Abstract: A method for removing contaminants from a natural gas stream such as a biogas/landfill gas stream. The natural gas stream is fed to a first adsorption unit for removal of certain contaminants and then to a second adsorption unit for the removal of additional contaminants. Alternatively, a membrane stage may be employed between the adsorption units. The method utilizes the external purge to enhance pressure swing adsorption working capacity so that the vacuum level required for regeneration is not as high.