Page 434 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Rapid Filtration 389

variation in demand over a 24 h period. See also Piezometer: A tube that penetrates the wall of a pipe with a
Rippl diagram in various texts. fluid on the other side will transmit the fluid pressure
Mechanical filtration: During the early years of the rapid at the point of penetration causing the fluid, gener-
filtration technology, for example, from about 1880 ally water, to rise to an elevation above the penetra-
to perhaps 1910, the technology was called ‘‘mech- tion point such that the pressure due to the fluid in
anical filtration.’’ the tube equals the pressure in the fluid at the point of
Monodisperse suspension: All suspended particles have the penetration. A piezometer is a special kind of man-
same size (Tobiason and Vigneswaran, 1994, p. 335). ometer characterized by an open end to the atmos-
Mudball: A mudball is the result of adhesion between media phere.
particles caused by inadequate removal of coagulant Pilot plant: A pilot plant is a physical model that emulates
chemicals. According to Mackay (1988a,b), mud- the full-scale filtration process. They may range
balls are formed when grains of filter media are not from coagulant injection into a pipe=elbow
cleaned thoroughly; the sticky residue causes the mixing and a simple tube filled with media to an
grains to clump together. The size of a mudball elaborate SCADA run system with alternative treat-
may be perhaps 25–100 mm (1–4 in.). ment trains.
Negative pressure: When the hydraulic grade line in a pipe Plenum: (1) A condition, space, or enclosure in which air or
or porous medium drops below the level of a given other gas is at a pressure greater than that of the
point in the pipe or porous medium, a negative outside atmosphere. (2) The condition of being full;
pressure results. By definition, the vertical distance fullness. (3) A space completely filled with matter.
between a point in a conduit and the hydraulic grade American Heritage Dictionary, Softkey Inter-
line is the pressure head. national, 1995.
Net water production: Net water production per filter run Porosity: Defined as the ratio of void volume to bed volume.
per unit area of filter bed is defined as Proprietary filters: Manufactured and sold by on particular
firm, usually under a patent. Examples of proprietary
NWP ¼ WP VB filters are:
. Hardinge ‘‘automatic backwash’’ (ABS) filter
where (comprised of filtration cells about 305 mm
NWP is the net water production unit area of filter (12 in.) wide that are individually backwashed
3
bed per filter run (m water produced=unit area one at a time by an apparatus that moves along
of filter bed=run) the filter bed) marketed presently by Infilco-
WP is the volume of water production per unit Dregemont.
3
area of filter bed per filter run (m water . Parkson Dynasande filter which is a moving
2
produced=m filter plan area=filter run) bed upflow filter with a sand removed continu-
VB is the volume of water required per unit of ously from the bottom, washed, and returned
3
filter bed area per backwash (m backwash to the bed at the top.
2
water=m filter bed area=filter run) . Culligan Multi-Teche is a pressurized pack-
age system with ‘‘contact’’ flocculation.
See also unit filter run volume (UVRV), which is . Environmental Products Division High Rate
the same neglects the VB term. Filtration Systeme, a pressurized cylinder
Orthokinetic flocculation: Refers to velocity gradient floc- oriented horizontally.
culation (see Ives, 1970, p. 206). Frequently, the proprietary filters are sold as ‘‘pack-
Packed bed reactor: Both the rapid and the slow sand filtra- age’’ systems, that is, coagulant feed, pumps,
tion processes are done in a bed of packed granular SCADA, etc. are provided such that the filter is
media. Also, a bed of granular activated carbon and an ready to operate. In some cases, the filters are
ion exchange column are both ‘‘packed bed’’ reactors. prefabricated and others may require construction
Particle: Any particle in suspension in the water applied to in accordance with specifications of the
the filter is termed here a ‘‘particle.’’ As applied to manufacturer.
rapid filtration, most of the ambient particles would Quality assessment (QA): A process of measuring and
be either charge neutralized with alum species evaluating quality. Often this assessment involves
attached or they might be enmeshed in hydroxide evaluating such information as control charts, repli-
precipitates and these would then be the particles-to- cate measurements, spiked samples, and standard
be-removed. reference materials (Symons et al., 2000, p. 384).
Particle counter: An instrument that measures particle num- Quality assurance: (1) An overall system of management
ber and sizes in the sample provided. Batch particles functions designed to provide assurance that a
counters are for a given sample and ‘‘in-line’’ particle specified level of quality is being obtained. It can
counters read the data at specified intervals for a be thought of as being composed of quality
continuous sample. control (QC) and quality assessment (QA). (2) The