Method for treating water by ballasted flocculation implementing a flocculent of natural origin

Method for treating water by ballasted flocculation comprising a step for injecting into said water at least a flocculent, a step for injecting into said water at least one particulate material that is denser than water, and a step for retrieving treated water, characterised in that said ballasted flocculation is performed under agitating at a mean speed gradient between 100 and 1400 s-1 and in that said flocculent consists of at least one carbohydrate polymer that is natural carbohydrate polymer having been functionalised by the addition of anionic groups or having groups which are or can be made anionic and having an anionic charge density between -900 and -4000 µeq/g.