Physical-chemical sludge treatment

Liming entails obtaining and maintaining a pH greater than 12 for several months. The lime dosage in the form of slaked lime varies from 20 to 50% depending on sludge type.

Using liming or nitrates to achieve chemical stabilization


It usually takes place after the dewatering stage by mixing the paste-like sludge and the pulverized lime together, although if the sludge is dewatered using a plate filter, then the lime is added upstream in the form of lime slurry at a ratio of 100 g per liter.


Veolia Water Solutions & Technologies has developed Saphyr™ which is a chemical stabilization technique that treats the thickened sludge with nitrites under acidic conditions (pH <3). Once the sludge has been stabilized using this process, it can then be stored either in a liquid or dewatered state for several months before its reuse or incineration in line with current legislation.

It is therefore a system that can be used as an alternative to liming, primarily in the following cases:

  • small sized facilities which do not dewater the sludge,
  • calcareous soil that is not particularly receptive to lime,
  • sludge incineration is a possible alternative unlike with liming.


However when pulverized lime is added after the dewatering stage, quicklime is often preferred as it is denser. This means it is not so costly to transport and store.

In addition, a hydration reaction (using the water within the sludge) accompanied by an increase in temperature, sanitizes and improves the dryness of the sludge.

Lime sludge is often highly valued by farmers, when it meets legal requirements pertaining to land application, as it provides a cheap form of liming material. A dryness level for landfill disposal of 30% is easily achievable. Widely used in France, this technique also has the added advantage of being inexpensive.

Dewatering

Saphyr™

Saphyr™

Veolia Water Solutions & Technologies provides a range of solutions to dewater sludge ranging from the gravity table used primarily by Aquaflow in the paper and pulp industry (AF Table), to screw presses (AF Press) as well as the comprehensive range of solutions from Edwards & Jones (Kruger UK).