GATE CE 2014 Set 1 — Question 56
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Environmental Engineering → Drinking Water Treatment → Chlorination
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Question
16 MLD of water is flowing through a 2.5 km long pipe of diameter 45 cm. The chlorine at the rate of 32 kg/d is applied at the entry of this pipe so that disinfected water is obtained at the exit. There is a proposal to increase the flow through this pipe to 22 MLD from 16 MLD. Assume the dilution coefficient, . The minimum amount of chlorine (in kg per day) to be applied to achieve the same degree of disinfection for the enhanced flow is
Correct answer
(A) 60.50
Solution
According to Watson's Law for disinfection: , where is the concentration of disinfectant, is the contact time, and is the dilution coefficient.
Given , we have .
The contact time is given by , where is the volume of the pipe and is the flow rate.
Substituting , we get .
The amount of chlorine applied per day is . Thus, .
Substituting into the relation , we get .
Therefore, .
Given kg/d, MLD, and MLD:
kg/d.
Given , we have .
The contact time is given by , where is the volume of the pipe and is the flow rate.
Substituting , we get .
The amount of chlorine applied per day is . Thus, .
Substituting into the relation , we get .
Therefore, .
Given kg/d, MLD, and MLD:
kg/d.
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