Competes with health related costs * EDTA complexes Ca & Mg

1
Hardness ChloridesPresentation

• By
• Douglas Rittmann, Ph.D., P.E.
• Water/Wastewater Consultant
• To
• CE 4143
• On
• February 14, 2006

2
Introduction to Hardness

• Causes Sources of Hardness

Source Rain contact with soil and rock
formations
3
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
4
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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Chlorides

• General Considerations

Chlorides occur in all natural waters in wide
concentrations
Upland and mountain streams are quite low
Sea and ocean waters are very high
Urine contributes about 6 grams per day
Chloride in sewage is about 15 mg/L higher than
water
Sewage discharges add considerable chlorides to
streams
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Sanitary Significance
Chlorides in reasonable amounts not harmful

• US Public Health Recommends Limit of 250 mg/L

Chlorides and Nitrogen tests used for detecting
sewage contamination
Chlorides used as tracer in Sanitary
engineering practice
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Methods of Determination

• Mohr Method uses silver nitrate titrant

Potassium Chromate used to detect endpoint of
titration
Each ml. of 0.0141N Silver nitrate 0.5 mg of
Chloride
Mercuric Nitrate Method
Has less interference than the Mohr method
At pH 2.5, mercury combines with chloride and
Diphenylcarbazone containing nitric acid is the
indicator of endpoint
At 0.0141N, each milliliter of Mercuric Nitrate
titrant 0.5 mg of Chloride