What is the primary sludge?

Step-by-step solution

Primary treatment basically involves 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. All solids that settle form the primary sludge , and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.