Abstract: A method for treating a spent emulsion of oil in water used in an industrial process, in particular an emulsion of cutting oil in water is described.The method comprises at least one stage in which heat energy is supplied continuously to said emulsion for evaporating a predetermined quantity of the water contained therein and to raise the concentration of said oil in the emulsion to a value such as to enable this latter to be burnt in an industrial burner, said heat energy being at least partly provided by utilizing solar energy, and further comprises at least one stage of burning the emulsion of said oil concentration in a burner in an industrial or heating plant.