Question

An activated sludge system with recycle (CMFR) uses to treat primary effluent after sedimentation.Use the appropriate kinetic coefficients for the influent water characteristics to CMFR. Influent Characteristics: Flow = 1000 m3/day; bsCOD= 192 g/m3; nbVSS= 30 g/m3; inert inorganics= 10 g/m3

Aeration Tank Data: MLVSS = 2500; g/m3; SRT or θc = 6-day

Calculate:

1.- Fraction of Biomass in MLVSS

2.- Observed yield

a) gVSS/ g bs COD

b) gTSS/g bs COD

3.- Oxygen Requirement Kg/day

Answer 1

Solution:- The whole solution is shown in below images. To calculate biomass fraction, first calculate the effluent bs COD concentration and biomass concentration (X) using formula shown in below images. Putting the respective values in formula to get biomass fraction. To calculate Observed yield of solids, first calculate the bs COD removed /d from the formula shown in below images. And then calculate solids wasted/d based on kg of VSS/d and based on kg of TSS/d. The ratio of solids wasted/d to the bs COD removed/d is the respective observed solids yield. To calculate the required oxygen value, first calculate the Px.bio using the formula given in below images and substitute in the oxygen required formula to get the respective value.

Final answer obtained :-

Part 1 :- Biomass fraction in MLVSS = 0.58

Part 2 :- a) Observed solid yield in g VSS / g bs COD = 0.428 g VSS / g bs COD

b) Observed solid yield in g TSS / g bs COD = 0.53 g TSS / g bs COD

Part 3 :- Oxygen required = 117.46 Kg/d