Which microorganisms are responsible for the formation of flocs in sewage treatment?

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

Before discharging municipal wastewater into natural water bodies like rivers and streams,it is passed through which of the following?

The domestic sewage in large cities

Select the correct sequence with respect to sewage treatment.
$i$. Removal of suspended solid particles by primary treatment.
$ii$. Wastewater screening
$iii$. Anaerobic bacteria digest activated sludge.
$iv$. Treatment by flocs in aeration tank.
$v$. Grit settling

Identify the stage of sewage treatment shown below.