Page 753 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

methanogenic process, the supply of standard elec- void spaces that facilitate the transport of ‘‘chunks’’
tron acceptors, i.e., O 2 ,NO 3 , and SO 4 , is minim- of sloughed-off biomass and airflow, to provide an
2

ized. Without these electron acceptors, only aerobic environment within the reactor. See also
fermenting and CO 2 -reducing organisms can thrive. trickling filter. (2) A ‘‘rotating biological contactor’’
Included among those microorganisms are the (RBC) consists of an array of disks, perhaps 3 m
methane-producing archaebacteria, the methano- (10 ft) diameter with spacing about 3 cm (1 in.), but
gens. Retention control is achieved by providing a is variable depending on the surface-area volume
very large surface area on the fluidized particles of density. The disks are rotated by a shaft through a
materials such as sand, coal, or granular activated trough that contains the settled raw-water flow; as
carbon. Cells able to attach to the small fluidized the submerged part of the disk emerges from the
particles are retained and accumulated. water the biofilm substrate is exposed to oxygen,
The controls on substrate supply and cell retention which may then diffuse to a reaction site.
are a form of applied ecology. The composition and ATP: (1) Adenosine 5 -triphosphate; the triphosphate of the
0
capabilities of the mixed population of microorgan- nucleoside adenosine, which is the high-energy mol-
isms are regulated by controlling the availability of ecule and serves as the cell’s major form of energy
the substrate and the retention of cells in the process. currency (Prescott et al., 1993, p. G2). The break-
Cells with the proper attributes fill the niche defined down of ATP to ADP and P i , is given (Prescott et al.,
by the controls (Rittman, 1987). 1993, p. 136) as
Anaerobic reaction: (1) The organic molecule being metab-
olized serves as both the electron donor and electron ATP þ H 2 O ! ADP þ P i DG
R
acceptor (Prescott et al., 1993, p. 155).
¼ 30:5 kJ=mol 7:3 kcal=molÞ
ð
Anoxic: (1) Electron acceptor is a mineral anion; NO 3 ,

NO 2 .SO 4 , are most common, with affinity in

2þ
In other words, ATP gives up 30.5 kJ=mol in the
order stated. (2) Electron acceptor is a mineral anion,
reaction, which ‘‘drives’’ the cell-synthesis reaction
2þ
e.g., NO 3 ,NO 2 .SO 4 with electron affinity in that
during which energy losses occur (i.e., enthalpy and
order. This category of reaction is also called ‘‘anaer-
entropy).
obic respiration’’ (Prescott et al., 1993, p. 158).
(2) The structure of ATP as adapted from Rawn
Archaea: Includes organisms that convert hydrogen and acet-
(1989, p. 239) is
ate to methane (methanogens); carbon dioxide is the
electron acceptor for hydrogen oxidation (Rittman
and McCarty, 2001, p. 21). For reference other O ( ) O ( ) O ( )
main groupings are prokaryotic and eukaryotic. j j j
( )
Archaeobacteria: Bacteria that lack muramic acid in their O P O P O P O CH 2
cell walls, have membrane lipids with ether-linked k k k j
branched chain fatty acids, and differ in many other O O O R
ways from eubacteria (Prescott et al., 1993, p. G-3).
Aromatic compound: See Glossary in Appendix 2.A. The R represents the adenosine part of the molecule
Arrhenius: (1) Svente Arrhenius (1859–1928), Professor of consisting of three five-sided carbon rings.
Chemistry, University of Uppsala, who in 1887 pro- Autotroph: (1) Organisms that use carbon dioxide for cell
posed in his doctoral dissertation the ion theory of synthesis (Rittman and McCarty, 2001, p. 16). (2)
solutions; the theory was not accepted until years Organism that uses inorganic matter as substrate. (3)
later (Ehret, 1947). (2) The well-known ‘‘Arrhenius Organism that obtains its energy from inorganic
equation’’ is used commonly to account for the effect compounds, such as ammonia, nitrite, nitrate. (4)
Bacteria that use inorganic compounds as their elec-
of temperature on the kinetic constant, i.e., ln k ¼
DH a =RT þ ln A, where k is the reaction rate tron donor and carbon dioxide as their source of
1
constant (s ); DH a is the activation energy carbon are called chemautotrophic bacteria, although
(J=mol); R is the universal gas constant (J=mol=K); most engineers call them autotrophs (Grady et al.,
T is the absolute temperature (K); A is the frequency 1999, p. 21). (5) An organism that uses carbon
1
factor (s ). The activation energy, DH a , is the dioxide as its sole or principal source of carbon,
‘‘energy hump’’ (Daniels and Alberty, 1955, such as an alga cell (Prescott et al., 1993, p. G2).
p. 341). The equation form is also given as k ¼ A Bacterial cell composition: (1) The elemental cell compos-
exp( DH a =RT); integration gives log(k 2 =k 1 ) ¼ ition for E. coli as an example is as follows: carbon,
(DH a =2.303RT) [(T 2 T 1 )=T 2 T 1 ]. 0.50; oxygen, 0.20; nitrogen, 0.14; hydrogen, 0.08;
Attached growth reactor: (1) The bulk of the biomass is phosphorous, 0.03; sulfur, 0.01; potassium, 0.01;
retained as a biofilm on fixed media such as rocks, sodium, 0.01; calcium, 0.05; magnesium, 0.05;
lath, plastic cross-sheets. The media are character- chlorine, 0.05; iron, 0.02; others, 0.03. An empirical
ized by high surface-area-to-volume ratio and large cell formula is C 5 H 7 NO 2 . The oxidation of a cell is