Page 279 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

and related mostly to wastewater treatment; the idea Stable suspension: A suspension of charged colloidal par-
was to propose an alternative to biological treatment. ticles, that is, a sol, which has not been ‘‘coagu-
pK a : Defined, pK a ¼ log K a . See also, equilibrium constant. lated.’’
Polyaluminum chloride: Alum that has been reacted with Stability constant: Equilibrium constant for a complex reac-
OH under special conditions forms a polynuclear tion, with complex as product.

complex that remains stable over a wide range of pH Stern layer: The fixed layer of positive ions associated with a
and temperature conditions. negatively charged colloid, usually only a few ang-
Polydisperse: Particles in a colloidal system are of different stroms in thickness, called the ‘‘fixed’’ layer or the
sizes, that is, they have a broad size distribution ‘‘Stern’’ layer.
(Myers, 1991, p. 192). Stoichiometric: Refers to the fact that chemical reactions
Potential barrier: The potential field of a charged particle occur with chemicals combining in ‘‘definite’’ pro-
varies, that is, increasing and then decreasing, with portions, that is, definite mole ratios.
radial distance from the edge of a colloidal particle. Streaming potential: (1) The electric field generated when a
The ‘‘hump’’ that characterizes the variation is called liquid is forced to flow past a stationary charged
the ‘‘potential barrier.’’ surface (Myers, 1991, p. 82). (2) When a solution
Polymer: A repeating chain of structural groups of atoms, is forced through a porous plug or tube of material
that is, monomers. A polymer may contain more which acquires charge in contact with solution, a
than one type of subunit. streaming potential is set up (Gregory, 1975, p. 65).
Polymer: A collection of monomers bonded by chemical An instrument that measures this is a streaming
forces. The polymer may have more than one current detector.
monomer. Supersaturation: A product concentration that exceeds that
Polyelectrolyte: A polymer having ionizable groups or which may exist in equilibrium with other constitu-
charged sites. ents.
Precipitate: A solid compound formed in a solution when the Surface potential: The potential, c o , at the surface of a
solubility product has been exceeded. colloid, also called the Nernst potential.
Restabilization: As coagulant is added to a suspension, set- Thermal energy: The usual measure of thermal energy is
tled water turbidity decreases at some critical coagu- given as kT.At258C, kT ¼ 25.7 mV (the kT value
lant (CCC) dosage. As dosage is increased further, was from Adamson, 1967, p. 212). The kT term is
‘‘charge reversal’’ occurs, which is ‘‘restabilization.’’ used often an energy reference, with kT being in the
Further addition of coagulant may result in precipi- denominator of a dimensionless ratio.
tation of the metal hydroxide with associated turbid- Total organic carbon (TOC): Organic carbon as measured
ity increase. by a TOC analyzer. See Chapter 2.
Salt: A compound that dissociates in solution into anions and Trivalent positive ion: An ion that has a valence of þ3, for
cations. example, A ,Fe .
3þ
3þ
Shulze-Hardy Rule: The rule states that coagulation effi- Turbidimeter: An instrument with a light source and a
ciency of coagulation increases with metal ion detector that measures the turbidity of a water. The
valence in the ratio of 1:100:1000 as the charge of instrument must be calibrated with a standard. For-
the counterion increases in the ratio of 1:2:3, for mizon has been used as an accepted standard. Turbi-
example, for Na ,Ca , and Al , respectively dimeters may be bench instruments or ‘‘online.’’
3þ
2þ
þ
(Sawyer and McCarty, 1967; O’Melia, 1969, p. 89, Turbidity: A measure of the light scattering property of a
p. 221). The rule is quoted frequently and fits with water by an instrument called a turbidimeter.
the double layer theory concept, except that Gregory Van der Waals interaction: Attractive forces between atoms
(2006, p. 82), mentions that while the theoretical and molecules were postulated earlier than 1870 by
6
3
dependence is 1=z , it is experimentally 1=z . van der Waals to explain the nonideality of real
Sol: (1) A colloidal suspension. (2) A dispersion composed of gases. The three types of forces are due to: (1)
particles smaller than 1 mm is considered a sol; a orientation, (2) induction, and (3) dispersion (Greg-
dispersion of particles larger in size is considered a ory, 1975, p. 77).
suspension. Emulsions and suspensions may exhibit Zeolites: Silicates with open 3D structures with ‘‘cages’’ of
colloidal properties and may be so treated (Sennett molecular dimensions containing water and cations
and Olivier, 1965, p. 33). (van Olphen, 1977, p. 64).
Zero point of charge (ZPC): (1) The concentration of an
Specific ultraviolet absorbance (SUVA): SUVA ¼ 100
[UV254 (cm)]=[DOC (mg=L)] additive, for example, an ion, to a colloidal suspen-
1
Units are m =mg=L (Edzwald, 1993, p. 21; sion at which the particles are rendered neutral is
Edwards, 1997, p. 80). To obtain SUVA, UV 254 is called the zero point of charge. If the recharging
plotted against different experimental values of DOC ions are Hþ or OH and the process is followed
(for a given water); the slope of the plotted line is by a change in pH, the pH at which the particles
defined as SUVA. See Chapter 2. do not move in an electric field is usually referred to