Answer:
(b) The primary treatment of waste
water involves physical removal of both larger and small particles (stable
particles) 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. All solids that settle form the primary sludge
and the supernatant forms the effluent. The effluent is taken for the secondary
treatment.
The primary treatment does not
remove the dissolved impurities (a), toxic substances(c) and harmful bacteria
(d).
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