The primary treatment of sewage water involves

What is the water obtained after the sedimentation process in sewage treatment called?

$A$ small part of the activated sludge is pumped back into which tank?

Which process is used to remove floating debris from sewage?

Three water samples namely river water,untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to $BOD$ test. The samples were labelled $A, B$ and $C$; but the laboratory attendant did not note which was which. The $BOD$ values of the three samples $A, B$ and $C$ were recorded as $20\, mg/L, 8\, mg/L$ and $400\, mg/L$ respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Which bacteria digest the bacteria and fungi present in the sludge during sewage treatment?