Abstract: An anaerobic waste treatment facility for producing methane gas or the like during anaerobic digestion of organic material. A digestor has a flexible cover therefor and apparatus associated therewith for removing evolved gases collected under the flexible cover at controlled rates. The flexible cover may assume an inflated, partially deflated, or completely deflated position. The digestor has an inlet, mixing zone, quiescent zone, clear zone, and an outlet. Liquid from the clear zone may be withdrawn and returned to pop-up rotary mixing apparatus in the mixing zone. A loading system for the digestor may comprise -- in addition to a raw sewage inlet -- a loading structure for receiving municipal garbage and the like. Apparatus is provided in the loading structure for substantially preventing the passage of non-digestible materials into the digestor, while allowing the passage of digestible materials entrained with liquid in the loading structure into the digestor.