Page 232 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Flotation 187

concentration difference between an equilibrium falls thought the air. Air bubbles are entrained as
level and that existing at a given time. the water falls into the water pool below and is
Mole fraction: Ratio of molecules of gas i in a given volume believed by some to be where most of the gas trans-
to the total number of molecules of all species with fer occurs.
number of molecules expressed as moles. Vacuum flotation: A technology that imposes a negative
Nozzle: Convergence, then divergence of a pipe. pressure on the surface of the flotation tank. Gas
Packing: A material or plate system within a saturator that is precipitation may occur if the incoming flow of
intended to cause bifurcations of the water stream to water to be treated is ‘‘saturated’’ with respect to
create a substantial interfacial area of water. The the local atmosphere of the raw water and would be
packing may be a granular media or a system of more successful at low elevation.
plates staggered one above the other or ‘‘rings’’ of
various sorts. An airflow occurs counter-current REFERENCES
within the pores of the packing material so as to
come into contact with the water. The water flow de Rijk, S. E., Jaap, H. J. M., van der Graaf, J. M., and den Blanken,
through the packing material must be ‘‘unsaturated’’ J. G., Bubble size in flotation thickening, Water Research,
so as to maintain a high water surface area (which is 28(2):465–473, 1994.
the intent of the packing material). Eckenfelder, W. W., Jr., Rooney, T. F., Burger, T. B., and Gruspier,
J. T., Chapter 2–10, in: McCabe, J., and Eckenfelder, W. W.,
Partial pressure: According to Dalton’s law, the partial pres-
Jr., Biological Treatment of Sewage and Industrial
sure of a gas i is proportional to its mole fraction.
Wastes (Volume II, Anaerobic Digestion and Solids-Liquid
Phenolphthalein: An indicator that changes color from pink Separation), Reinhold Publishing Corporation, New York,
at pH < 8.3 to colorless when pH 8.3, as in titra- 1958.
tion with N=50 sodium hydroxide solution to deter- Edzwald, J. K., Principles and applications of dissolved air flotation,
mine dissolved carbon dioxide concentration Water Science and Technology, 31(3–4):1–23, 1995.
(Sawyer and McCarty, 1967, p. 67). Edzwald, J. K. and Walsh, J. P., Dissolved Air Flotation: Laboratory
and Pilot Plant Investigations, American Water Works Asso-
Reaction zone: Zone in flotation basin just after bubble for-
ciation Research Foundation, Denver, CO, 1992.
mation and as the particle stream enters in the flow
Fukushi, K., Matsui, Y., and Tambo, N., Dissolved air flotation:
Q to provide the opportunity for bubble–particle Experiments and kinetic analysis, Aqua, 47(2):76–86, 1998.
contacts. Same as ‘‘contact zone,’’ which was the Haarhoff, J., Factors influencing bubble formation in dissolved air
term adopted by a consensus of persons discussing flotation, International Association of Water Quality Year-
the terminology at the 1994 International Joint book, 1994–95, 1995.
Specialized Conference on Flotation Processes in Haarhoff, J. and Rykaart, E. M., Rational design of packed
saturators, Water Science and Technology, 31(3–4):179–190,
Water and Sludge Treatment, Orlando, Florida,
1995.
April, 1994.
Haarhoff, J. and van Vuuren, L., Design parameters for dissolved air
Recycle: The portion of the flow that leaves the flotation flotation in South Africa, Water Science and Technology,
basin that is returned to the saturator to pick up 31(3–4):203–212, 1995.
dissolved air and then return to the flotation tank. Hendricks, D. W., Oxidative Liquor Return to the Eimco Clari-
Recycle ratio: The fraction, r, of the flow, Q, that is recycled, Thickener, The Eimco Corporation, Internal Report, Salt
i.e., R, to pass through the saturator, i.e., R=Q. Lake City, UT, 1966.
Kalinske, A. A., Flotation in waste treatment, Chapter 2–7, in:
Saturator: A tank under pressure that has some means of
McCabe, J. and Eckenfelder, W. W., Jr., Biological Treatment
creating an interfacial area between air and water.
of Sewage and Industrial Wastes (Volume II, Anaerobic
One method is to use a ‘‘packing.’’ Another is to Digestion and Solids-Liquid Separation), Reinhold Publishing
create a high surface area of air bubbles within the Corporation, New York, 1958.
saturator. Leopold, Dissolved Air Flotation, brochure, The F.B. Leopold
Separation zone: The zone in the flotation basin after the Company, Inc., Zelienople, PA, 8pp., 1996 (revised 2001,
contact zone for particle–bubble agglomerates to rise 2003).
Masterson, E. M. and Pratt, J. W., Application of pressure flotation
to the surface.
principles to process equipment design, Chapter 2–8, in:
Skimmer: Horizontal blades that traverse the surface of the
McCabe, J. and Eckenfelder, W. W., Jr., Biological Treatment
flotation basin and are translated in the longitudinal of Sewage and Industrial Wastes (Volume II, Anaerobic
direction by means of a chain drive. Digestion and Solids-Liquid Separation), Reinhold Publishing
Transport coefficient: The ratio of the number of bubbles Corporation, New York, 1958.
contacting floc particles to the number of bubbles in Matsui, Y., Fukushi, K., and Tambo, N., Modeling, simulation, and
a given volume within the contact zone. operational parameters of dissolved air flotation, Aqua, 47(1):
9–20, 1998.
Unpacked saturator: Saturator without packing. The water
Nemerow, N. L., Liquid Wastes of Industry, Theories, Practices, and
enters the saturator at the top and falls through air at
Treatment, Addison-Wesley, Reading, MA, 1971.
high pressure to a pool of water at the bottom of the Ødegaard, H., Optimization of flocculation=flotation in chemical
tank. The entering water may impinge against a wastewater treatment, Water Science and Technology,
splash plate to increase the interfacial area as it 31(3–4):73–82, 1995.