Summary of Chemistry Behind Water Treatment

An understanding of chemistry is so important to the water-treatment process that water-treatment facilities hire many chemists to analyze the quality of the water and oversee its treatment. One of the most fundamental chemical principles in water treatment is solubility. It is imperative to understand which contaminants are soluble (forming solutions) and which are insoluble (forming suspensions), in order to determine how they can be effectively removed. Insoluble contaminants can usually be removed by physical-separation processes, including screening, sedimentation, and filtration. These physical processes may be aided by chemical processes, such as coagulation, that help to entrap the suspended particles. Soluble contaminants, on the other hand, must be removed by chemical methods that render them insoluble, so that they can then be removed by physical means, such as sedimentation and filtration. Furthermore, an understanding of solubility is essential in choosing reactants that will generate insoluble precipitates with the dissolved contaminants. Solubility guidelines, such as those listed in the introduction to this Experiment, can be instrumental in choosing the proper reagents for water treatment.

Another critical chemical concept used in water treatment is concentration (i.e., the amount of a substance contained per unit volume). The concentrations of contaminants in the water supply must be carefully measured (typically using chemical-analysis methods that are not discussed in this tutorial) in order to determine whether they fall within acceptable ranges, and to determine how much must be removed. An understanding of concentration is also necessary to calculate the proper amount of a treatment chemical that must be added to achieve the desired effect in treating the water.

It is interesting to note that many of the water-treatment methods described in this tutorial, especially precipitation, filtration, and adsorption, are routinely used (on a smaller scale) in the chemistry laboratory. You will perform many of these procedures in your chemistry-laboratory (and biology) courses, as well as in many research laboratories you might join.

References:

Greenwood, N.N. and Earnshaw, A. In Chemistry of the Elements, Pergamon Press, 1984, p. 1269.

Letterman, D., ed. Water Quality and Treatment, 5th Edition. American Waterworks Association.  New York: McGraw-Hill.1999

Oxtoby, D.W. and Nachtrieb, N.H. Principles of Modern Chemistry, 3rd ed., Fort Worth: Saunders College Publishing, 1996, p. 140-144.

Persistence of Vision Ray Tracer (POV-Ray). URL: http://www.povray.org.

Tebbutt, T.H.Y. BASIC Water and Wastewater Treatment, London: Butterworths, 1990.

Viessman, W. and Hammer, M.J. Water Supply and Pollution Control, 6th ed., Menlo Park, CA: Addison-Wesley, 1998.

"Where is Earth's Water Located?" Water Science for Schools. United States Geological Survey, 1999. URL: http://wwwga.usgs.gov/edu/earthwherewater.html.

Acknowledgements:

The authors thank Dewey Holten, Michelle Gilbertson, Jody Proctor and Carolyn Herman for many helpful suggestions in the writing of this tutorial.

The development of this tutorial was supported by a grant from the Howard Hughes Medical Institute, through the Undergraduate Biological Sciences Education program, Grant HHMI# 71199-502008 to Washington University.