Environmental Engineering Reference
In-Depth Information
samples simultaneously. If testing in the field is important, meters designed
for field use can be obtained for around the same cost mentioned above. If
samples will be collected in the field for later measurement, the sample bottle
should be a glass or polyethylene bottle that has been washed in phosphate-
free detergent and rinsed thoroughly with both tap and distilled water.
Factory-prepared Whirl-Pak
®
bags may also be used.
Total Alkalinity
Earlier, we pointed out that alkalinity is a measure of the capacity of water to
neutralize acids. Alkaline compounds in the water, such as bicarbonates (bak-
ing soda is one type), carbonates, and hydroxides, remove H
+
ions and lower
the acidity of the water (increasing the pH). They usually do this by combin-
ing with the H
+
ions to make new compounds. Without this acid-neutralizing
capacity, any acid added to a stream would cause an immediate change in the
pH. Measuring alkalinity is important in determining the ability of a stream
to neutralize acidic pollution from rainfall or wastewater—one of the best
measures of the sensitivity of the stream to acid inputs. Alkalinity in streams
is influenced by rocks and soils, salts, certain plant activities, and certain
industrial wastewater discharges. Total alkalinity is determined by measur-
ing the amount of acid (e.g., sulfuric acid) required to bring the sample to a pH
of 4.2. At this pH, all the alkaline compounds in the sample are used up. The
result is reported as milligrams per liter of calcium carbonate (mg/L CaCO
3
).
Analytical and equipment Considerations
For total alkalinity, a double-endpoint titration using a pH meter (or pH
“pocket pal”) and a digital titrator or burette is recommended. This can be
done in the field or in the lab. If alkalinity must be analyzed in the field, a
digital titrator should be used instead of a burette, because burettes are frag-
ile and more difficult to set up and use in the field. The alkalinity method
described below was developed by the Acid Rain Monitoring Project of the
University of Massachusetts Water Resources Research Center (River Watch
Net work, 1992).
Burettes, Titrators, and Digital Titrators for Measuring Alkalinity
The total alkalinity analysis involves titration. In this test, titration is the
addition of small, precise quantities of sulfuric acid (the reagent) to the
sample until the sample reaches a certain pH (the endpoint). The amount of
acid used corresponds to the total alkalinity of the sample. Alkalinity can be
measured using a burette, titrator, or digital titrator (described below):
