Page 551 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

different molecular weight substances. Macropore A mathematical model is useful particularly when
distributions may be correlated with rates of adsorp- the interactions among variables are complex.
tion (USEPA, 1973, p. A-5). Computer simulations provide a means of keeping
Porosity (P): Defined as the volume of voids (pores) divided track of these changes. (2) A sequence of events
by total volume, i.e., volume of solids plus volume especially when imagined; especially, an account or
of voids. synopsis of a possible course of action or events.
Powdered activated carbon: See PAC. Simulation: A modeling process in which the behavior of a
Profile: As used here, the adsorbate concentration distance prototype system is ‘‘simulated’’ by another system.
along the direction of flow in an adsorbent packed An electric analog is a good example, in which
bed. voltage may simulate hydraulic head and current
Pulsed-flow reactor: An upflow reactor bed in which GAC is simulates flow of water in a pipe.
added at the top either continuously or intermittently, Sorption: A term that is inclusive of both adsorption and
i.e., as a ‘‘pulse,’’ and removed continuously at the absorption.
bottom. Stochastic: A random or probabilistic occurrence. The occur-
Random walk: A model of diffusion in which each ‘‘step’’ rence of Giardia cysts in a sampling of a stream may
of a molecule or particle is a random vector, be ‘‘stochastic.’’
i.e., with respect to direction and distance trav- SOC: Acronym for synthetic organic compound.
eled, before a collision that causes another vector Structure: Structure determines the size of molecules which
reaction. can be adsorbed and the capabilities of the acti-
Reactor: Adefined volume in which a reaction may vated carbon to permit the migration of the adsorb-
occur. The reactor may be ‘‘batch’’ or ‘‘continuous ates within the pores (as measured by a diffusion
flow.’’ coefficient).
Real density: The density of the skeleton of a carbon particle Superficial velocity: Same as hydraulic loading rate, HLR,
and usually comes close to that for graphite i.e., Q=A.
(USEPA, 1973, p. A-6). Surface area: Defined as the surface area per unit mass of
Refractory: Contaminants that are not removed by conven- carbon. Usually, the surface area is determined from
tional treatment. the nitrogen adsorption isotherm by the Brunauer–
Regeneration: The restoration of a portion of the adsorp- Emmett–Teller method, i.e., BET method. Usually
2
tion capacity of virgin carbon. About 0.9 restora- surface area is expressed as m surface area=g carbon
tion is common. Usually, the regeneration is by (USEPA, 1973, p. A-6).
thermal means, i.e., at 9008C–9548C (16508F – Tertiary treatment: A term that came into use in the 1960s,
17508F). probably as an outgrowth of the USPHS AWTR
Reticular: Resembling a net in appearance or structure program in which research was conducted to
(http:==www.merriam-webster.com=). develop treatment processes that could be added
Safe Drinking Water Act: PL93-523 passed by U.S. Con- to biological treatment to result in an effluent
gress in 1974. The legislative basis for regulations water quality that met some more stringent criterion,
and guidelines promulgated by the U.S. Environ- such as for further use of the water (Morris and
mental Protection Agency that have resulted in the Weber, 1962, p. 7).
definition of contaminants and the specifications of TOC: Total organic carbon. According to Anon. (USPHS,
MCLs (maximum contaminant levels) for drinking 1965, p. 89) the Dow Chemical Company developed
water and MCL goals. a dry oxidation system for organic compounds in
Saturated: (1) When the carbon is at equilibrium with the water that employed a hot tube furnace and an infra-
influent solution adsorbate concentration, i.e., C 0 , the red CO 2 analyzer. The system was acquired by
carbon is ‘‘saturated’’ with respect to the adsorbate. Beckman Instruments by 1968.
(2) Same as ‘‘exhausted.’’ TOX: Total organic halogens.
Saturation: The maximum amount of adsorbate that an Transport kinetics: As used here, the term ‘‘transport kinet-
adsorbent may adsorb per unit mass for a given ics’’ refers to the advection of adsorbate to the diffu-
adsorbate concentration. The ‘‘maximum’’ is actu- sion proximity to an adsorbent particle.
ally the equilibrium amount as defined by an Tyler sieve series: A sieve series used to provide a size
isotherm. distribution of granular media.
Scenario: (1) The construction of a set of imposed condi- U.S. standard sieve series: A sieve series used to provide a
tions, hypothetical, for which possible outcomes are size distribution of granular media. Sieve sizes and
generated by means of a model of some sort. The openings are given in the table following for both the
model may range from ones imputing outcomes Tyler and the U.S. series (U.S. series data from Culp
based on one’s imagination to the results of quanti- and Culp, 1971, p. 151; Tyler series equivalencies
tative computations based upon a computer model. from Spotts, 2003).