Design of Aeration Tank


1. DIMENSION OF TANK

    No. of units: two or more, each capable of independent operation
    Depth: 10 ~ 30 ft, 15 ~ 25 ft for diffuser aeration
    Freeboard: 1~2 ft diffuser aeration
                      3~5 ft mechanical aeration
    W: D = 1:1 ~ 2:1 spiral flow mixing in plug flow
    L : W > 5:1 excepted for complete-mixed flow

2. INLET AND OUTLET

  • Shall permit the peak hourly flowrate to be carried with any single aeration tank out of service.
  • Flexible operation arrangement

3. CONDUIT

  • Suitable arrangement for draining the any segment of aeration tank
  • Maintain self-cleansing velocity

4. FROTH CONTROL SYSTEM

    Antifoaming agent - effluent spray nozzle

5. AERATION SYSTEM

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6. DIFFUSERS

    - Various types

    Selection depends on the transfer efficiency, maintenance and type of reactors.

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Diffused-air Aeration Devices
(a). Fine bubble diffuser cylindrical shape
(b). Fine bubble diffuser tube with fine sheath and holding clamp
(c). Coarse bubble diffuser
(d). Fine bubble dome diffuser assembly
(e). Tubuler diffuser
(f). Jet diffuser

7. BLOWERS

    - Provided in multiple units for varying the volume of air delivered in proportion to the load demand of plant and arranged in such capacity as to meet the maximum air demand with the single largest unit out of service. Consider blower capacity at 40°C and power required in winter.

    Types of blower:

  • Centrifugal: for higher capacity (>3,000 ft3/min) and lower pressure 7 ~ 9 psi, adjustable flow by throttling inlet
  • Rotary positive displacement: for lower capacity (<3,000 ft3/min) and higher pressure > 8 Psi, more noise and adjustable flow by variable speed driver
  • Air filter: remove impurities to prevent diffuser internal clogging
  • Silencer: installed at both inlet and discharge pipe of blowers
  • Piping: From blower outlet to diffuse aerator inlet and sized such that headloss not exceed 0.5 psi at average operation.
    Fiction headloss: HL = f L/D hv
    hv=(v/1096)2 ra
    ra ¾ specific weight of air at operation temperature and pressure, lb/ft3
    V ¾ air velocity in pipe, ft/min
    f ¾ friction factor
    L/D ¾ length and diameter of pipe
    Usually, use HL-D-Q chart to calculate HL, hi and D
    Fitting head loss: calculated by using equivalent length Le
    Le = 55.4 Ci D1.2
    Ci - depends on types of fittings

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If you have any suggestion, please email Professor Roy at droy@poly.edu