Page 73 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

28 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

became feasible (such as in gas chromatography). The ability
BOX 2.3 THE IONISTS to measure organic compounds at concentrations in the range
of micrograms per liter made possible the development of
To give an idea of how recent the notion of water
water quality standards in the same range.
quality has been, the idea of expressing concentrations
of mineral substances in terms of ion concentration did
not catch on until after about 1900 (and certainly not 2.4 CATEGORIZATIONS OF CONTAMINANT
before 1890). By about 1890, Svante Arrhenius of
SPECIES
Uppsala, Jacobus Henricus van’t Hoff at Amsterdam,
and Wilhelm Ostwald at Leipzig had formulated a com- Contaminantspeciesnumberinthemillions.Suchalargenumber
prehensive theory of solutions and became known as of species must be dealt with in terms of a classification system.
the ‘‘Ionists’’ (from Servos, 1990, pp. 13–43).
To put in perspective the ionic theory of solutions, 2.4.1 SYSTEMS OF CATEGORIZATION
the notion at the time was that a salt in solution retained
There are several kinds of systems available for organizing
its identity as an undissociated compound. Thus, com-
water quality knowledge. Examples include
pounds in solution were called sulfate of alumina, sul-
fate of calcium, chloride of sodium, etc., and not as
. Alphabetical
ions, e.g., Ca ,Cl ,SO 4 , etc. The ionic theory
2
2þ

. Chemical Abstract System (CAS) number
was not embraced with enthusiasm as one might expect
. Chemical category such as organic, synthetic
(e.g., being a conceptual ‘‘breakthrough’’), but rather
organic, inorganic, metal, etc.
with skepticism and doubt. The ionic theory displaced
. Class within a category such as alcohols, aldehydes,
the prevailing notions of solution only gradually, with
phthalates, etc.
tradition hanging on for several decades after discovery.
. Regulatory lists, e.g., Safe Drinking Water Act
The practical significance is that if we are interested, for
Regulated Contaminants, Priority Pollutant List, etc.
example, in water quality data c. 1900, we must be
prepared to deal with the old expressions.
Information concerning these contaminants was available in
the EPA Register of Lists (USEPA, 1991; Miller, 1993). The
Register of Lists (not available by web access in 2010) cross-
referenced the chemicals with the statute listing and the EPA
2.3.2 MEASUREMENT TECHNOLOGIES
office administering. Such listing permitted cross-
Prior to 1960, coliforms, turbidity, and pH were the main referencing in terms of CAS number, contaminant type (e.g.,
concerns in drinking water, along with selected anions and polycyclic aromatic hydrocarbon, amine, organic acid, par-
cations—mainly those associated with hardness and alkalin- ticulate, etc.), empirical formula, contaminant classification
ity. Water supplies with heavy metals were avoided. Chlorine (e.g., organic, synthetic organic, volatile organic, inorganic,
was an added constituent that required measurement. In was- metal), and the law or regulation under which the contaminant
tewater, BOD and SS were the main concerns (after floatables, is regulated (e.g., Priority Pollutant List, CWA Section 304,
scum, oil, and settable materials). The coliform density was CAA Section 112, RCRA, Sludge Regulations of February,
measured by the most probable number (MPN) method, 1993, SARA Section 313, SDWA).
which was supplemented about 1960 by the membrane filter
method. Cations and anions were measured by traditional wet
2.4.2 ILLUSTRATIVE SYSTEM OF CONTAMINANT
chemistry methods involving titrations to some end point or
CATEGORIZATION
conversion of a given substance to a colored complex that
followed the Lambert–Beer law and could be measured by a As noted, contaminants may be categorized by a variety of
spectrophotometer. The Jackson tube measured turbidity; this systems. Table 2.4 is another illustrative categorization of
was a tube with gradations, which was filled with water until contaminants. The system shown was devised, for use here,
the light from a candle at the bottom was extinguished. The to illustrate the broad scope of contaminant categories, the
reading was stated as Jackson Turbidity Units (JTU). large number of contaminant species, and the idea that con-
By the early 1960s, a major technological revolution was taminant categorization may be devised to suit the purpose at
underway in instrumental analysis. The TOC analyzer was hand (but is not done arbitrarily). Table 2.5 lists some of the
developed, along with the atomic absorption instrument for many pathogenic organisms, showing the associated diseases,
metal ions, the gas chromatograph for organic compounds, and is included to give some idea of the microbial hazards of
polarography for specific ion probes, and the mass spectro- untreated water. Figure 2.1 shows just three organisms that
graph for any compounds. While these instruments became may be found in ambient waters; tens or hundreds of micro-
available technologies in the 1960s, they were not used organism species are found commonly in a given sample of
widely in water treatment until years later. These instruments ambient water, depending on the source. Counts of an indi-
developed further in the 1970s in the degree of sensitivity, and vidual organism species could range from a few to several
soon measurement in the range of micrograms per liter thousand.