1. DESIGN OF WASTEWATER TREATMENT PLANT
Activated Sludge Design

2. Aeration Tank Loading Aeration period = Detention time = V/Q
BOD loading per unit volume (g/m3.d)
Interrelated with aeration period
Dependent on the concentration of BOD in the wastewater and volume of aeration tank
F/M ratio = Q x BOD (g/m3)
V x MLSS (g/m3)
Where:
MLSS = Mixed Liquor Suspended Solid
F/M ratio = Food to Microorganism Ratio = BOD Loading in proportion to Microbial Mass in the systems.

3. Removal Efficiencies
BOD removal =
SS removal =

4. Sludge Age Sludge age = MLSS (mg/L) x V (m3). SSe x Qe + SSw x Qw
Where:
Sludge age = Mean cell residence time. Also can expressed in terms of volatile suspended solids.
SSe = Suspended Solids in Wastewater Effluent
SSw = Suspended Solids in Waste Sludge

5. Return sludge rate Expressed as percentage of raw wastewater effluent.
Return sludge age = Recirculation flow
Wastewater flow

6. Example: