Patent ID: 7147778

Claim:
A process of nitrifying and denitrifying wastewater and reducing or minimizing the DO concentration in a denitrification zone of a nitrification/denitrification system that includes an aerobic reactor having one or more immersed membranes contained therein comprising: a. alternatively directing a wastewater influent into first and second zones; b. at various times during the process maintaining the first zone as a nitrification zone and maintaining the second zone as a denitrification zone, and at various other times, maintaining the first zone at a denitrification zone and the second zone as a nitrification zone; c. directing wastewater from either of the first or second zones to the downstream aerobic reactor having the one or more immersed membranes therein; d. aerating the aerobic reactor; e. directing wastewater in the aerobic reactor into the one or more immersed membranes and separating the wastewater into a permeate and return activated sludge; f. pumping the permeate from the one or more immersed membranes in the aerobic reactor; g. returning activated sludge from the aerobic reactor to either of the first or second zones; and h. during the process reducing or minimizing the DO concentration in the denitrification zones by selectively directing the return activated sludge to one of the first or second zones being maintained as a nitrification zone and switching the flow of the return activated sludge during the process between the first and second zones so as to direct the return activated sludge to the first or second zone being maintained as the nitrification zone.