DESIGN OF WASTEWATER TREATMENT PLANT Activated Sludge Design
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.
Removal Efficiencies BOD removal = SS removal =
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
Return sludge rate Expressed as percentage of raw wastewater effluent. Return sludge age = Recirculation flow Wastewater flow
Example: