What is the composition of flocs?

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

What is sewage? In which way can sewage be harmful to us?

Whose $BOD$ (Biochemical Oxygen Demand) is greater?

Sewage or municipal waste should not be directly passed into rivers,streams and other water bodies because
$I.$ it contains human excreta and other organic waste
$II.$ it contains a number of pathogenic microbes
Which of the statement given above is/are correct?

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