Engineering Questions with Answers - Multiple Choice Questions
Environmental Engineering MCQ’s – Lime Soda Process
The permanent hardness can be removed by adding lime and soda.
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.
The time required for the mixing of lime and soda in lime soda process is _____________
d) 80 min
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.
The temperature at which the softening of water takes place by lime soda process is ____________
Explanation: The lime soda process can be operated continuously or intermittently at either 10o-21oC or at 100oC.
Which chemical is used for removing the permanent hardness of Calcium chloride?
d) Both lime and soda
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.
Softening chemicals, lime and soda do not depend on ____________
a) Free carbon dioxide present
b) Non carbonate hardness
c) Total magnesium
d) Carbonate hardness
Explanation: Lime and soda depend on free carbon dioxide present, non carbonate hardness, total magnesium and does not depend on carbonate hardness.
The detention period of a lime soda treatment plant is ____________
Explanation: The detention period of a lime soda treatment plant is 2-4 hours to obtain greater clarification.
The minimum reaction time allowed in the recarbonation basin is ____________
Explanation: During lime soda treatment, the recarbonation of water is done in recarbonation basin where the minimum reaction time is 20minutes.
What is the pH at which recarbonation should be done?
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.
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
Explanation: The recarbonated water in lime soda treatment plant is passed through the rapid filter to ensure complete clarification.
What is the detention time of a water softening accelerator?
c) 30 minutes
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.
The sludge in water softening accelerator is deposited at ____________
a) Sedimentation tank
b) Reaction zone
d) Secondary mixing zone
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.