GATE CE 2021 Set 2 — Question 61
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Environmental Engineering → Wastewater Treatment Processes → ASP Design (F/M, MLSS, SVI)
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Question
An activated sludge process (ASP) is designed for secondary treatment of of municipal wastewater. After primary clarifier, the ultimate BOD of the influent, which enters into ASP reactor is . Treated effluent after secondary clarifier is required to have an ultimate BOD of . Mix liquor volatile suspended solids (MLVSS) concentration in the reactor and the underflow is maintained as and , respectively. The hydraulic retention time and mean cell residence time are and , respectively. A representative flow diagram of the ASP is shown below.
The underflow volume (in , round off to one decimal place) of sludge wastage is __________.
Correct answer
37 to 38
Solution
Given:
Influent flow rate,
MLVSS in reactor,
MLVSS in underflow,
Hydraulic retention time,
Mean cell residence time, Step 1: Calculate the volume of the reactor ()Step 2: Calculate the sludge wastage rate ()
The formula for mean cell residence time () is:Assuming effluent suspended solids () are negligible as they are not provided in the problem:Substituting the given values:The underflow volume of sludge wastage is .
Influent flow rate,
MLVSS in reactor,
MLVSS in underflow,
Hydraulic retention time,
Mean cell residence time, Step 1: Calculate the volume of the reactor ()Step 2: Calculate the sludge wastage rate ()
The formula for mean cell residence time () is:Assuming effluent suspended solids () are negligible as they are not provided in the problem:Substituting the given values:The underflow volume of sludge wastage is .
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