Page 177 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

Short circuiting: The main flow within a basin is direct from the dispersion patterns were to be observed, such
inlet to outlet with little participation by the intended tracers as potassium permanganate and methylene
volume. blue dyes have been used. Later, fluorescein was
Sink: The outlet of a flux. used, but as it decayed in light, it was replaced by
Sludge volume index (SVI): The volume (using a graduated Rhodamine-B and Rhodamine-WT. The latter can be
1000 mL cylinder) of 1 g of sludge after 30 min detected at very low concentrations by means of a
settling. The measurement usually is applied to a fluorometer. Sodium chloride is often used since the
sample of activated sludge from an aeration basin to chloride ion can be detected easily by titration or by
provide and index of settling behavior. SVI ¼ 100 is a specific ion electrode, or a conductivity meter may
the same as a sludge concentration of 10,000 mg=L, be useful when source waters are low specific elec-
i.e., 1000 mg=0.10 L, and is considered a desired trical conductivity. Specific ion electrodes have also
target for settled sludge, and thus for X r (see also been used to detect fluoride ion. Online instruments
Dick and Vesilind, 1969). Abbreviated SVI. can be used in place of sampling.
Solids contact clarifier: Other names are reactor clarifier and Tracer test: The procedure of injecting a tracer, such as a dye
sludge blanket clarifiers. These are circular basins to or salt, into a flow with measurement of tracer con-
remove colloidal particles or to create a chemical floc centrations in the effluent so that a dispersion curve
in which chemical mixing is accomplished in a rapid can be constructed. Two methods of conducting the
mix unit in the center of the unit. The chemically test are the step dose and the slug dose, with the latter
treated water is forced to flow through a solids blan- being most common and easiest to conduct.
ket and upward and over weirs at the surface of the Tube settler: An array of square tubes, usually 25 mm (1 in.)
basin. Most systems are proprietary and are sold as a square, inclined at 608, which functions the same as
system. They are used to remove colloidal solids and plate settlers. The suspension settles to the lower
in chemical reactions, such as softening. surface of the tubes and is removed by sliding to a
Solids loading rate: Solids flux per unit of area, e.g., removal zone below the tubes.
2
kg=min=m . Type I settling: Discrete particle settling.
Source: The source of a flux. Type II settling: Flocculent particle settling.
Stokes equation: The relationship for laminar flow condi- Type III settling: Settling in which there is mutual interfer-
tions that relates fall velocity of a particle to the ence between settling particles; an interface forms.
shear resistance. Type IV settling: Settling that occurs by the displacement of
Stream tube: The volume between two streamlines such that water due to the weight of the mass of particles
the flow within each streamtube is the same. above a given level.
Streamline: Locus of points of a velocity vector in a flow Up-flow basin: A settling basin with weirs arranged across
field. Any given streamline is perpendicular to the the entire basin. Flow is forced upward to be
potential gradient at any point. An array of stream- removed by the weirs.
lines and potential lines done according to certain Weir loading rate: The flow per unit length of weir, e.g.,
3
rules is a ‘‘flow net.’’ In a general sense, streamlines m =day flow=m weir length.
are the same as flux lines.
Surface overflow rate (SOR): Flow divided by plan area, i.e., REFERENCES
SOR ¼ Q=(wL), also called surface loading rate, over-
ASCE, Civil Engineering Classics, Outstanding Papers of Thomas R.
flow velocity, and overflow rate. Although SOR and
Camp, American Society of Civil Engineers, New York, 1973.
v o may be used interchangeably, the sense of the two ASCE-WPCF, Sewage Treatment Plant Design, ASCE Manual of
are different. The SOR is also an ‘‘intensive’’ variable Practice No. 36, WPCF Manual of Practice No. 8, American
and is the hydraulic loading applied to the plan area. A Society of Civil Engineers and Water Pollution Control Fed-
complementary idea is the surface overflow velocity, eration, Headquarters of the Society, New York, 1959.
v o (surface overflow velocity). For plate settlers, SOR AWWA-ASCE, Water Treatment Plant Design, 3rd edn., McGraw-
Hill, New York, 1998.
Bhargava, D. S. and Rajagopal, K., Differentiation between transi-
(plate settlers) ¼ Q=Sn(plates) w(plate) L(plate)
cos u; in other words, it is the flow divided by the
tion zone and compression in zone settling, Water Research,
total plate area projected on to the horizontal plane. 27(3):457–463, 1993.
Surface overflow velocity (v o ): Flow divided by plan area, i.e., Burns and Roe, Inc., Process Design Manual for Suspended Solids
v o ¼ Q=(wL), or the rate at which the water surface will Removal, Environmental Protection Agency, Washington, DC,
hypothetically fall in transport from a basin entrance October 1971.
to its exit. When compared with the fall velocity of Camp, T. R., A study of the rational design of settling tanks, Sewage
Works Journal, 8:742–758, 1936.
particles, it must be true then that all particles will be
Camp, T. R., Discussion of paper, Slade, J. J. Jr., Sedimentation in
removed for which, v s v o , for the ideal basin.
quiescent and turbulent basins, Transactions of the ASCE,
Tracer: A chemical that dissolves in water and has negligible 102:306–314, 1937.
effect on density, which can be detected easily and Camp, T. R., Sedimentation and the design of settling tanks, Trans-
accurately at low concentrations. In cases in which actions, of the ASCE, III:895–958, 1946.