Design of Activated Sludge Systems:
Design of activated-sludge process involves details of sizing and operation of the following main elements.
- Aeration tank (reactor)-capacity and dimensions.
- Aeration system-oxygen requirements and oxygen transfer system.
- Final sedimentation tank – (deifier)
- Return activated sludge system.SV1
- Excess activated sludge withdrawal system and subsequent treatment and disposal of waste sludge. Since the whole process takes place in a liquid medium the hydraulic regime essentially in the aeration tank and final sedimentation tank.
- MLSS – a mixture of settled sewage + activated sludge dissolved oxygen < 2mg/l
- F/M ratio = 0.2 – 0.5 day -1 or 0.2 – 0.5 kg BOD's / kg MLSS – d
- Detention time (aeration time) of sewage = 6 to 6 hours
- MLVSS or MLSS = 1500 -3000 mg/l
- Air supply = 10m3/m3 sewage treated
- return sludge = 0.25 -10 of Q (influent sewage flow) Qr / Q = 0.20-0.30 = Vs/100Vs (Volume of sludge)
- Depth = 3-5m
- L=W ratio =5:1
- SVI 50-150 ml/gm
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