Page 275 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

is necessary for dispersing the chemicals throughout Coordination compound: Has one or more central atoms or
the water (Conley and Evers, 1968). central ions, usually metals, with a number of ligands
Coagulation=flocculation: Moffett (1968, p. 1256) noted attached. Same as a complex.
that the terms coagulation and flocculation are Copolymer: If the polymer molecule is formed from more
ambiguous, as used in the water field. This was than one type of repeating chemical unit, it is called a
affirmed by O’Melia (1970), who stated that coagu- copolymer (Singley et al., 1971).
lation and flocculation have no commonly agreed Coprecipitation: Contamination of a precipitate by an
upon definitions. Opinion seems to have converged, impurity that is otherwise soluble under the condi-
however, on the following definitions: tions of precipitation (Randtke, 1988, p. 41).
1. Coagulation refers to the chemical alteration of a Coulomb: Quantity of electric charge. Charge is related to
colloid such that aggregation between destabilized current by the relation, q ¼ i t, in which q ¼ quantity
colloids and coagulant chemicals can occur upon of charge (C), i ¼ current (A), and t ¼ time (s). For
mutual contact reference, 1.00 As ¼ 1.00 C.
2. Flocculation is the process of aggregating coagu- Coulombic interaction: Attraction or repulsion between
lant chemicals and colloids by contact induced by charged particles in accordance with Coulomb’s
some transport mechanism, for example, Brown- law, that is,
ian motion or turbulence.
Colloid: Small particles that do not settle due to an electric q 1 q 2
F ¼ 2 (G9:1)
surface charge, usually negative. The characteristic 4pDe o r
size range is 10 9 to 10 5 m (10–100 Å or 10 mm).
Sennett and Olivier (1965, p. 34) suggest an upper where
size limit of 1 mm for purposes of classifying a F is the force between q 1 and q 2 (N)
‘‘sol,’’ but point out that larger particles may exhibit q 1 is the charge on particle ‘‘1’’ (coulombs)
characteristics of a colloid. q 2 is the charge on particle ‘‘2’’ (coulombs)
2
12
Colloidal system: A ‘‘classical’’ colloidal system is a sol, that e o ¼ 8.854 10 (C =(mJ)
is, dispersions of small solid particles in a liquid D is the dielectric constant (dimensionless)
medium. These small particles are larger than the r is the separation distance between particles ‘‘1’’
molecular size. In a colloidal system there are two and ‘‘2’’ (m)
phases: (1) the dispersed phase, a solid, liquid, or gas
that is finely divided and dispersed uniformly Thus such forces are found only in systems contain-
throughout a second substance which is the disper- ing charged species. The strengths of the interactions
sion medium or continuous phase, and (2) the con- equal or exceed those of the covalent bonds (Myers,
tinuous phase may be a solid, liquid, or gas (Myers, 1991, p. 39).
1991, pp. 187–195). An emulsion is a liquid dis- Covalent bond: When two atoms bind to form a typical
persed in another liquid. A second class of colloids nonionic molecule, the forces involved in bond for-
is where the aggregates of molecules that may be mation are termed, covalent. The characteristic of
simultaneously a molecular solution and a true col- such a bond are shared electrons between two or
loidal system (FA and HA would be in this cat- more atoms. The covalent bonds are short range,
egory). Yet another class of colloids is the lyophilic that is, they act over a bond distance of 0.1–0.2 nm.
colloids which are solutions but in which the solute The energies of normal covalent bonds range from
molecules, that is, polymers, are much larger than 150 to 900 kJ=mol (100–300 kT), and generally
those of the solvent. decrease in strength as the bond length increases
Color: Substance in water that causes ‘‘color’’ as measured (Myers, 1991, p. 39).
on the cobalt scale. Two kinds of color are ‘‘appar- Critical coagulant concentration (CCC): The minimum
ent’’ color and ‘‘true’’ color. The former is the result concentration of coagulant above which destabiliza-
of a measurement using a sample of water ‘‘as-is’’ tion will take place (Stumm and O’Melia, 1968,
and the latter is the same measurement after filtering. p. 516).
Organic color is associated with NOM. Cross-linking: Incorporation of divinylbenzene into the
Complex: In aqueous solution, free metal ions are complexed polymerization of styrene results in two vinyl groups
with water. The metal ions are said to be hydrated. participating in two separate chains, producing a
The interaction of these hydrated metal ions with three dimensional network. Polystyrene, for
acids and bases is a ligand exchange reaction that example, is soluble in many solvents but with 0.1%
is commonly called hydrolysis (or protolysis). A divinylbenzene the polymer no longer dissolves
complex is the same as a coordination compound. but only swells (Streitwieser and Heathcock, 1985,
To summarize, p. 1113).
Crystal lattice: A solid that has a regular geometric arrange-
ligand þ central metal ion ! complex ment of atoms in space that determine its properties.