Biomedical Engineering Reference
In-Depth Information
CHAPTER 4
BIOAUGMENTATION WITH
DEHALOCOCCOIDES
:
A DECISION GUIDE
Hans F. Stroo,
1
David W. Major,
2
Robert J. Steffan,
3
Stephen S. Koenigsberg
4
and C. Herb Ward
5
1
HydroGeoLogic, Inc., Ashland, OR 97520;
2
Geosyntec Consultants, Inc., Guelph, Ontario,
Canada;
3
Shaw Environmental, Inc., Lawrenceville, NJ 08648;
4
Brown and Caldwell, Irvine, CA
92612;
5
Rice University, Houston, TX 77005
4.1 INTRODUCTION
Many bacterial species are capable of the initial steps in reductive dechlorination, i.e., the
conversion of perchloroethene (PCE; also termed tetrachloroethene) and trichloroethene
(TCE) to
cis
-1,2-dichloroethene (
cis
-DCE). However, the only anaerobic organisms known
so far that are able to efficiently dechlorinate
cis
-DCE to vinyl chloride (VC), and VC to the
innocuous product ethene, are strains of
Dehalococcoides
spp. (Maym ยด -Gatell et al.,
1997
;
He et al.,
2003
; Cupples et al.,
2004a
). These organisms are widespread, but not ubiquitous
(Hendrickson et al.,
2002
), and often are present in low numbers in contaminated ground-
waters (van der Zaan et al.,
2010
). Therefore, introducing cultures containing competent
Dehalococcoides
(
Dhc
) strains into the saturated zone of contaminated aquifers (bioaug-
mentation) often improves the performance of
in situ
bioremediation systems (SERDP and
ESTCP,
2005
; Ritalahti et al.,
2005
;Strooetal.,
2010
). However, it can be difficult to decide if
bioaugmentation with
Dhc
is needed or will be beneficial at a specific site.
There is no doubt that bioaugmentation can lead to complete reductive dechlorination at
some sites where dechlorination is stalled at
cis
-DCE or VC (Ellis et al.,
2000
; Major et al.,
2002
;
ESTCP,
2007
). Incomplete dechlorination is of concern not only because it leaves contaminants
of regulatory concern in place, but it also may result in plume expansion, increased vapor
intrusion risks, inefficient use of added electron donors and increased methane and sulfide
generation (Hood et al.,
2008
). At such persistently stalled sites, bioaugmentation may be
essential for effective
in situ
bioremediation.
More commonly, sites have low numbers of competent
Dhc
present in the subsurface, and
these numbers typically increase after additions of electron donor sources without the addition
of organisms (i.e., biostimulation). After biostimulation, the
Dhc
numbers usually increase over
time, resulting in complete dechlorination to ethene after a lag period until there is sufficient
growth and dispersal throughout the treatment area (Koenigsberg et al.,
2003
). This lag period
may be several months to more than a year (Morse et al.,
1998
; AFCEE et al.,
2004
), and
bioaugmentation at the start of treatment can reduce the lag period considerably (Adamson
et al.,
2003
; Lendvay et al.,
2003
).
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