Question

Which of the following is not correct regarding the primary treatment of waste-water?

(a) Initially floating debris is removed by distillation

(b) Grit and pebbles are removed by sedimentation

(c) Solids that settle form the primary sludge

(d) Supernatant forms the effluent

The question was posed to me in final exam.

This intriguing question comes from Microbes in Sewage Treatment topic in portion Microbes in Human Welfare of Biology – Class 12

Answer 1

The correct answer is (a) Initially floating debris is removed by distillation

For explanation: In primary treatment, initially floating debris is removed by sequential filtration. Then grit and small pebbles are removed by sedimentation. All solids that settle form the primary sludge while the supernatant forms the effluent.