Page 464 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Slow Sand Filtration 419

volume is calculated by summing the product of the Gravel support: Coarse media on which the filter media is
flow rate and the duration of that flow rate over the placed, and which surrounds and covers the under-
time period of interest. drains.
d 10 : The size of the sieve opening through which 10% of Headloss: Loss of media permeability; increased flow resist-
the sand will just pass; also called the ‘‘effective ance.
size.’’ Headwater: The raw water in the filter box directly above the
Design flow: The maximum daily flow for a projected popu- filter bed; also called supernatant water.
lation. Hydraulic conductivity: Permeability, reported as length=
Detritus: Nonliving organic matter. time.
Dewatering: Draining the water level in the filter box to Hydraulic grade line, HGL: The piezometric head line, that
below the sand bed surface. The ‘‘headwater,’’ that is, a graphic representation of what would be the free
is, the water above the sand bed surface, should be surface if one could exist, and the same conditions of
drained first by pipe outlets above the sand bed. flow were maintained; if the velocity head is con-
Diatomaceous earth: High-silica skeletal remains of algae, stant, the drop in the hydraulic grade line between
used as a filtration material. any two points is the value of the loss of head
Drawdown: Drainage of the headwater. between those two points.
Effective size: See d 10 . Hydraulic loading rate: Volumetric flow rate divided by
Energy grade line, EGL: A graphic representation of the filter surface area, resulting in units of length=time.
total energy head, which shows the rate at which Log removal, log R: Defined: log R log N in log N out in
energy decreases; the EGL always drops downward which N in is the concentration in the influent and
in the direction of flow unless there is an energy N out is the concentration in the effluent of whatever
input from a pump. constituent species is being measured. Conversion to
Enteric bacteria: (1) Members of the family enterobacter- %R is: %R ¼ 1 10 log R .
iaceae (gram negative, straight rods, etc.). (2) Bac- Mature: The state of a filter when coliform removal has
teria that live in the intestinal tract. (Prescott et al., reached its optimum level. Also, a ‘‘ripened’’ filter.
1993, p. 435, p. G9). Included are the genera, Mature filter bed: Maximum development of biofilm within
Escherichia, Enterobacter, Proteus, Salmonella, filter bed for given conditions.
and Shigella (pp. 435–438). Salmonella typhi causes Newton: Unit of force. 1 N ¼ 0.2248 lb force.
typhoid fever and gastroenteritis; Shigella, bacillary NPDES: National Pollution Discharge Elimination System
dysentery; some strains of E. coli cause gastroenter- (an acronym introduced with PL-500).
itis (p. 438). NPDOC: Non-purgable dissolved organic carbon.
Enterovirus: Genus of viruses of the human GI tract (of Package plant: A commercially available prefabricated filter.
2
the family Picornaviridae); polio is an example Pascal: Unit of pressure. 1 Pascal ¼ 1 Newton=m ¼
2
(Prescott et al., 1993, p. A29). 0.000145 lb=ft .
Fecal coliform: Coliforms derived from the intestinal tract Peak flow: A community’s maximum daily water demand.
of warm-blooded animals, which can grow at Percent removal, %R: Defined: (N in N out )=N in 100, see
44.58C. also log removal.
Filter harrowing: Disturbing the filter media surface with a Performance capacity: The flow rate above which the per-
large implement consisting of a series of teeth or formance of the filter (effluent turbidity, rate of head-
disklike blades. loss development, etc.) no longer satisfies regulatory
Filter mats: Nonwoven synthetic fabrics placed on the or community requirements.
surface of the filter media to facilitate cleaning. PFU: A measure of the number of cell-infectious viruses
Filter-to-waste: The process of disposing of tailwater (filter capable of forming plaques per unit volume.
effluent) while the filter product water is of unaccept- Pilot plant: A small-scale replica of a proposed or existing
able quality. full-scale facility, useful in determining, at relatively
Fines: The smallest particles in unwashed sand. low expense, the feasibility of the full-scale plant in
Gas precipitation: A phenomenon whereby dissolved gas achieving the desired finished water quality given the
comes out of solution due to supersaturation. raw water characteristics.
2
Giardia: Name often used in conversation for the pathogenic Poise: Unit of dynamic viscosity. 1 poise ¼ 0.10 N s=m .
organism, Giardia lamblia. Actually, there are sev- Poliovirus: The poliovirus is of the family Picornaviridae
eral species of Giardia. (MW 2.5 106, diameter 22–30nm),generaEntero-
Giardia lamblia: A protozoan pathogenic to humans which virus (viruses of the gastrointestinal tract), (Prescott
causes severe diarrhea. The organism is ingested in et al., 1993, p. A29). The shape of the poliovirus is
cyst form. Excystation occurs in the stomach. spherical (Ibid., p. 356) with a protein shell surround-
Giardia muris: A protozoan that infects mice and thought to ing its nucleic acid, called a ‘‘capsid’’ (Ibid., p. 355).
be not pathogenic to humans. Poliovirus, attenuated: A poliovirus inactivated, unable to
Giardiasis: Disease caused by protozoan Giardia lamblia. cause infection.