Question

How much percent of impurities are enough to make domestic sewage unfit for humans?

(a) 0.1 percent

(b) 1 percent

(c) 5 percent

(d) 10 percent

I had been asked this question in an international level competition.

My question is based upon Environmental Issues topic in chapter Environmental Issues of Biology – Class 12

Answer 1

Correct option is (a) 0.1 percent

The explanation: To make domestic sewage unfit for humans 0.1 percent of impurities are enough. These 0.1 percent impurities contain dissolved materials (ammonia, nitrate, sodium, etc.), colloidal materials (bacteria, cloth, fecal matter, etc.) and suspended solids (clay, sand, and silt).