Page 369 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

whereby the water is applied directly to the filter
GLOSSARY
without prior clarification by sedimentation, and
Adhesion: Attachment of floc to filter grains (Hannah et al., which is designed to bring about coagulation, floc-
1967, p. 844). culation, and solids separation directly in the filter
Aging: The irreversible change of texture and floc structure bed (Shea et al., 1971, p. 41).
from the moment flocs are completely formed, Density: See floc density.
i.e., when they have their maximum dimension Eddy: Localized circular motion of fluid.
(François, 1987a, p. 523). Electrostatic forces: Forces that cause repulsion or attraction
Anisotropic turbulence: Anisotropic turbulence is charac- between like charge and unlike charged particles,
terized by unequal strain rates, i.e., velocity gradi- respectively (Hannah et al., 1967, p. 845). Insoluble
ents, with respect to direction. According to hydrous oxide formed from alum or iron salts may
Tennekes and Lumley (1972, p. 262), small eddies have either a positive or negative charge depending
exhibit ‘‘local isotropy,’’ where any sense of direc- on pH.
tion is lost with turbulence being increasingly Floc: (1) An aggregate of particles created by collisions from
scrambled at small scales. The range of wave num- smaller particles that adhere to one another by bond-
bers exhibiting local isotropy is called the equilib- ing forces likely to be van der Waal’s. The shape,
rium range. usually, is ill-defined, i.e., is amorphous, or fractal.
Bioflocculation: The aggregation of microbes is called ‘‘bio- (2) The aggregate of destabilized particles known as
flocculation’’; usually, the objective is to attain a micelles (Argaman, 1971, p. 775).
larger mass that is settleable. Floc density: The density of a floc, r F , is the mass of particles
Blowdown: Continuous periodic removal of a solids and includes water divided by the envelope volume.
stream so that there is no buildup of solids but a The ‘‘effective’’ density, r E , is this value minus the
concentration maintained at some specified level. density of water, i.e., r E ¼ r F r W (Gregory, 1989,
The rate of generation of solids must equal the flux p. 216).
of solids leaving the system by means of ‘‘blow- Floc specific gravity: The specific gravity of a floc is the
down.’’ density of floc particles relative to the density of
Bond: Forces of adhesion or cohesion between particles and water, i.e., SG(floc) ¼ r F =r W .
another surface or between particles and particles, Floc strength: Resistance of floc to shear stress as induced
respectively (Hannah et al., 1967, p. 844). by hydraulic velocity gradients (Hannah et al., 1967,
Bridging: 1 Reactive functional groups located along long- p. 843).
chain polymers form chemical-type bonds at reactive Flocçulent: (1) The term flocculent is used by many, e.g.,
sites on the surface of particles to be agglomerated, Halvorson and Panzer (1980, p. 489), to mean the
thereby forming interparticle bridges (Ham and chemical agents that create microflocs from colloidal
Christman, 1969, p. 482). particles. (2) The term flocculent is used more com-
Brownian motion: Random thermal motion of molecules monly in practice to designate a chemical, i.e., a
(Hannah et al., 1967, p. 845). Such motion may polymer, added to the beginning of the flocculation
cause buffeting of small particles, i.e., 1 mm but process (the inflow to a flocculation basin) intended
is generally not sufficient to cause flocculation to cause interparticle bridging to aid in floc growth
within time frames important in water treatment. and toughness (shear resistance).
Carryover: Refers to floc in suspension leaving the floc Flocculation: (1) The grouping and compacting of coagu-
blanket and carried with the flow to the overflow lated particles into larger assemblages called ‘‘floc’’
weirs leaving the basin. particles. Flocculation time should be, ordinarily
Coagulation: The process of chemical reaction of a coagu- 30 u 60 min (Hudson and Wolfner, 1967,
lant in water that requires intense mixing to distrib- p. 1257). [Tambo and Watanabe (1979, p. 429)
ute the coagulating agent uniformly throughout the define flocculation as including what is called here,
water so that it makes contact with the suspended coagulation. This seems not uncommon and is men-
particles before the reaction is completed; particle tioned here so that the reader is aware of this alter-
7
concentrations in water are nominally 10 #=mL native, more inclusive definition.] (2) A primary
(Hudson and Wolfner, 1967, p. 1257). water treatment process that changes the size distri-
Cohesion: Attachment of floc to other floc particles (Hannah bution of particles from a large number of small
et al., 1967, p. 844). particles to a small number of large particles for
Contact flocculation: (1) Contact between primary particles removal in later processes (Casson and Lawler,
and floc particles causing a growth in the floc par- 1990, p. 54). (3) The term is used by some
ticles (see Tambo and Hozumi, 1979, p. 441). (2) researchers in a more inclusive sense to mean charge
Larger suspended flocs adsorb incoming primary neutralization and the subsequent agglomeration
particles on their surfaces (Tambo and Hozumi, (see, for example, Gregory and Guibai, 1991,
1979, p. 448). (3) A water clarification process pp. 3–4).