Environmental Engineering Reference
In-Depth Information
averaged approximately 680 mg/kg from 0 to 7.5 cm (0 to 3 in.) depth and
100 mg/kg for 7.5 to 15.0 cm (3 to 6 in.) depth. Below 15 cm (6 in.), PCB
concentrations were below the 2 mg/kg target level. The thermal blanket
was heated to about 900˚C for 21 h, with temperatures at the 15 cm depth
maintained at 250˚C for about 29 h after the heaters were turned off. In most
cases, soil PCB concentrations were reduced to well below the 2 mg/kg
target. The costs for thermal blanket remediation were estimated at $150 to
$200/ton for a larger site (>6 ha) for a treatment depth of 15 cm (6 in.). These
costs may be viewed as rather optimistic because they were based on a
scaled-up application (not the actual test case) and the depth of treatment
was only 6 in. Limitations and concerns of this technology include:
•
Small depth of treatment
•
Potential for downward migration of mobilized PCBs
•
Potential formation of undesirable low-temperature thermal prod-
ucts near the edge of the treated zone
6.2 Objectives
6.2.1 Overall objectives
The primary objectives of the research described herein was to:
• Develop genetically engineered organisms that will grow on PCBs
• Evaluate surfactants and FeSO
4
to enhance PCB dechlorination
• Implement and test PCB bioremediation in pilot-scale reactors
The goal of the first objective was to construct pathways for PCB deg-
radation that would result in bacteria capable of using PCB congeners as a
growth substrate, and to use these organisms to remove products of anaer-
obic reductive PCB dechlorination (i.e., the less chlorinated mono-, di-, and
trichlorobiphenyls, predominantly ortho-
and ortho+para-chlorinated con-
geners). To achieve this goal, two metabolic capabilities were combined in
the same organism, (a) cometabolism of PCBs to chlorobenzoates and dechlo-
rination and (b) mineralization of chlorobenzoates as a growth substrate.
Our research activities have focused on several biphenyl-degrading,
PCB-cometabolic bacterial strains studied in our laboratory and the dechlo-
rination genes found, isolated, and studied as part of the Great Lakes and
Mid-Atlantic Hazardous Suibstance Research Center (GLMAC HSRC)
project. Once those strains were constructed, the ability of the designed
organisms to enhance PCB degradation in soils was evaluated. The practical
effectiveness of constructed bacteria was tested at the U.S. Army Engineer
Waterways Experiment Station (WES).
The second objective of the project was designed to identify and evaluate
surfactants capable of enhancing the bioremediation of PCBs in soils
and sediments. Research activities specifically focused on the selection of
