I need to calculate sludge retention time of membrane bioreactor. For that I need flow rate of waste activated sludge as well as flow rate of effluent. Please someone provide the formulas for calculating the flow rates.
The activated sludge operational parameters calculated by the Excel formulas in the spreadsheet are: recycle activated sludge flow rate, Q r; waste activated sludge flow rate, Q w, and aeration tank food to microorganism ratio, F:M. The equations used are as follows: Q r = (X – X o)/(X w – X)
Activated sludge plant involves: wastewater aeration in the presence of a microbial suspension, solid-liquid separation following aeration, discharge of clarified effluent, wasting of excess biomass, and return of remaining biomass to the aeration tank.
Loading Rate-A loading parameter that has been developed over the years is the hydraulic retention time (HRT), q, d
q = V
Q
V= volume of aeration tank, m3, and Q= sewage inflow, m3/d
Another empirical loading parameter is volumetric organic loading which is defined as the BOD applied per unit volume of aeration tank, per day.
A rational loading parameter which has found wider acceptance and is preferred is specific substrate utilization rate, q, per day.
q= Q (SO - Se)
V X
A similar loading parameter is mean cell residence time or sludge retention time (SRT), θc, d
θc = V X
QwXr + (Q-QwXe)
where SO and Se are influent and effluent organic matter concentration respectively, measured as BOD5 (g/m3), X, Xe and Xrare MLSS concentration in aeration tank, effluent and return sludge respectively, and Qw= waste activated sludge rate.
Under steady state operation the mass of waste activated sludge is given by
QwXr = YQ (SO - Se) - kd XV
where Y= maximum yield coefficient (microbial mass synthesized / mass of substrate utilized) and kd = endogenous decay rate (d-1) .
From the above equation it is seen that 1/qc = Yq - kd
If the value of Se is small as compared SO, q may also be expressed as Food to Microorganism ratio, F/M
F/M = Q(SO- Se) / XV = QSO / XV
The θc value adopted for design controls the effluent quality, and settle ability and drain ability of biomass, oxygen requirement and quantity of waste activated sludge.
@augistine sir, thanks for providing srt formula. Sir here, I have doubt regarding two parameters i.e. average daily SAS flow and average solids in final effluent. How to determine these two parameters
@augustine Sir but how I can calculate flow (flow of waste activated sludge and effluent) for calculating sludge retention time
-@Augustine Sir what's the purpose of 0.8 here in formula you mentioned. In addition for calculating SRT, flow rate of waste activated sludge also required. How to calculate that?
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