Environmental Engineering Reference
In-Depth Information
constant at 14 and 19%, respectively. Hydrolysis of
carbohydrates (e.g., sugars) may be responsible for
C
org
acid dissolution, because carbohydrates are a
major labile component of TOC in soils, in contrast
with other more stable compounds, such as humic
substances and lignin. The authors found a linear
relation between TOC and acid insoluble C
org
for
both Himalayan and Amazonian River sediments.
Based on these results, they proposed a calibration
law to enable calculation of total C
org
content from
the experimentally obtained acid insoluble C
org
content. This method would be adequate to study
the C
org
content and isotopic composition in carbon-
ate-rich materials, but must be calibrated for each
individual river system because they may present
different C
org
pool compositions.
and applications of this technique in the study of
environmental colloids.
Light can be used as a non-perturbative probe to
obtain information about particle structure, such as
size, size distribution, shape, and dynamics, meas-
ured as the diffusion coeffi cient in solution (Schmitz
1990). When a laser beam, namely coherent and
monochromatic light, passes through a solution or
colloidal dispersion, the particles scatter light in all
directions. It is possible to observe time-dependent
fl uctuations in the scattered intensity
I
(
t
) using a
suitable detector. Analysis of the scattered light
signal can be made in two ways: static or dynamic.
The static light-scattering (SLS) technique measures
time averaged scattering intensities
I
(
θ
) at one spe-
cifi c scattering angle (
θ
) but fl uctuations in
I
(
t
) are
not considered.
The net intensity of light scattering by larger
particles is given by the equation
3.3 Sediment analysis
Kc
RMP
1
(2)
()
=
3.3.1 Characterization of natural colloidal
suspensions by light scattering
θ
()
θ
w
where
c
and
M
w
are the concentration and molecular
mass of the particle, respectively.
R
(
Colloidal particles play an important role in the
aquatic environment because they act as media for
sedimentation, transport, redistribution, bioavaila-
bility, and adsorption of numerous chemical com-
pounds (such as organic pollutants, nutrients, toxic
trace metals, and radionuclides) (Ledin
et al.
1995;
Filella
et al.
1997). In the past, there have been few
studies of natural colloids because the methods for
their isolation, detection, and characterization were
inadequate. Nowadays, the development of effi cient
methods for colloid fractionation like fl ow-fi eld fl ow
fractionation (FIFFF) coupled with light-scattering
techniques have allowed a better understanding of
the role of colloids in the environment, particularly
their particle size, size distribution and shape, inter-
action with contaminants and aggregation kinetics.
Briefl y, FIFFF is a separation technique based on the
hydrodynamic principle of separation of particles
owing to their interaction with the cross-fl ow-fi eld
force and their translational diffusion (Beckett
et al.
1987; Chantiwas
et al.
2002; Baalousha
et al.
2006).
This technique separates particles into slices, each
slice containing particles with a very narrow distri-
bution of sizes (Wyatt 1998). The rest of this section
presents an introduction to the general theory of
light scattering, as well as advantages, drawbacks,
) is the Rayleigh
ratio, and
K
is the optical constant given by
θ
( )
2
2
2
4
π
n
d
d
n
c
0
K
=
(3)
N
λ
4
A
0
where
n
0
is the refractive index of the medium,
N
A
is Avogadro's number,
0
is the vacuum wavelength
of the incident laser and d
n
/d
c
is the increase in the
particle's refractive index.
P
(
λ
) is the particle form
factor, which is related to particle size (radius of
gyration,
R
g
,) by the Guinier approximation:
θ
qR
22
g
P
()=−
θ
1
(4)
3
θ
→
0
where
q
= (
4
π
n
λ
)
sin
(
θ
2
)
(5)
00
is the scattering vector. Experimentally, the light-
scattering intensity of a solution is measured at
several angles and extrapolating
Kc
/
R
(
θ
) to a zero
angle gives the
R
g
of the particle.
Dynamic light scattering (DLS) through photon
correlation spectroscopy analyzes fl uctuation of
light-scattering intensity with time owing to thermal
