Patent ID: 6946073

Claim:
A method for removal of biological nutrients from a wastewater yielding a low phosphorous output comprising: a) providing a serial multistage bioreactor containing activated sludge comprising in hydraulic series an anaerobic zone, an upstream aerobic zone, a downstream aerobic zone and an immersed membrane filter operatively associated with the downstream aerobic zone, each zone having an upstream inlet and a downstream outlet; b) providing a wastewater to the anaerobic zone inlet; c) adding a quantity of chemical to precipitate soluble and particulate phosphorous in an amount sufficient to yield a low phosphorous output downstream of the upstream aerobic zone and upstream of the immersed membrane filter; d) separating treated water from the activated sludge and precipitated phosphorous by the immersed membrane filter; and e) recycling return activated sludge separated by the immersed membrane filter from treated water to the anaerobic zone.