Page 757 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

‘‘lock-and-key’’ model, in which the enzyme is rigid Food-to-microorganism ratio: Aeration tank loading par-
in shape and has a configuration that fits exactly a ameter. Food may be expressed in kg suspended
given substrate which binds to the surface of solids, COD, or BOD added per day to the aeration
the enzyme; (b) the ‘‘induced-fit’’ model, in which tank. Microorganisms may be expressed as mass
the enzyme changes shape such that it surrounds the (kg) of mixed liquor suspended solids (MLSS) or
substrates. The enzyme may bring the substrates mixed liquor volatile suspended solids (MSVSS) in
together at the active site, concentrating them, and the aeration tank (URS, 1973, p. K-2).
lowering the activation energy of the reaction, and F=M ratio: (1) Food-to-microorganism ratio; below a certain
thus speeding up the rate of the reaction perhaps by a value, food is rate limiting (McKinney, 1963). (2)
5
factor of >10 (Prescott et al., 2005, p. 158). Also called a ‘‘loading factor’’ measured as substrate
Equilibrium constant: See Gibbs free energy. mass applied to reactor over a day divided by the
Eucarya: Fungi, algae, protozoa, rotifers, nematodes, and mass of solids under aeration.
other zooplankton; all are characterized by a defined Free energy: See Gibbs free energy.
nucleus within the cell. The larger of this group may Fungi: The decomposers of such difficult-to-degrade matter
be defined as animals and plants but the smaller as lignin, an aromatic polymer that binds cellulose in
organisms cannot be so divided since the boundaries trees and grasses by means of peroxidase, the key
are blurred at the smaller scale (Rittman and enzyme for such breakdown, which also enables
McCarty, 2001, p. 22). degradation of some resistant organic chemicals.
Eucaryotic: Cells that have a membrane-delimited nucleus. Their slow rate of reaction makes the fungi not
For reference, other groupings are archaeobacteria useful for reactor applications (Rittman and
and procaryotic (Prescott et al., 1993, p. G-8; Pre- McCarty, 2001, p. 23).
scott et al., 2005, p. 90). The eucarya and the pro- Geosmin: A group of compounds produced by actinomycetes
carya are similar in principle with respect to and cyanobacter that cause a characteristic ‘‘musty’’
underlying metabolic processes and most of their odor of soils and often exhibited in natural waters
most important biochemical pathways (Prescott (adapted from Prescott et al., 1993, p. G11).
et al., 2005, p. 91). Gibbs free energy: Defined as, DG ¼ DH T DS, in which,
Exergonic: A reaction in which the standard free energy of G is the Gibbs free energy (kJ), H is the enthalpy
reaction is negative, DG R 8 < 0 and consequently, the (kJ), T is the temperature in Kelvin (K), S is the
equilibrium constant, K eq , is greater than one, i.e., entropy (kJ). DH is the change in heat content of a
K eq > 1. The reaction is spontaneous and releases given substance and DS is the change in entropy.
energy to the ‘‘surroundings.’’ See also, endergonic. Gibbs free energy of formation: Free energy of the forma-
Facultative bacteria: Bacteria that can function in either tion of a compound from its elements.
aerobic or anaerobic conditions. The most significant Gibbs free energy of reaction
1. For a given reaction (Rawn, 1989, pp. 265–272),
are those that reduce nitrates to nitrogen gas, NO 3
to N 2 , called ‘‘denitrification,’’ which occurs in an
‘‘anoxic’’ environment (see Grady et al., 1999,
aA þ bB $ cC þ dD,
p. 22).
Fermentation: (1) An energy-yielding process in which
organic molecules serve as both electron donors the ‘‘standard’’ values for the free energy of reac-
and acceptors (Prescott et al., 1993, p. G10). (2) A tion, enthalpy of reaction, entropy of reaction, are
metabolic pathway in which sugars are broken down respectively,
to simpler organic molecules and ATP is produced
by the reaction of ADP with Pi. Fermentation is X X
G (reactants): Also,

R
f
anaerobic, i.e., without oxygen as an electron DG (reaction) ¼ G (products) f
X X
acceptor, but loss of electrons occurs (Campbell, DH (reaction) ¼ H (products) H (reactants), and

f
R
f
1991, p. 18). X X
S (reactants)

f
R
Fermentation reaction: An energy-yielding reaction in DS (reaction) ¼ S (products) f
which organic molecules serve as both electron
donors and electron acceptors (Prescott et al., 1993, The subscripts ‘‘f’’ on the right sides of the respective
p. 155). equations refer to the ‘‘formation’’ values; G f 8(A) is
Filamentous: Organisms that provide a ‘‘backbone’’ struc- the ‘‘standard free energy of formation’’ of the element
ture for activated-sludge flocs that may resist shear or compound ‘‘A.’’ The values of G f 8(A), G f 8(B), etc.,
and permit settling in the final clarifier; when present may be obtained from handbooks for most elements
in excess, filamentous organisms do allow compac- and compounds, including Lide’s Handbook of Chem-
tion of the organisms during settling, called ‘‘bulk- istry and Physics, Lange’s Handbook of Chemistry.
ing’’ (from Jenkins and Richard, 1982, p. 66, For compounds of interest to water treatment, text-
Richard et al., 1985a,b). books, e.g., Grady et al. (1999), Rittman and McCarty