What are flocs?

What is the free water above the primary sludge called?

Statement $S$: In the primary stage of sewage treatment,physical particle matter is removed from water through filtration and sedimentation.
Reason $R$: Through sedimentation,soil or small pebbles are removed.

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

Which process is used to remove grit (soil and small pebbles) from sewage during primary treatment?

$A$: More sewage treatment plants are required in proportion to the human population.
$R$: Biogas,which is a fuel energy,is produced in $STPs$.