NOVELTY - System comprises a bioreactor vessel (20) for receiving a volume of feedstock, a fluid circulation system (40) for recirculating waste fluids through the feedstock, a biogas collection system for collecting biogas generated by the feedstock, and an aeration system for aerating the feedstock. The bioreactor vessel: comprises an elongated plastic bag (22) having a sealed first end extending to a sealed second end and at least one ventilation port; and defines a plenum (28) for collecting biogas generated by the feedstock. The volume of feedstock has an upper portion opposite a ground side.    USE - The system is useful for the anaerobic digestion of organic material to biogas and post-digested fiber (claimed).    DETAILED DESCRIPTION - System comprises a bioreactor vessel for receiving a volume of feedstock, a fluid circulation system for recirculating waste fluids through the feedstock, a biogas collection system for collecting biogas generated by the feedstock, and an aeration system for aerating the feedstock. The bioreactor vessel: comprises an elongated plastic bag having a sealed first end extending to a sealed second end, and at least one ventilation port; and defines a plenum for collecting biogas generated by the feedstock. The volume of feedstock has an upper portion opposite a ground side. The fluid circulation system: comprises a collection reservoir for collecting waste fluid draining from the volume of feedstock; and further comprises a pump fluidly connected to the collection reservoir. The pump is used for pumping collected waste fluid to the upper portion of the feedstock. The biogas collection system comprises a collection conduit within the plenum. The collection conduit is fluidly connected with a biogas storage system. The aeration system: comprises at least one ventilation conduit extending below at least a portion of the volume of feedstock in the bioreactor vessel; and further comprises a blower fluidly connected to the ventilation conduit. The blower is used for supplying a ventilation airflow stream to the ventilation conduit. The ventilation airflow stream blows through the feedstock and out the ventilation port. An INDEPENDENT CLAIM is included for a method for the anaerobic digestion of organic material to biogas and post-digested fiber, comprising inserting the ventilation conduit into the bioreactor vessel comprising an elongated plastic bag, inserting the feedstock having a fiber into the elongated plastic bag on a top of the ventilation conduit, sealing the feedstock within the bioreactor vessel in a first stage, collecting waste fluid draining from the feedstock, spraying collected waste fluid onto the upper portion of the feedstock, collecting biogas generated by the feedstock in a second stage, opening at least one vent in the elongated plastic bag, supplying an airflow to the ventilation conduit, aerating the feedstock through use of the airflow to create a post-digested fiber, and removing the post-digested fiber from the elongated plastic bag.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a system for the anaerobic digestion of organic material to biogas and post-digested fiber.    Bioreactor vessel (20)    Bag (22)    Plenum (28)    Ventilation port (30)    Fluid circulation system. (40)