Environmental Engineering Reference
In-Depth Information
Note:
The role of pH in water is also associated with corrosivity, hardness,
acidity, chlorination, coagulation, carbon dioxide stability, and alkalinity.
Alkalinity
Alkalinity is a measure of the ability of water to absorb hydrogen ions with-
out significant pH change. Simply stated, alkalinity is a measure of the buff-
ering capacity of water and is thus a measure of the ability or capacity of
water to neutralize acids. The major chemical constituents of alkalinity in
natural water supplies are bicarbonate, carbonate, and hydroxyl ions. These
compounds are mostly the carbonates and bicarbonates of sodium, potas-
sium, magnesium, and calcium. These constituents originate from carbon
dioxide (from the atmosphere and occurring as a byproduct of microbial
decomposition of organic material) or minerals (primarily from chemical
compounds dissolved from rocks and soil). Highly alkaline water is unpalat-
able; however, this condition has little known significance on human health.
The principal problem with alkaline water is the reactions that occur between
alkalinity and certain substances in the water. The resultant precipitate can
foul water system equipment. Alkalinity levels also affect the efficiency of
certain water treatment processes, especially the coagulation process.
Note:
Total alkalinity
is determined by titration with sulfuric acid or other
strong acids of known strength to the end point of indicators (APHA-
AWWA-WEF, 2005). The result is expressed in mg/L of equivalent cal-
cium carbonate.
Hardness
Water
hardness
is commonly defined as the sum of the polyvalent cations
dissolved in the water. The most common cations are calcium and magne-
sium, although iron, strontium, and manganese may contribute. Hardness is
usually reported as an equivalent quantity of calcium carbonate. Generally,
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The density of water is 1 gram per cubic centimeter at 39.2°F and 0.95865
gram per cubic centimeter at 212°F.
