The high amount of $E. coli$ in water is the indicator of

$BOD$ is related to which of the following?

Which bacteria are used to treat sewage water?

Given below are two statements about sewage. Based on them,select the correct option given below.
Statement $I$: The sediment in the settling tank is called floc.
Statement $II$: Sewage is first passed in the grit chamber,then it is screened.

What kind of process is secondary treatment?

Measuring Biological Oxygen Demand $(BOD)$ is a method used for