Flocs = $.........$

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

Secondary treatment of sewage

What is obtained as a byproduct in the process occurring in $STPs$?

$Floc$ is . . . . . .

Polluted water can be purified by using