Competes with health related costs * EDTA complexes Ca & Mg

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Alkalinity, Hardness, Lime/Soda Ash Softening

• By
• Douglas Rittmann, Ph.D., P.E.
• Water/Wastewater Consultant
• Presented to
• CE 5345
• On
• Sept., 2006

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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- - gtpH 8.3 lt pH 10
C. Hydroxide, OH- - gt pH 10.0
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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
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Method of Analysis
1. Phenolphthalein Alkalinity
A. Phenolphthalein indicator
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
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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 CaCO3
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Alkalinity Relationships
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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

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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.
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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
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Introduction To Hardness

• By
• Douglas Rittmann, Ph.D., P.E.
• Water/Wastewater Consultant
• Presented to
• CE 5345
• On
• Sept., 2006

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Introduction to Hardness

• Causes Sources of Hardness

Source Rain contact with soil and rock
formations
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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
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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
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Types of Hardness

• Calcium and Magnesium Hardness
• Total Hardness Calcium Hardness Magnesium
  Hardness

Carbonate and Noncarbonate Hardness
When alkalinity lt 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.
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By Douglas Rittmann, Ph.D.,
P.E. Water/Wastewater Consultant Presented
to CE 5345 On Sept., 2006
Effective Lime/Soda Ash Water Softening
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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
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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 gt 150 mg/L
B. T. Hardness, mg/L, as CaCO3 (Ca X 2.5)
(Mg X 4.12)
(MW100) (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
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Water Softening
III. Methods of Softening
A. Lime-Soda Ash Chemistry
1. 1st Stage Treatment (Lime only)
a. Carbon Dioxide Removal (lt 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 gt10.8)
c. Magnesium Hardness Removal (gtpH 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
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IV. Chemical Analyses Interpretations
A. Calcium Alkalinity Ca Hardness or T.
Alkalinity whichever is smaller
B1. Magnesium Alkalinity Mg. Hardness if T.
Alkalinity gt or than total hardness
B2. Magnesium Alkalinity Total Alkalinity
calcium hardness if total alkalinity is gt 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)
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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
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Total CaO required
186mg/L Soda Ash Requirement NCH 280 170
110 mg/L Soda Ash
(Na2CO3) (110) (106) / (100) 117 mg/L
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Questions???