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Sludge treatment − rotary drum thickening

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Dewatered cake product from a belt press operation, collected in a red skip

How rotary drum thickening works

Rotary drum thickening increases the sludge solids concentration (i.e. thickens the sludge) by agitating the solids in a slowly-rotating vessel with porous walls though which the water (or filtrate) drains.

A rotary drum thickener (RDT) is based on the same principle as a gravity belt thickener (GBT), in that water drains from the sludge through a retaining porous medium. For an RDT the porous medium is the cylindrical wall of a 0.5−1.5 m diameter drum which rotates at speeds between 5 and 20 RPM while the sludge continually passes through it.

The porous wall may be fabricated from a range of materials, including polymers, steel and ceramics. A spray system is used to clean the drum and prevent the pores blocking.

Rotary drum thickener Credit: Judd Water & Wastewater Consultants
Rotary drum thickener
Rotary drum thickener, where sludge is passed along the length of a rotating cylinder with porous walls through which water drains to form a thickened sludge at the cylinder exit.Credit: Judd Water & Wastewater Consultants

Rotary drum thickener, Andritz

Rotary drum thickener, Andritz Source: ANDRITZ GROUP / YouTube

RDTs can achieve solids concentrations up to 9% and corresponding solids recoveries of 90−99%, depending on the sludge source and the conditioning employed. Conditioning by polymer dosing is normally conducted in a mixing drum upstream of the RDT.

Table 1. RDT DS concentration of feed and thickened sludge, water removal and solids recovered, % (Metcalf and Eddy, 2014; Andreoli et al, 2007)
Sludge source Feed Thickened Water removed Solids recovered
Mixed, primary + WAS2−45−95093−98
Anaerobically digested2.5−55−95090−98


Andreoli, C.V., von Sperling, M., & Fernandes. F. (2007). Sludge treatment and disposal, IWA Publishing (Lon, NY)

Metcalf & Eddy (2014). Wastewater engineering, treatment and resource recovery, 5th ed. Eds. Tchobanoglous, G., Stensel, D., Tsuchihashi, R., and Burton, F., McGraw-Hill (NY)

YouTube channel, Andritz,

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'Sludge treatment − rotary drum thickening' was written by Simon Judd

This page was last updated on 01 June 2022


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