Abstract: An aqueous slurry containing dissolved solids and a high concentration of suspended solids is positioned as a mat between a pair of porous endless belts to provide a composite structure. The composite structure is moved through a treating zone and subjected to alternate stages of compression and relaxation. In a preferred mode, the compression and relaxation are achieved by passing the composite structure over a series of spaced rolls in a manner such that a first belt of the pair is in direct contact with one of the rolls and a second belt of the pair is in contact with the next adjacent roll. A liquid stream containing a high concentration of dissolved solids is cascaded over the mat in a countercurrent fashion, with the result that dissolved solids of the liquid stream are dissolved in the aqueous phase of the mat when the mat is subject to relaxation. The mat containing the increased concentration of dissolved solids and suspended solids can then be compacted and the solid residue can be landfilled.