Engineering Questions with Answers - Multiple Choice Questions

Environmental Engineering MCQ’s – Lime Soda Process

1 - Question

The permanent hardness can be removed by adding lime and soda.
a) True
b) False

View Answer

Answer: a
Explanation: The permanent hardness can be removed by adding Ca (OH)2 as lime and sodium carbonate as soda in water and the process is called lime soda process.




2 - Question

The time required for the mixing of lime and soda in lime soda process is _____________
a) 10min
b) 20min
c) 40min
d) 80 min

View Answer

Answer: c
Explanation: The time required for the mixing of lime and soda in water in lime soda process is between 30-60min to allow completion of the chemical reaction. Precipitated chemicals are removed by sedimentation or filtration or both.




3 - Question

The temperature at which the softening of water takes place by lime soda process is ____________
a) 10o-21oC
b) 20o-30oC
c) 39o-45oC
d) 90oC

View Answer

Answer: a
Explanation: The lime soda process can be operated continuously or intermittently at either 10o-21oC or at 100oC.




4 - Question

Which chemical is used for removing the permanent hardness of Calcium chloride?
a) Lime
b) Chlorine
c) Soda
d) Both lime and soda

View Answer

Answer: b
Explanation: Only soda ash is used for removing the permanent hardness of Calcium chloride whereas for magnesium chloride both lime and soda are used for removing the permanent hardness.




5 - Question

Softening chemicals, lime and soda do not depend on ____________
a) Free carbon dioxide present
b) Non carbonate hardness
c) Total magnesium
d) Carbonate hardness

View Answer

Answer: d
Explanation: Lime and soda depend on free carbon dioxide present, non carbonate hardness, total magnesium and does not depend on carbonate hardness.




6 - Question

 The detention period of a lime soda treatment plant is ____________
a) 1hour
b) 3hours
c) 2-4hours
d) 4-7hours

View Answer

Answer: c
Explanation: The detention period of a lime soda treatment plant is 2-4 hours to obtain greater clarification.




7 - Question

The minimum reaction time allowed in the recarbonation basin is ____________
a) 5minutes
b) 10minutes
c) 15minutes
d) 20minutes

View Answer

Answer: d
Explanation: During lime soda treatment, the recarbonation of water is done in recarbonation basin where the minimum reaction time is 20minutes.




8 - Question

What is the pH at which recarbonation should be done?
a) 7
b) 4.5
c) 8.2
d) 9.5

View Answer

Answer: d
Explanation: The carbonation of water containing excess lime will form a colloidal precipitate of calcium carbonate that is less soluble at pH 9.4-9.6, so the recarbonation should not be done below this range.




9 - Question

Which filter is normally used in the lime soda treatment plant?
a) Slow sand filter
b) Rapid sand filter
c) Dual media filter
d) Mixed media filter

View Answer
Answer: b
Explanation: The recarbonated water in lime soda treatment plant is passed through the rapid filter to ensure complete clarification.



10 - Question

What is the detention time of a water softening accelerator?
a) 1-6minutes
b) 20minutes
c) 30 minutes
d) 1-2hours

View Answer

Answer: d
Explanation: A water softening accelerator is a device that is used for mixing, flocculation and clarification of water and they have a short detention period in comparison to a sedimentation tank that is 1-2hours.




11 - Question

The sludge in water softening accelerator is deposited at ____________
a) Sedimentation tank
b) Reaction zone
c) Concentrator
d) Secondary mixing zone

View Answer

Answer: c
Explanation: The sludge in water softening accelerator is deposited at a concentrator which can be discharged through a pipe continuously or can be discharged upon a schedule that can operate automatically.

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