Biomedical Engineering Reference
In-Depth Information
inhibit degradation of other contaminants. Thus, in a soil cocontaminated with 2,4-D and
cadmium (II) (Cd[II]), different cadmium-resistant inocula were used to reduce the Cd(II)
concentrations to a level where 2,4-D degradation could be accomplished by a
second inoculum or by gene bioaugmentation (Roane et al., 2001 ; Pepper et al., 2002 ).
In another example, soil from a decommissioned industrial area in Italy was remediated in
microcosms using a two-step bioaugmentation process (Baldi et al., 2007 ). The first step
involved heavy metal removal by a Klebsiella culture known to create a metal-sequestering
gel. In the second step, the remaining organic pollutants were removed by fungi that were
inhibited at the original free heavy metal concentration.
1.8 SUMMARY
Bioaugmentation - the addition of biocatalysts to promote the degradation of pollutants -
has undergone a remarkable evolution over the last 30 years. It was viewed initially with
enthusiasm by researchers and practitioners, leading to the development and testing of a
wide variety of bioaugmentation agents to treat contaminants in soils and waters. Originally,
most bioaugmentation efforts focused on fuel hydrocarbons. Until the late 1990s, most of the
early bioaugmentation agents failed to show consistent enhancements of biodegradation in
controlled field tests when compared to biostimulation alone. Soils and aquifers generally have
large microbial populations, and indigenous organisms capable of degrading most contami-
nants can multiply quickly given favorable environmental conditions.
As a result, bioaugmentation came to be viewed with considerable skepticism. However,
over the last decade, bioaugmentation has been particularly successful in treating chlorinated
solvents, particularly the chlorinated ethenes such as PCE and TCE. These solvents are
widespread recalcitrant groundwater contaminants, and the success of bioaugmentation with
cultures containing Dehalococcoides species in this application has prompted renewed interest
in bioaugmentation for other situations.
If used properly, bioaugmentation can be a very cost- and time-effective way to expedite
in situ site remediation in a relatively noninvasive manner. The technology often can be applied
using injection and monitoring wells, or even by one-time direct injections of solutions contain-
ing concentrated cultures. As this volume demonstrates, bioaugmentation has progressed to the
point that useful guidance and quality control protocols have been developed. While it already
has proven to be a valuable remediation technology for some cases and a profitable commercial
practice, there is room for future improvements and exciting new applications as our knowl-
edge of molecular biology and genetics grows.
Bioaugmentation is still a relatively young field, but its history does have some lessons for
future research and development. Successful bioaugmentation requires extensive site charac-
terization, informed selection of the type and manner of inoculation and a profound under-
standing of the way the inoculum will interact with the environment. The Dehalococcoides
story has shown the value of a firm scientific understanding of the bioaugmentation culture
and its genetics, physiology and ecology. Future successes, possibly expanding bioaugmenta-
tion techniques to include GEMs and MGEs, will likely rely on a similar strong basis of
microbiology, biochemistry and genetics.
REFERENCES
Abhilash PC, Jamil S, Singh N. 2009. Transgenic plants for enhanced biodegradation and
phytoremediation of organic xenobiotics. Biotechnol Adv 27:474-488.
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