NOVELTY - Treating waste oil comprises heating the raw waste oil to sequentially layer waste oil raw material into waste oil layer, oil-water-dreg three-phase mixture layer, waste water layer and sand precipitate layer; separating the waste oil layer into waste oil, waste water and dreg, and performing oil-water separation to the waste oil to obtain waste oil and waste water which can be used for preparing chemical raw materials or biofuel; collecting and filtering oil-water-dreg three-phase mixture layer to obtain a filtrate and residue; and carrying out centralized treatment on sand precipitate layer.    USE - The method is useful for treating waste oil (claimed).    ADVANTAGE - The method subjects the waste oil raw material to concentrated closed collection and transportation by utilizing a professional refuse collector, and thus secondary pollution to the pavement and environment can be avoided in the shipment process, and a waste edible oil finished product, and methane, biogas slurry organic fertilizer, boiler fuel and other finished products with economic values can be furthest extracted and separated regarding the ingredients of the waste oil raw material, so that the problem that waste edible oil is extracted into swill-cooked dirty oil by lawbreakers can be solved, high economic benefit can be generated, and the waste edible oil can be turned into wealth from waste.    DETAILED DESCRIPTION - Treating waste oil comprises: (i) heating the raw waste oil to sequentially layer waste oil raw material into waste oil layer, an oil-water-dreg three-phase mixture layer, a waste water layer and a sand precipitate layer due to the different density from top to bottom; and (ii) collecting and separating the waste oil layer into waste oil, waste water and dreg, and performing oil-water separation to the waste oil to obtain waste oil and waste water which can be used for preparing chemical raw materials or biofuel; (iii) collecting and filtering the oil-water-dreg three-phase mixture layer to obtain a filtrate and residue, and (a) mixing the filtrate with wood sawdust and stirring to form a mixture, (b) pressing the mixture to obtain squeezed sawdust bread and juice, (c) heating the juice, separating heated juice into waste oil, waste water and slag, and performing oil-water separation to the waste oil to obtain waste oil and waste water which can be used for preparing chemical raw materials or biofuel; (iv) collecting and treating the wastewater of step (ii) and (iii) with the waste water layer of step (i); (v) processing the pressed cake and slag of step (iii) with slag of step (i) and (ii); and (vi) carrying out centralized treatment of the sand precipitate layer.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the waste oil treating device.    Box body (1)    Centrifuge (2)    Waste oil separator (3)    Biogas digester (4)    Boiler (5)