Operational Experience of Sludge Pre-Liming With Delayed Reactivity Lime Before Filter Plate Press Dewatering

Berbers, W.1 and Forman, A.2, 1Carmeuse Coordination Centre, Belgium, 2Singleton Birch


The use of lime for sludge conditioning before dewatering in filter presses is a widely used concept.
Lime (usually as milk of lime – MOL) is added as a chemical conditioner to liquid sludge together with a
metal salt to coagulate and flocculate fine particles, enabling an improved dewatering besides sanitising
the sludge. A delayed reactivity lime called CODECAL® has been developed by CARMEUSE, which
enables the addition of quicklime in powder form directly into the liquid sludge, without going through the milk of lime production stage, thereby facilitating the process considerably and enhancing sludge quality.

This CODECAL® , which is powdered quicklime, increases the pH of the sludge up to around 12 after
addition and reacts exothermically with the water of the sludge, only after dewatering. The relative coarse particle size (¯x50 = ~80µ) compared to hydrated lime (¯x50 = ~5µ) mineralises the sludge, enhancing the dewatering. This technique has been successfully applied in France and in the Benelux and represents a real breakthrough in sludge dewatering. It enables the formation of a dryer filter cake while using less quantities of lime and iron chloride. Another advantage of the process is the productivity increase of the filter plate presses, which considerably shortens the filtration time.

This paper describes the process and its advantages, as well as details different long-term experiences in
both urban and industrial waste water treatment plants.

Delayed reactivity lime (DRL), sludge conditioning, Sludge sanitisation (also called hygienisation),Odour
mitigation, De-phosphatising, Waste water sludge (WWS).

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