The present disclosure provides a method for separating and purifying a landfill gas stream. In one embodiment, the method includes a step of collecting a crude landfill gas stream which includes at least methane, carbon dioxide, oxygen, and nitrogen gases. The method also includes a step of separating the crude landfill gas stream into at least an intermediate landfill gas stream and a first waste gas stream using a membrane separation unit, wherein the intermediate landfill gas stream is enriched in methane and depleted in carbon dioxide relative to the crude landfill gas stream. The method further includes a step of separating the intermediate landfill gas stream into at least a final landfill gas stream and a second waste gas stream using a pressure swing adsorption separation unit, wherein the final landfill gas stream is enriched in methane and depleted in carbon dioxide, oxygen, and nitrogen relative to the intermediate landfill gas stream. The first and second waste gas streams are collected to form a fuel composition and the fuel composition is delivered to a generator unit so that the fuel composition may be used to produce electricity.