Water softening

Question 1

Moderate hard to hard is
Scale from 0-250

Answer 1

91-130 mg/l of CaCO3

Question 2

Hardness is caused mainly by

Answer 2

The salts of calcium and magnesium, such as bicarbonate, carbonate, sulfate, chloride, and nitrate

Question 3

Total hardness is commonly measured by

Answer 3

Commonly measured by titration and is described in two ways:
1. Sum of hardness caused by both calcium and magnesium ions expressed (CaCO3)

2. The sum of carbonate (temporary) and non carbonate (permanent) hardness

Question 4

Calcium carbonate (CaCO3) equivalent is

Answer 4

An expression of the connection of a chemical in terms of their equivalent value to calcium carbonate

Question 5

Carbonate hardness is caused by

Answer 5

alkalinity present in the water up to the total hardness. It’s the total measure of the waters alkalinity

Question 6

Non carbonate hardness is

Answer 6

That portion of the total hardness in excess of the alkalinity. Requires use of both lime and soda ash to remove

Question 7

Alkalinity is the capacity… and measures

Answer 7

The capacity of water to neutralize acids.
It’s measure of how much acid must be added to a liquid to lower ph to 4.5. This capacity is caused by the water’s content of bicarbonate, carbonate, hydroxide, and sometimes borate, silicate and phosphate

Question 8

Two types of lime

Answer 8

1. Quick (CaO)- calcium oxide
2. Hydrated (Ca(OH)2

Question 9

You should never use the same conveyor or container for quicklime because

Answer 9

It could explode under certain conditions

Question 10

Types of alkalinity that can be present at ph values (7)

Answer 10

1. Below 4.5 only CO2 present, no alkalinity
2. Between 4.5 to 8.3, CO2 and bicarbonate present
3. Above 8.3, alkalinity may consist of bicarbonate, carbonate, and hydroxide (no CO2 present)
4. When above 8.3 the amount of titrant used to reach ph 8.3 is the phenolphthalein alkalinity
5. Between 10.2 to 11.3 carbonate and hydroxide
6. At 9.4 calcium carbonate becomes insoluble and precipitates
7. At 10.6 magnesium hydroxide becomes insoluble and precipitates

Question 11

Hardness relationship to alkalinity (2)

Answer 11

1. Alkalinity > total hardness (All hardness is in carbonate form)
   TH=CH
2. Alkalinity < total hardness (both carbonate and non carbonate hardness is present)

CH=alkalinity

TH=CH+ NCH

Question 12

Alum sludge has a tendency to

Answer 12

Harden the soil

Question 13

What can you use when water can’t be softening to desired level

Answer 13

Soda ash or caustic soda

Question 14

Hardness in water (2)

Answer 14

1. High concentrations of calcium (Ca2+) and magnesium (Mg2+) ions cause water hardness
2. Water with more than 100mg/l of calcium carbonate is considered hard

Question 15

Methods of removing hardness (3)

Answer 15

1. Lime softening (chemical precipitation) - solubility level of about 35 mg/l (CaCO3)
2. RO (nanofiltration) ( membrane filtration) - 85-90% removal
3. Ion exchange (chemical exchange) - basically zero water must be blended

Question 16

(6) benefits of lime softening

Answer 16

1. Removal of Ca and Mg hardness
2. Removal of iron, manganese, arsenic and uranium
3. Reduction of solids, turbidity, and TOC
4. Removal and inactivation of bacteria and viruses due to high ph
5. Raise ph and prevent corrosion
6. Removal of excess fluoride

Question 17

(4) chemical precipitation

Answer 17

1. Hardness causing ions converted from soluble to insoluble at high ph
2. Adding lime increases the hydroxide concentrations, increasing the ph
3. Adding lime converts alkalinity from bicarbonate form to carbonate causes calcium to precipitate
4. Adding lime the phenolphthalein alkalinity increased to a level where hydroxide becomes present allowing magnesium to precipitate

Question 18

Following the softening process the (3)

Answer 18

1. Ph is high
2. Water is supersaturated with excess caustic alkalinity in either hydroxide or carbonate form
3. Carbon dioxide can be used to decrease the causticity and scale forming tendency before filtration

Question 19

Chemical titration with methyl orange (T) (2)

Answer 19

1. Methyl orange is used to determine the combination of alkalinity provided by carbonate, bicarbonate, and hydroxide or total alkalinity
2. Added until color is absent then the total alkalinity (T) is computed

Question 20

Chemical titration with phenolphthalein (P) (2)

Answer 20

1. P is used to determine the carbonate and hydroxide alkalinity present
2. Added to color is absent then hydroxide and carbonate alkalinity (P) then computed

Question 21

(5) lime softening limitations

Answer 21

1. Unable to remove all carbonate and non carbonate hardness
2. High degree of operator control
3. Color removal may be hindered due to high ph
4. Improper ph can cause scaling or corrosion
5. Sludge handling and disposal can be costly

Question 22

Primary coagulants used in lime softening (2)

Answer 22

1. Acidic compounds- alum (Al2(SO4)3, Ferris sulfate, ferric sulfate and ferric chloride
2. Basic compounds- sodium aluminate

Question 23

Split treatment

Answer 23

1. 80% treated and 20% raw
2. Used to reduce eliminate carbon dioxide

Question 24

Quicklime slaked (2)

Answer 24

Dry powder must be soaked for 15/30 minutes at cold temps

Slaking produces calcium hydroxide

Question 25

Sodium alum, bentonite, sodium silicate, synthetic canonic are all

Answer 25

Secondary coagulation aids

Question 26

Recarbonation in lime softening

Answer 26

1. Water is supersaturated
2. If not recarbed ca and mg will form in filters and piping