Removal of phosphates and BOD from wastewaters

Claim 1

In an activated biomass process wherein recycled activated biomass is (1) initially admixed with a phosphate- and BOD-containing wastewater influent to form a mixed liquor under anaerobic conditions effecting selective production of microorganisms capable of sorbing BOD under both anaerobic and oxidizing conditions, followed by (2) subjecting the mixed liquor to contact with oxygen-containing gas under oxic treating conditions effecting accumulation of phosphates in solid biomass component, and (3) subsequently separating the thus oxidized mixed liquor into supernatant liquid and biomass, a portion of which biomass is returned to said admixture with the wastewater influent to provide the aforesaid activated biomass; the improvement which comprises: maintaining the mixed liquor in contact with oxygen-containing gas under said oxic conditions for a time sufficient to cause sorption of BOD and P from the surrounding liquor, but less than that required to effect 40% oxidation of the sorbed BOD, and separately subjecting at least part of the recycled portion of the biomass to further oxidation by contact high oxygen-containing gas prior to admixture of said recycled biomass with the wastewater influent, such that any bleed back of phosphorus from the sludge to the liquor is reversed during the separate oxidation and at least 50% of the total soluble and insoluble BOD is removed in the overall process.