Softener Systems

Question 1

Lime will precipitate noncarbonate hardness from the water,

but it also forms noncarbonate salts that cause

noncarbonate hardness. what are these salts?

Answer 1

CaSO₄

&

CaCl₂

Question 2

In the lime-soda ash softening process, smaller plants find

that _______ is less expensive to purchase; regardless

of the size of the plant, ________ needs to be mixed long

enough because it dissolves rather slowly.

Answer 2

• calcium hydroxide
• lime

Question 3

Because lime slurries have a _______ and a _______ in

water, calcium carbonate will _______ on anything the

slurry touches.

Answer 3

• high pH
• low solubility
• precipitate

Question 4

After water has been softened, it is close to pH 11; thus,

it needs to be stabilized by a process known as

recarbonation. What small amount of hardness chemical

is formed and what is precipitated in this process?

Answer 4

• calcium bicarbonate

and

• magnesium carbonate

Question 5

What two major problems will improperly stabilized

softened water cause?

Answer 5

Scale deposits

or

Corrosive water

Question 6

How is hardness expressed in the ion exchange process?

Answer 6

Grains/gal

Question 7

How is magnesium noncarbonate hardness removed?

Answer 7

With lime then soda ash

Question 8

The excess lime-softening process is used so that _______

will precipitate out of the water.

Answer 8

Magnesium hydroxide

Question 9

Preoxidation has been shown to improve _________.

Answer 9

Floccculation, Sedimentation, Filtration

Question 10

What is conventional treatment?

Answer 10

Coagulation, Flocculation,

Sedimentation, and Filtration

Question 11

What type of flash-mixing process gives the best

mixing and control?

Answer 11

Mechanical mixers

Question 12

The lime-softening process used in removing iron works in

the pH range of ________.

Answer 12

10pH to 11pH

Question 13

What plant-operating factor could make a difference in

the proper development of floc?

Answer 13

Inadequate flocculation time.

Question 14

When sodium fluoride solutions are used with hard water,

insoluble compounds of ________ can form.

Answer 14

calcium and magnesium fluoride

Question 15

Lime should be added to the water being treated with

as _______ a distance between the feeder and

the water as possible.

Answer 15

short

Question 16

To comply with the enhance coagulation requirements, a

softening plant would need to remove _______ of

________ hardness.

Answer 16

• 10 mg/L
• magnesium

Question 17

Which type of hardness usually calls for a two-stage softening process?

a. Calcium hardness above 100 mg/L
b. Magnesium hardness
c. Noncarbonated hardness
d. Carbonate hardness

Answer 17

c. Noncarbonated hardness