Anaerobicoxic Ao Process

Part a in Figure 7.38.4 is a schematic representation of the A/O process. The unique feature of this aerobic (oxic) activated-sludge process is an anaerobic (both oxygen- and nitrate-deficient) zone at the influent end of this process. The anaerobic and aerobic zones are each divided into several equally sized compartments. Influent wastewater and return activated sludge (RAS) are fed to the first compartment of the anaerobic zone. Typically, either centrally mounted or submersible mixers provide gentle mixing in the anaerobic zone. Wastewater treatment facilities can use various aeration methods, such as fine-bubble diffusers, surface mechanical aerators, and oxygen aeration to meet the oxygen demands in the oxic zone.

The A/O process is a high-rate process characterized by low hydraulic detention times (2.5-3.5 hr) and high F/M ratios (0.5-0.9 1/day). Wastewater treatment facilities can adapt this process for simultaneous phosphorus removal and nitrification by simply adjusting for the aerobic sludge age. Depending on climatic conditions and influent characteristics, especially influent TSS, the hydraulic detention time in the oxic zone can range from 4.0 to 8.0 hr, while the anaerobic detention time remains approximately 1 hr. More than sixty plants in the United States have used this process configuration. Figure 7.38.5 shows the operating and performance data of the North Plant at Titusville, Florida (no nitrification required), while Figure 7.38.6 shows the operating data at a plant in Lancaster,

Pennsylvania (nitrification using pure oxygen aeration).

Even though simultaneous phosphorus and nitrogen removal has been successful, excessive nitrate concentrations in the RAS stream are a concern in the anaerobic zone. Therefore, environmental engineers recommend a modified basin configuration (see Part b in Figure 7.38.4). This process removes the nitrate in the return sludge before it is mixed in the anaerobic zone.

A. A/O Process Influent

B. Modified A/O Process

Waste Activated Sludge

A. A/O Process Influent

B. Modified A/O Process

Waste Activated Sludge

Primary Clarifier

Primary Clarifier

To Digester Fermente Anaerobic

(Sludge Nitrification)

C. OWASA Process

Influent

To Digester Fermente Anaerobic

(Sludge Nitrification)

C. OWASA Process

Influent m

Phase 1 Phase 2 Phase 3 T Phase 4 Phase 5 ± Fill Anaerobic Oxidation ' Settling Decant "

Air Waste Activated Sludge

Mixing

Influent

Influent

Waste Activated Sludge

E. PhoStrip Process

Chemical Sludge

FIG. 7.38.4 Schematic diagrams of the phosphorous removal processes. (Reprinted, with permission, from S.N. Hong, 1982, A biological wastewater treatment system for nutrient removal, presented at the EPA Workshop on Biological Phosphorus Removal, Annapolis, Md., 1982); C.S. Block and S.N. Hong, 1984, Treatment of wastewater containing phosphorus compounds, U.S. patent 4,488,967; K. Kalb et al., 1990, Nutrified sludge—An innovative process for removing nutrients from wastewater, presented at the 63rd WPCF Conference, Washington, D.C. 1990; J.F. Manning and R.L. Irvine, 1985, The biological removal of phosphorus in sequencing batch reactors, J. WPCF 57:87; and R.T. Irvine et al., 1982, Summary report—workshop on Biological Phosphorus Removal in Municipal Wastewater Treatment, Annapolis, Md.)

f \ Effluent JClarifieij-^

Waste Activated Sludge

E. PhoStrip Process

Chemical Sludge

FIG. 7.38.4 Schematic diagrams of the phosphorous removal processes. (Reprinted, with permission, from S.N. Hong, 1982, A biological wastewater treatment system for nutrient removal, presented at the EPA Workshop on Biological Phosphorus Removal, Annapolis, Md., 1982); C.S. Block and S.N. Hong, 1984, Treatment of wastewater containing phosphorus compounds, U.S. patent 4,488,967; K. Kalb et al., 1990, Nutrified sludge—An innovative process for removing nutrients from wastewater, presented at the 63rd WPCF Conference, Washington, D.C. 1990; J.F. Manning and R.L. Irvine, 1985, The biological removal of phosphorus in sequencing batch reactors, J. WPCF 57:87; and R.T. Irvine et al., 1982, Summary report—workshop on Biological Phosphorus Removal in Municipal Wastewater Treatment, Annapolis, Md.)

Effluent

0 0

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