Presence of $E. coli$ in water indicates

Statement $P$: $A$ major portion of organic matter in water is consumed by chemical processes.
Statement $Q$: Microorganisms,including bacteria,consume organic matter present in water.

What is the process of treating wastewater by municipalities in cities called?

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

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.

In how many stages is the process of sewage treatment plants carried out?