General Description of Activated Sludge Process

Used for secondary level of wastewater treatment to remove the soluble organic and provide further removal of suspended   solids.

Consists of aeration tank and clarifier.

1. BASIC REQUIREMENT

  • Mixed populations of active microorganisms (suspended growth in aeration tank and returned sludge from secondary clarifier)
  • Availability of oxygen --- aeration system
  • Good contact between the microorganisms and food (organic) - agitation of air and sufficient contact time
  • Availability of nutrient --- P., N. and others
  • Favorable environmental conditions --- T(oC), pH.

2. TYPES OF REACTORS

  • Complete mixed flow
  • Plug flow
  • Arbitrary flow
  • In practice, it is difficult to obtain a true plug flow regimes and it is interesting to note that the hydraulic detention time of complete-mix and plug-flow reactors are about same.

3. PROCESS AND PROCESS MODIFICATIONS

  1. Conventional

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  2. Complete mixed flow
  3. Tapered aeration

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  4. Step aeration

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  5. Contact stabilization
  6. Extended aeration
  7. Pure oxygen

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