METHOD AND PLANT FOR PROCESSING WATER BY BALLASTED FLOCCULATION AND DEPOSITION

The invention relates to a method for processing water in a plant that comprises the steps of contact water, a ballast and a flocculation agent in a flocculation area (1) for forming a flocculate, introducing the mixture thus formed into a deposition area (11), separating the processes water, extracting the sludge and ballast mixture in the lower portion of the deposition area (1) and feeding it to an agitation area for intermediate mixture (19), extracting the sludge and ballast mixture present therein (19) an submitting it to a sludge/ballast separation step (26) by hydro-cycloning, recycling the underflow in the flocculation area (1) extracting a portion of the sludge for the underflow and recirculating the other portion into the intermediate area (19), characterised in that it comprises the step of continuously measuring at least one parameter representative of the impurity concentration in the water before or during its entry in the flocculation area, and the step of using the results of the measurement thus made in order to continuously derive the ballast amount to be used in order to obtain processed water having a predetermined quality.