NOVELTY - The method comprises collecting a crude landfill gas stream (14) including 45-55 mol.% of methane, 20-40 mol.% of carbon dioxide, oxygen, 5-20 mol.% of nitrogen, hydrogen sulfide gas, water vapor and volatile organic compounds, removing a portion of the hydrogen sulfide gas from the crude landfill gas stream, separating the crude landfill gas stream into an intermediate landfill gas stream (20) and a first waste gas stream (22) using a membrane separation unit (16), and separating the intermediate landfill gas stream into a final landfill gas stream (24) and a second waste gas stream.    USE - The method is useful for separating and purifying a landfill gas stream including methane, which is useful as an energy source or a feedstock for manufacturing hydrocarbon product.    ADVANTAGE - The method is capable of efficiently and economically separating and purifying the landfill gas stream with reduced power consumption thus minimizing the corrosive effects of hydrogen sulfide gas of the landfill gas stream.    DETAILED DESCRIPTION - The method comprises collecting a crude landfill gas stream (14) including 45-55 mol.% of methane, 20-40 mol.% of carbon dioxide, oxygen, 5-20 mol.% of nitrogen, hydrogen sulfide gas, water vapor and volatile organic compounds, removing a portion of the hydrogen sulfide gas from the crude landfill gas stream, separating the crude landfill gas stream into an intermediate landfill gas stream (20) and a first waste gas stream (22) using a membrane separation unit (16), separating the intermediate landfill gas stream into a final landfill gas stream (24) and a second waste gas stream using a pressure swing adsorption separation unit (18), collecting the first and second waste gas streams to provide a fuel composition, and delivering the fuel composition to a generator unit so that the fuel composition is used to produce electricity. The intermediate landfill gas stream is enriched in methane and depleted in carbon dioxide relative to the crude landfill gas stream. The first waste gas stream is enriched in carbon dioxide and depleted in methane relative to the crude landfill gas stream. The final landfill gas stream is enriched in methane and depleted in carbon dioxide, oxygen and nitrogen relative to the intermediate landfill gas stream, is provided to the fuel composition, and is depleted in oxygen, water vapor and volatile organic compounds relative to the crude landfill gas stream. The second waste gas stream is enriched in carbon dioxide, oxygen and nitrogen relative to the intermediate landfill gas stream. A portion of the crude landfill gas stream is separated into a first recycle gas stream using the membrane separation unit. The first recycle gas stream is provided to the fuel composition, and comprises 30-40 mol.% of the crude landfill gas stream. A portion of the intermediate landfill gas stream is separated into a second recycle gas stream using the pressure swing adsorption separation unit. The second recycle gas stream is provided to the fuel composition, and comprises 17-22 mol.% of the intermediate landfill gas stream. An INDEPENDENT CLAIM is included for a system for separating and purifying a landfill gas stream.    DESCRIPTION OF DRAWING(S) - The diagram shows a flowchart of a landfill gas purification system.    Crude landfill gas stream (14)    Membrane separation unit (16)    Pressure swing adsorption unit (18)    Intermediate landfill gas stream (20)    First waste gas stream (22)    Final landfill gas stream. (24)