Biology Reference
In-Depth Information
strains were randomly selected for column experiments. These experiments were conducted
in borosilicate glass columns with an inner diameter of 2.5 cm (Omnifit, Cambridge, U.K.)
with polyethylene frits (25 m pore diameter) and one adjustable endpiece. The column was
packed wet with the quartz sand with vibration to minimize any layering or air entrapment.
The column sediment length was 7 cm. All column experiments were conducted in artificial
groundwater (AGW) at a velocity of 0.25 PV per minute (fluid approach velocity = 10
-4
m/s).
Prior to each experiment, and in order to remove retained cells of the previous experiment,
the column was rinsed with 1 PV of 1.9 M HCl, immediately followed by a pulse of 1.5 M
NaOH to restore pH. The column was then equilibrated by flushing for 50-60 pore volumes
with AGW to restore pH and EC. To conduct bacteria transport experiments, a suspension of
E. coli
with a concentration of ~10
9
cells/mL was flushed through the column for 4 minutes
(approximately equal to one pore volume) followed by a flush of
E. coli
-free AGW. The
E.
coli
concentration was determined using optical density measurements (at 254 nm) with a 1
cm flow-through quartz cuvette and a spectrophotometer (Cecil 1021, Cecil Instruments Inc.,
Cambridge, England). Cell numbers were deduced after calibration with plate counts on
Chromocult agar (Merck, Whitehouse Station, NJ). To check whether the flush with HCl
followed by NaOH had indeed removed all bacterial cells, at the beginning of each
experiment, effluent samples were plated in triplicate. All plates of all experiments were
negative, indicating that, after the previous experiment, all viable bacterial cells had indeed
been removed from the column.
7.2.8 Transport model
The one dimensional (macroscopic) mass balance equation for mobile bacteria suspended in
the aqueous phase excluding bacteria growth and decay is normally expressed as
(Corapcioglu and Haridas, 1984, 1985.; Foppen et al., 2007)
2
∂
c
∂
C
∂
C
Ρ
Θ
∂
S
=
D
−
v
−
bulk
(7.1)
2
∂
t
∂
x
∂
x
∂
t
Where
C
is the mass concentration of suspended bacteria in the aqueous phase (# of
cells/ml),
t
is time (min),
D
is the hydrodynamic dispersion coefficient (cm
2
/min),
v
is the
pore water flow velocity (cm/min),
S
is total retained bacteria concentration (#cells/g)
bul
Ρ is
the bulk density (g/ml),
x
is the distance traveled (cm), and Θ is the volume occupied by the
fluid per total volume medium (-). We applied the two-site sorption model (Cameron and
Klute, 1977) in this study. The model describes the interaction of mass between the aqeous
phase and the solid phase by a first order kinetic reaction together with instantaneous
equilibrium sorption. The model assumes that, interaction can be divided into two fractions
(7.2)
S
=
S
+
S
e
k
where
S
is the mass adsorbed at equilibrium sites (type-1 sites),
S
is the mass adsorbed at
kinetically controlled sites (type-2 sites). The relation between the total adsorbed mass and
the mass adsorbed at type-1 and type-2 sorption sites respectively are
S
=
fS
(7.3)
e
S
=
fk C
(7.4)
e
s
S
=
(1
−
f S
)
(7.5)
k
Search WWH ::
Custom Search