The use of either quick or slaked lime for sludge stabilization is an attractive and cost effective way to reduce odours, killed pathogens and converts sludge into a usable product for land application in case of acid soil. Because lime has low solubility in water, lime molecules persist in biosolids. This helps to maintain the pH above 12 and prevent regrowth of pathogens.
The targets of this sludge treatment are :
- the stabilization of the sludge, which objective is to reduce its fermentability in order to decrease or remove the odors
- the reduction of the sludge water content, which results of a sludge volume decrease and improve its physical properties (such as enhanced storage properties : angle of repose)
- hygienization which target is to kill all the pathogens
Post liming sludge stabilization
Dewatered sludge is mixed with lime, preferably quick lime instead of hydrated lime, in order to increase their pH to 12 though killing pathogens and micro-organism. The addition of lime increase also the sludge dry material content as lime react with water and vapor is released.
A dry material content of 30% can be easily reached whatever the type of dewatering equipment used upstream.
Sludge and lime should be mixed intimately and homogeneously to ensure that each lime molecule reacts.
Sodimate provides customers with complete packages from lime storage and dosing system, sludge mixing up to limed sludge conveyors towards storage skips or storage area.
Sodimate offers alternative storage solutions adapted to the customer’s need, depending on the product consumption and its procurement difficulties: silo, Big Bag or sack tip hopper. The Sodimate sludge mixer does not alter sludge structure, contrary to the other types of mixing systems.
Pre liming sludge stabilization
The pre liming sludge stabilization is usually used for 2 types of application
1 ° / Sludge dewatering by filter press
A lime milk made of hydrated lime (lime milk preparation tank) or quick lime (lime slaking systems) is injected into the conditioning tank allowing increased dewatering performances.
2 ° / Sludge dewatering by centrifugal
The use of quick lime which has a “delayed reactivity” allows a pre liming sludge treatment with centrifuges, whereas centrifuges are generally associated with post liming application. The delayed reactivity quick lime is discharged, dosed and injected into a maturing tank where it is mixed together with liquid sludge before being sent to the centrifuge.
The centrifuged sludge is transferred by screw conveyor and it is only once the sludge is discharged into the storage skips or the storage area that the lime starts its exothermic reaction.
Precipitation of phosphates, sulphates and heavy metals by injection of milk of lime.