26. Aeration of water is done to remove

1. 1. Suspended Impurities

   
   
   

   2. Colour

   
   
   

   3. Dissolved Salts

   
   
   

   4. Dissolve Gases

   
   
   

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1. View Hint View Answer Discuss in Forum

   Duration of operation of slow sand filter is 1-3 months.

   Correct Option: D

   Duration of operation of slow sand filter is 1-3 months.

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27. The disinfection efficiency of chlorine in water treatment.

1. 1. is not dependent on pH value.

   
   
   

   2. is increase by increased pH value.

   
   
   

   3. remains constant at all pH value.

   
   
   

   4. is reduced by increased pH value.

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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28. Use of coagulants such as alum

1. 1. results in reduction of pH of the treated water.

   
   
   

   2. results in increase of pH of the treated water.

   
   
   

   3. results in no change in pH of the treated water.

   
   
   

   4. may cause and increase or decrease of pH of the treated water.

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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29. 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. 1. 60.50

   
   
   

   2. 44.00

   
   
   

   3. 38.00

   
   
   

   4. 23.27

   
   
   

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1. View Hint View Answer Discuss in Forum

   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
   	V		Q/A

   
   

   t =	LA
   	Q

   
   

   L =	W
   	Q

   
   where, W = weight of disinfectant/day
   Q = discharge/day
   t₁Cⁿ₁ = t₂Cⁿ₂
   

   	LA	×	w1	=	LA	×	W2	×
   	Q1		Q1		Q2		Q2

   
   

   ∴ W2 =	Q²2	× W1
   	Q²1

   
   

   =		22		²	× 32 = 60.5 kg/d
   		16

   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
   	V		Q/A

   
   

   t =	LA
   	Q

   
   

   L =	W
   	Q

   
   where, W = weight of disinfectant/day
   Q = discharge/day
   t₁Cⁿ₁ = t₂Cⁿ₂
   

   	LA	×	w1	=	LA	×	W2	×
   	Q1		Q1		Q2		Q2

   
   

   ∴ W2 =	Q²2	× W1
   	Q²1

   
   

   =		22		²	× 32 = 60.5 kg/d
   		16

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30. A water treatment plant is designed to treat 1 m³/s of raw water. It has 14 sand filters. Surface area of each filter is 50 m². What is the loading rate (in (m³/days.m²)) with two filters out of service for routine backwashing?

1. 1. 214 m³/day.m²

   
   
   

   2. 124 m³/day.m²

   
   
   

   3. 174 m³/day.m²

   
   
   

   4. 144 m³/day.m²

   
   
   

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1. View Hint View Answer Discuss in Forum

   Hydraulic loading rate =	Q
   	A

   
   

   =	1	m³/sec.m²
   	12 × 50

   
   

   =	1 × 24 × 60 × 60	m³/day.m²
   	12 × 50

   
   = 144 m³/day.m²

   Correct Option: D

   Hydraulic loading rate =	Q
   	A

   
   

   =	1	m³/sec.m²
   	12 × 50

   
   

   =	1 × 24 × 60 × 60	m³/day.m²
   	12 × 50

   
   = 144 m³/day.m²

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