Page 120 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Unit Process Principles 75

definition. The concentration of A within a packed- bieneusi; Nosema conneri; Pleistophora; Trachi-
bed reactor, for example, an adsorption column, pleistophora hominis; and Vittaforma corneum
changes continuously along its length. An infinitesi- (Symons et al. 2000, p. 264).
mal slice of the reactor may be assumed homoge- Organism, Microsporidium: A ‘‘catch-all’’ genus name for
neous and thus the materials balance may apply in microsporidia that have not yet been classified; see
differential form. also microsporidia (Symons et al. 2000, p. 264).
Infinitesimal volume: The small hypothetical volume used Plug flow: (1) Advective flow in which there is no turbulent
as the basis for a mathematical formulation. diffusion or dispersion. (2) In plug flow, an element
Iteration: The solution of a finite difference equation within a of thickness, DZ, and area, A, may be advected
one-step change, such as a Dt. downstream with no transfer of mass across the
Kinetics: A description of the rate of a chemical reaction. boundaries and the mass balance equation is that
Usually, the description is in terms of the rate of the observed rate of change of C within the element
disappearance of a reactant or, alternatively, the is the rate of reaction that is occurring. (3) Alterna-
rate of appearance of a product. tively, a volume element may be fixed in space with
Kinetics, first order: The rate description which is propor- mass transfer occurring across the boundaries; a
tional to the concentration at any given instant. finite difference solution is required.
Kinetics, second order: The rate description which is pro- Porous media: In water treatment, a packed bed of granular
portional to the concentration squared at any given media. A ground water aquifer is also porous media.
instant or to the concentrations of two constituents. Potential: A term used in the field of ground water that is the
Materials balance: For a given complete-mix reactor, the sum of pressure head and gravity head, that is,
observed mass rate of change of a substance within ø ¼ p=g þ h.
a reactor equals the mass flow in minus the mass Potential line: A locus of points that describes a surface of
flow out plus or minus the mass rate of reaction constant pressure in a flow field.
within the reactor summed for all reactions. Product: In any chemical reaction the substances synthesized
Model: A mimic of a full-scale system in which a one-to-one from the reaction are called ‘‘products’’ (see also
correspondence is sought between the system mim- reactant).
icked and the model. Models may be mathematical Reactant: In any chemical reaction the substances utilized
or physical. and transformed by the reaction are called ‘‘react-
Numerical solution: A solution to a differential equation ants’’ (see also product).
expressed in finite difference form. Reaction: A transformation of substance from one ‘‘state’’ to
Organism, Cryptosporidium parvum oocyst: The survival another ‘‘state’’; boiling water would be a reaction in
form of the protozoan in the phylum Apicomplexa this rather broad definition. In a stricter sense, a
that are referred to as coccidia that affect humans. reaction is the transformation of substances, that is,
The organism is round and about 5 mm in diameter. reactants, to substances, that is, ‘‘products,’’ such
Dubey et al. (1990) list 21 species. that the products are a molecularly different chemical
Organism, Cyclospora: (1) A family of protozoan organisms species than the reactants.
in the subclass Coccidia, distributed worldwide. (2) Reaction, adsorption: A reaction in which an adsorbent is
Cyclospora cayatensis: A coccidian parasite distrib- one of the reactants.
uted worldwide related to Cryptosporidium parvum Reactor: A volume in which a reaction occurs, or in which
about 9–10 mm in size; organism infects immuno- there is some other kind of treatment.
competent and immunosuppressed children and Reactor, batch: A volume in which the flow across its
adults (Symons et al. 2000, p. 100, 101). boundaries is zero.
Organism, Giardia lamblia cyst: The survival form of a Reactor, biological: A reactor in which one of the reactants
protozoan infectious to humans and is about 5 10 is an organism, usually a bacteria. Also, a product
mm in size and is common to sewage and should be may be bacteria.
assumed present in any ambient water. Reactor, column: A reactor which is not homogeneous from
Organism, Microspora: (1) Phylum in subkingdom Proto- top to bottom. Packed-bed reactors, such as a granu-
zoa: They are small microsporans, 3–6 mm, and are lar activated carbon or a trickling filter, are examples.
obligatory intracellular parasites (Prescott et al. Reactor, complete mix: A reactor that is mixed in such a
1993, p. 552, 556). (2) Microsporidia. Small, unicel- way that the contents are homogeneous throughout
lular, obligate intracellular, spore-forming (spores the volume and therefore the materials balance equa-
1–4.5 mm) protozoan parasites that are widely dis- tion is applicable.
tributed in nature and include more than 100 genera Reactor, continuous flow: A reactor volume in which mass
and about 1000 species. They are pathogens of crosses its boundaries continuously.
insects, fish, birds, and mammals, including humans. Reactor, homogeneous: A reactor that is mixed in such a
Species found in humans include Encephalitozoon way that the contents are spatially non-varying
cuniculi; E. Hellem; E. intestinalis; Enterocytozoon and are thus homogeneous throughout the volume