Method for treating fluids containing amounts of tramp oil comprising the steps of placing a treatment unit (20, 20') inside a volume of fluid to be treated, which treatment unit (20, 20') comprises a UV radiation member capable of emitting. UV radiation, radiating said volume of fluid with UV radiation, whereby said UV radiation is capable of creating radicals in said fluid, which radicals react with said tramp oil for causing it to polymerise and coagulate, rendering it easily separated from the cutting fluid.
