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Water requirements miscellaneous

  1. 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, n = 1. The minimum amount of chlorine (in kg per day) to be applied to achieve the same degree of disinfection for the enhanced flow is
    1. 60.50
    2. 44.00
    3. 38.00
    4. 23.27
Correct Option: A

We know, tcn = k
where C is the concentration and n is the direction coeff.
t is time required to kill organism.
Here n = 1

t =
L
V

where, L = length of pipe
V = velocity of flow
t =
L
=
L
VQ/A

t =
LA
Q

L =
W
Q

where, W = weight of disinfectant/day
Q = discharge/day
t1Cn1 = t2Cn2
LA
×
w1
=
LA
×
W2
×
Q1Q1Q2Q2

∴ W2 =
2
× W1
1

=
22
² × 32 = 60.5 kg/d
16



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