NOVELTY - The process comprises filling enclosure with the wastes, and anaerobic degrading of wastes in filled enclosure, during which methane is produced. During the filling step, a large enclosure (1) and a small enclosure (2) are filled respectively of low organic wastes and highly organic wastes. The large enclosure has a volume capacity of 25 times greater than the volume capacity of the small enclosure. The low organic wastes have organic filler lower than the highly organic wastes, which are degradable in less than three years.    USE - The process is useful for treating wastes and producing methane, where the wastes are low organic wastes such as household garbage and/or general industrial wastes, and highly organic wastes such as solid, sludge of urban waste water treatment plant, a fermentable fraction of household wastes, organic wastes from waste treatment of food waste, garden waste, agro-food industry waste and agricultural residues.    ADVANTAGE - The process ensures simple and rapid treatment of wastes and efficient production of methane.    DETAILED DESCRIPTION - The process comprises filling enclosure with the wastes, and anaerobic degrading of wastes in filled enclosure, during which methane is produced. During the filling step, a large enclosure (1) and a small enclosure (2) are filled respectively of low organic wastes and highly organic wastes. The large enclosure has a volume capacity of 25 times greater than the volume capacity of the small enclosure. The low organic wastes have organic filler lower than the highly organic wastes, which are degradable in less than three years. During the degrading step, a liquid fraction generated in the large enclosure is introduced in the small enclosure. The liquid fraction generated in the small enclosure is introduced in the large enclosure. The filling step is not preceded by any mechanical treatment of wastes. The process further comprises digging of degraded wastes of the small enclosure, an inoculation operation for introducing microorganisms, fungi and/or enzymes in the small enclosure and/or the large enclosure for anaerobic degradation of wastes. A small enclosure (3) in liquid medium is continuously or intermittently filled with highly organic liquid wastes. The large enclosure is a bin for installation of non-hazardous waste storage, and an operation of pre-treatment consisting of treating the generated liquid fractions in the large enclosure, the small enclosure and in the enclosure (3) before introduced into any of these enclosures, by heat treatment, nitrification, and by adding buffer, micro-organisms, enzymes and/or fungi. The large enclosure has a volume capacity of 25 times the volume capacity of the enclosure (3), and in which the liquid fraction generated in the large enclosure and/or the small enclosure is introduced in the enclosure (3). An INDEPENDENT CLAIM is included for an installation for treating wastes and producing methane.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of an installation for treating wastes and producing methane.    Large enclosure (1)    Small enclosures (2, 3)    Flow. (4, 5, 6, 7, 8, 9, 10, 11)