METHOD FOR TREATING A WASTE STREAM IN AN ANAEROBIC MEMBRANE BIOREACTOR

摘要

A waste stream having anaerobically biodegradable components is fed to an anaerobic reactor where the components react with microorganisms to biodegrade the components and produce biomass and biogas. Mixing occurs in select portions of the anaerobic reactor, particularly the bottom and top portions of the reactor. Relatively heavy solids settle to the bottom and are mixed with the mixed liquor while relatively light or fine solids float to the top portion of the anaerobic reactor where they are mixed with the mixed liquor. This leaves an intermediate or middle portion of the anaerobic reactor where the concentration of solids is relatively lower compared to the concentration of solids in the upper or lower portion of the anaerobic reactor. Mixed liquor is pumped from the intermediate portion of the anaerobic reactor to a membrane separation unit where the mixed liquor is separated into a permeate stream and a retentate stream that is concentrated with solids. The retentate stream is recycled back to the anaerobic reactor and mixed with the mixed liquor therein. Further, mixed liquor and the relatively heavy solids are pumped from the bottom of the anaerobic reactor to a solids separator such as a hydrocyclone. Here the mixed liquor and solids are separated into a stream concentrated with heavier solids including a high percentage of inorganic precipitants and a lighter solids stream that contains a high percentage of biomass. This lighter solids liquid stream containing mixed liquor is recycled back to the anaerobic reactor for further treatment while the solid stream can be directed to a dewatering unit.