THICKENING

Thickening is the process by which the water in excess is eliminated, the volumes are reduced and the solid phase of sludge becomes homogeneous. The sludge extracted from the hoppers of the primary and secondary sedimentation tanks is thickened by gravity in a circular basin equipped with a scraping system and thickening pickets.
While rotating inside the tank, the pickets connected to the arms disgregate the sludge flocs, supporting the elimination of water and gas from sludge, and so its sedimentation. Given the long period of permanence, it is possible that the sludge produces some surface crusts.
To break the surface crusts some “counter pickets” are installed on the bridge over the tank. The liquid phase of sludge is evacuated by means of surface weirs and is conveyed to the head of the plant with the drained water, while the bottom scrapers convey the thickened sludge into the central drain well.