Abstract: The method and system for methane separation and purification from a biogas includes collecting a raw Biogas gas stream having methane, carbon dioxide, water, sulfur compounds and non-methane organic compound (NMOC) constituents. The Biogas stream is fed into the intake of a liquid sulfur scrubber or a sulfur adsorber unit where the Biogas is separated into a main gas stream routed downstream in the system and a sulfur compounds stream removed from the system. The main gas stream is then processed by an NMOC absorber and further downstream, by an NMOC adsorber. NMOC produced by both NMOC processes is liquefied, removed from the system and stored. Upstream from the NMOC processes, the main gas stream is processed by at least one CO2, N2, O2 gas separation unit that produces a usable product stream of enriched methane gas, and an off-gas stream, which a VPSAU processes for venting and recycling.