Page 436 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Rapid Filtration 391

Steady state: Influent flow and water quality are not changing van der Waals force: About 1875, van der Waals postulated
with time. The term may refer to characteristics of the the presence of intermolecular forces to explain the
filtration process, as well, such as the ‘‘steady state’’ fact that the behavior of real gases deviated from the
portion of the C(t) curve, or that the shape of the ideal gas law at high pressures. Three types of inter-
Z¼Z o
C(Z) t curve has attained a ‘‘steady state’’ shape. The molecular forces were postulated by others: (1) orien-
sense of the term is that a phenomenon or character- tation effects due to two molecules having permanent
istic does not change with time. dipole moments, (2) induction effect due to one
Stochastic: The random occurrence of the magnitude of a molecule having a permanent dipole moment inducing
variable would be considered as ‘‘stochastic.’’ A a dipole in a neighboring molecule and (3) dispersion
‘‘random variable’’ in a statistical sense has the char- effect due not to a permanent dipole of either molecule
acteristic of being ‘‘stochastic.’’ The occurrence of but to fluctuating dipoles due to the random motion of
Giardia lamblia cysts in a river, as detected by sam- electrons within a molecule. The van der Waals forces
pling, is ‘‘random,’’ and thus is ‘‘stochastic.’’ The are likely to be the major cause of attraction and bond-
opposite of stochastic is ‘‘deterministic.’’ ing between say a destabilized floc particle and a
Straining: A particle in suspension that is larger than the mineral filter grain, or a floc coated mineral grain
interstitial pores of a medium is removed by strain- (Adapted from Myers, 1941, pp. 41–67).
ing. As d(particle)=d(pore) ! 1, interception Wave front: The concentration versus distance profile at any
becomes straining, which is the limiting condition given time, that is, C(z) t . The concentration may be
of interception (Ives, 1975b, p. 194). any parameter; usually turbidity or particle counts
Streaming potential: The potential established when a solu- would be measured. See also, ‘‘clogging front.’’
tion is forced through a porous plug (or tube) of Zeta potential: The potential at the boundary between the
material which acquires a charge in contact with fixed and mobile phases of the double layer associ-
the solution (Gregory, 1975, p. 65). ated with a colloid particle, that is, at the ‘‘slipping
Subfluidization: Backwash velocity, v, in which v v mf ,in plane,’’ which is just outside the Stern layer
which v mf is the minimum velocity for incipient (Gregory, 1975, p. 65).
fluidization.
Surface wash: An adjunct to backwash. High pressure jets
with nozzles about 25 mm (1 in.) above the media
REFERENCES
are directed into the media before the backwash and
during the backwash as the bed expands. Adin, A. and Rebhun, M., A model to predict concentration and
Technology: (1) The scientific study of mechanical arts and headloss profiles, Journal of the American Water Works Asso-
ciation, 69(8):444–453, August 1977.
applied sciences (as engineering). (2) These subjects
Adin, A., Baumann, E. R., and Cleasby, J. L., The application of
and their practical application in industry, etc.
filtration theory to pilot-plant design, Journal of the American
(Oxford American Dictionary, Oxford University Water Works Association, 71(1):17–27, January 1979.
Press, New York, 1980). Al-Ani, M. Y., Hendricks, D. W., Logsdson, G. S., and Hibler, C. P.,
Theory: (1) A set if ideas formulated by reasoning from Removing Giardia cysts from low turbidity waters by rapid
known facts to explain something; 4 A statement of rate filtration, Journal of the American Water Works Associ-
the principles on which a subject is based (Oxford ation, 78(5):66–73, May 1986.
Amirtharajah, A., Fundamentals and theory of air scour, Journal of
American Dictionary, Oxford University Press, New
the Environmental Engineering Division, 110(EE3):573–590,
York, 1980).
June 1984.
Transport: A suspended particle is ‘‘transported’’ to the Amirtharajah, A., The interface between filtration and backwashing,
proximity of a ‘‘collector’’ (a media grain) where it Water Research (Journal of the International Water Quality
may come under the influence of surface forces. Association), 19(5):581–588, May 1985.
Transport coefficient: The ratio of particles striking a filter Amirtharajah, A. and Cleasby, J. L., Predicting expansion of filters
grain to those approaching. during backwash, Journal of the American Water Works Asso-
ciation, 64(1):52–59, January 1972.
Turbidimeter: An instrument that measures particle turbidity
Amirtharajah, A. and Wetstein, D. P., Initial degradation of effluent
in the sample provided. Bench turbidimeters are for a
quality during filtration, Journal of the American Water Works
given sample and ‘‘in-line’’ turbidimeters read the Association, 72(9):518–524, September 1980.
data at specified intervals for a continuous sample. Baker, M. N., The Quest for Pure Water, American Water Works
See also ‘‘turbidity.’’ Association, New York, 1948.
Uniformity coefficient: The uniformity coefficient, U,is Baylis, J. R., Experiences in filtration, Journal of the American
defined as the ratio d 10 =d 60 . Water Works Association, 29(7):1010–1048, 1937.
Baylis, J. R., Seven years of high rate filtration, Journal of the
Unit filter run volume (UFRV): Volume of water filtered
American Water Works Association, 48(5):585–596, 1956.
per unit of area per run, which is the product of
3 Beverly, R. P., Gravity-Filter Design and Maintenance 101, Water-
filtration velocity and run time. Units are m world Review, Pennwell Publishing Company, Tulsa, OK,
2
water=m 2 filter bed area=filter run (gal=ft =run). January=February 1995. (Re-printed by Leopold Water and
Reference is Kawamura (1999, p. 80). Wastewater Products).