A method is provided for thickening sludge produced through a ballasted flocculation
process. The sludge and granular material from the ballasted flocculation process
are directed to a sludge separator where the sludge is separated from the granular
material. Thereafter the separated sludge is sent to a degassing area and the sludge
is degassed. A flocculating agent is mixed or injected into the sludge. The sludge
is directed to a sludge thickener with a load at a sill calculated on the surface
of the thickener greater than 200 kgMIS/m2/day. This process produces
a thickened sludge having a concentration greater than 10 gm/I.