Environmental Engineering Reference
In-Depth Information
PCE
×
No Evidence
but -
Δ
G
Biotransformations for
Chloroethenes
×
No Evidence
but -
TCE
Δ
G
?
trans
-DCE
1, 1-DCE
CO
2
cis
-DCE
Some Field
Evidence
Reductive
Transformation
Vinyl Chloride
CO
2
Oxidative
Catabolism
Ethene
Ethane
CO
2
Figure 5.1
Biotransformation pathways for chlorinated ethenes.
subsurface and groundwater environments. Under some conditions, the less
chlorinated chloroethenes (VC and perhaps DCE) may undergo oxidative
catabolism under anaerobic conditions. This process may be an important
mechanism for mass removal of vinyl chloride in locations where redox
potentials increase, such as leading edges of contaminant plumes or areas
with high dispersion or oxygen diffusion.
5.1.4 Technology status:
in situ
bioremediation
Bioremediation and natural attenuation are two
in situ
technologies often
used for remediation of dissolved phase contaminants. Bioremediation is
defined as using the metabolic processes of microorganisms to degrade,
detoxify, or mineralize contaminants. Bioremediation in the context of con-
taminated subsurface environments (soil, sediments, groundwater) usually
involves the injection of nutrients to stimulate the desired biological pro-
cesses. This is also referred to as biostimulation. A less common, although
growing, approach is to introduce or inject specific microorganisms, usually
in combination with nutrients — a process referred to as bioaugmentation.
Natural attenuation is a remedial option that takes advantage of the
widely observed phenomenon that concentrations of contaminants in the
subsurface tend to decrease over time. This is due to a combination of
physical, chemical, and biological processes that degrade, immobilize, or
transform dissolved contaminants. For most contaminants, the most impor-
tant of these attenuation mechanisms is biodegradation by native micro-
organisms. The relative treatment costs of these technologies are low, and in
