Lime Softening

Question 1

Water that has the hardness concentration > ___ mg/l as CoCO3 is considered very hard.

Answer 1

180 mg/L

Question 2

Water that has a hardness concentration of ___ to ___ mg/l as CaCO3 is considered hard.

Answer 2

121 - 180 mg/l

Question 3

Water that has a hardness concentration of ___ to ___ mg/l as CaCO3 is considered moderately hard.

Answer 3

61 to 120 mg/l

Question 4

Water that has a concentration of ___ to ___ mg/l as CaCO3 is considered soft.

Answer 4

0 - 60 mg/l

Question 5

Raw water can usually be softened by only using lime when it contains little or no ___ hardness.

Answer 5

Non-carbonate

Question 6

___ and ___ are the two main constituents of water hardness.

Answer 6

Calcium and Magnesium

Question 7

When softening water using lime-soda ash softening process, soda ash dosage is based on the amount of ___ ___ to be removed.

Answer 7

non-carbonate hardness

Question 8

The double-stage process in excess-lime softening is designed to achieve greater ___ removal.

Answer 8

Magnesium

Question 9

___ is required to stabilize the water following the lime softening process to prevent the CaCO3 from precipitating out on the filters.

Answer 9

Re-carbonation

Question 10

Another name for non-carbonate hardness is ___ ___.

Answer 10

Permanent hardness

Question 11

___ ___ will produce a cake that is both difficult and hazardous to handle when it comes into contact with moisture.

Answer 11

Soda Ash

Question 12

Water that is too soft will cause your skin to feel slippery after washing with soap due to a ___ ___ feeling on your skin.

Answer 12

soap scum

Question 13

Raw water requires both ___ and ___ ___ when there are nominal amounts of magnesium hardness in the water.

Answer 13

lime and soda ash

Question 14

The lime softening process can cause the formation of Trihalomethanes (THM’s) due to the high pH levels required since THM formation ___ as pH ___.

Answer 14

increases as pH increases

Question 15

It takes about ___ to ___ minutes to slake lime in a detention-time lime slacker.

Answer 15

20 to 30

Question 16

The slaking process should be maintained at ___ degrees F or higher for best results.

Answer 16

160 F

Question 17

The sludge blanket in a softening plant’s contact clarifier should have a solids concentration in the range of ___ to ___% total solids.

Answer 17

5 - 15%

Question 18

Ion exchange softening process can be used for direct ground-water treatment as long as ___ and ___ levels are not too high.

Answer 18

Turbidity and iron