Abstract: A multi-stage process for the digestion or conversion of organic matter includes supplying organic material-containing liquid (with or without solid) feed stock mixture to an inlet port in a multi-stage reactor vessel and causing micro organic or catalytic agents to digest or otherwise convert the organic matter within the interior of the reactor vessel to form liquid and/or gaseous by-product(s). The reactor includes an outer body portion defining an internal chamber and an inner rotatable rotor assembly. The rotor assembly has at least two plate members placed about a common central axis and constructed to divide the chamber into a series of three or more compartments, each compartment being bounded by a pair of oppositely located plate members or by a plate member and an end of the vessel.