Patent ID: 7481933

Claim:
A process for treating BOD, nitrogen and phosphorus containing wastewater, the process comprising: providing wastewater influent into an anaerobic zone having activated sludge; mixing the wastewater influent with the activated sludge in the anaerobic zone to form a first mixed liquor; providing the first mixed liquor into an oxygen-deficit aeration zone; mixing the first mixed liquor with activated sludge in the oxygen-deficit aeration zone to form a denitrified mixed liquor; recycling a portion of the denitrified mixed liquor from the oxygen-deficit aeration zone to the anaerobic zone for mixing therein with the wastewater influent; transferring the denitrified mixed liquor from the oxygen-deficit aeration zone to an oxygen-surplus aeration zone; mixing the denitrified mixed liquor with activated sludge in the oxygen-surplus aeration zone to form a third mixed liquor; transferring a portion of the third mixed liquor from the oxygen-surplus aeration zone to a membrane bioreactor wherein a filtrate is separated from a sludge; providing oxygen to the membrane bioreactor; introducing oxygen provided to the membrane bioreactor into the sludge to form an activated sludge with a dissolved oxygen level of between about 4 mg/L and about 8 mg/L; and recycling at least a portion of the activated sludge to the oxygen-deficit aeration zone.