Activated Sludge Process Design

Design of Activated Sludge Systems:

Design of activated-sludge process involves details of sizing and operation of the following main elements.

1. Aeration tank (reactor)-capacity and dimensions.
2. Aeration system-oxygen requirements and oxygen transfer system.
3. Final sedimentation tank – (deifier)
4. Return activated sludge system.SV1
5. 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.
6. MLSS – a mixture of settled sewage + activated sludge dissolved oxygen < 2mg/l

Design Criteria

1. F/M ratio = 0.2 – 0.5 day -1 or 0.2 – 0.5 kg BOD's / kg MLSS – d
2. Detention time (aeration time) of sewage = 6 to 6 hours
3. MLVSS or MLSS = 1500 -3000 mg/l
4. Air supply = 10m3/m3 sewage treated
5. return sludge = 0.25 -10 of Q (influent sewage flow) Qr / Q = 0.20-0.30 = Vs/100Vs (Volume of sludge)
6. Depth = 3-5m
7. L=W ratio =5:1
8. SVI 50-150 ml/gm