Patent ID: 6517723
Filing Date: 2003-02-11
Classification: C02F,Y02W

Abstract:
A method for removal of biological nutrients from a wastewater, comprising:providing a serial multistage bioreactor containing activated sludge having in hydraulic series an anaerobic zone, an upstream anoxic zone, an upstream aerobic zone, a downstream anoxic zone and a downstream aerobic zone, each zone having an upstream inlet and a downstream outlet; providing wastewater to the anaerobic zone inlet; filtering treated water from the activated sludge in the downstream aerobic zone through an immersed membrane filter; purging solids from the immersed membrane filter with an oxygen containing purge gas; recycling return activated sludge charged with oxygen associated with the oxygen containing purge gas from the downstream aerobic zone to near the inlet of the upstream aerobic zone; recycling a nitrogen rich recycle from near the upstream aerobic zone outlet to near the upstream anoxic zone inlet; and recycling a de-nitrified mixed liquor from near the upstream anoxic zone outlet to near the anaerobic zone inlet.