NOVELTY - The method comprises collecting a raw biogas stream (2) including methane, carbon dioxide, water, hydrogen sulfide and non-methane organic compounds (NMOC), performing a raw biogas stream separation procedure in which the raw biogas stream is separated into a sulfur compounds stream and a main gas stream, where the sulfur compounds stream is removed from further processing and the main gas stream is purified from the hydrogen sulfide, and adsorbing a first NMOC liquid stream (9) from the main gas stream, where the NMOC liquid stream is removed from further processing.    USE - The method is useful for the separation and purification of methane from a biogas generating sources such as anaerobic digesters and landfills.    ADVANTAGE - The method ensures efficient separation and purification of the methane from the biogas generating sources without the creation of carbon dioxide gas streams thus providing purified methane stream interchangeable with natural gas.    DETAILED DESCRIPTION - The method comprises collecting a raw biogas stream (2) including methane, carbon dioxide, water, hydrogen sulfide and non-methane organic compounds (NMOC), performing a raw biogas stream separation procedure in which the raw biogas stream is separated into a sulfur compounds stream and a main gas stream, where the sulfur compounds stream is removed from further processing and the main gas stream is purified from the hydrogen sulfide, adsorbing a first NMOC liquid stream (9) from the main gas stream, where the NMOC liquid stream is removed from further processing and the main gas stream is purified from the NMOCs, performing a main gas stream separation procedure in which the main gas stream is separated into an off-gas stream composed of carbon dioxide, nitrogen and oxygen gas and a product stream composed of purified methane gas, performing an off-gas stream adsorbing procedure for forming a vent gas stream and a recycle stream, venting the vent gas stream into the atmosphere, and mixing the recycle stream with the main gas stream after the step of performing the raw biogas stream separation procedure and before the step of absorbing the first NMOC liquid stream. The step of performing the main gas stream separation procedure comprises producing a recycle stream and feeding the recycle stream into the main gas stream after the step of performing a raw biogas stream separation procedure and before the step of absorbing a first NMOC liquid stream. The NMOC absorbing step comprises absorbing the NMOC using a sponge solution, and thermodynamically regenerating the sponge solution as a function of a vapor point pressure of the NMOC stream and the sponge solution. The step of performing the off-gas stream adsorbing procedure comprises forcing the off-gas stream to come in contact with nanoporous and or microporous adsorbent materials selective for methane, NMOC and nonselective for carbon dioxide, oxygen and nitrogen. The raw biogas stream separation procedure further comprises capturing the hydrogen sulfide for removal from the raw biogas stream using a solid adsorption material, and oxidizing inorganic sulfur compounds, including hydrogen sulfide to elemental sulfur or sulfates for removal from the raw biogas stream, using aerobic bacteria action. The step of adsorbing the first NMOC liquid stream is performed by adhesion of molecules of the NMOCs to surfaces and pores of selective adsorbent materials. The method further comprises: absorbing a second NMOC liquid stream from the main gas stream prior to the step of performing a main gas stream separation procedure, where the second NMOC liquid stream is removed from further processing and the main gas stream is partially purified by removal of the absorbed non-methane organic compounds; regenerating the selective adsorbent materials by exposing the selective adsorbent materials to a carrier gas with temperature and pressure control to reverse adhesion of the NMOC molecules to the selective adsorbent materials for creating a mixed NMOC gas carrier stream; and condensing the NMOC out of the mixed NMOC gas carrier stream to form a NMOC liquid stream. An INDEPENDENT CLAIM is included for a system for methane separation and purification from a biogas stream.    DESCRIPTION OF DRAWING(S) - The diagram shows a block diagram of a system for methane separation and purification from biogas.    Raw biogas stream (2)    Sulfur adsorber unit (3)    Sulfur compound stream (4)    Gas effluent pipe (6)    NMOC absorption unit (7)    First non-methane organic compounds stream. (9)