25. An activated sludge system is designed to treat population of 50 000. The wastewater that enters into 200 mg/L has to be reduced to 20 mg/L in order to co A complete-mix reactor is to be used and from a values are 0.5 kg/kg and 0.05 per day respectively. (i) If the food and micro organism rat Ica 00

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Chapter2: Loads On Structures
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Wasterwater Engineering Civil engineering 

25. An activated sludge system is designed to treat a domestic wastewater from a
population of 50 000. The wastewater that enters into the aerated reactor with BODs of
200 mg/L has to be reduced to 20 mg/L in order to comply with the Standard A.
A complete-mix reactor is to be used and from a pilot plant study, the Y and ka
values are 0.5 kg/kg and 0.05 per day respectively.
(¹1)
If the food and micro organism ratio is given as 0.3 kg BOD, per
kg MLSS per day and the biomass concentration in the aerated
reactor has to be maintained at 2500 mg/L, calculate the volume of
the aerated reactor.
(ii)
Determine the mean cell-residence time.
(iii)
From the answers obtained in part (i) and (ii) and also the
information given above, compute the daily amount of biomass to
be wasted.
(iv)
Determine the recycle ratio of the system. Assuming an underflow
concentration of 8,000 mg/L from the secondary clarifier.
Transcribed Image Text:25. An activated sludge system is designed to treat a domestic wastewater from a population of 50 000. The wastewater that enters into the aerated reactor with BODs of 200 mg/L has to be reduced to 20 mg/L in order to comply with the Standard A. A complete-mix reactor is to be used and from a pilot plant study, the Y and ka values are 0.5 kg/kg and 0.05 per day respectively. (¹1) If the food and micro organism ratio is given as 0.3 kg BOD, per kg MLSS per day and the biomass concentration in the aerated reactor has to be maintained at 2500 mg/L, calculate the volume of the aerated reactor. (ii) Determine the mean cell-residence time. (iii) From the answers obtained in part (i) and (ii) and also the information given above, compute the daily amount of biomass to be wasted. (iv) Determine the recycle ratio of the system. Assuming an underflow concentration of 8,000 mg/L from the secondary clarifier.
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