtained by sludge thickening or sludge concentration, is done for the following purposes:

Methods of Sludge Thickening

Sludge thickening is commonly achieved by the following three methods:

Gravity Thickening

Gravity thickening increases the solids concentration by allowing the particles to settle to the base of a vessel, producing a concentrated (thickened) solids stream at the vessel base and a supernatant (diluted) stream at the surface.

Flotation Thickening

Dissolved air flotation (DAF) provides thickening of sludge by encouraging the solids to float to the surface, rather than allowing them to sink to the tank base as with gravity thickening, where they can be removed by a skimmer. DAF is applied when the sludge solids are neutrally buoyant (i.e. neither sink nor float) and so cannot be readily removed by conventional settling.

Centrifugal Thickening

Centrifugal thickening increases the sludge concentration (i.e. thickens the sludge) by encouraging the particles to migrate to the walls of a rapidly rotating cylindrical vessel under the influence of a centrifugal force.

However, in order to meet the requirements of high treatment capacity, small footprint, and low energy consumption, the choice is usually made between the following three types of equipment.

Decanter Centrifuge

A decanter centrifuge works by exerting a high centrifugal force on the slurry of solids and liquids. A rotating conveyor pushes out the heavier solids that settle on the decanter wall. The lighter liquid exits the decanter through the liquid outlet port on the other end of the bowl.



Belt Filter Press

A belt filter press (BFP) provides sludge dewatering by pressing the sludge to force the water through a permeable medium.



Plate and Frame Type Filter Press

The working principle of plate and frame type filter presses is that slurry is pumped into the machine such that solids are distributed evenly during the filling cycle. Solids build up on the filter cloth, forming the filter cake; the filtrate exits the filter plates through the corner ports into the manifold, yielding clean filtered water.



To sum up, the decanter centrifuge will be more cost-effective in comparison, but the filter press also has advantages in solid-phase water content. If you care more about flexibility and high capacity, a decanter is a good choice, and if you have enough space and want drier solids then you may choose filter presses. All in all, companies should decide according to the actual situation when making the choice.

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