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Screw presses for sludge dewatering

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How screw presses work

A screw press (SP) provides sludge dewatering by conveying the sludge along the inside of a permeable cylinder. It is based on a slowly-rotating (~5 RPM) Archimedean screw within a cylindrical screen (otherwise termed drum filter/screen or basket). It is normally inclined by ~20° to the horizontal to assist with the draining of water into the sump. The screen generally has an aperture rating below 0.5 mm and is based on wedge-wire or occasionally perforated metal.

The screens are less susceptible to clogging than the filter media used for other thickening and dewatering processes. Consequently, spray-cleaning is applied only intermittently for around 2−4% of the operating time.

As with all thickening and dewatering processes, the product solids (or cake) content is dependent on the feedwater sludge quality. The cake solids content has been shown to be inversely proportional to the volatile solids (VS) of the feed sludge.

Screw press Credit: Judd Water & Wastewater Consultants
Screw press
Screw press containing and inclined screw which transports the sludge along a porous cylindrical channel though which the water drains as the sludge travels up the cylinderCredit: Judd Water & Wastewater Consultants

Huber Q-PRESS® screw press

Huber Q-PRESS® screw press Source: HUBER SE / YouTube

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Table 1. Screw press dewatering DS concentration of dewatered sludge (cake), solids recovered and polymer dose (Metcalf & Eddy, 2014; Andreoli et al, 2007)
Sludge origin % cake solids % solids capture Polymer dose − g/kg DS
Waste activated sludge (WAS)15−2288−958.5−11
Anaerobically-digested (AD) primary22−28≤9010−17.5
Anaerobically-digested WAS15−2588−958.5−17.5
Aerobically-digested, WAS15−2088−958.5−17.5
Mixed, primary + WAS25−35≤905−10
Mixed, AD primary + WAS17−25≤9010−17.5


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, HUBER SE

About this page

'Screw presses for sludge dewatering' was written by Simon Judd

This page was last updated on 22 April 2022


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