Anaerobic digester-membrane bioreactor for treating a waste stream

An anaerobic membrane bioreactor for anaerobically biodegrading components in a waste stream, comprising:

• a. an anaerobic reactor having an inlet for permitting the waste stream having anaerobically 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;
• b. one or more 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;
• c. one or more 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;
• d. a first pump for pumping mixed liquor from the intermediate portion of the anaerobic reactor to a membrane separation unit and separating the mixed liquor into a permeate stream and a retentate stream concentrated with the biomass;
• e. a first recycle line for recycling the retentate stream to the anaerobic reactor and mixing the retentate stream with mixed liquor in the anaerobic reactor;
• f. a 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
• a second recycle line for recycling at least a portion of the second stream to the anaerobic reactor and mixing the second stream with the mixed liquor in the anaerobic reactor.

A method of treating a waste stream having anaerobically biodegradable components, comprising:

• a. feeding the waste stream having the anaerobically biodegradable components into an anaerobic reactor;
• b. reacting the biodegradable components with anaerobic biomass in the anaerobic reactor to reduce the amount of biodegradable components and in the process produce biomass and biogas;
• c. stratifying the mixed liquor in the anaerobic reactor by forming a first lower mixed liquor zone where the mixed liquor in the first lower mixed liquor zone includes a relatively high concentration of solids, and forming a second mixed liquor zone above the first lower mixed liquor zone where the mixed liquor in the second zone includes a solids concentration substantially less than the concentration of solids in the mixed liquor in the first lower mixed liquor zone;
• d. directing mixed liquor from the second mixed liquor zone in the anaerobic reactor to a membrane separation unit and separating the mixed liquor into a permeate stream and a retentate stream concentrated with biomass;
• e. recycling at least a portion of the retentate stream to the anaerobic reactor and mixing the retentate stream with mixed liquor in the reactor;
• f. directing the mixed liquor and solids from the first lower mixed liquor zone to a solids separator and separating the mixed liquor and solids from the first lower mixed liquor zone into a heavier solids stream and a lighter solids stream containing biomass;
• and
• g. recycling at least a portion of the lighter solids stream containing biomass from the solids separator to the anaerobic reactor and mixing the lighter solids stream with the mixed liquor in the anaerobic reactor.

A method of treating a waste stream having anaerobically biodegradable components, comprising:

• a. feeding a waste stream having the anaerobically biodegradable components into an anaerobic reactor;
• b. reacting the biodegradable components with anaerobic biomass in the anaerobic reactor to reduce the amount of biodegradable components and in the process produce biomass and biogas;
• c. stratifying the mixed liquor in the anaerobic reactor into three mixed liquor zones by forming a first lower mixed liquor zone where the mixed liquor in the first lower mixed liquor zone includes relatively heavy solids, forming a second mixed liquor zone above the first lower mixed liquor zone where the mixed liquor in the second mixed liquor zone includes a solids concentration substantially less than the concentration of solids in the first lower mixed liquor zone, and forming a third mixed liquor zone over the second mixed liquor zone where the third mixed liquor zone includes relatively light solids;
• d. directing mixed liquor from the second mixed liquor zone in the anaerobic reactor to a membrane separation unit and separating the mixed liquor into a permeate stream and a retentate stream;
• and
• e. recycling at least a portion of the retentate stream to the anaerobic reactor and mixing the retentate stream with the mixed liquor in the reactor.

A method of treating a stream containing soluble and insoluble COD in an anaerobic membrane bioreactor, the method comprising:

• a. feeding the stream having soluble and insoluble COD into an anaerobic reactor;
• b. reacting the soluble and insoluble COD with anaerobic biomass in the anaerobic reactor to reduce the amount of soluble and insoluble COD and in the process produce a mixed liquor and biogas in the anaerobic reactor;
• c. providing a mixing action in a lower portion of the anaerobic reactor to mix the relatively heavy solids in the mixed liquor;
• d. providing a mixing action in an upper portion of the anaerobic reactor to mix the relatively light solids in the mixed liquor:
• e. wherein in an intermediate portion of the anaerobic reactor a relatively lower concentration of solids in mixed liquor is present;
• f. pumping the mixed liquor from the intermediate portion of the anaerobic reactor to a membrane separation unit and separating the mixed liquor into a permeate stream and a retentate stream which substantially contains the concentrated biomass;
• g. recycling at least a portion of the retentate stream to the anaerobic reactor and;
• h. pumping mixed liquor with the relatively heavy solids from the bottom portion of the anaerobic reactor to a solids separator, and separating the heavier solids from the lighter solids containing biomass;
• and
• i. recycling at least a portion of the lighter solids containing the biomass to the anaerobic reactor.