Page 85 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

2.A.4 DISINFECTANT SELECTION added to a liter of water is a contaminant. (3) To
make impure or corrupt by contact or mixture. A
Whenever disinfection occurs, oxidation also occurs. For a
contaminant is a substance that is added to a pure
‘‘safe’’ disinfection technology, (1) use a ‘‘safe’’ disinfectant
substance.
and (2) remove the precursors to oxidation by-products before
Criterion: A standard, rule, or test on which a judgment or
disinfecting (Trussell, 1992).
decision can be based.
Regarding the distribution system, maintenance of a disin-
Disinfection by-products (DBPs): The reactions of various
fectant residual is important. For factors to consider, include
disinfectants, e.g., chlorine, bromine, and ozone,
(1) residual stability, (2) residual toxicity, (3) effectiveness
with organic matter—natural organic matter in par-
in biofilm control, and (4) Oxidation by-product issues
ticular—result in a variety of by-products.
(Trussell, 1992).
Disinfection by-product precursor: The reactions of various
disinfectants, e.g., chlorine, bromine.
2.A.5 OTHER NOTES Dissolved organic carbon (DOC): Organic carbon passing a
The formation of chlorinated by-products increases with 0.45 mm filter (Edzwald, 1993, p. 24).
elapsed time. To illustrate, Figure 2.A.2 shows experimental Fulvic acid: Similar to humic acids, except it is soluble at
data from chlorination of fulvic acids (HOCl ¼ 20 mg=L, pH ¼ 1.0 and believed to be in true solution vis-à-vis
pH ¼ 7.0, TOC ¼ 4.1 mg=L) (Reckhow and Singer, 1984). being colloidal (Randtke, 1988, p. 43). MW < 5000
The total halide concentration, TOX, was greater than 1100 and can be removed by GAC. Most DBPs are due to
mg=L after 300 h, with about 600 mg=L after 10 h. Also, as reactions with fulvic acid.
seen, the CHCl 3 , TCAA, and DCAA concentrations were Geometric mean (n.): Mathematics (1) The nth root,
significant fractions of the TOX concentration. usually the positive nth root, of a product of n fac-
tors. Parkhurst (1998) states: The geometric mean
is the antilog of the mean logarithm of a set of
GLOSSARY
numbers or, equivalently, the nth root of the product
Aromatic compound: A class of molecules with six carbons of n numbers. State health departments use this
and six hydrogens in a ring. A key property is their term frequently in referring to concentrations of
remarkable stability (Aihara, 1992, p. 62), which organisms.
makes them valuable for many uses, e.g., paint thin- Humic acids: High-MW negatively charged macromolecules
ner, mothball, gasoline additive, solvents, and as a having colloidal properties (Edzwald, 1993, p. 24).
source for synthetic fibers, resins, and dyes. The Also, they are insoluble at pH ¼ 2.0 (Van Benscho-
carbons are arranged in a closed hexagonal ring—a ten and Edzwald, 1990, p. 1527). MW > 30,000.
structure that does not want to react. The ring structure Humification: Humification is a process by which biomass
is the distinguishing aspect of the aromatic com- consisting of dead plant and animal remains is con-
pounds. Ordinary combustion produces a wide variety verted to humis; this is one of the basic steps of the
of aromatic compounds. Ideally, when hydrocarbon carbon cycle.
fuels burn, they should form carbon dioxide and Log-normal distribution: The logarithms of the concentra-
water; in reality, complete combustion is rare, and tions have a normal distribution. It is common stat-
the soot and smoke contain a number of multiring or istical practice to transform such sample
polycyclic, aromatic compounds, some of which are concentrations to logs before estimating confidence
highly toxic. limits or performing statistical tests such as analysis
Benzene: A ring compound with six carbons and six hydro- of variance or t tests (Parkhurst, 1998). This term is
gens, it is the prototype of a class of molecules found frequently in the literature.
known as the aromatic compounds. Molality: Mass of a solute per unit mass of solvent, i.e.,
Carcinogen: Substance that may cause the development of moles(solute)=moles(solvent).
cancer after exposure at some threshold level or time Molarity: Mass of a solute per unit volume of solvent, i.e.,
duration. moles(solute)=V(solvent).
Color: Substance in water that causes ‘‘color’’ as measured Mole fraction: In a given volume, the amount of a dissolved
on the cobalt scale. Two kinds of color are ‘‘appar- substance i in moles, i.e., n i , divided by the summa-
ent’’ color and ‘‘true’’ color. The former is the tion of the moles of all substances in the solution, n;
result of a measurement using a sample of water i.e., mole fraction i ¼ n i =n.
‘‘as is,’’ and the latter is the same measurement Natural organic matter (NOM): The whole group of natural
after filtering. Organic color is associated with nat- organic substances of which humic substances are
ural organic matter. a part.
Contaminant: (1) A substance in water other than molecular Normative: Of, relating to, or prescribing a norm or standard:
water. (2) A species added to another species that normative grammar. Related to the ‘‘norms’’ of a
serves as a matrix. A few molecules of sodium chloride given culture.