Page 329 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

to Kolmogorov’s microscale, and to provide advice on tion’’ should be used in describing bulk movement of
several books that were consulted on the topic. Professor fluids; ‘‘advection’’ has been adopted here and seems
Robert Meroney, Department of Civil Engineering, Colorado to be favored in the literature and by those with whom
State University, also gave advice about turbulence and I have discussed the matter.
clarified points concerning ‘‘computational fluid dynamics’’, Agitation: Induced motion of a material in a specified fash-
i.e., cfd. ion, usually a circulatory pattern within a vessel
Professor Adrian Hanson, Department of Civil Engineer- (McCabe et al., 1993, p. 235). Purposes of agitation,
ing, New Mexico State University, shared his knowledge they say (p. 236), are: to suspend solid particles, to
on turbulence and on Kolmogorov’s microscale in several blend miscible liquids, to disperse a gas through a
sessions in Jackson, Wyoming, Fort Collins, and Angel Fire, liquid in the form of small bubbles, dispersing a
New Mexico, over a 2 year period. second liquid, immiscible with the first, to from an
Kevin Gertig, Water Resources and Treatment Operations emulsion of suspension of fine drops. See also,
Manager, City of Fort Collins Utilities, provided photographs ‘‘mixing’’ and ‘‘blending.’’
of mixing systems used at the Fort Collins WTP, and many Axial flow: Advective flow along the axis of an impeller.
other photographs, some of which were used in this chapter. Back-mix reactor: (1) Mixing between the fluid elements
In addition he was always available for discussions regarding which have been present in the reactor for different
his experiences with mixing systems. Bob Reed, superintend- lengths of time (Stenquist and Kaufman, 1972, p. 7).
ent, and Steve Hall, operator, Soldier Canyon WTP, Fort The consequence is, they stated, that reactants enter-
Collins, shared their experiences with jet mixers and provided ing the mixer may ‘‘react’’ with previously formed
access to Soldier Canyon WTP to examine their installations ‘‘reaction’’ products rather than with the constituents
and spent considerable time in reviewing drawings of their jet- of the water stream of concern. (2) See ‘‘CSTR,’’
mixer systems. ‘‘recycle reactor,’’ or ‘‘mixed reactor’’ (Levenspiel,
Tim Rice, Municipal Treatment, Inc., Lakewood, Color- 1972, p. 97). (3) The connotation is that flow returns
ado, arranged for the use of Figures 10.3c and 10.24a and b ‘‘back’’ through the reaction zone, either by returning
with Glen P. Sundstrom, product promotion manager, Sie- a discrete flow or by the circulation caused by an
mens Water Technologies Corp., Rockford, Illinois, who impeller in a closed tank. The raw water once blended
granted permission to use the figures and updated informa- with coagulant chemicals, for example, is recycled
tion on Siemens products. Sundstrom also provided high- back through the reaction zone (see also Kawamura,
resolution photographs of the Water Champ mixing system 1991, p. 74). (4) Amirtharajah (1979, p. 133) desig-
for use in the text. nates a ‘‘mechanical mixer’’ as a back-mix reactor.
All references to Spraying Systems Co. products and lit- Baffle: In mixing, a flat blade attached to the side of a tank,
erature found in this book were provided with the permission oriented vertically.
of Spraying Systems Co., Wheaton, Illinois. Scott Monson, Basin: Adefined volume usually associated with some pur-
Monson & Associates, Olathe, Kansas, regional representative pose such as storage, settling, reaction, etc. A tank is
for Spraying Systems Co. (2010), arranged for permission to volume having geometric proportions, which may or
use catalog material (http:==www.spray.com=misc=legal.asp). may not be true for a basin.
Terry Naughton, director of order processes, Chemineer, Blender, in-line: Mixer placed in a pipeline.
Dayton, Ohio re-granted permission to use the materials as Blending: Mixing to achieve molecular solution of one spe-
obtained from the Chemineer Website, and references to the cies with another, e.g., of a saline solution with
Chemineer-Kenicse brand name. The original contact with a water solution, or of a tracer dye solution with a
Naughton was through Jim Martinson, Falcon Supply, Niwot, water solution. A criterion for achievement of suffi-
Colorado. cient blend may be set arbitrarily. For batch blending
this could be at the time when the concentration is
0.999 times the concentration at mixing at time
GLOSSARY
equals infinity (the latter could be defined as the
Advection: (1) Transport of a fluid mass; the transport gener- time when further change in concentration is not
ally is in response to a potential gradient as in pipe detectable). If the blending is to be achieved for
flow, an open channel, an ocean current, etc. (2) The a continuous flow reactor, e.g., with an impeller
transfer of a property of the atmosphere, such as heat, in a tank, with a relatively large flow of raw water
cold, or humidity, by the horizontal movement of an and a very small flow of coagulant, such as a neat
air mass; the horizontal movement of water, as in an liquid alum solution, the blending may be considered
ocean current. (3) Latin: advecti, advectin, act of to be achieved when the concentration of alum is
conveying; from advectus, past participle of advehere, 0.999 times the theoretical concentration of mixing
to carry. (2) and (3) From Merriam-Webster Online: when the two proportions are combined. The effi-
http:==www.merriam-webster.com on November 27, ciency of the impeller–tank system may be evaluated
2001). See also ‘‘convection.’’ Some difference of by means of a dye or salt solution being injected at
opinion relates to whether ‘‘advection’’ or ‘‘convec- the desired location in the system and under the