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Abstract

There is disclosed an activated sludge wastewater treatment process which comprises aerating a mixed liquor comprising phosphate-containing influent wastewater and activated sludge in an aeration or high-purity oxygen zone to reduce the BOD/COD content of the wastewater and to cause the microorganisms present to take up phosphate. A phosphate-enriched sludge in which the phosphorus is present primarily in the sludge solids is separated from the mixed liquor to provide a substantially phosphate-free effluent. At least a portion of said phosphate-enriched sludge is passed to a phosphate pre-stripping zone, either in a separate tank or within the phosphate stripper tank itself, where BOD/COD-containing water, or feedwater, containing at least 50 mg/L of BOD, is added to poise the sludge organisms to begin enhanced rapid release of dissolved phosphate by pre-stripping it from the sludge or poising the sludge for rapid, enhanced release of phosphate. Then, the sludge is passed to a phosphate stripping zone. In the phosphate stripping zone, the sludge settles to form a supernatant liquor in the stripping zone upper section and settled sludge in the stripping zone lower section. The settled sludge is maintained under anaerobic conditions for a time sufficient to complete the release of the desired amount of phosphate from the sludge solids to the liquid phase of said settled sludge. At least a portion of the anaerobic sludge from the phosphate stripping zone is recycled to the aeration or high-purity oxygen zone as activatd sludge. The phosphate-rich supernatant from the phosphate stripping zone may be applied directly to land, or treated with a chemical precipitating agent to precipitate the phosphate therefrom and the precipitated phosphate may then be removed through the use of a reactor/clarifier, primary or secondary clarifier or other tankage, thus preparing the phosphate for final disposal directly or as fresh, digested or otherwise treated sludge.

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First Claim