Environmental Engineering Reference
In-Depth Information
tracked by plating on rifampicin-containing Luria agar plates (Figure 6.18).
Direct bacterial counts of the sediment before inoculation averaged 4.82 ×
10
8
cells g
-1
sediment. Indigenous bacteria could not be isolated below our
limit of detection. Bacterial counts increased for both high- and low-density
inoculation treatments. In the high inoculation treatment, RHA(
fcb
) and
LB400(
ohb
) cell numbers increased to 7.8 × 10
6
and 1.4 × 10
7
cells/g sediment,
respectively. Increases in cell numbers were also observed in the low-density
treatment at day 15. LB400(
ohb
) colonies were not observed on agar plates
for the noncontaminated treatment, whereas RHA1(
fcb
) colonies increased
from 1.0 × 10
4
to 2.2 × 10
5
cells/g soil. The calculated CFUs/g
sediment, using
real-time PCR, for RHA1(
fcb
) and LB400(
ohb
) with TaqMan-
fcb
and -
ohb
probes were 5.3 × 10
6
and 4.4 × 10
6
cells/g sediment, respectively, at day 15.
Sediment samples taken from noninoculated controls did not show fluores-
cence above the threshold level. The
fcb
and
ohb
operons in strains RHA1
and LB400, respectively, appeared to be stable, as verified by PCR amplifi-
cation with the
ohb
and
fcb
gene-specific primers.
Similar degradation patterns for Aroclor 1242 were observed for high
and low cell densities (Figure 6.19) by day 30 of the experiment. PCB removal
for high and low cell densities was 57 and 54%, respectively, and 4% of PCBs
were degraded in the noninoculated treatment, indicating that the inoculated
strains were actively degrading the products of the anaerobic dechlorination
of Aroclor 1242. It should be noted that degradation of PCBs in these 50%
solid microreactors was significantly lower than the results of flask experi-
ments. To investigate whether these rates were affected by water content,
we conducted a similar test in 20% solids (wt/v) microslurries. The slurries
were aerated at room temperature for 15 days and sacrificed for PCB extrac-
tion and analyses. Under these conditions, the Aroclor 1242 dechlorinated
products (60 ppm) were degraded to a final concentration of 16 ppm.
In conclusion, using a model system of River Raisin sediment historically
contaminated with Aroclor 1242, we validated the proposed two-phase
anaerobic-aerobic PCB bioremediation scheme. In these experiments,
enhanced anaerobic PCB dechlorination was achieved using Hudson River
inoculum and resulted in a shift in the congener profile from highly to
lower-chlorinated PCB congeners. The anaerobic treatment was followed by
inoculation with aerobic PCB-growing GEMs. This resulted in 78% removal
of PCBs. Whereas the aerobic incubation caused a slight degree of intrinsic
PCB degradation, inoculation with the PCB-growing GEMs was essential to
achieve rapid PCB removal.
6.4.1.10 Developing protocol for inoculum delivery
To find out if we could enhance the delivery of inoculum to the soil, we
compared two methods of inoculation: addition of cells directly to the soil
and addition of cells to vermiculite, which was then added to the soil. We
chose vermiculite over other possible inoculum carriers such as rice hulls,
perlite, and calcium alginate beads because vermiculite is inexpensive,
readily available, and graded for size uniformity.
