Page 550 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Adsorption 505

quadrupole-quadrupole attractive interactions, con- one of two tests, molasses number ¼ K B=A, where
stituting the London dispersion forces of physical K is the molasses value of standard carbon, B is the
adsorption.’’ (Weber and Van Vliet, 1980, p. 17). optical density of filtrate from standard carbon, A is
Macromolecule: A molecule, usually a polymer, that may the optical density of filtrate from test carbon
6
4
have 10 < MW < 10 . (USEPA, 1973, p. B-6).
Macropore: Pores in activated carbon larger than 1000 A, Numerical solution: A computer solution of a finite-differ-
i.e., 1 mm (USEPA, 1973, p. A-4). ence form of a differential equation that relies on
Macroreticular: See reticular. small increments of change of a variable to calculate
Mass-transfer zone: The portion of the wave front in a GAC a new solution, e.g., solution at t 2 ¼ solution at
column in which mass transfer is occurring; in other t 1 þ Dt solution increment.
words, the adsorbate is being taken up, i.e., adsorbed, PAC: Powdered activated carbon; size range is less than U.S.
by the adsorbent in the MTZ. The shorter the length of mesh size 50, i.e., <0.3 mm. Others give <0.1 mm
the zone, the higher is the rate of uptake. as the mean particle diameter of PAC.
Materials-balance equation: A mathematical relationship Particle density: The mass weight of adsorbent divided by
that accounts for a given substance in terms of a volume of adsorbent particles.
given volume that says, basically, that mass flux-in Particle kinetics: Refers to the rate of change of adsorbate in
minus mass flux-out equals mass created or depleted. solution due to diffusion within the pores of the
Mathematical model: A mathematical equation or a set of GAC particles.
linked equations that is intended to simulate the Particle size: Usually refers to sizes of two screens, either in
behavior of certain variables of a physical system. the U.S. Sieve Series or the Tyler Series between
Mesh size: Mesh size refers to the number of open spaces in a which the bulk of the carbon sample falls. For
square inch of screen through which particles pass example, 8 30 means most of the carbon passes a
(Spotts, 2003). For a 20 50 mesh size, the 20 refers No. 8 screen but is retained on a No. 30 screen
to the largest size that the particles pass, e.g., 0.03 frac- (USEPA, 1973, p. A-5).
tionmaybelargerthana20meshscreen.The50refersto Partition: The relationship between two phases of a given
the smallest size that the particle can pass, e.g., 0.01 substance, e.g., the solution phase and the adsorbed
fraction may pass the 50 mesh screen (Spotts, 2003). phase of an adsorbate.
The sizes of particles are measured by obtaining a Phenomenological: (1) An observable fact or event, e.g., an
sample,e.g.,100g,andpassingthroughanestofsieves, item of experience or reality. (2) appearance of
from larger to smaller (sizes of very small particles are things as contrasted with their true being; (3) a fact
determinedbysettlingtests).Thesievenumber,e.g.,#8, or event susceptible to scientific description and
#12,...,#300,etc.,isinsequence,largersizetosmaller, explanation (adapted from http:==www.merriam-
respectively. Most particles of a given kind, e.g., sand, webster.com=).
anthracite, activated carbon, occur as a distribution of Physical forces: Physical adsorption is due to van der Waals
sizes. Conventions in designating sizes vary with the forces, which comprise London dispersion forces
and classical electrostatic forces.
purpose.Infiltration,d 10 andd 60 ,i.e.,10%passesthed 10
size and 60% passes the d 60 size, respectively. In acti- Physical–chemical treatment (PCT): A treatment sequence
vated carbon, the size is given in terms of sieve size in which physical and chemical processes are used to
passing all material and sieve size retaining all material the exclusion of biological processes (USEPA, 1973,
of the sample. For example, 8 30 means that the p. A-5). A PCT treatment scheme has been consid-
sample passes the #8 sieve and is retained by the #30 ered as a substitute for conventional biological was-
sieve. Common GAC sizes include 8 30, 8 30, tewater treatment and was an idea in vogue in the
12 40, etc. Two common sieve standards are the late 1960s and early 1970s. The concept probably
U.S. sieve series and the Tyler sieve series, with the had its origin in the USPHS Advanced Wastewater
United States being most common (Spotts, 2003). Treatment Program (AWTR, c. 1961–1968). A PCT
Methylene blue number: Defined as the mg methylene blue scheme following an existing biological treatment
adsorbed by 1.0 g carbon in equilibrium with a train is called ‘‘tertiary’’ treatment.
solution of methylene blue having a concentration Pore size distribution: A measure of the pore structure of
of 1.0 mg=L (USEPA, 1973, p. B-12). activated carbon which gives the relationship
Micropore: Pores in activated carbon smaller than 1000 A, between pore size and the volume of pores smaller
i.e., 1 mm (USEPA, 1973, p. A-4). or larger than that size. Pore size distributions in the
Model: A representation of a portion of reality, e.g., a draw- micropore range are determined from nitrogen
ing, a photograph, a mathematical model, etc. See adsorption isotherms while distributions in the
Chapter 3. macropore range are measured by means of a
Molasses number: An index of the adsorption capacity of a mercury penetrometer. Micropore distributions
given carbon as compared to a standard. Referring to can be related to the adsorptive capacities of