Activated sludge system question

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Homework Statement

for this question i think the sludge age is wrong.

Homework Equations

The Attempt at a Solution

Based on the formula given , The suspended solid in effulent should be = (Q-Qw) , which is 8100-150= 7950 , am i right ? Correct me if i am wrong ...

Or the 8100 m3/s given is the flow of effluent ?

 

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Anyone can try to help ?