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Control of activated sludge wastewater treating process for enhanced phosphorous removal

  • US 4,271,026 A
  • Filed: 10/09/1979
  • Issued: 06/02/1981
  • Est. Priority Date: 10/09/1979
  • Status: Expired due to Term
First Claim
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1. In an activated biomass process which inhibits the proliferation of filamentous biomass and effects the storage of phosphates in the biomass by first mixing recycled activated biomass with a phosphate- and BOD-containing influent to form a mixed liquor having both liquid and solid components and initially treating the mixed liquor under anaerobic conditions such as to be substantially free of oxygen and oxidizing agents and to contain a concentration of less than about 0.7 ppm dissolved oxygen;

  • thereby effecting selective production of nonfilamentous microorganisms capable of sorbing BOD under both anaerobic and oxidizing conditions and capable of accumulating phsophates under oxidizing conditions;

    subjecting the anaerobically treated mixed liquor to a subsequent oxygenating treatment by contact with oxygen-containing gas admitted to said treatment under oxic conditions such as to have maintained in the treatment a dissolved oxygen content of at least about 1 ppm to oxidize BOD in the mixed liquor to cause further removal of BOD from the liquid component and to cause accumulation of phosphates in the solid biomass component;

    subsequently separating the oxically treated mixed liquor into supernatant liquid and biomass; and

    returning a portion of the separated biomass to an initial anaerobic treatment to provide the activated biomass admixed therein with the influent;

    the improvement which comprises maintaning within the process system encompassing the initial anaerobic treatment and extending through the process up to, but not including, the separating step and including any internal recycle streams, a BOD5 to phosphorous (BOD/P) ratio from about 5;

    1 up to about 50;

    1, wherein BOD5 is expressed as milligrams of soluble BOD5, exclusive of BOD attributable to ammonia, per liter of influent and P is soluble phosphate expressed as milligrams of elemental phosphorous per liter of influent, and a food to biomass (F/M) ratio from about 0.09 up to an upper limit of about 1.4 wherein F is the total weight of soluble BOD5 introduced into the process per 24 hour day, and M is the weight of volatile suspended solids in the process system.

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