Page 758 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Biological Reactions and Kinetics 713

(2001), or papers, for example, McCarty (1975), growth curve. The stages of the growth curve
provide such data with examples on how to calculate includes the following phases: (1) lag phase, in
DG R 8 (reaction). which the organism ‘‘acclimatizes’’ to the media,
2. The designation, ‘‘standard’’ values mean that the val- synthesizing the needed enzymes to metabolize the
ues were obtained under ‘‘standard’’ conditions, mean- substrate at hand; (2) the log phase, in which the
ing for ‘‘A,’’ T(A) ¼ 298 K; p(A) ¼ 1.0 atm; or solution organism growth rate is proportional to the concen-
concentration of ‘‘A’’ is [A] ¼ 1.0 molar, and pH(bio-
tration of organisms in suspension, i.e., dX=dt ¼
logical reactions) ¼ 7.0. m(max) X; (3) the declining growth phase, in
3. The values for DG, DH, DS without the ‘‘8’’ superscript which the growth rate is limited by the substrate or
mean that they pertain to ‘‘physiological’’ conditions, some limiting nutrient, defined by the Monod equa-
i.e., whatever conditions occur in the cell or externally tion; (4) the stationary growth phase, in which
as may be the case, dX=dt ¼ 0; (5) the death phase, in which the lack of
nutrients causes a decline in organism concentration;
X X (6) log death phase, in which the nutrients have been
G f (reactants): Also,
exhausted and the rate of decline in organism popu-
DG R (reaction) ¼ G f (products)
X X
H f (reactants), and
DH R (reaction) ¼ H f (products) lation is proportional to the concentration of organ-
X X isms, i.e., dX=dt ¼ k d X; (7) death phase, in which
S f (reactants)
DS R (reaction) ¼ S f (products)
death takes over the culture and the growth cycle is
complete (McKinney, 1962, p. 118).
An algebraic example of a calculation is (from Rawn,
Growth factor: An organic compound that must be supplied
1989, p. 271)
externally because it cannot be synthesized by the
organism (adapted from Prescott et al., 1993,
p. G11).
DG R (reaction) ¼ cG f (C) þ dG f (D)½ Š aG f (A) þ bG f (B)Š
½
Heavy metal: Antimony, arsenic, beryllium, cadmium, chro-
mium(III), chromium(IV), copper, lead, mercury,
where G f (A) is the Gibbs free energy of formation of
nickel, selenium, silver, thallium, zinc.
‘‘A’’ (kJ=mol A).
Heterotroph: (1) Microorganism that uses organic matter as
Also, for physiological conditions, i.e., any conditions,
a substrate. (2) Bacteria that use organic compounds
as their electron donor and their source of carbon for
DG R (reaction) ¼ DG (reaction) cell synthesis (Grady et al., 1999, p. 21). (3) An

R
c d a b
þ 2:303RT log [C] [D] = [A] [B] organism that uses organic molecules as its principal
source of carbon (Prescott et al., 1993, p. G12).
where Krebs cycle: A name sometimes used for the citric acid cycle
a
[A] is the molar concentration of ‘‘A’’ (mol A=L after Sir Hans Krebs, who first investigated the path-
ways and for which he received the Nobel Prize in
solution)
1953 (Campbell, 1991, p. 336).
a are moles of ‘‘A’’ in stoichiometric,balancedequation
Kjeldahl nitrogen: (1) Most of the nitrogen in domestic
4. Gibbs free energy is defined, DG ¼ DH TDS, where wastewaters occurs as proteins or their degradation
DG is the Gibbs free energy change, DH is the entropy products, such as polypeptides and amino acids.
change, T is the temperature in K, and DS is the entropy The concept behind the Kjeldahl method of meas-
change, for any process, including a chemical reaction. urement is to oxidize the carbon and hydrogen to
Gibbs free energy, enthalpy, and entropy are ‘‘state’’ carbon dioxide and water by sulfuric acid (called
functions, meaning that the values are independent of ‘‘digestion’’). The amino group is released as ammo-
the path taken between states, e.g., a biochemical path- nia and, due to the acid pH, in the form of NH 4 .
þ
way. The solution is neutralized to give pH 8.0.
5. Nomenclature of thermodynamic functions: for stand- The ammonia as NH 3 may be measured by Nessler-
ard state the designations are usually given as, DG R 8 , ization or back titration with a standard acid solution
DH R 8 , DS R 8 . (foregoing from Sawyer and McCarty, 1967, p. 428).
Glucose: The most common sugar, when assembled one way (2) The Kjeldahl method of protein analysis
can form starch and assembled another way can form was invented by Johan Kjeldahl of Denmark in
cellulose (Campbell, 1991, p. 69). 1883 and remains common. The analysis has three
Glycosis: Fermentation of glucose to pyruvate and acetyl major steps in the original procedure: (a) digestion in
CoA, dominated by the Embden–Meyerhoff path- sulfuric acid at high temperature, which converts
way (Bailey and Ollis, 1977, pp. 233, 243). all nitrogen to ammonium acid sulfate; (b) distilla-
Growth curve: Bacteria multiply by binary fission. A few tion in which the digest is made alkaline and
bacteria immersed in a beaker will thus multiply and the liberated ammonia is steam distilled into a stand-
decline in population in accordance with a classic ard acid receiver; (c) titration in which the ammonia