A process for producing methane and/or high purity hydrogen from anaerobically decomposed organic materials as well as a methane and/or high purity hydrogen generation system that operates in accordance with this process, are provided. The inventive system, which is capable of delivering at least 40 slpm of the desired product gas or gases, is completely self-contained, requiring no outside sources of energy, and is made up of fewer components, thereby allowing for a reduced plant footprint, and a more cost-effective source of renewable methane and hydrogen.