A three phase fluidized bed water purifying process comprises purifying effluents in a three phase fluidized bed (1) composed of solid particles (4), an effluent, and a gas (13) in fluidized state, the solid particles being made by mixing a binder with an inorganic material based on aluminium silicate, granulating the resulting mixture, and firing the granules to sinter them. Such a process permits the purification of effluent for a long period of time without oxygen deficiency.