1. Lime-soda ash softening is used to remove calcium, magnesium, and non-carbonate hardness from water. Lime is added first to precipitate carbonates and hydroxides, then soda ash to remove non-carbonates. 2. Analyzing total hardness, calcium hardness, magnesium hardness, and alkalinity can help interpret which hardness forms are present and how much lime and soda ash are needed. 3. The process produces large volumes of sludge and leaves sodium in the treated water, but it is effective at lowering total dissolved solids and improving aesthetics by removing scale-causing ions.

1. Alkalinity, Hardness,
& Lime/Soda Ash Softening
BY
Muhammad Fahad Ansari
12IEEM14

2. General Considerations
1. Its capacity to neutralize acids or its buffering capacity.
2. 3 major classes of materials
A. Bicarbonates, HCO3- - pH 4.0 ≤ pH 8.3
B. Carbonates, CO3- - >pH 8.3 < pH 10
C. Hydroxide, OH- - > pH 10.0

3. Sanitary Significance
1. Lime/Soda Ash Softening
2. Effects on Coagulant Dosing
3. Total Dissolved Solids compliance
4. Industrial Wastes Discharges
5. Calcium Carbonate Stability

4. Method of Analysis
1. Phenolphthalein Alkalinity
A. Phenolphthalein indicator Acrobat Document
B. pH 8.3 endpoint of titration
C. Measures Carbonates and Hydroxide ions
2. Total Alkalinity
A. Bromcresol green or Methyl Orange indicator
B. pH 4.5 endpoint of titration
C. Measures Bicarbonates

5. Methods of Expressing
1. Phenolphthalein Alkalinity as CaCO3
P. Alk. = ml 0.02N sulfuric acid (1000/ml sample) = mg/L as CaCO3
2. Total Alkalinity as CaCO3
T. Alk. = ml 0.02N sulfuric acid X (1000/ml sample) = mg/L as CaCO3
3. Hydroxide, Carbonate, and Bicarbonate Alkalinity as CaCO 3

6. Alkalinity Relationships
Titration OH- CO3- HCO3-
Result Alkalinity as Alkalinity as Alkalinity as
CaCO3 CaCO3 CaCO3
P=0 0 0 T
P<1/2 T 0 2P T-2P
P=1/2 T 0 2P 0
P>1/2 T 2P – T 2(T- P) 0
P=T T 0 0

7. Standard Solutions
 General Considerations
1. Saves Time in calculating results
2. Selection of Proper Normality is convenient
* 1 mg/ml or 1000mg solution
* 1/eq.wt., example: Alkalinity as CaCO3 = 0.02 N
3. Preparation of Solution of Proper Normality
* Material of Known purity is weighed & transferred to
volumetric flask
* Purchase Solutions of known Normality

8. Preparation of 1N Acid
Solution
* Sulfuric acid used for Alkalinity Test
1 GMW = 98 g pure H2SO4 = 2.016 g H+
1 GMW/2 = 49 g pure H2SO4 = 1.008 g H+
Acid is 96% pure, then 49/0.96 = 51 g = 1.008 g H+
Make 5% stronger = 51 X 1.05 = 53.5 g
Procedure: Weigh about 53g of conc. acid into a small beaker on
Trip balance. Place 500 ml of distilled water in 1-liter graduated cylinder
And add the acid to it. Rinse the contents of the beaker into the cylinder
With distilled water, and add water to the 1-liter mark. Mix by pouring
Back and forth from the cylinder into a large beaker. Cool to room temp.

9. Primary Standard
* Sodium Carbonate is a convenient primary standard
MW = 106 of Na2SO3
1EW or 1N = 53g/L when reacting with H2SO4 to pH 4.5, T. Alk endpoint
Preparation of 0.02 N Acid or N/50 can be made from 1N based on
ml X N = ml X N
Example: ml X 1.0 = 1000 X 0.02
ml = 20

10. Alkalinity and hardness -
what is it?
 Alkalinity:
a measure of the ability of a
water sample to neutralize strong acid
– Expressed as mg CaCO3 per liter or micro-
equivalents
– Alkalinities in natural waters usually range
from 20 to 200 mg/L
 Hardness: a measure of the total
concentration of calcium and
magnesium ions
– Expressed as mg CaCO3 per liter

11. Alkalinity and hardness -
how to sample
 Usuallycollected at
the surface in lakes
(0 to 1m depth)
 Keep the sample
cool (4oC
refrigerated) and
out of direct
sunlight

12. Alkalinity and hardness- why
measure?
 Thealkalinity of natural waters is usually due
to weak acid anions that can accept and
neutralize protons (mostly bicarbonate and
carbonate in natural waters).
– Usually expressed in units of calcium carbonate
(CaCO3)
 The ions, Ca and Mg, that constitute
hardness are necessary for normal plant and
animal growth and survival.
 Hardness may affect the tolerance of fish to
toxic metals.

18. Introduction to Hardness
* Causes & Sources of
Hardness
Cations causing Anions
hardness
Ca++ HCO3-
Mg++ SO4=
Sr++ Cl-
Fe++ NO3-
Mn++ SiO3=
* Source – Rain contact with soil and rock formations

19. Sanitary Significance
* Reasons to Soften
1. Reduce Soap Consumption
2. Improve Aesthetics of Water
3. Hot Water Heaters last longer
* Reasons not to Soften
1. Expensive Process
2. May be less healthy
3. Competes with health related costs

20. Method of Analysis
* EDTA – Ethylenediaminetertraacetic Acid
Method
* EDTA complexes Ca & Mg
* Eriochrome Black T serves as an indicator when
EDTA is in excess of the complexed hardness ions.
* Color change is from red to blue

21. Types of Hardness
* Calcium and Magnesium Hardness
* Total Hardness – Calcium Hardness = Magnesium Hardness
* Carbonate and Noncarbonate Hardness
* When alkalinity < Total Hardness, CO3 Hardness = T. Alkalinity
* When alkalinity ≥ Total hardness, CO3 Hardness = T. Hardness
* CO3 hardness removed by boiling or lime (Temporary Hardness)
* Noncarbonate Hardness (permanent) = T. Hardness – CO3 Hardness
* Pseudo-Hardness
* Associated with Na+ which causes soap consumption but not
considered part of hardness.

22. Effective Lime/Soda Ash
Water Softening
By
Douglas Rittmann, Ph.D., P.E.
Water/Wastewater Consultant
Presented to
CE 5345
On
Sept., 2006

23. Water Softening
I. Introduction
A. Reasons to Soften
1. Reduce Soap Consumption
2. Improve Aesthetics of Water
3. Hot Water Heaters last
longer
B. Reasons not to Soften
1. Expensive Process
2. May be less healthy
3. Competes with health related costs

24. Water Softening
II. What is Hardness?
A. Hardness Classifications
a. Soft Water = 0 to 70 mg/L
b. Moderate Hardness = 71 to 150 mg/L
c. Hard Water = > 150 mg/L
B. T. Hardness, mg/L, as CaCO3 = (Ca X 2.5) + (Mg X 4.12)
(MW=100) (40 X 2.5 = 100) (24.3 X 4.12 = 100)
C. Carbonate Hardness as CaCO3 = T. Alkalinity as CaCO3
a. Removed by Boiling
b. Removed by Lime
D. Non-Carbonate Hardness = T. Hardness – T. Alkalinity
a. Unaffected by boiling
b. Removed by Soda Ash

25. Water Softening
III. Methods of Softening
A. Lime-Soda Ash Chemistry
1. 1st Stage Treatment (Lime only)
a. Carbon Dioxide Removal (< 8.3 pH)
* CO2 + Ca(OH)2 CaCO3 + H2O
b. Carbonate Hardness Removal
* Ca + 2HCO3 + Ca(OH)2 2CaCO3 + 2H2O(pH 8.3-9.4)
* Mg + 2HCO3 + Ca(OH)2 CaCO3 + Mg + CO3 + 2H2O(pH >10.8)
c. Magnesium Hardness Removal (>pH 10.8)
* Mg + CO3 + Ca(OH)2 CaCO3 + Mg(OH)2
* Mg + SO4 + Ca(OH)2 Ca + SO4 + Mg(OH)2
2. 2nd Stage Treatment (Soda Ash)
* Ca + SO4 + Na2CO3 Na2SO4 + CaCO3
* Ca + Cl2 + Na2CO3 CaCO3 + 2NaCl

26. IV. Chemical Analyses Interpretations
A. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smaller
B1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardness
B2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > than
calcium hardness but less than total hardness.
C. Sodium alkalinity = total alkalinity – total hardness
D. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH)
Analyses Water #1 Water #2 Water #3
Total Hardness 300 300 300
Calcium 200 200 200
Hardness
Mg Hardness 100 100 100
Total Alkalinity 150 250 350
Interpretations Water #1 Water #2 Water #3
Calcium Alkalinity 150 200 200
Mg. Alkalinity None 50 100
Sodium Alkalinity None None 50
Ca N.C. 50 None None
Hardness
Mg. N.C. 100 50 none

27. Water Softening
V. Theoretical versus Practical
A. Theoretical Solubility of Ca & Mg:
Mg(OH)2 = 9 mg/L Solubility
CaCO3 = 17 mg/L Solubility
Total = ~ 26 mg/L Solubility
B. Practical Minimum Total Hardness = 50 to 80 mg/L
Example: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement to
Reduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excess
Lime-soda ash process.
Analyses: Total Hardness = 280 mg/L as
CaCO3
Mg++ = 21 mg/L
Alkalinity = 170 mg/L as CaCO3
Carbon Dioxide = 6 mg/L
Lime Requirement: Carbon Dioxide = (6) (56) / (44) = 8
Alkalinity = (170) (56) / (100) = 95
Mg ++ = (21) (56) / (24.3) = 48
Excess Lime = = 35
Total CaO required = 186mg/L
Soda Ash Requirement: NCH = 280 – 170 = 110 mg/L
Soda Ash (Na2CO3) = (110) (106) / (100) = 117 mg/L

29. Water Softening
 Hardness is an important water quality
parameter in determining the suitability of water
for domestic and industrial uses
– Hard waters require considerable amounts of soap to
produce foam
– Hard waters produce scale in hot-water pipers, heaters
and boilers
Ca2+ + 2HCO3- → CaCO3 (s) + CO2 (g) + H2O
 Groundwater is generally harder than surface
water
 Principal cations causing hardness and the
major anions associated with them (in
decreasing order of abundance in natural
Water Treatment Chemistry Water Softening 29
waters)

30. Water Hardness
 Hardness expressed in mg/L as CaCO3
mg/L CaCO3 Degree of hardness
0-75 Soft
75-150 Moderately hard
150-300 Hard
300 up Very hard
 Methods of determination
– Calculation (see example)
Hardness (mg/L) as CaCO 3 = M 2+ (mg/L) x 50 / EW
of M 2+
– EDTA titrimetric method
M2+ + Eriochrome Black T (blue) → (M · Eriochrome Black T)complex (wine red)
 Water softening is needed when hardness is above
150-200 mg/L; Hardness 50-80 is acceptable in
treated Chemistry
Water Treatment water Water Softening 30

31. Lime-Soda [Ca(OH) 2 -Na 2 CO 3 ] Process:
Recarbonation by bubbling CO 2 after
softening
 Recarbonation is usually required
after lime-soda process
 Why?
– To prevent super-saturated CaCO3 (s) and
Mg(OH)2 (s) from forming harmful deposits or
undesirable cloudiness in water at a later time
CaCO3 (s) + CO2 + H2O Ca2+ + 2HCO3-
MgCO3 (s) + CO2 + H2O Ca2+ + 2HCO3-
– To neutralize excessively high pH caused by
Na2CO3
OH- + CO2 HCO3-

32. Lime - Soda Ash
Softening
Advantages
 􀂄 potential for significantly reducing total
dissolved solids
 􀂄 removes hardness
 􀂄 lime added to process is removed
precipitates soluble iron and manganese
(groundwater)
 􀂄 disinfection
 􀂄 aids in coagulation

33. Lime - Soda Ash Softening
Disadvantages
 􀂄 large quantities of sludge
 􀂄 sodium remains after adding soda
ash
(however, hardness removed by soda
ash is usually a small percentage of
total hardness)

34. Water Softening
A. Reasons to Soften
1. Reduce Soap Consumption
2. Improve Aesthetics of Water
3. Hot Water Heaters last
longer
B. Reasons not to Soften
1. Expensive Process
2. May be less healthy
3. Competes with health related costs

35. IV. Chemical Analyses Interpretations
A. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smaller
B1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardness
B2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > than
calcium hardness but less than total hardness.
C. Sodium alkalinity = total alkalinity – total hardness
D. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH)
Analyses Water #1 Water #2 Water #3
Total Hardness 300 300 300
Calcium 200 200 200
Hardness
Mg Hardness 100 100 100
Total Alkalinity 150 250 350
Interpretations Water #1 Water #2 Water #3
Calcium Alkalinity 150 200 200
Mg. Alkalinity None 50 100
Sodium Alkalinity None None 50
Ca N.C. 50 None None
Hardness
Mg. N.C. 100 50 none

36. Water Softening
V. Theoretical versus Practical
A. Theoretical Solubility of Ca & Mg:
Mg(OH)2 = 9 mg/L Solubility
CaCO3 = 17 mg/L Solubility
Total = ~ 26 mg/L Solubility
B. Practical Minimum Total Hardness = 50 to 80 mg/L
Example: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement to
Reduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excess
Lime-soda ash process.
Analyses: Total Hardness = 280 mg/L as
CaCO3
Mg++ = 21 mg/L
Alkalinity = 170 mg/L as CaCO3
Carbon Dioxide = 6 mg/L
Lime Requirement: Carbon Dioxide = (6) (56) / (44) = 8
Alkalinity = (170) (56) / (100) = 95
Mg ++ = (21) (56) / (24.3) = 48
Excess Lime = = 35
Total CaO required = 186mg/L
Soda Ash Requirement: NCH = 280 – 170 = 110 mg/L
Soda Ash (Na2CO3) = (110) (106) / (100) = 117 mg/L

37.  Pb. Result of chemical analysis of a sample of raw
water is given below:
Ca++=80mg/l
Na+=2.5 m.eq/l
Total alkalinity=80mg/l
Total hardness=120mg/l
SO-4=20mg/l
Cl-=140mg/l
NO3-=5mg/l
Prepare bar chart program of raw water.
Estimate the quantity in kg/day of CaO(90%) and
Soda ash as (95% ) to softener 4 million liters of
this water.

38. Ion Exchange
Ion exchange is an adsorption phenomenon
where the mechanism of adsorption is
electrostatic. Electrostatic forces hold ions to
charged functional groups on the surface of the
ion exchange resin. The adsorbed ions replace
ions that are on the resin surface on a 1:1 charge
basis. For example:

40. Applications of ion exchange in water & wastewater
• Ca, Mg (hardness removal) exchange with Na or H.
• Fe, Mn removal from groundwater.
• Recovery of valuable waste products Ag, Au, U
• Demineralization (exchange all cations for H all
anions for OH)
• Removal of NO3, NH4, PO4 (nutrient removal).

41. Ion Exchangers (types)
• Natural: Proteins, Soils, Lignin, Coal. Metal
oxides, Aluminosilicates (zeolites)
(NaOAl2O3.4SiO2).
• Synthetic zeolite gels and most common
-polymeric resins (macroreticular, large pores).