Abstract: The present invention relates to a method of treating alkaline waste water originating from washing spent oil which has undergone an alkaline treatment with water and which contains organic material. This method can produce water which can be discharged into conventional industrial water treatment facilities or which can be used directly as a base for preparing fertilizers or for preparing an agent for preventing ice formation on road surfaces.

Abstract: An alkaline treatment method for refining used oils, wherein (a) the used oils are distilled; (b) the resulting distillate is treated with an alkaline agent in the presence of a solvent selected from water, a monoalcohol, a polyalcohol and a mixture of said a alcohols, said alkaline agent being present in a percentage by weight, based on the weight of the distillate, equal to the product F.times.(IA+IS), where F is a multiplier between 2 and 50 and IA and IS are the acid value and the saponification value respectively of said distillate, at a temperatue of around 80-330.degree. C. for 2-200 minutes; (c) the reaction medium is washed with water then decanted to recover the oily phase; and (d) said oily phase is distilled. The method is useful for producing refined oils having excellent properties in that they are odorless and nearly colorless and in that they have a very low chlorine, phosphorus and sillicon content.