NOVELTY - Treating waste stream involves reacting biodegradable components with anaerobic biomass in anaerobic reactor (12); stratifying mixed liquor in anaerobic reactor by forming a lower mixed liquor zone where mixed liquor in a lower mixed liquor zone includes a relatively high concentration of solids, and forming second mixed liquor zone above the lower mixed liquor zone; directing mixed liquor from second mixed liquor zone in anaerobic reactor to membrane separation unit (14) and separating mixed liquor into apermeate stream and retentate stream concentrated with biomass.    USE - For treating a waste stream having anaerobically biodegradable components (claimed) e.g. total solids including soluble and insoluble chemical oxygen demand.    ADVANTAGE - The anaerobic membrane bioreactor is a compact purification system combining an anaerobic digestion process with a membrane separation process. The system is effective to treat waste streams having biodegradable constituents or components by digesting these constituents and producing biogas and new biomass. By stratifying the mixed liquor in the reactor, a higher concentration of solids is maintained in the reactor while supplying a less concentrated stream to the membrane separation unit. This prevents or reduces membrane fouling and enhances the highest possible membrane flux rates per unit of membrane system energy input and in turn prolongs the life of the membranes that comprise the membrane separation unit by minimizing the number of clean in place (CIP) cycles.    DETAILED DESCRIPTION - Treating a waste stream having anaerobically biodegradable components involves feeding the waste stream having anaerobically biodegradable components into an anaerobic reactor (12); reacting biodegradable components with anaerobic biomass in anaerobic reactor to reduce the amount of biodegradable components and in the process produce biomass and biogas; stratifying mixed liquor in anaerobic reactor by forming a first lower mixed liquor zone where mixed liquor in first lower mixed liquor zone includes a relatively high concentration of solids, and forming a second mixed liquor zone above first lower mixed liquor zone where the mixed liquor in second zone includes a solids concentration less than concentration of solids in the mixed liquor in the first lower mixed liquor zone; directing mixed liquor from second mixed liquor zone in anaerobic reactor to a membrane separation unit (14) and separating mixed liquor into a permeate stream and a retentate stream concentrated with biomass; recycling at least a portion of retentate stream to anaerobic reactor and mixing retentate stream with mixed liquor in the reactor; directing the mixed liquor and solids from first lower mixed liquor zone to a solids separator and separating mixed liquor and solids from the first lower mixed liquor zone into a heavier solids stream and a lighter solids stream containing biomass; and recycling at least a portion of the lighter solids stream containing biomass from the solids separator to anaerobic reactor and mixing the lighter solids stream with the mixed liquor in anaerobic reactor. An INDEPENDENT CLAIM is included for anaerobic membrane bioreactor for anaerobically biodegrading components in a waste stream, comprising an anaerobic reactor having an inlet for permitting the waste stream having anaerobicaily biodegradable components to be directed into the anaerobic reactor resulting in the reaction of the biodegradable components with anaerobic biomass in the reactor to reduce the amount of biodegradable components and produce biomass and biogas in the anaerobic reactor; first mixers for providing a mixing action in a lower portion of the anaerobic reactor and mixing the mixed liquor and relatively heavy solids in the bottom of the anaerobic reactor; second mixers for providing a mixing action in an upper portion of the anaerobic reactor and mixing the mixed liquor and relatively light solids in the upper portion of the anaerobic reactor such that mixed liquor in an intermediate portion of the anaerobic reactor includes a relatively lower concentration of solids and biomass; first pump for pumping mixed liquor from the intermediate portion of anaerobic reactor to a membrane separation unit and separating mixed liquor into a permeate stream and a retentate stream concentrated with the biomass; first recycle line for recycling the retentate stream to the anaerobic reactor and mixing retentate stream with mixed liquor in the anaerobic reactor; second pump for pumping mixed liquor and at least some of the relatively heavy solids from the bottom portion of the anaerobic reactor to a solids separator and separating the relatively heavy solids into two streams, a first stream including relatively heavy solids and a second stream including relatively lighter solids; and g. a second recycle line for recycling at least a portion of the second stream to anaerobic reactor and mixing second stream with the mixed liquor in anaerobic reactor, where the solids separator includes a hydro cyclone.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of anaerobic membrane bioreactor.    Anaerobic membrane bioreactor (10)    Anaerobic reactor (12)    Membrane separation unit (14)    Equalization tank (16)    Mixing tank (18)    Chemical injectors (20)    Reactor feed pump (22)    Heat exchanger (24)