Abstract: A system and a process for producing methane gas by anaerobic digestion of feed materials containing suitable organic materials. The system includes a plurality of digestion modules arranged primarily in series. Each digestion module is positioned with its slurry inlet port at a slightly lower elevation than the slurry outlet port of the preceding digestion module. The number of digestion modules is dependent upon the particular feed material to be digested. Each digestion module can be sampled and controlled independently. The process includes grinding and pulping the feed material, mixing the feed material with a liquid to prepare a slurry, charging the initial digestion module with slurry and transferring the digesting slurry to the next successive digestion module and subsequently to each successive digestion module after predetermined time periods until the digestion process has been completed. The liquid is separated from the digested slurry for recycle through the system.

Abstract: A compact vertical array of concentrically stacked and interfaced anaerobic digestion modules which comprise an anaerobic digestion sub-system. Each individual digestion module is an open-ended reaction vessel having an external flange on each end. Each pair of adjacent reaction vessels has a suitably sloped plate positioned at their interface and fastened to the bottom flange of the upper vessel and the top flange of the lower vessel. In this manner, each plate creates two individual digestion modules by serving as a bottom for the reaction vessel immediately above it and as a top for the reaction vessel immediately below it. Suitable openings are provided between adjacent digestion modules for transfer of digesting slurry from the module above to the module below. Each such opening is provided with a suitable valve for closing the opening during normal anaerobic digestion operations.