Patent ID: 6712970
Filing Date: 2004-03-30
Classification: C02F,Y02W,Y10S

Abstract:
In a sewage treatment plant and process having a liquid side in which nitrogen removal is effected, a method of operating the liquid side of the treatment process so as additionally to remove phosphorus, comprising:(a) maintaining an aerobic/anoxic zone receiving plant influent wastewater, (b) maintaining dissolved oxygen concentration in the aerobic/anoxic zone in a fluctuating range, (c) with dissolved oxygen concentration toward the lower end of said range and tending to promote denitrification, monitoring the status of bacteria in the aerobic/anoxic zone and detecting when bacteria near the centers of flocs turn anaerobic, (d) allowing the anaerobic condition to develop in the flocs to a preselected extent and thereby causing phosphorus to be released into the liquid, then adding dissolved oxygen to the aerobic/anoxic zone to effect recovery of at least some of the bacteria from the anaerobic condition and causing uptake of phosphorus, as well as effecting nitrification, (e) then limiting dissolved oxygen to the aerobic/anoxic zone to an extent to allow the bacteria to consume the dissolved oxygen, (f) repeating steps (c) through (e), and (g) moving effluent from the aerobic/anoxic zone to an aerobic zone in which dissolved oxygen concentration is maintained in a higher range sufficient to enhance biological phosphorus uptake, whereby nitrification, denitrification, phosphorus release and some biological phosphorus uptake occur in the aerobic/anoxic zone, and further nitrification and biological phosphorus uptake are enhanced in the aerobic zone.