In secondary treatment,what do bacteria remove from the primary effluent?

$A$ very high concentration of $E. coli$ in water indicates $.........$

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?

Secondary sewage treatment is primarily a ......

In the first stage of sewage treatment,which materials are removed through filtration and sedimentation?

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