Page 169 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

WATER TREATMENT AND PURIFICATION 4.5

and detergents. Naturally occurring impurities include lignins, tannins, humic and fulvic acid,
and other biodecomposition products.

Alkalinity
All natural water contains some alkalinity. Alkalinity is a measure of the quantity of dis-
solved earth minerals in water, and reflects the water’s ability to neutralize acids. It is
mainly the sum of the carbonate, bicarbonate, and hydroxide ions in water, with borate,
phosphate, and silicate ions partially contributing to the total. It is reported as the ppm
equivalent of calcium carbonate. Alkalinity is regarded as the most important characteristic
in determining the scale-forming tendency of water.
Alkalinity is measured using two end-point indicators. The phenolphthalein alkalinity,
or P alkalinity, measures the strong alkali in the solution. The methyl orange alkalinity, or M
alkalinity, measures all of the alkalinity present in the solution. M alkalinity is often called
total alkalinity because it also includes P alkalinity. Alkalinity is not a measure of pH.

Iron

The most common form of iron is ferrous bicarbonate. It is also considered a form of hard-
ness of water. Iron causes problems with many ion exchange resins.

Magnesium
The most common forms are magnesium carbonate, magnesium bicarbonate, and magnesium
chloride. These impurities tend to deposit scale on surfaces they come in contact with.

Silica
The three most common kinds of silica are soluble, colloidal, and particulate. Soluble silica
is often referred to as reactive silica, and colloidal silica is sometimes called nonreactive
or polymeric. The most common form in solution is silicon oxide; in suspension it is found
as a fine colloid. These impurities tend to deposit a scale on surfaces they come in contact
with and form a gelatinous mass on RO membranes.

Sodium and Potassium
Both elements form similar salts, with the three most common being sodium or potassium
chloride, sodium or potassium carbonate, and sodium or potassium bicarbonate.

Chlorides and Sulfates

The most common forms are dissolved salts of sodium, potassium, calcium, and magne-
sium. These impurities tend to deposit a scale on surfaces they come in contact with.

Hardness
Hardness is the total amount of calcium, magnesium, iron, and other metallic elements that
contribute to the “hard” feel of water. Carbonate, sulfate, and chloride salts of these elements are

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