Why is primary treatment of sewage required? Explain.

Sewage contains a huge amount of organic matters that are toxic. Sewage treatment removes the toxic organic matter.

These treatment steps basically involves physical removal of particles through filtration and sedimentation. These are removed in the stages:

1. Floating materials are removed by sequential filtration.

2. Grit(soil and small pebbles) are removed by sedimentation

All solids thats settle form the primary sludge and effluent. The effluent from the primary tank is taken for secondary treatment.