The primary treatment of waste water involves in removal of which of the following?

Both 1 and 3 .

a- Large and small particles .

b- Harmful bacteria.

c- Floating debris .

d- Both 1 and 3 are correct .

Primary treatment involve physical removal of particles – large and small – from the sewage through filtration and sedimentation. These are removed in stages; initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by sedimentation.