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

Select the correct statement from the following:

What is the full form of $STPs$?

Select the correct option regarding flocs.

Which option represents the correct sequence of components formed during the process of sewage treatment in $STPs$ until biogas is produced?

$(a)$ What would happen if a large volume of untreated sewage is discharged into a river?
$(b)$ In what way is anaerobic sludge digestion important in sewage treatment?