Page 231 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

8.16 Sizing a System by Table of Equipment Sizes ment, Orlando, Florida, April, 1994. The term
Reference is Section 8.4.4 and Tables 8.6 and 8.4. ‘‘contact zone’’ was favored over ‘‘reaction zone’’
Given at the conference; the definitions are the same.
3
Assume Q ¼ 0.044 m =s (1.0 mgd). DAF: Acronym for dissolved air flotation.
Detention time: Defined as the volume of a basin divided by
Required
flow, i.e., u ¼ V=Q.
Select a package plant for the flow given.
Diffuser: A device with many small orifices for flow of a
fluid for the purpose of mixing with another fluid.
ACKNOWLEDGMENTS Diffusion: Transport of material by random motion, such as
molecular diffusion caused by the thermal motion of
The photographs in Figure 8.13 were taken by the author
molecules. Turbulent diffusion is due to the random
and used by permission from the late Paul Grundeman, super-
motion of turbulence.
visor, Marcy Gulch Wastewater Treatment Plant, Highlands
Dissolved air flotation: Flotation process in which the air
Ranch, Colorado. Dr. John Hendrick, General Manager of the
bubble source is dissolved air that ‘‘precipitates’’ in
district gave permission to use the photographs taken at the
a zone of lower pressure where contacts are made
plant for this book (2010).
with the solid particles.
Film thickness: For any motion of a fluid across a surface, a
GLOSSARY velocity gradient exists with zero at the surface to a
finite value in the bulk of flow; the distance is called
Air: A mixture of gases; nitrogen and oxygen comprise
the ‘‘boundary layer.’’ If such a fluid motion exists
0.9903 mole fraction of air. The other gases are Ar,
across a concentration gradient, say in water, then
CO 2 , Ne, He, Kr, Xe, CH 3 , and H 2 ,O 3 , and Rn.
the distance from the gas–water interface where the
Adding the mole fractions of argon and carbon diox-
concentration could be say that in equilibrium with a
ide to those of oxygen and nitrogen give 0.9999971.
gas, to a point in the bulk of the solution where the
The molecular weights and mole fractions are given
concentration gradient has become near zero is
along with Henry’s constants, where available.
called the ‘‘film thickness.’’
Float layer: The collected air–solid-particle agglomerates
that have risen to the water surface.
N 2 O 2 Ar CO 2 Ne
Flotation: Unit process in which air bubbles are brought into
MW 28.0134 31.9988 39.948 44.0098 20.1797 contact with solid particles to cause the latter to
X(gas) 0.78084 0.209476 0.00934 3.14 10 4 1.818 10 5 become buoyant and rise to the surface, where they
H(208C) 19.01 43.39 1688 are skimmed by blades into a collection trough. The
He Kr Xe CH 3 H 2 solid particles may be pretreated by means of coagu-
lation and flocculation to form a floc.
MW 4.0026 83.80 131.29 16.0428 2.01588 Gas precipitation: Formation of gas bubbles due to gas
X(gas) 5.24 10 6 1.14 10 6 8.7 10 8 2 10 6 5 10 7
concentration in water exceeding the equilib-
H(208C) 23.18 1.603
rium concentration for the local pressure of the
Notes: (1) Data from Table H.1. (2) H(208C) is Henry’s constant at bubbles.
208C with units (mg gas i=L water=atm gas i). Gas saturation: Concentration of gas, species i, in water
that is in equilibrium with the partial pressure of
gas i in the gas phase across a common gas–water
Attachment: Bonding of one particle to another by an adhe- interface.
sion force. For two particles that have opposite Henry’s constant: An equilibrium constant defined here as
charges, e.g., a negatively charged bubble and a the ratio of concentration of gas i dissolved in water
positively charged floc particle (i.e., after coagula- to the partial pressure of i in the gas phase. Magni-
tion), the force is electrostatic. For particles without tude depends upon the units for aqueous phase con-
charge, bonding is by van der Waal’s force. centration and gas pressure. Also, some definitions
Attachment coefficient, a: Ratio of particle–bubble attach- are the reciprocal of others.
ments to particle–bubble contacts. Henry’s law: Concentration of gas species i in water is pro-
Bifurcation: Division of a fluid flow. portional to partial pressure of i in the gas phase. See
Contact zone: Zone in flotation basin just after bubble for- also Appendix H.
mation and as the particle stream enters in the flow Hydraulic grade line (HGL): Locus of points of pressure
Q to provide the opportunity for bubble–particle head (in meters), i.e., pressure divided by specific
contacts. The term ‘‘contact zone’’ was adopted by weight of water (r w g).
a consensus of persons discussing the terminology at Interfacial area: Surface area of air–water interface.
the 1994 International Joint Specialized Conference K L a: Mass-transfer coefficient that says the rate of transfer
on Flotation Processes in Water and Sludge Treat- of a gas between phases is proportional to the