A method for the treatment and filtration of fluids, i.e. liquid effluents such as raw water containing organic pollutants in a solution, using gravity separation means (10) such as a decantation and flotation means, and membrane separation means (13) in a finishing stage, wherein a first pulverulent reagent (1) is introduced into the flow of a fluid to be treated upstream from gravity separation, and a second pulverulent reagent (2) is introduced downstream from the membrane separation. The inventive method is characterized in that the coagulant required for separation is injected before the first pulverulent reagent; in that the first and second pulverulent reagents (1,2) have different characteristics, i.e. in terms of granulometry, adsorption capacity adapted to the pollutants which are to be eliminated; and in that the second pulverulent reagent (2) is recycled from membrane separation means (13) upstream from the gravity separation means (10).