Environmental Engineering Reference
In-Depth Information
•
Evaluate the effects of different solids' loading rates (i.e., water con-
tents) on the application of amendments and GEMs and the biore-
mediation of PCBs.
•
Determine the maximum solids' loading rate for optimum activity
of GEMs in order to offset subsequent dewatering costs for the dis-
posal/reuse of stabilized soils.
•
Identify PCB-contaminated sites available for the field test and eval-
uate feasibility of their PCB treatment.
•
Conduct
ex situ
two-phase anaerobic-aerobic PCB remediation pi-
lot-scale tests and evaluate efficiency of the PCB removal and per-
formance of GEMs.
6.3 Technical approach
6.3.1 Summary
This project addresses key barriers to bioremediating PCBs, which are to:
•
Develop microorganisms that will grow on the major congeners pro-
duced by anaerobic dechlorination of PCBs
•
Improve bioavailability of PCBs through use of surfactants
•
Optimize field delivery of anaerobic-aerobic PCB bioremediation
technology
•
Validate the new two-phase anaerobic-aerobic bioremediation strat-
egy in a pilot-scale test
Three central components of the project were: the use of a combination
of genetically engineered organisms that will grow on PCBs, the use of
surfactants to enhance the bioavailability, and bioslurry experiments as a
first stage in a flask-to-field transfer technology (Figure 6.2). The lack of
organisms that grow on PCBs results from the fact that organisms with PCB
(biphenyl moiety)-cometabolizing activity do not seem to have the ability to
use the chlorobenzoate product for growth. Moreover, those few organisms
that have this ability would attempt to metabolize it via the chlorocatechol
pathway, forming an acyl halide, which is immediately toxic. Hence, if any
organism in nature does have the capacity to grow on PCBs, it would be
suicidal. Through the use of dechlorination genes, we have devised a scheme
to remove chlorines before chlorocatechols are formed, thereby providing
an energy (growth) product and avoiding toxicity. This approach should be
a more desired solution for PCB remediation because it would avoid the
need to manage cometabolism, which can be difficult to achieve
in situ
.
One of the biological barriers to effective PCB remediation is slow rates
of intrinsic anaerobic dechlorination. The first step in optimizing a sequential
anaerobic-aerobic biotreatment process for PCBs is to maximize the extent
of dechlorination. Several dechlorination processes, generally believed to be