Page 762 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Biological Reactions and Kinetics 717

(Rittman and McCarty, 2001, p. 35). A characteris- tling sludge, if present in large numbers. The bacteria
tic of the organism is its two wheel-like ciliates that may attach to solid surfaces and may occur as mas-
cause an inflow of particles for feeding. (2) A single sive growths if nutrients are available such as asso-
ciliate may ingest 60–70 bacteria per hour; in acti- ciated with paper mill wastes, dairies, etc. (Gaudy
vated sludge, ciliates may remove suspended bac- and Gaudy, 1980, p. 365). Sphaerotilus has been
teria that have not settled (Prescott et al., 2005, seen by the author growing, below a trout farm, as
p. 590). a stringy thick grey mass on the rocks of a fast
RNA: (1) A linear polymer of ribonucleotide repeating units moving mountain stream.
(composed of the sugar ribose, phosphate, and one of Spore: (1) An encapsulated form, with heavy cell wall, of a
four heterocyclic bases); RNA is used in several bacterium that permits the organism’s survival
ways to convert the genetic code to protein products under adverse environmental conditions that do
(Rittman et al., 1990, p. 24). (2) Single-stranded not permit metabolism. The organism is encapsu-
helix-shaped molecule, similar to DNA, that serves lated in a protein shell. An example is the
as a ‘‘template’’ for the synthesis of protein mol- Salmonella typhosa that forms a cyst after it is
ecules; uracil is a part of the molecule instead of excreted and enters a nonsupportive environment.
thyamine. The three forms of RNA are messenger (2) Most bacteria do not form spores; those that do
RNA (mRNA), which carries the information for are mostly of two genera of gram-positive rods,
protein synthesis from the DNA; transfer RNA, Bacillus and Clostridium. A spore is dormant until
which carries amino acids to their proper site on induced to germinate and may remain viable for
the mRNA for the synthesis of a given protein; and many years in the dormant state (Gaudy and
ribosomal RNA (rRNA) which serves as the struc- Gaudy, 1980, p. 165).
tural and catalytic components of the ribosomes, the Stoichiometry: The procedure of balancing a chemical rela-
sites where the proteins are synthesized. tion such that the same molar quantities of elements
Secondary treatment: The methods of wastewater treatment are present on both sides of the equation, i.e., for the
that remove a high fraction of fine suspended col- reactant side and for the product side.
loidal solids, dissolved solids, and organic matter by Strain: A population of organisms that descends from a sin-
biological oxidation (URS, 1973, p. A-1). gle organism or a pure culture (Prescott et al., 1993,
Sequencing batch reactor: A sequence of batch reactors. p. G24).
Each reactor ‘‘reacts’’ for a finite time; the contents Substrate: (1) Compound that serves as the source of energy
are then emptied to the next reactor; the previous for a microbiological reaction (Eckenfelder and
reactor is filled again. See, for example, Orhon and Grau, 1992, p. 2). The compound may be organic
Artan (1994, pp. 255–260). or inorganic. (2) An organic molecule that reacts
Sludge: An accumulation of cells into a discernible mass. with an enzyme (adapted from Prescott et al., 1993,
Sludge age: (1) In activated sludge, the average number of p. 140). (3) A substance that an enzyme acts on
days that the solids remain in the aeration system, as (Prescott et al., 1993, p. G24).
computed as the mass of solids in the aeration tank Suspended-growth reactor: A reactor in which microorgan-
divided by the mass flux of solids leaving the system isms are suspended and mixed in water, making
per day, i.e., u c VX=RX r (d). (2) Mathematically, contact with the substrate by turbulent transport
u c ¼ [XV(reactor) þ additional mass in system]= with the final transport step by diffusion. Activated-
[RX r þ (Q R)X e ], which is essentially the same as sludge reactors are the classic example. See activated
given by Lawrence and McCarty (1970, p. 769). sludge.
Sludge-density index: The reciprocal of SVI. Suspended solids (SS): The suspended solids that are
Sludge-volume index (SVI) removed by filtration as measured in the laboratory
from an aeration basin sample (mg=L).
volume of sludge after 30 min settling in1 L cylinder Sphaerotilus: A filamentous organism, Sphaerotilus natans,
mass of MLSS in cylinder associated with sludge bulking.
SVI ¼
Sphaerotilus natans: A filamentous organism.
(mL settled sludge=g oven-dried settled sludge). Stoichiometric: The coefficients in a balance chemical
Sludge wasting: Sludge wasted from final settling tank; a equation.
fraction of the sludge settled solids is ‘‘wasted’’ and Strain: A population of genetically identical cells (Rittman
the other fraction is returned to the aeration tank. et al., 1990, p. 24).
Sphaerotilus: A strict aerobe, rod-shaped sheathed bacteria TCA cycle: Tricarboxylic acid cycle; a name sometimes used
species that grows in chains of cells. The sheath may for the citric acid cycle, since some of the molecules
be surrounded by a polysaccharide slime layer. The involved are acids with three carboxyl groups
organism is one of those commonly found in acti- (Campbell, 1991, p. 336). The Krebs cycle is another
vated sludge and which is likely to cause poor set- name sometimes used for the citric acid cycle.