Environmental Engineering Reference
In-Depth Information
concentrations of carbonate that reflected those most commonly encountered in nat-
ural waters (10 mM) [73]. Biofilm activity and uranium removal were evaluated
during the operation of reactors supplied with 12.6
μ
M (3-mg/L) and 126
μ
M (30-
mg/L) U(VI). The reactor with a feed of 126
M U(VI) immobilized 72.3% of
the uranium. It was expected that in the reactor fed with less U (12.6
μ
M) all of
the U would be immobilized. However, their results showed that 30.4% of the ura-
nium was removed from that reactor. The difference in U(VI) removal between the
two reactors could be attributed to biofilm detachment, which was observed but
not quantified. In general, the uranium removal extent and rate were surprisingly
satisfactory in the presence of bicarbonate buffer.
Transmission electron microscopy (TEM) and selected area electron diffrac-
tion (SAED) analysis showed that in both reactors uranium accumulated mostly
on microbial cell membranes and in the periplasmic space [73]. Energy-dispersive
spectrometry (EDS) analysis revealed that the deposits contained uranium and phos-
phates. High-resolution transmission electron microscopy (HRTEM) showed that
the deposits had amorphous or poor nanocrystalline structures [73].
μ
S. oneidensis MR-1 Biofilms on Glass Surfaces
To compare U immobilization by biofilms of SRB and DIRB,
S. oneidensis
MR-1
biofilms were grown in identical flat plate reactors and the reactors were operated
under comparable conditions. The mass of U immobilized in
S. oneidensis
MR-1
biofilms is shown in Fig. 1.6. The total amount of U immobilized in the biofilm
was found to increase linearly with time during the operation of the reactor. At least
96% of the U was immobilized consistently using
S. oneidensis
MR-1 biofilms.
The experimental data from the first five days showed that U immobilization using
sulfate- and iron-reducing biofilms growing on redox-insensitive surfaces in the
presence of carbonate was comparable.
In
in situ
bioremediation, fractures are usually present in contaminated sub-
surface sites, which can change the local substrate flux and redox conditions [7].
120
100
U(VI) delivered to the
flat plate reactor
80
Fig. 1.6
Total amount of
uranium accumulated in
S.
oneidensis
MR-1 biofilms.
The flat plate reactor was fed
with 126
μ
M U(VI) at a flow
rate of 30 mL/h. The
continuous line shows the
cumulative amount of
uranium delivered to the
reactor (or maximum possible
uranium accumulation)
60
40
20
0
0
1
2
3
4
5
6
Time (day)
