Question

The normal dose of chlorine during pre chlorination is ___________

(a) 0.5-1ppm

(b) 0.1-0.2ppm

(c) 0.1-0.5ppm

(d) 1-2ppm

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

My query is from Forms of Chlorination topic in section Properties of Disinfection of Environmental Engineering

Answer 1

Right choice is (c) 0.1-0.5ppm

Easy explanation: The normal dose of chlorine during pre chlorination is 0.5-1ppm. This results in the oxidization of organic matter and reduce the amount of coagulants required in the water.