Page 121 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

and therefore the materials balance equation is Transport, diffusion: The transport of a substance by the
applicable. random motion of molecules.
Reactor, nonsteady state: A reactor in which the mass flow Transport, dispersion: As a part of the dispersion that
in or out or both varies with time. occurs in fluid flow, molecules, say dye, will be in
Reactor, packed bed: A reactor packed with some kind of a part of the fluid mass that has moved ahead of the
media such as granular activated carbon, sand, or mean flow, or similarly, with respect to the fluid
rocks. mass retained. See also dispersion.
Reactor, pond: A volume that may vary from one design to Transport, gas transfer: The transport of a gas across a gas–
another, usually several hectares in area with depth water interface.
varying from 1 m to perhaps 10 m, depending on the Transport, sedimentation: The movement of particles under
kind of pond. the influence of gravity to a ‘‘sink.’’
Reactor, steady state: A reactor in which the mass rate of Transport, turbulence: The random motion of a fluid caused
flux in and=or out is constant. by energy dissipation.
Reactor, trickling filter: A kind of biofilm reactor in which a Turbulence: Random motion of fluid mass from one
depth of rocks, usually about 80–120 mm in size, are momentum neighborhood to another causing a fluid
in a ‘‘column’’ form. shear, which becomes a work that is dissipated as
Sink: A site where a reaction occurs or a surface where par- heat.
ticles are removed from the reactor. The term, ‘‘sink’’ Wave, frontal: The tracer test result caused by a ‘‘step’’
is not unusual in the literature; as used here, however, function input of a tracer.
it has a broader connotation that while not contrary to Wave, pulse: The tracer test result caused by a ‘‘pulse’’
normal usage, it is used in a more explanatory sense. function input of a tracer.
Streamline: The locus of points that may define boundaries
that confine equal flows and in which there is no REFERENCES
advective flow across. Streamlines respond to the
geometrical configurations that shape the boundary. Beran, M. J., Dispersion of soluble matter in slowly moving fluids,
Tracer: A nonreactive substance that can be used to obtain Microfilm copy of unpublished PhD dissertation, Harvard
concentration time curves at some point downstream University, Cambridge, MA, 1955.
Champlin, T. L. and Hendricks, D. W., Treatment train modeling
in an advective flow. Salt, that is, the chloride ion of
for aqueous contaminants, in: Matrix of Contaminants and
sodium chloride, is a suitable tracer since the chloride
Treatment Technologies, Vol. II, Environmental Engineering
ionisnonreactive.Rhodamine-WTisanother.Atracer
Technical Report 53-2415-93-2, Department of Civil Engin-
may be used to develop isoquants of constant concen- eering, Colorado State University, Fort Collins, CO, May
tration in two- or three-dimensional flow situations. 1993.
Tracer test: The injection of a tracer at some upstream loca- Prescott, L. M., Harley, J. P., and Klein, D. A., Microbiology, 2nd
tion as a ‘‘slug’’ or as a ‘‘step’’ function with the edn., Wm. C. Brown Publishers, Dubuque, IA, 1993.
ensuing measurement downstream by a set of grab Rifai, M. N. E., Kaufman, W. J., and Todd, D. K., Dispersion
phenomena in laminar flow through porous media, Report
samples or by an in situ sensor.
No. 2, I.E.R. Series 90, Sanitary Engineering Research Labora-
Transport: The movement of a constituent (or a fluid mass)
tory, University of California, Berkley, CA, 1956.
from one set of spatial coordinates to another. Symons, J. M., Bradley, L. C. Jr., and Cleveland, T. C., The Drinking
Transport, advection: The transport of a substance by Water Dictionary, American Water Works Association,
advective flow. Denver, CO, 2000.