Environmental Engineering Reference
In-Depth Information
where b is bacterial concentration, C is chemoattractant concentration, R is the
retardation factor, v
x
is the advective ground-water velocity, v
c
is the chemo-
tactic velocity, Y is the yield coefficient, q
m
is the maximum chemoattractant
utilization rate, k
s
is the half-saturation constant, k
d
is the bacterial decay rate, t
is time, and x is the spatial coordinate in the direction of ground-water flow. D
b
and D
c
represent the longitudinal bacterial and chemical dispersion coefficients,
respectively, and are given by:
D
b
¼
v
x
þ
eff
"
(7
:
10)
and
D
c
¼
v
x
þ
D
eff
"
(7
:
11)
where
is the longitudinal dispersivity, e is porosity,
eff
is the effective bacterial
motility coefficient in porous media, and D
eff
is the effective diffusion coeffi-
cient of the chemoattractant.
7.5 Review of Bacterial Chemotaxis Toward
Environmental Pollutants
Various natural and anthropogenic activities have led to the expulsion of simple
and polycyclic aromatic hydrocarbons (PAHs), nitroaromatic compounds
(NACs) and chlorinated compounds into the environment [24]. Although the
biodegradability of many of these compounds has been studied, bacterial
chemotaxis toward environmental pollutants, which may be used to enhance
remediation rates, has received relatively little attention [5]. Recently, a number
of soil inhibiting bacteria were found to be chemotactic toward a variety of
environmental pollutants and have been extensively reviewed by Pandey and
Jain [5] and Parales and Harwood [7]. In several studies [5, 7, 20, 23, 25, 33], a
direct or indirect correlation between chemotaxis and biodegradation has been
reported and it is speculated that chemotaxis may potentially enhance biore-
mediation of contaminated soil and ground water. A comprehensive list of
environmental pollutants and the identified bacterial strains that exhibit che-
motaxis toward them is presented in Table 7.2.
7.5.1 Chemotaxis Toward Simple Aromatic Compounds
A large number of simple aromatic compounds are environmental pollutants,
including benzene and toluene. Petroleum products, asphalt, coal tar, creosote,
and incomplete combustion of fossil fuel are the major sources of these
