Page 66 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

2 Water Contaminants

Contaminants in water encompass a wide variety of sub- parameter range, e.g., 3.3 pH 10.7 for trout (McKee and
stances. A sampling might include inorganic ions, organic Wolfe, 1963, p. 236). A water quality standard is a quasi-legal
molecules, chemical complexes, mineral particles, microor- limit for a contaminant concentration or parameter value, i.e.,
ganisms, and even heat. Larger kinds of contaminants may the value may be referenced in a law but may be either ‘‘recom-
include oil and scum, natural debris, fish, boards, rags, and mended’’ or ‘‘enforced,’’ depending upon the severity of the
whatever may be discarded to the sewer or to ambient waters. effects and the levels that are economically achievable. Usually,
Contaminants can number, literally, in the millions. Those there is nothing absolute about the foregoing definitions.
that are regulated in the United States number about 4000. Table 2.1 illustrates a water quality description for a pro-
Typical source waters for various purposes include moun- posed industrial waste discharge. Points of interest in Table
tain streams, lower reaches of rivers, municipal wastewater, 2.1 are (1) some 37 contaminants are listed; (2) concentration
treated municipal wastewater, hazardous waste sites, etc. Each limits are shown for each contaminant; (3) two places for
has a typical ‘‘profile’’ of water quality, and some kind of discharge—a publicly owned treatment works and a river—
treatment is always required prior to use in order to meet the are shown, each with its own respective discharge limits; (4)
criteria or standards of that use. Then, after a use of water, and limits are given in terms of the monthly average and the daily
prior to discharge to rivers, lakes, and seas, the product water maximums; (5) a variety of organic compounds are listed; and
must meet the standards and=or criteria established for such (6) a variety of heavy metals are listed. Each treatment situ-
discharge. The treatment train selected depends upon the ation is different and would have a different list of contamin-
particular combination of source water available and product ants and different limits. A similar tabular description, but
water required. The source water quality available and prod- with different constituents, would apply to a municipal waste-
uct water quality required, along with cultural, economic, and water discharge, a drinking water treatment plant product
operation factors, is the treatment ‘‘context.’’ Thousands of water, or another industrial waste situation.
such combinations are possible, making each treatment con-
text unique.
2.1.1 CONTAMINANTS
A contaminant is defined as a substance that makes another
2.1 WATER QUALITY: DEFINITIONS
substance impure. As applied to water, any material that is
The term water quality has to do with the description of present in the water other than molecular water would be a
given water in terms of its characteristics. Characteristics of contaminant. Often, the term has a negative connotation; in
water quality include temperature; concentrations of various other words, we most often refer to an undesired substance as
kinds of particles; concentrations of dissolved materials; and a contaminant. The term’s constituents and characteristics
parameters such as turbidity, pH, color, conductivity, etc. have more neutral connotations and are used here almost
The term characteristic is more inclusive than the term interchangeably with the word contaminant. As noted, how-
contaminant and would include temperature, color, turbid- ever, the term characteristic is more inclusive and would
ity, conductivity, etc. Two of these categories of character- include such things as temperature and turbidity.
istics, i.e., particles and dissolved materials, would include A pollutant is a synonym of the word contaminant but is
thousands of species each. A particular combination, or set, more often identified as an introduced contaminant from an
of characteristics would comprise a water quality profile. anthropogenic source. The definition of a pollutant by the US
Those contaminants that interfere with a particular use may Public Health Service drinking water standards (USPHS,
be considered pollutants. 1962) was
To add further to the definitions that circle about the same
idea, the term parameter is used frequently. Water quality Pollution, as used in these Standards, means the presence of
parameters might include temperature, BOD, pH, specific any foreign substance (organic, inorganic, radiological, or
electrical conductance, UV 254 absorbance, etc. biological) in water, which tends to degrade its quality so as
With respect to uses of water, the terms criterion and stand- to constitute a hazard or impair the usefulness of the water.
ard are important. A water quality criterion is a contaminant
concentration limit that, if exceeded, may impair a use or As used later by the regulations pursuant to PL92-500—the
cause a toxic effect in certain animals or plants. As an example, 1972 Clean Water Act—the term pollutant is associated
aboron limit of 0.5 mg=L is considered appropriate for with an introduced contaminant and implies impaired utility
citrus crops. A criterion could also specify a contaminant or of water.

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